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Computational Fluid Dynamics - Science topic

Computational Fluid Dynamics are numerical methods to solve and analyze problems that involve fluid flows.
Questions related to Computational Fluid Dynamics
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Good afternoon,
I am currently simulating a combustion in CFD on ANSYS FLUENT and I am trying to get the best mesh possible out of this geometry. It is a rather simple one, with four inlets that lead to the combustion chamber. My question is, since I am quite new to ANSYS, what is the best way to mesh this geometry? Of course the inlets will have to be more refined than the rest of the mesh but I was asking the best methods to approach this. I am having trouble meshing the inside of the furnace because I am always getting really insconsistent tetrahedral cells.
Thank you very much.
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Hello,
As the geometry is relatively simple, you can proceed with a structured hexa mesh. Here are some advantages of hexa grids over other topologies (tetra, prism, poly)
(1) Hexa grid provides best orthogonal quality. The cell elements can be aligned with the flow direction, so loss of accuracy because fluxes decomposition is minimal
(2) Computation time is less, as grid nodes can be references by simple i,j,k indices
(3) You can tailor the boundary layer with a wide variety of inflation layers
You can use ICEM CFD to build it. If you are not familiar with it, you can refer to the may tutorials that are over the internet.
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Hello dear Researchers :
Does anyone have modeled, or have literature on how to mathematically model a :
Fluid Flow of a :
- Non-Newtonian Fluid
- Non-Isotermal Flow
- Compressible Flow
- Polymer.
Thank you for any help, I'll appreciate it !
Best Regards !:)
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Hi Franklin and all.
This is a well-known case of violation of the famous “no slip condition” in Fluid Mechanics: the fluid (polymer melt in this case) slips on the walls of the extrusion machinery. Transversal velocity gradients in the melt are small so that plug-flow model (full slip flow) is used sometimes. In general, the relative rugosity of the wall surface in contact with the melt is irrelevant regarding pressure drop. In a way, it is as if Bernoulli equation holds. However, with polymer melts you have simultaneous flow and heat transfer. Look for “slip-flow models” or “polymer melts slip-flow models” at the Internet.
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It can be any type of DNA like pUC18. The DNA should change it's location with time when a force will be applied to the microfluidic device like electric force, magnetic force etc.
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Hello,
Would you like to share any idea about it with me? I am also looking for it.
Thanks
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Hello everyone,
I know this is a very general question, but I have encountered this topic of debate during the review phase of some of my research work.
For my research I am working potential-based solvers for the prediction of unsteady lifting flows around wings and also for the prediction of sheet cavitation phenomena.
Apart from the computational cost, which is obviously significantly lower when potential methods are used compared to more sophisticated higher-fidelity CFD tools, what are other advantages lower-fidelity methods have? Are such tools when developed for specific applications still considered obsolete?
Cheers,
Dimitra
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Potential flow (and other similar field solutions to Laplace's equation) can be quite useful and informative. Just because a solution requires more effort (computational time, setup, post-processing, etc.) doesn't necessarily mean that it's more accurate or informative. If you don't really know what the boundary conditions are, you have at least two options: 1) apply what may be the wrong boundary conditions; or 2) use a method that has "natural" boundary conditions (such as potential flow). Rigorously applying the wrong boundary conditions (or constituent equations or localized properties or presumed cavitation criteria, etc.) may give the appearance of remarkable results and produce fascinating graphics but may or may not reveal anything meaningful about the processes you're hoping to better understand. I have lots of examples of potential and viscous flows plus free software http://dudleybenton.altervista.org/projects/CFD/index.html
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Hello, I am modeling steel filling up a chamber. My problem is that when steel falls inside the chamber it does not fill it and it sticks to the walls and goes out (Please see image). I have used VOF and Eulerian VOF two-phase flow models. I have used fine and coarse meshes. I have used K-epsilon and K-omega SST models. But I am getting almost the same results. Do you know what is the problem? Thanks
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Thank you so much for providing your experience.
Best regards,
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Hello,
I've successfully simulated the closure of a flapper non-return valve as illustrated.
The inlet velocity increases gradually with a specific acceleration.
The following UDF is used to specify the motion of the flapper:
#include "udf.h"
DEFINE_SDOF_PROPERTIES(flappers_motion, sdof_prop, dt, time, dtime)
{
Six_DOF_Object *sdof_obj = NULL;
sdof_prop[SDOF_MASS] = 2.73e-3; /* flapper's submerged weight */
sdof_prop[SDOF_IXX] = 2161.86e-9; /* around the hinge */
sdof_prop[SDOF_IYY] = 367.96e-9;
sdof_prop[SDOF_IZZ] = 2471.27e-9;
real m= sdof_prop[SDOF_MASS];
real L= 0.024479 ;
sdof_prop[SDOF_LOAD_M_X] = 0 ;
sdof_prop[SDOF_LOAD_M_Y] = 0.0;
sdof_prop[SDOF_LOAD_M_Z] = 0.0;
real th_deg = theta * 180 * 7 / 22 ; /* valve opening angle, in degree */
sdof_obj = Get_SDOF_Object(DT_PU_NAME(dt));
if (NULLP(sdof_obj))
{
/* Allocate_SDOF_Object must be called with the same name as the udf */
sdof_obj = Allocate_SDOF_Object(DT_PU_NAME(dt));
SDOFO_1DOF_R_P(sdof_obj) = TRUE; /*1DOF rotation*/
SDOFO_DIR(sdof_obj)[0] = 1.0;
SDOFO_DIR(sdof_obj)[1] = 0.0;
SDOFO_DIR(sdof_obj)[2] = 0.0;
SDOFO_CENTER_ROT(sdof_obj)[0] = 0.0;
SDOFO_CENTER_ROT(sdof_obj)[1] = 0.0;
SDOFO_CENTER_ROT(sdof_obj)[2] = 0.0;
SDOFO_CONS_P(sdof_obj) = TRUE; /* constrained motion */
if (SDOFO_CONS_P(sdof_obj))
{
SDOFO_LOC(sdof_obj) = 0.0;
SDOFO_MIN(sdof_obj) = -0.0349 ; /* min allowable angle */
SDOFO_MAX(sdof_obj) = 1.0471 ; /* max allowable angle */
SDOFO_INIT(sdof_obj) = SDOFO_LOC(sdof_obj);
SDOFO_LOC_N(sdof_obj) = SDOFO_LOC(sdof_obj);
}
}
}
But now I want to simulate the closure of the flapper, taking into account the friction at the flapper's hinge.
I tried to just assign the friction value to "sdof_prop[SDOF_LOAD_M_X]" ,but the flapper started to move backwards (opening) until the flow increases, which is not correct.
So I want to get the value of the hydrodynamic torque of the flapper, and compare it to the friction with some kind of "if statement" that may look like this:
real static_friction= 50;
real kinetic_friction=40;
real hydraulic_torque =??? ;
If (hydraulic_torque<static_friction)
{
sdof_prop[SDOF_LOAD_M_X]=0
}
else
{
sdof_prop[SDOF_LOAD_M_X]=-1*kinetic_friction;
}
BUT THE PROBLEM IS :
I don't know the udf code that can get the actual value of the hydraulic_torque on the flapper to compare it to the friction value.
Your help is highly appreciated.
Thanks a lot in advance.
