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# Boundary Layer - Science topic

Explore the latest questions and answers in Boundary Layer, and find Boundary Layer experts.
Questions related to Boundary Layer
Question
Hello Everyone
I now estimate the height of the Atmospheric Boundary Layer (ABL) using SODAR data, but I'm now attempting to use Radiosonde data to estimate and analyse the seasonal and annual ABL height. Please assist me in determining the ABL height using radiosonde data.
A little outside my expertise, but I did find this...
Let us know if this helps!
Question
Hello all,
I've got a 2D simulation case in which the flow separates from the sharp leading edge of rectangular bluff body and reattaches to the wall some distance downstream. The main goal is a accurate prediction of pressure distribution along the body's face parallel to the flow.
I'm doing a transient simulation using SST model in conjunction with gamma-Re transition model. The time- cord-averaged y+ is less than 2~3 and the inflation layer around the face of interest contains 10 prism layers. The Re number based on the body's width (perpendicular to the flow) is 1.7e+4.
The problem is that my model overpredicts the reattachment length, which in turn leads to delayed pressure recovery.
I have a suspicion that longitudinal decay of turbulence values specified at the inlet might be to blame. Consulting the Ansys CFX-solver Modeling Guide, I learnt that one solution is to prescribe appropriate turbulence values at the inlet based on the desired values at the body. An alternative approach also suggests some additional source terms for k and w transport equations in order to preserve the inlet values up to some distance upstream the body, from where decay is allowed.
Here are my questions:
1- Is my suspicion valid in the case of my problem?
2- Is the decay of turbulence of physical basis or a numerical artifact?
3- which of the two methods works better? Are there any attempts in the literature?
trying to achieve a match with experimental measurements is not a simple task. In your formulation you should match the statistics of the experimental inflow and that is not straightforward also for a laminar flow problem as detailed in Sec.4 here
A further issue could be also due to the fact your grid resolution is not sufficient to resolve the BL. You should be able to set at least 3-4 nodes at y+<1 along the surface of the body.
Again, I strongly suggest to try your setting for the well studied problem of the backward facing step turbulent flow. You can find a lot of results in literature.
Question
Is the similarity transformation the sole way of transforming the boundary layer governing PDEs into ODE ?Or do we have any alternative ways of doing it??
The following references shows how one can use various transforms to aid in solving specialized PDE's by transforming into problems that can be solved by ODE's. The Fourier transform is one.
Of course separation of variables is a well known technique when the variables can be decoupled. In the analysis of the Hydrogen atom, one can use the fact that the potential is spherically symmetric (only depends on the distance from the proton) and the problem can be transformed into the the analysis of the equivalent Strum-Louisville problem in ODE.
For first order PDE, the method of characteristics can be used to generate an equivalent set of PDE's. For a rigid body in three space, the dynamics is described by ODE instead of PDE since the dynamics is invariant under SO(3), the Lie Group of rotations in R^3.
In general symmetry that results by the invariance of a Lie Group action the PDE will lead to the decoupling and/or reduction of variables. This can often head to solution by ODE. However, it is very equation dependent.
Question
Hello,
I have a hot-wire measurement record in the boundary layer in the wind tunnel. There should be fully developed turbulent boundary layer in the wind tunnel flow. I used Matlab to calculate the integral lentgh scale a then the non dimensional spectra. In the pictrure, I used the pspectrum function (red), Welch (cyan), Fast-Fourier transform (blue) to calculate the spectral densities. Then I added the von Karman spectrum (green), but the slope of its right part is not the same as the others. I added also the Kolmogorov inertial scale f^(-5/3) and its slope corresponds with the calculated spectrums. Do you have any ideas why the von Karman spectrum is tilted and the Kolmogorov scale is not? I am running out of ideas, thanks for help.
Sorry to say that the figures have no sense, why do you have different range of resolved frequencies?
And if you are in the BL, the flow is not homogeneos, the spectra will depends on y+.
You should clarify the way you are measuring the velocity.
Question
Hi, I tried to mesh a 3D airfoil with vortex generator. There are two ways, one is to use multizone and divide each faces. Another way is using Cutcell. In the second type of mesh, the inflation command is not applied to create the boundary layer and the software gives an error. And in the first type of mesh, the vortex generator part does not mesh correctly. Thank you for guiding me in this regard.
Is there another way to mesh apart from these two methods?
The software used is Ansys Meshing.
try these.. geometry looks simple enough to have adequate meshing.
Question
Planetary Boundary Layer Height and its diurnal change
A tough question in any kind of complex terrain. The classic definitions do not work
Question
Hallo,
the normal Rosseland radiation model that I can select in Ansys fluent only simulates thermal radiation from a surface to a fluid (or another surface). Is this correct? I would like to take a look at thermal radiation inside a thick fluid (with rosseland approximation). A hot fluid boundary layer "radiates" toward a cold boundary layer. Do I need to do this via user defined function? Does anyone have experience with this in Ansys? I look forward to any hints or comments.
best regards
From a theorethical point of view, radiation does not require a material to propagate, in fact, light propagates better in vacuum.
In a medium light is partially absorbed and the rest is transmitted. The part of light which is absorbed, depends of the interaction of light with the molecules and after it this reemited as Rutherford Scattering. Then Roseland does not apply.
If you have experimental data of absorbance and transmitance spectra, you could introduce the information through an external routine in fortran, but would need to create the model.