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Ok, I've found how,
In case of someone else has the same issue,
Use the macro :
Compute_force_and_moment
Within the 6dof code
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I am looking for a skeletal methane combustion mechanism in chemkin format, which has 17 species and 25 reactions. I have searched through many web sites but i can't get it. It is propably called skeletal25. Any body who can help with this problem is appreciated. Thank you
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The study of combustion is important to optimize the design and operating parameters of a combustor. The combustion between the fuel and air involves the conversion of the chemical energy of the species to heat energy. Complete combustion is desirable to get the maximum thermal efficiency out of it. Incomplete combustion is not desirable as it emits hazardous unburnt hydrocarbon as well as CO2, NOx, etc to the environment.
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Does any one have some experience with creating 3D geometries with FreeCAD and subsequently editing it to the OpenFOAM CFD software? Could you share any tutorial or demo links with me?
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You cannot directly import a CAD file into Openfoam. You need to convert it into a good surface mesh (STL) and then use snappyHexMesh or cfMesh to create a hex-dominant mesh. Then, use checkMesh utility to verify the mesh quality. Also, you can visualize the mesh in Paraview.
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I am working on a model in Ansys-Fluent. In the Mesh Morpher module, I want to define a parameter as a variable in a given direction (for example X dir). After assigning the defined parameter (TestParameter in the attached figure), to the Mesh Morpher (par1), the calculation can not proceed and the following error is shown (also shown in the attached figure):
Error: access: unbound variable
Error Object: active?
When I delete the defined parameter (TestParameter), the calculation proceeds normally.
You may suggest to bound the parameter (par1). I have also tried this, but it didn't help.
How can I resolve the problem, and get no errors?
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I'm getting the following error. how to resolve it?
Error: eval: unbound variable
Error Object: frequency
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Do the six jump conditions (difference between inner and outer limits of pressure, x-velocity, and v-velocity and these three quantities' normal derivatives) for these two problems change with respect to time, i.e. have a time variable "t"; or do these conditions don't have time variable "t", but still need to be updated when interface changes? The following two membrane problems are found in Sections 10.2.6 and 10.3 in textbook on immersed interface method (IIM), The Immersed Interface Method Numerical Solutions of PDEs Involving Interfaces and Irregular Domains by Zhilin Li.
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The figures address a time-dependent problem, where is written that the solved equations are steady?
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Energy conservation can be expressed in different ways, such as the temperature equation and the enthalpy equation. However, the two equations do not behave the same way when used in Computational Fluid Dynamics (CFD) simulation (finite difference method and finite volume method). My question is: why? If someone can give me a brief explication.
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The physical conserved energy is the total energy. You can write equations for other forms of energy but they are never conserved.
The equation for temperature (intensive variable) must be deduced from the equation of the internal energy.
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Hello all,
I intend to perform a CFD analysis of the well-known bridge pier scour problem. I am considering two software packages for this purpose: Ansys Fluent and Flow 3D. I am trying to explore the pros and cons of each package for my case.
I would appreciate your comments on any of the following.
1- In order to make a sound comparison, I need to understand the modelling details implemented in Flow 3D, especially a clear description of the way sediment transport is modelled and coupled with the hydrodynamic solver, and how the interphase interaction is realized. Despite lots of research, I have not been able to find detailed information on this.
2- Any study on comparing the performance of these two packages for bridge pier scour problem.
Regards,
Armin
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First difference (discretization method): FLOW-3D implements finite differences while Ansys Fluent solves using finite volumes.
Second ("speed"): FLOW-3D is numerically "faster", due to the discretization method and because it has the possibility to simulate a single fluid (Water). Fluent resolves both fluids (Air-Water), at least with VOF.
Third (sediment transport): FLOW-3D allows coupling semi-empirical models of sediment transport to flow hydrodynamics (somewhat simplified, but better than nothing!). Until the version I have handled in Fluent (2019R2), there is no way to model sediment transport. You need to make a UDF for this purpose or try with particle models, for different grain sizes (field unknown to me!).
In my opinion, FLOW-3D is much more suitable CFD software for solving river hydraulics problems. In that aspect it seems to me that it has a great advantage over Fluent,
Good Luck,
Leonardo
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Hi all,
I am trying to simulate a case in 3D and two phases thought a twoPhaseEulerFoam solver but in every time I encounter the same error i.e. "Negative initial temperature T0" . Is anyone has a clue how to tackle it?
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Jonatan R. Mac Intyre, that's right!
Also, Abdulbasit Abdulsayid, It’s often a common issue when using turbulent models. The problem could relate to the model geometry, the boundary conditions, and even the convection state; i.e., transient or steady-state. First, ensure that your boundary conditions are correct, then try using both transient and SIMPLE algorithm solvers in different cases to see if the flow is established.
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Hello, I want to simulate flow over an aerofoil. I read that the SST k-omega model and Spalart---Allmaras both give good results. Since the SA model is one equation model it is computationally less expensive. Is there any other reason to choose the SA model over SST? And when should we use SST over SA?
I am new to CFD, any suggestions/advice would be very helpful
Thanks.
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The selection of the model depends on the specific problem, no turbulence model is suited for every case. Fine-tuning is required. SST model uses good mesh at boundary and with wall treated usually works in most cases, but again it is problem specific.
There are numerous turbulence models and many different sets of parameter settings around, and you can produce a wide range of solutions depending on which model and which numerical mesh you choose.
A qualitative reasonable result at a low cost is obtained with Spalart-Allmaras. In any case, you have to use an appropriate mesh as a starting point which an experienced user will easily pick, and once you have a solution you have to check Y+ values (i.e. the distance of the first grid point from the wall), since depending on the turbulence model some ranges of Y+ values yield completely unphysical answers. Once you have the Y+ values you know whether you have too coarse or too fine a mesh near the airfoil.
Regards
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  • I have done an MRF and Sliding mesh analysis of the centrifugal pump. I need to know how to calculate and show the production of entropy.
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Dudley J Benton, thank you so much
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Are there any good algorithms for doing Particle Shifting near solid walls in SPH? This is needed to avoid the SPH particles passing through the solid boundary.
Cristian
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Hello,
Thanks for the reply. Unfortunetely in my case the only option is to have a a good shifting strategy.
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Hello everyone
Hope you are fine. I have a doubt in the area of CFD, in my case a multiphase bubbly flow with Eulerian formulation. The solvers often mention implicit or explicit schemes specially when setting up the discretization of the equations, is this related to the way in which the solver calculates the field partial derivative equations? If so I want to know if these formulations have an effect on: convergence stability, accuracy of results, duration time of the simulation, etc. Thanks in advance for any suggerence about the usage of those formulations.
Walter Nolasco
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It basically depends on the order of discretization in your source and convection terms. If you are using first-order differencing explicit is okay, though in the case of second-order implicit works.
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I am using Gamma-Re theta transition model for an asymmetrical airfoil. For the academic Ansys Fluent version, the maximum allowable cell limit is 512000 cells. Is it possible to have a good mesh quality in the academic version for transition modelling? If yes, what can i do to improve my mesh quality? Thank you very much.
Maximum aspect ratio = 438.08
Maximum skewness = 0.84746
Minimum orthogonal quality = 0.10908
Y+ < 1
Total cell number = 504400
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I suggest you visit https://aeroptimal.com/mesh (you must create an account to use this module), where you can create a full structured airfoil mesh - https://youtu.be/4Opu0zk7gFk . You can export .su2 .msh .foam .vtk
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Hello!
I am using Ansys Fluent v18.0 -> MHD module -> Magnetic Induction method to model MHD flows in square ducts. I would like to see the electric potential distribution in the cross-section, but I see no option for that in the post-processing section. UDS tab only has B_x, B_y and B_z, and User defined memory tab only has B_0_xyz, B, J_xyz, E_xyz, F_xyz, etc., but no sight of electric potential phi. I believe you could display it older versions of Fluent, maybe I am wrong.
So my question is simple:
Is it possible to display the electric potential distribution when using the Magnetic Induction method in Ansys Fluent v18.0?
Thank you!
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Sina Salahshour depends what you want to see exactly, but your way seems fine. Not sure about selecting interfaces. For vectors in volume just select your interior regions of interest. For surface representation select your predefined surfaces or define new surfaces. Best of luck!
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I am going to couple anaerobic digestion model no.1 (ADM1) with CFD modelling. I need some data for validation. Where or in which research paper can I find those?
Is it necessary to validate the coupled CFD-ADM1 or the validation of CFD part is sufficient?
Best regards
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Check out my articles, you might benefit from them
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Dear all
I intend to model the fluid flow through porous media using coupled DEM-CFD (LBM). It is mainly about the 3D behavior and interactions of soil grains in the presence of interstitial water flow. Soil particles are non-spherical, and they are assumed to be potentially detachable (not fixed); thus, fluid boundaries are deformable. I do not have any experience with any of these software tools, and I'm not sure which one I should use. Ease of use, performance, and the ability to model non-spherical particles are considered as the most important factors.
I suppose that OpenFOAM can be coupled with LIGGGHTS and solve DEM-CFD problems. There is also the CFDEM which does the same, and of course, there is an LBM flow engine implemented in YADE. Which one do you recommend?
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Yade is open source and allows the use of non-spherical particles (angular polyhedral or clumps of round particles to make complex one). It works with granular flow, but you can also have your solid particles in a fluid by using the integrated version with OpenFoam (you need to compile it and can't use the version that is pre-compiled). It works rather well and it is easy to install and use on Linux. There is a good library of examples and tutorials.
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Dear all,
I am writing my thesis on "CFD analysis on hydrogen assisted diesel engine". I am seeking help to construct the kinetic mechanisms for hydrogen diesel co-combustion. I managed to find the two separate CHEMKIN files for diesel and hydrogen combustion. Could anyone please help me with how to integrate these two files and load into 3D CFD software? If you have a CHEMKIN file for such analysis, please share it with me. I would be so grateful to you.
Thanks in advance for your time and support.
-Dasaradh
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Dasaradh Palagiri thats great to see some one using the H2 integration. I am struggling with the same, can you share the thermo set and kinetics file. Further, do u have any idea how to obtain contour images in the chemkin
many thanks, Manisek87@gmail.com
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Which model in Fluent CFD solution should be addressed when using phase change material inside a circular copper tube placed inside a cabinet?
and What boundary condition should be applied.
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Solidification and Melting model
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PLEASE I am trying to add a lag to this code after each period. Does any one have an idea how to do that?
"#include "udf.h"
DEFINE_PROFILE(unsteady_velocity, thread, position)
{ face_t f; real t = CURRENT_TIME;
begin_f_loop(f, thread)
{ F_PROFILE(f, thread, position) =A*sin(w*t);
} end_f_loop(f, thread) }"
Basically, I want the loop to initially run for "X" seconds, stop and then start again at "Y" seconds instead of it running continuously as default.
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Hi Victor,
I hope the below mentioned link helps you
You can change the logic depending on your requirement using conditional statements.
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I am writing a cfd code for solving N-S equation on a structured collocated grid (lid- driven cavity), my code is slow because of the above reason.
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I am facing the same problem. I am solving with python. I have tried to use try and accept block where I can use multiple solvers.
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Hello, I have a project coming up with Delayed detached eddy simulations.
I am trying to understand how LES works right now. can someone suggest a lecture series or video series on how to understand Delayed detached eddy simulation? How does LES evolve into Delayed detached eddy simulation?
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First of all, what about the textbooks you are already considering to understand LES?
In general you have to consider first the idea of the evolution of LES into DES and then into DDES:
P.R. Spalart, S. Deck, M.L. Shur, K.D. Squires, M.K. Strelets, and A. Travin. A New Version of Detached-eddy Simulation, Resistant to Ambiguous Grid Densities. Theoretical and Computational Fluid Dynamics, 20(3):181–195, 2006.
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Hello,
I am doing a parameter study for different grids doing wall modeled large eddy simulation for a channel flow. Could someone recommend me some papers which discuss the recommendations for such grids? I read papers which give clear recommendations but I dont find a lot why specific grids perform well. Its clear that at some point the grid is just too coarse, so I relate to fine enough grids with different aspect ration for example. I thought maybe it has to do with typical sizes of eddies in the turbulent channel flow but could not find many information about this. I know that it has much to do with the numerics used but are there also some physical reasons eg. elongated eddies in streamwise direction so that x+/y+ > 1 is reasonable? . Also I wonder about some results, eg. a 160*160*160 (x+*y+*z+) grid performing better than a way finer 40*40*40 grid in means of the mean velocity results. The simulations are carried out at Re_tau = 2000 on a finite volume code using WALE and Werner Wengle wall model.
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As stated by Filippo, in my experience, comparing the velocity profile is never enough in LES, especially for implicitly filtered LES in the channel flow. For example, with certain codes and discretizations, a mass error due to the pressure discretization can directly affect the mean velocity profile and make it look good while all the other quantities would signal a completely wrong solution.
For what concerns the wall and SGS model, in my opinion, a single combination doesn't allow to really take effects apart. Also, there isn't much around on the Werner & Wengle model, which makes it more difficult to understand.
Are you using a specific code or is this an in-house solver?
More generally, you want to build confidence on your tool for this case, but you are exploring a very little portion of the parameter space that is known to strongly affect results, especially at high Re.
The main rule of thumb that I can suggest is that, because the main dynamics at the wall is due to the streamwise streaks, you don't want to represent it uncorrectly. Now, dx+ = 40 is kind of good also for a wall resolved LES so, one effect you might be observing is that your choice of completely equal grid sizes in the 3 coordinate directions is kind of altering (trough the numerics etc.) a local dynamics that is obviously anisotropic and demands a different aspect ratio for the cells. But, again, this is just a guess. There are no two LES codes that perform the same given identical conditions.
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I'm simulating a 3D wing with winglet (on the tip) using ANSYS Fluent. I'm confused about how to calculate the area in reference values section. Please check the attached pictures of my wing model.
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For an entire wing, the reference area is usually the projected area from the top view. If you take just the tip my suggestion would be to parameterize the results for a certain range of the wing reference area (if the winglet has a defined dimension)
.
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I guess my question is quite simple: you know how for compressible CFD codes we have the Sod Shock tube problem that we can use as a benchmark. What if I now want to expand my code and add chemical reactions to it, what would be a good/similar test problem that I could use to validate how well my code runs?
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According to the link provided above, one may be tempted to suggest a simple combustion test case involving hydrogen oxidation to validate the "in-house" developed chemical kinetics CFD code. Thanks.
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Hye;
I want to ask related to a formula for calculation of friction force for journal bearing by using CFD ANSYS FLUENT. Which formula should use ya..the first one or the second one. I find both formulas in the article. Thanks in advance.
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I have a 2D simulation of the capillary rise between two identical parallel plates. I am using the Phase Field method and the software COMSOL Multiphysics. For validation I am using this paper: https://onlinelibrary.wiley.com/doi/epdf/10.1002/ceat.201500089
My problems are:
1) I don't get the capillary height from the paper
2) The water/air interface won't settle down to an equilibrium. Even after 15 seconds it still moves
Did anyone ever had the same problem and knows how to fix it?
Thanks a lot.
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Aynur Atalay Try setting chi higher, e.g. more than 10.
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I need to do simulation and analyses using one or two of the various types of software commonly used, but the problem is that I can't feel sure about advantages and disadvantages of any. Considering types of the analyses I need ( CFD and shadow behaviour) and type of the place (an urban space among various buildings (nearly a neighbourhood in size)), I'd be grateful if you share your knowledge in this field.
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Also, Comsol software can be useful.
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We are studying the generation of thermal winds in mountainous areas, using computational fluid dynamics software. In particular, now we are focusing on the simulation of the full diurnal cycle, with a temperature boundary condition that is periodic with period 24h.
When we check the results, we obtain that the maximum speed of the katabatic wind (nighttime, down-slope flow) is always smaller than the maximum speed of the anabatic wind (daytime, up-slope flow). We think that this is sound, given the actual geometry of the mountain-valley system that we are simulating, and the boundary conditions that we are using (please, see image below) but still we would appreciate some input and confirmation, given that, in some references, we have seen different results.
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Dear Dr. Gregorio,
The problem of anabatic winds is much more complicated than the katabatic winds driven by the cooling of a slope. I would suggest to consult the note by Scorer (1965) and the recent study by Güttler et al. (2016) in order to identify all relevant processes and to define a list of non dimensional numbers that are useful for a systematic analysis of your results.
The papers mentioned above are available on the web:
Scorer (1965) Anabatic winds
and
Energetics of slope flows: Linear and weakly nonlinear solutions of the extended Prandtl model.
Güttler et al. (2016)
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I have been trying to simulate flow through a rocket nozzle for both underexpansion and overexpansion for a steady flow using 2D planar model. The residuals converged in the case of under-expansion, however they simply keep oscillating forever for the case of over-expansion. What could probably cause this to happen.
I am new to CFD . I even tried changing the CFL number and decreasing the under-relaxation factors, but to no use. A little bit of help would be much appreciated.
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Sometimes it happens in the higher Reynolds in the turbulent flow. Try to reduce URFs and in the next step try to a transient solution.
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I want to do FEM analysis on cold extrusion.
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hi every body i will appreciate that if you introduce me screw design software
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The complete flow equations for a third grade flow can be derived from the differential representation of the stress tensor. Has anyone ever obtained any results, experimentally or otherwise, that indicate the space-invariance (constancy) of the velocity gradient, especially for 1D shear flow in the presence of constant wall-suction velocity? Under what conditions were the results obtained?
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Academic resources on Fluid Mechanics are provided on
SINGLE PHASE AND MULTIPHASE TURBULENT FLOWS (SMTF) IN NATURE AND ENGINEERING APPLICATIONS | Jamel Chahed | 3 publications | Research Project (researchgate.net)
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This Discussion is to help people that are both experts and newbies in the field of CFD and simulation to help each other and to give links to websites and drop materials that are invaluable to push us to the frontiers.
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Academic resources on Fluid Mechanics are provided on:
SINGLE PHASE AND MULTIPHASE TURBULENT FLOWS (SMTF) IN NATURE AND ENGINEERING APPLICATIONS | Jamel Chahed | 3 publications | Research Project (researchgate.net)
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Modeling multi-phase flow propagation using Ansys Fluent, OpenFOAM, Flow-3D, etc., how the force, such as Drag force and Surface Tension, apply to each of the phases?
What about other forces? Do the forces such as, Added Mass, and Basset Force apply in the all phases? How?
Is there any concise reference or instruction for the modeling of multicomponent fluids?
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Some math about your questions and useful references.
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I am working on a heat pipe, where there is a wick structure adjacent to a hollow space. The wick structure is filled with liquid water. And the hollow space is for vapor to flow in the heat pipe.
I want to model an interface at saturation temperature exactly at the boundary of the wick structure.
In the Evaporator section of the heat pipe, the liquid in the wick structure is evaporating at the interface. And in the condensation section of the heat pipe, the vapor is condensating at the interface.
In both cases, there is heat and mass transfer across the interface.
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Sir,
Did you use the UDF to model the mass transfer across the interface?
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Cold water flow through a solar water heater straight tube(with side body) with 27 degrees C, Flow rate is 0.05 Kg/sec, Density 998.2 kg/m^3, having thermal conductivity of 0.6 w/m-k and Cp specific heat is 4182 j/kg-k, Viscosity = 0.001 kg/m-s. Solar water heater tube added with some solar radiation added to the system with glass on the tubes. So find the Maximum Pressure and Maximum Velocity of the tube and also find the outlet temperature of the water. If something is missing please take required values like Area and dimensions to calculate the maximum Velocity and Pressure. Can also find temperature efficiency and overall heat coefficient if it is required to find.
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I have also done the same thing.. i have calculated the non uniform heat flux on the absorber tube of parabolic trough collector using Monte Carlo Ray Tracing code.. and once i get the non uniform heat flux from code.. i have used that non uniform hear flux as a input in the fluent and then develop the model in fluent. And run the simulations..
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When I try to link the external time-dependent flow rate data( two columns, with a csv extension) to the mass source, the solver always terminates with a fatal error that shows information below:
***********************************************
** fatal error **
** external time-dependent table for **
** total flow rate **
**of source 1, is not currently supported:**
** import the table into the input file **
***********************************************
Therefore, I switch to import the data into the table and it turns out that I can only import data of at most 500 time steps, which the reference manual does not mention (while in fact, in order to ensure the accuracy, I have 2000 steps);
I also try to modify the 'prepin' file and it doesn't work as well.
So how should I successfully import data of more than 500 lines?
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I am also surprised, such error should not come.
Have you verified the unit consistency?
The other option is you can import the data file from the CFD in .txt/excel and do the comparison in another software like excel/origin/matlab.
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Hi, i need to perform a mesh sensitivity analysis for a stenosis CFD analysis. Is it sufficient to try some different meshes and look if the residuals (x-velocity,y-vel,z-vel) converge?
Thank you all, I'm a desperate beginner..
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At first you should start with a coarse mesh (may be the software default), then check the targeted parameters.
Then increase the accuracy of the mesh ( make it finer) and check the same targeted parameter.
Then further repeat it with finer and finer meshes, and check the same output parameter.
You should repeat it till you got a mesh independent solution.
And you can present this data in your paper.
Best regards
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All materials whether solids or fluids (liquids/gases) can change the shape under application of external force or stress.
In case of fluid, the force is generally termed as 'pressure' as it is uniform from all the directions. But how do we judge the solid/fluid is susceptible to change in the volume upon application of forces/pressure. Thus, in a simple word, Compressibility is a measure of change in the volume of fluid
under the effect of force/pressure or stress.
So, can we say Compressibility is a fluid property or a flow property?
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I simulated a case where a bubble collides with a wall using my code, but now I want to replace the top wall boundary with a symmetrical (mirrored) boundary condition. Does anyone know how to implement it? Any suggestions will be very helpful to me.
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Hello everyone.
I have used the CCD to build a table of 25 runs (4 variables and 2 responses). The responses have been calculated based on CFD results. Thus the center point can not be repeated due to constant values in results.
to enhance the precision of models, 15 more runs have been added to the table of experiments (totally 40 runs).
Finally, after analysis, the R2 (adjusted and predicted) is more than 95% for both of responses.
But, I cant see any data about "lack of fit" in ANOVA and fit summery sections.
Could you help me about this problem?
Is it necessary to report the "lack of fit" data in this analysis?
It should be noted that the model predict the responses well.
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Sajed Hadi Bafekr Please check the step-wise linear model regression.
You can change the second degree Quadratic to next degree of the model known as Cubic
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So far world knows agile has emerged from IT/software solution projects. The methodology/ concept of agile is so highly effective that companies now want to explore its scope in managing mechanical product development.
1 biggest challenge i see before even embarking on the concept is, having an agile approach in CAD. A CAD engineer will take several days in general to modify or create a new model. Similarly, FEA/CFD will take days to iterate constraints to reach a solution. This cycle time is too big to go the agile way. How can we break down this work chain and check midway to make sure the progress is in right direction and effort will not need a redo?
Mechanical engineers are orthodox in working pattern so to say. There has been many improvisations and upgrades in CAD software but none in working style or thinking style.
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In CAD, there are ways to simplify and reduce your design time. if you use creo, there is a feature called Skelton concept, with Top-Down and Bottom-Up Design. we are using this concept to reduce the design time. every new design we make few master models, linked with family table and reference. this method reducing more than 75% of our design time. even we can have parametric drawings, no need to make separate drawing for the new design.
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after doing mesh i can't open CFX Setup.
could you help me to find solution.
Error message
Update failed for the Setup component in CFX. There is no previously saved CFX Setup to refresh or update. Please edit this cell first.
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Hello Dr. Th. Frank and Mr. Mohammad
actually i tried a lot to solve the problem.
the problem began when cfx solution was working, i closed the program by mistake.
finally i made format for my laptop and reinstall ansys program.
now everything is working fine.
thanks.
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It helps to develop thermal modelling using CFD analysis.
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I need more information to answer this question. For this reason I offer you a list of very timely scientific contributions that will be of use to you.
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I'm looking for publications regarding the Two-Relaxation Time Lattice Boltzmann Method's forcing schemes without passing through the Multi-Relaxation Time's full procedures
I'm specifically searching for the TRT implementation of Shan-Chen forcing scheme (ueq=u+tau*F/Rho)
Any contribution is highly appreciated
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Almost a year later, but anyways:
I wrote together with someone else an article that probably suits your needs:
Preprint is on researchgate.
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Hello everyone,
In the process of creating a real-gas flamelet in CANTERA, I came to know about two open-source packages through the CFD Forum.
1. opensmoke++ suite
Has anyone used this package before?  Is it a real-gas capable?
2. CoolFOAM: The CoolProp wrapper for OpenFOAM
Has anyone used this package before?  Is it a real-gas capable for generating flameLets?
Thank you !!
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Interesting
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The threats that global warming has recently posed to humans in many parts of the world have led us to continue this debate.
So the main question is that what actions need to be taken to reduce the risk of climate warming?
Reducing greenhouse gases now seems an inevitable necessity.
In this part in addition to the aforementioned main question, other specific well-known subjects from previous discussion are revisited. Please support or refute the following arguments in a scientific manner.
% -----------------------------------------------------------------------------------------------------------%
% ---------------- *** Updated Discussions of Global Warming (section 1) *** ---------------%
The rate of mean temperature of the earth has been increased almost twice with respect to 60 years ago, it is a fact (Goddard Institute for Space Studies, GISS, data). Still a few questions regarding physical processes associated with global warming remain unanswered or at least need more clarification. So the causes and prediction of this trend are open questions. The most common subjects are listed below:
1) "Greenhouse effect increases temperature of the earth, so we need to diminish emission of CO2 and other air pollutants." The logic behind this reasoning is that the effects of other factors like the sun's activity (solar wind contribution), earth rotation orbit, ocean CO2 uptake, volcanoes activities, etc are not as important as greenhous effect. Is the ocean passive in the aforementioned scenario?
2) Two major physical turbulent fluids, the oceans and the atmosphere, interacting with each other, each of them has different circulation timescale, for the oceans it is from year to millennia that affects heat exchange. It is not in equilibrium with sun instantaneously. For example the North Atlantic Ocean circulation is quasi-periodic with recurrence period of about 7 kyr. So the climate change always has occurred. Does the timescale of crucial players (NAO, AO, oceans, etc) affect the results?
3) Energy of the atmospheric system including absorption and re-emission is about 200 Watt/m2 ; the effect of CO2 is about how many percent to this budget ( 2% or more?), so does it have just a minor effect or not?
4) Climate system is a multi-factor process and there exists a natural modes of temperature variations. How anthropogenic CO2 emissions makes the natural temperature variations out of balance.
6) Some weather and climate models that are based on primitive equations are able to reproduce reliable results.  Are the available models able to predict future decadal variability exactly? How much is the uncertainty of the results. An increase in CO2 apparently leads in higher mean temperature value due to radiative transfer.
7) How is global warming related to extreme  weather events?
Some of the consequences of global warming are frequent rainfall, heat waves, and cyclones. If we accept  global warming as an effect of anthropogenic fossil fuels, how can we stop the increasing trend of temperature anomaly and switching to clean energies?
8) What are the roles of sun activities coupled with Milankovitch cycles?
9) What are the roles of politicians to alarm the danger of global warming? How much are scientists sensitive to these decisions?
10) How much is the CO2’s residence time in the atmosphere? To answer this question precisely, we need to know a good understanding of CO2 cycle.
11) Clean energy reduces toxic buildups and harmful smog in air and water. So, how much building renewable energy generation and demanding for clean energy is urgent?
% -----------------------------------------------------------------------------------------------------------%
% ---------------- *** Discussions of Global Warming (section 2) *** ---------------%
Warming of the climate system in the recent decades is unequivocal; nevertheless, in addition to a few scientific articles that show the greenhouse gases and human activity as the main causes of global warming, still the debate is not over and some opponents claim that these effects have minor effects on human life. Some relevant topics/criticisms about global warming, causes, consequences, the UN’s Intergovernmental Panel on Climate Change (IPCC), etc are putting up for discussion and debate:
1) All the greenhouse gases (carbon dioxide, methane, nitrous oxide, chlorofluorocarbons (CFCs), hydro-fluorocarbons, including HCFCs and HFCs, and ozone) account for about a tenth of one percent of the atmosphere. Based on Stefan–Boltzmann law in basic physics, if you consider the earth with the earth's albedo (a measure of the reflectivity of a surface) in a thermal balance, that is: the power radiated from the earth in terms of its temperature = Solar flux at the earth's cross section, you get Te =(1-albedo)^0.25*Ts.*sqrt(Rs/(2*Rse)), where Te (Ts) is temperature at the surface of the earth (Sun), Rs: radius of the Sun, Rse: radius of the earth's orbit around the Sun. This simplified equation shows that Te depends on these four variables: albedo, Ts, Rs, Rse. Just 1% variation in the Sun's activity lead to variation of the earth's surface temperature by about half a degree.
1.1) Is the Sun's surface (photosphere layer) temperature (Ts) constant?
1.2) How much is the uncertainty in measuring the Sun's photosphere layer temperature?
1.3) Is solar irradiance spectrum universal?
1.4) Is the earth's orbit around the sun (Rse) constant?
1.5) Is the radius of the Sun (Rs) constant?
1.6) Is the largeness of albedo mostly because of clouds or the man-made greenhouse gases?
So the sensitivity of global mean temperature to variation of tracer gases is one of the main questions.
2) A favorable climate model essentially is a coupled non-linear chaotic system; that is, it is not appropriate for the long term future prediction of climate states. So which type of models are appropriate?
3) Dramatic temperature oscillations were possible within a human lifetime in the past. So there is nothing to worry about. What is wrong with the scientific method applied to extract temperature oscillations in the past from Greenland ice cores or shifts in types of pollen in lake beds?
4) IPCC Assessment Reports,
IPCC's reports are known as some of the reliable sources of climate change, although some minor shortcomings have been observed in them.
4.1) "What is Wrong With the IPCC? Proposals for a Radical Reform" (Ross McKitrick):
IPCC has provided a few climate-change Assessment Reports during last decades. Is a radical reform of IPCC necessary or we should take all the IPCC alarms seriously? What is wrong with Ross argument? The models that are used by IPCC already captured a few crudest features of climate change.
4.2) The sort of typical issues of IPCC reports:
- The summary reports focus on those findings that support the human interference theory.
- Some arguments are based on this assumption that the models account for most major sources of variation in the global mean temperature anomaly.
- "Correlation does not imply causation", in some Assessment Reports, results gained from correlation method instead of investigating the downstream effects of interventions or a double-blind controlled trial; however, the conclusions are with a level of reported uncertainty.
4.3) Nongovernmental International Panel on Climate Change (NIPCC) also has produced some massive reports to date.
4.4) Is the NIPCC a scientific or a politically biased panel? Can NIPCC climate reports be trusted?
4.5) What is wrong with their scientific methodology?
5) Changes in the earth's surface temperature cause changes in upper level cirrus and consequently radiative balance. So the climate system can increase its cooling processes by these types of feedbacks and adjust to imbalances.
6) What is your opinion about political intervention and its effect upon direction of research budget?
I really appreciate all the researchers who have had active participation with their constructive remarks in these discussion series.
% -----------------------------------------------------------------------------------------------------------%
% ---------------- *** Discussions of Global Warming (section 3) *** ---------------%
In this part other specific well-known subjects are revisited. Please support or refute the following arguments in a scientific manner.
1) Still there is no convincing theorem, with a "very low range of uncertainty", to calculate the response of climate system in terms of the averaged global surface temperature anomalies with respect to the total feedback factors and greenhouse gases changes. In the classical formula applied in the models a small variation in positive feedbacks leads to a considerable changes in the response (temperature anomaly) while a big variation in negative feedbacks causes just small variations in the response.
2) NASA satellite data from the years 2000 through 2011 indicate the Earth's atmosphere is allowing far more heat to be emitted into space than computer models have predicted (i.e. Spencer and Braswell, 2011, DOI: 10.3390/rs3081603). Based on this research "the response of the climate system to an imposed radiative imbalance remains the largest source of uncertainty. It is concluded that atmospheric feedback diagnosis of the climate system remains an unsolved problem, due primarily to the inability to distinguish between radiative forcing and radiative feedback in satellite radiative budget observations." So the contribution of greenhouse gases to global warming is exaggerated in the models used by the U.N.’s Intergovernmental Panel on Climate Change (IPCC). What is wrong with this argument?
3) Ocean Acidification
Ocean acidification is one of the consequences of CO2 absorption in the water and a main cause of severe destabilising the entire oceanic food-chain.
4) The IPCC reports which are based on a range of model outputs suffer somehow from a range of uncertainty because the models are not able to implement appropriately a few large scale natural oscillations such as North Atlantic Oscillation, El Nino, Southern ocean oscillation, Arctic Oscillation, Pacific decadal oscillation, deep ocean circulations, Sun's surface temperature, etc. The problem with correlation between historical observations of the global averaged surface temperature anomalies with greenhouse gases forces is that it is not compared with all other natural sources of temperature variability. Nevertheless, IPCC has provided a probability for most statements. How the models can be improved more?
5) If we look at micro-physics of carbon dioxide, theoretically a certain amount of heat can be trapped in it as increased molecular kinetic energy by increasing vibrational and rotational motions of CO2, but nothing prevents it from escaping into space. During a specific relaxation time, the energetic carbon dioxide comes back to its rest statement.
6) As some alarmists claim there exists a scientific consensus among the scientists. Nevertheless, even if this claim is true, asking the scientists to vote on global warming because of human made greenhouse gases sources does not make sense because the scientific issues are not based on the consensus; indeed, appeal to majority/authority fallacy is not a scientific approach.
% -----------------------------------------------------------------------------------------------------------%
% ---------------- *** Discussions of Global Warming (section 4) *** ---------------%
In this part in addition to new subjects, I have highlighted some of responses from previous sections for further discussion. Please leave you comments to support/weaken any of the following statements:
1) @Harry ten Brink recapitulated a summary of a proof that CO2 is such an important Greenhouse component/gas. Here is a summary of this argument:
"a) Satellites' instruments measure the radiation coming up from the Earth and Atmosphere.
b) The emission of CO2 at the maximum of the terrestrial radiation at 15 micrometer.
b1. The low amount of this radiation emitted upwards: means that "back-radiation" towards the Earth is high.
b2. Else said the emission is from a high altitude in the atmosphere and with more CO2 the emission is from an even higher altitude where it is cooler. That means that the emission upwards is less. This is called in meteorology a "forcing", because it implies that less radiation /energy is emitted back into space compared to the energy coming in from the sun.
The atmosphere warms so the energy out becomes equals the solar radiation coming in. Summary of the Greenhouse Effect."
At first glance, this reasoning seems plausible. It is based on these assumptions that the contribution of CO2 is not negligible and any other gases like N2O or Ozone has minor effect. The structure of this argument is supported by an article by Schmidt et al., 2010:
By using the Goddard Institute for Space Studies (GISS) ModelE radiation module, the authors claim that "water vapor is the dominant contributor (∼50% of the effect), followed by clouds (∼25%) and then CO2 with ∼20%. All other absorbers play only minor roles. In a doubled CO2 scenario, this allocation is essentially unchanged, even though the magnitude of the total greenhouse effect is significantly larger than the initial radiative forcing, underscoring the importance of feedbacks from water vapour and clouds to climate sensitivity."
The following notions probably will shed light on the aforementioned argument for better understanding the premises:
Q1) Is there any observational data to support the overall upward/downward IR radiation because of CO2?
Q2) How can we separate practically the contribution of water vapor from anthropogenic CO2?
Q3) What are the deficiencies of the (GISS) ModelE radiation module, if any?
Q4) Some facts, causes, data, etc relevant to this argument, which presented by NASA, strongly support this argument (see: https://climate.nasa.gov/evidence/)
Q5) Stebbins et al, (1994) showed that there exists "A STRONG INFRARED RADIATION FROM MOLECULAR NITROGEN IN THE NIGHT SKY" (thanks to @Brendan Godwin for mentioning about this paper). As more than 78% of the dry air contains nitrogen, so the contribution of this element is not negligible too.
2) The mean global temperature is not the best diagnostic to study the sensitivity to global forcing. Because given a change in this mean value, it is almost impossible to attribute it to global forcing. Zonal and meridional distribution of heat flux and temperature are not uniform on the earth, so although the mean temperature value is useful, we need a plausible map of spatial variation of temperature .
3) "The IPCC model outputs show that the equilibrium response of mean temperature to a doubling of CO2 is about 3C while by the other observational approaches this value is less than 1C." (R. Lindzen)
4) What is the role of the thermohaline circulation (THC) in global warming (or the other way around)? It is known that during Heinrich events and Dansgaard‐Oeschger (DO) millennial oscillations, the climate was subject to a number of rapid cooling and warming with a rate much more than what we see in recent decades. In the literature, these events were most probably associated with north-south shifts in convection location of the THC. The formation speed of North Atlantic Deep Water (NADW) affects northerly advection velocity of the warm subtropical waters that would normally heat/cool the atmosphere of Greenland and western Europe.
I really appreciate all the researchers who have participated in this discussion with their useful remarks, particularly Harry ten Brink, Filippo Maria Denaro, Tapan K. Sengupta, Jonathan David Sands, John Joseph Geibel, Aleš Kralj, Brendan Godwin, Ahmed Abdelhameed, Jorge Morales Pedraza, Amarildo de Oliveira Ferraz, Dimitris Poulos, William Sokeland, John M Wheeldon, Michael Brown, Joseph Tham, Paul Reed Hepperly, Frank Berninger, Patrice Poyet, Michael Sidiropoulos, Henrik Rasmus Andersen, and Boris Winterhalter.
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Yes. Please see the following useful link for insights.
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hi,
I am trying to simulate thrombus (clot) formation under blood flow, I have to solve the convective mass transfer to find the concentration of Red blood cells, by growing the clot the velocity profile will change. I am looking for a way to couple these equations to transfer data between them.
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Khalid B. Saleem Thanks for your answer. I tried to do it, but I was not successful. I am new on Anysy Fluent. But, as far as I know, species transport is not valid for blood flow. It is only valid for mixed flows which already has been defined on the fluent database. Am I wrong?
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when using streamline "surface streamline" in an area between two blocks, streamline disconnected as mention in the pic attached
thanks for your help
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It can be due to the streamlines ending where the integration ended and more of a visualization problem rather than accuracy issue Try plotting with more element density. The streamline plots can be also generated using Tec plot or other similar tools where the shifting of seed points are not noticeable. Proper node to node connectivity of mesh/grids will eliminate this problem but then mesh sizing to be carefully done. Ahmed Fouad
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In certain research papers, I have observed that they have carried out steady state simulation using CFD through ANSYS for solar collectors.
Apart from saving computational time, storage, and efforts, what is the benefit of doing steady-state simulation for a process which in real life is time-dependent due to the intermittent nature of solar radiations and other weather conditions?
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A simulation is always an approximation of reality. It is the analyst's task to decide whether a less expensive steady-state simulation can be a reasonable approximation of a transient phenomenon. If this is not the case, a transient analysis is necessary.
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Hello everyone,
I'm trying to model the motion of a cylinder in both CF and IL directions, but the UDF code that I have only can move the cylinder in the CF direction. Sadly I have never had the chance to learn to code UDF. Can someone please help me?
I will share the code below.
I really appreciate any help you can provide or at least promote this question to find the best answer to my issue.
FYI, this code is for Vortex-Induced Vibration of cylinders
####################################################
#include "udf.h"
#include "dynamesh_tools.h"
#include "unsteady.h"
FILE *fout;
static real v_prev;
DEFINE_SDOF_PROPERTIES(stage,prop,dt,time,dtime)
{
Thread *t;
Domain *d=Get_Domain(1);
real x_cg[3],force[2],moment[3];
real cg; /*Center of gravity position*/
real vel; /*Cylinder velocity*/
real Fy; /*Lift Force*/
real mass=8.88; /*Cylinder mass*/
real fn=1.06; /*System frequancy*/
real wn=2*M_PI*fn; /*System angular velocity*/
real z=0.002; /*Damping coefficeint*/
real k=mass*wn*wn; /*System stiffness*/
real c=2*mass*wn*z; /*System damping*/
/*Get the thread pointer for this which motion is define*/
t=DT_THREAD(dt);
prop[SDOF_MASS]=8.88; /*System mass of the 6DFOF*/
prop[SDOF_ZERO_TRANS_X]=TRUE;
prop[SDOF_ZERO_TRANS_Z]=TRUE;
prop[SDOF_ZERO_ROT_X]=TRUE;
prop[SDOF_ZERO_ROT_Y]=TRUE;
prop[SDOF_ZERO_ROT_Z]=TRUE;
cg=DT_CG(dt)[1];
vel=DT_VEL_CG(dt)[1];
prop[SDOF_LOAD_F_Y]=-k*cg-vel*c;
fout=fopen("results.txt", "a"); /*Open file*/
/*Wrtie data into file*/
fprintf(fout, "%g %g %g\n",time,DT_CG(dt)[1],DT_VEL_CG(dt)[1]);
fclose(fout);
}
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In an article, the authors obtained the Nusselt number like 6.487. When I apply the same operating conditions for the same geometric model, I obtained the Nusselt number like 3.741. How can ı found the nearest value to authors? Thanks for your interest.
Note: I use the (h*Dh/k) for Nusselt number calculation. For the calculation, I obtained surface heat transfer coefficient from Fluent in Excel and I took the average values at thermally developed region for heat transfer coefficient values. In article, thermally developed region was used for calculations.
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I concur with Hayder Jaffal
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I've read in some research articles that they have used anode stoichiometry nearly 2, and cathode stoichiometry more than 2. Is there any thumb rule to fix the stoichiometry of the reactant flow?
Also, if we have more anode stoichiometry, is it practically possible to recirculate the excess hydrogen [from outlet] in an open anode PEMFC in automotive perspective?
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Hi
In my opinion, the stoichiometry of reactant gas (O2 /H2) is most dependent on the flow field and manifold. To control gas velocity and manage the water content in the channel, in some flow fields you must increase the stoichiometry.
There is no clear rule for correcting stoichiometry but you consider that the best stoichiometry is the minimum amount of it which the PEMFC works stable and has maximum performance.
Most of the time, the recommended stoichiometry of the PEMFC stack is given by the stack manufacturer or power system integrator.
Yes, we have three methods for PEMFC stack operation: Flow-through, Dead-end, and Recirculation. In the third method what you said is happening.
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It's not unusual to hear comments like "I don't use CFD, I make my own codes" from professors or researchers. The issue with this is that most of them are not even interested in using CFD software, namely understanding the code, learn how to modify it and validating it before making a judgement. They think of it as a black box which takes garbage in and spits garbage out.
The problem is that we don't have tenure positions at academic institutions like they do, so we don't have the time to write complex codes for --academic problems--, doing so in real life would get us fired from a job. They claim to write their own code, but being honest, most of the time they only tackle academic problems with academic geometries. It's good to learn how to write your own code but you can't always do that for every problem you encounter.
I believe they're not preparing their undergraduates for real-life problems. Now you can access open source codes like OpenFOAM, but to be honest, most college professors don't even care about it. You won't get a job easily if all you did as a PhD student was to write a code for a specific problem, like Freeman Dyson says "I don't like the PhD system because they spend so much time on the same problem".
I think it's better not to try to reinvent the wheel, if there's something free and available, try it! Then make a judgment but do not say things like "CFD is useless" because the people who wrote those codes are not stupid. College professors and researchers have the privilege of spending too much time on the same project, I think.
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This question is interesting and I try to give my opinion.
To answer correctly to this question, let me first clarify what is CFD and what about the role of a professor. Indeed you have to think about it in terms of a very large discipline: fluid dynamics, math, numerical analysis, IT, are the roots of CFD. So you should realize that a student has an educational path to follow, without jumps in it. That is a long way and the use of a CFD code is at the end of this path.
If you think that CFD is only to become an user of a CFD code, you are simply wrong because you are jumping the education to learn CFD and to analyze (and criticize) your results. You don't have to go to the university to learn setting some parameters in a GUI, you can read the users' guide, you can see a lot of youtube tutorial.
Commercial codes are indeed a black box. The references to the methods do not really tell you how the method is implemented. Using a CFD code in a professional way means that you know that, from your previous CFD educational path.
So, a CFD code is a tool, not CFD education by itself. I agree that it should be used in the academy but at a course of applied fluid dynamcs, after the fundamental CFD courses. And you can see the meaning of CFD in any present textobook of relevant authors.
As a real experience, you can read a lot of question on cfd-forum that any experienced CFD student would resolve by itself. As well as you can see a lot of garbage simulations on LinkedIn just because someone has a CFD code to run.
To avoid getting garbage from a CFD code you need to be much more than a simple CFD user. But the present idea of democratization in CFD is more a damage than a progress. A CFD code is not like a TV to simply turn on.
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My field of expertize is in CFD and not in climatology. But I would start a discussion about the relevance of the numerical methods adopted to solve physical models describing the climate change.
I am interested in details in physical as well as mathematical models and the subsequent numerical solution.
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Thank you for the very thoughtful remarks. I know the literature mentioned in your note and I admire the style and depth of these books. In many ways, the book "Big Breasts and Wide Hips" connects in my perception with Marquez's "One Hundred Years of Solitude" due to a subtle and mysterious surrealism.
Regarding the Nobel prize examples from your comment, I would like to suggest an article in The Atlantic:
(I disagree with some of the opinions above but the paper is very interesting).
As far as my philosophy is concerned, I see a big role for the models of a continuum which, in the present mathematical form, were introduced by Euler in the 1750s. I also think that we can considerably improve our numerical weather prediction models, but I also share some of your skepticism about very long-term digital projections.
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I am currently working on Nozzle CFD analysis using ANSYS FLUENT application; I have since been able to plot some flow parameters contours and profile. Now, I am having challenges plotting the turbulence intensity contour.
Any idea from anyone on how to go about this?
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Thanks for your accurate answer
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Hi All,
I have multiple 3D snapshots of a tractor trailer exported from CFD. I am doing some other data analysis on them and then I want to visualise the contour of this processed data. To start, I am just trying to plot CFD data directly using x,y,z cordinate and velocity values.
The problem I am mainly having is:
a. Contour does not capture the geometry boundaries properly and the shape looks distorted. My x,y,z,u,v, and w are column vector. when I make mesh grid of x.y at z=0, I use griddata command to reshape my velocity vector into the same n by n vector as mesh grid is.
b. When I was trying to reshape my velocity vector on the meshgrid using GRIDDATA() command, it was giving warning of duplicate data points have been detected and averaged. I resolved this using unique() command but this has not made any improvement n visualisation.
I have attached some matlab pictures of my results and a picture of CFD result which I am expecting to see.Please find the link below of one snapshot of data if someone wants to give a try.
below is the code I am using. I use for loop as later I will be using multiple files.
clear all; clc; close all;
%Read data Files%
dataName='saved_data'; % save a file in the directory to keep all data
save(dataName); %Save empty file
dinfo = dir('*.txt'); %Read directory for all text files
files={dinfo.name}; %save names of all text files in files to use in the loop
delimiterIn=' '; %How data is seperated
headerlinesIn=1; %is there any header
n=numel(files); % number of snapshots
for j=1:n
currentFile=files{1,j}; %load jth snapshot
raw_data=importdata(currentFile,delimiterIn,headerlinesIn); %read data in the snapshot
%and save it in raw data
end
%% Raw data%%
X=raw_data.data(:,2);
Y=raw_data.data(:,3);
Z=raw_data.data(:,4);
U=raw_data.data(:,11);
V=raw_data.data(:,12);
W=raw_data.data(:,13);
%% Scatter interpolant%%
[~, I, ~] = unique([X Y Z],'first','rows'); %here I noticed that there were some duplicate data points which I removed
X1 = X(I);
Y1 = Y(I);
Z1 = Z(I);
U1=U(I);
V1=V(I);
W1=W(I);
U2 = scatteredInterpolant(X1, Y1, Z1, U1); %this does not have any duplicate warning now
V2 = scatteredInterpolant(X1, Y1, Z1, V1);
W2 = scatteredInterpolant(X1, Y1, Z1, W1);
spacing=200;
x1=(linspace(min(X)/5,max(X)/4,spacing))';
y1=(linspace(min(Y),max(Y)/8,spacing))';
z1=(linspace(min(Z)/4,max(Z)/4,spacing))';
[xmesh, ymesh] = meshgrid(x1,y1,0:0);
%% Make velocity grid with U, V and W%%
u1=griddata(X1,Y1,U2.Values,xmesh,ymesh); % Again giving duplicate data point warning and removed however the size is still 20 by 200.
v1=griddata(X1,Y1,V2.Values,xmesh,ymesh);
w1=griddata(X1,Y1,W2.Values,xmesh,ymesh);
res_vel=sqrt(u1.^2+v1.^2+w1.^2);
%% Contourf Plot U,V data%%
h_fig1 = figure(1);
contourf(xmesh,ymesh,res_vel,0.0001:20)
colorbar()
caxis([-1, 27]);
To summarise, Any suggestion how to make velocity background better in the contour.
secondly, if the problem is not with the griddata then any way of improving the quality of boundary captured and results. I noticed the velocity in the surrounding area is high but the contour is showing a small value.
I really appreciate any help as I am stuck here for a long time.
Thanks
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Alsalamo alikom,
I think you can add arrows by coding or the plotting commands options or one by one separately for the figure editor. or add markers with another color.
Best wishes
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I have a question on Cp in the wind turbine. I have calculated the moment in the z-axis as my rotor also rotors along the z-axis. I got the moment values from my simulation. I applied the procedure which ansys recommended formula (P= torque x rotational velocity) for extracting power from the turbine. I got huge discrepancies between actual and theoretical. After calculating power, I have calculated Cp it comes around 0.8 to 1, but the Betz limit is 0.59. plz help me to calculate the Cp.
Conditions :
Turbine Aera =17.5 m2
R=3.5m
V=3
omega=2.14 rad/s
TSR=2
Fluid water (990 is the density)
 
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Rajasekarababu Kb please follow the video and the steps elaborated i hope it will help you a lot .
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hello, I'm using Ansys 2021r2 Academic edition, I finished the mesh setting on my laptop and get the desired output , then cleared the generated mesh and saved the file as" wbpz "
when running this file on my remote pc the out mesh is not like what I get first
as you can see in the attached pic the good one is done on the laptop, and the bad one on remote .
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I think mesh output is independent of computer spec. Have you checked the mesh setting (I mean the main Mesh node on the "Outline" tree) on both computers side by side??
Archive stores the local mesh boundaries properly and they shall be identical on both computers. However, some of the mesh settings that are governed by the "Option" in "Mechanical" interface. "Mechanical" stores last setting every time you close the interface and that is why the settings can be slightly different on different computers.
If you want to make sure that all the settings are identical on both computers you need to do the following steps:
1. Find the following folder on the computer that provides good mesh.
C:\Users\XXXXX\AppData\Roaming\Ansys\vXXX
2. Copy this folder on the computer that doesn't provide good mesh. I assumed that you are using same version of ANSYS on both computers. ****Also, make sure you have backup from this folder in case you want to restore it to what it was before.
By doing this, you ensured that all the settings for both software are identical and then you will definitely get same result.
Hope this answer helps!!
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Hello, I have attached an interval to alter the deposition of energy with time. How can we write this code using the expression language in FLUENT or CFX ?
Thank you very much !
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