Perhaps is better to quantify if convection and difussion are more important than radiation
Question
I am working on Shock wave boundary layer interaction in hypersonic intake. So, could anybody suggest me some methodology that I can use to simulate the same in ANSYS Fluent or any other CFD analysis tool?
Of course, the ANSYS Fluent can be used to simulate the shock wave/boundary layer interaction. Firstly, the SBLI is a compressible flow problem, we can choose the density-based solver for simulation when the flow Mach number is high or the pressure-based solver for simulation when the flow Mach number is low. Secondly, the energy equation should be activated. Thirdly, the turbulence model is significant for the simulation results: if the inflow Reynolds number is low so that the boundary layer is in a laminar state, the laminar flow should be chosen, or the RANS model such as SA, SST, etc., which can predict the flow separation induced by an adverse pressure gradient, should be selected. Moreover, we can also try the LES or RANS/LES simulation method. That's a little self-experience for simulating SBLI. Hope that can help you. :)
Question
Hi everyone,
I want to calculate the boundary layer thickness in a pipe of water and Re number 12000. Is there any formula that gives the bl thickness for internal flows?
Nikos.
This is a classical problem of wall-bounded parallel flow. Let D be the pipe diameter, Re the Reynolds Number, nu the kinematic viscosity, Ro the fluid density and y is the distance to the wall. In the logarithmic zone, the turbulent shear stress Roxu*^2 is constant where u* is the friction velocity. We should have:
Ro*u*2*Pi*D*dx=dp*pi*D2/4 so that we have:
(dp/dx)=4*Ro*u*2/D
So if we may calculate the pressure loss (dp/dx) using for example Blasius Formula for smooth pipe : (dp/dx)=Lamda*Ro*V2/2 with Lamda=0.316/Re0.25 (or any other head loss formula for rough pipes) we will thus be in a position to calculate the friction velocity u*. Let's define the Reynolds number y+(adimensional distance to the wall) y+=u*y/nu The thickness for internal flows (y) is so that y+=11
Question
to study the adsorption kinetics of COD of wastewater by activated carbon.
the Intra-particle diffusion model was applied but we found the value C (which is related to the boundary layer thickness) is a negative value and the coefficient of regression between 0.95 and 0.99??
the C is wrong to value or no.
the equation: qt = kid t(0.5) +C
if just .what is the interpretation??
Intraparticle diffusion kinetic model is explained herein: https://youtu.be/iwi1c_-_qyQ
Question
Hello everyone,
I am trying to understand the phase change boundary layer formation for flow between two parallel plates. Both plates are at -20 degrees and the water inlet temperature is 10 degrees. I am initially trying to visualize the phase change boundary layer (i.e., ice layer) on both plates. Trying to understand the steady-state case.
However, velocity & thermal boundary layer formation is perfect. Once I switch on the solidification/melting model in FLUENT, the solution becomes wrong. Velocity and thermal boundary layer becomes wrong and no phase change happens.
Any help/insight is greatly appreciated.
Please send me the case file
Question
I am designing a turbine and predicting the Performance of the Vertical Axis Turbine. I have the experimental results of the same turbine with me. The problem is after the optimum TSR, the performance of don't go down its continuously increasing and goes above the Bitz limit. May be its not concluding stall due to high TSR. How do i resolve it?
Geometry -- Mesh -- CFx
Doubt i have but need help to resolve,
* I unable to capture the correct boundary layer, if it so then how could i capture it?
*Maybe i am using Turbulence model which is not correct, But i have chosen shear stress transport which is be better choice, mabe?
* Also share if you any any other.
I will be very thankful, and please make it urgent.
Ahmed Gharib Yosry Thanks for your assistance. i tried to reverse the boundary conditions, replace the inlet and outlet with each other. but the torque doesn't goes down the optimum value.
Question
If a well developed laminar flow passes through a tube with a rough inner surface, will the laminar boundary layer merge at the tube center, or it just stabilizes very close to the rough tube wall? The tube inner diameter is around 10 mm.
In this case you can find boundary layer thickness less than tube radius between zero and tube radius X. The approximate experimental expression for the tube inlet length (L) calculation is: L/D=0.0288ReWhere, d  is tube diameter, Re  is Reynolds number.
All the best Guo Li
Question
My question is back
I'm running the WRFV3.8,
I would like to have more vertical levels within the boundary layer.
I know the way of doing that. But I lack the ability to customize the vertical levels quickly. My main worry in the above is time-consuming.
How may I determine quickly that eta level 1 corresponds to 8m AGL without consuming time?
Then if I have to set, for example, 109 eta levels for my particular interest such as increasing the number of layers within the boundary layer, how to do that without consuming time?
Is there any way of generating them automatically?
I think there is a file called "namelist" which you can edit it by changing the input characteristics such as vertical level number.
Question
I am studying the effect of inserting perforated baffles inside a rectangular channel on heat transfer enhancement and flow friction features inside the channel. The upper and lower surfaces of the channel are thermally active while the side walls are considered adiabatic. The study is a numerical one using a Fluent three-dimensional model. I need to determine the thermal boundary layer thickness on the thermally active walls (upper and lower walls) where the baffles are mounted on these walls in a staggered fashion. I want to analyze the effect of baffles' presence on the development of thermal boundary layer and heat transfer augmentation as well. Thus, how could I measure the thermal boundary layer thickness using ANSYS Fluent program?
Hi,
In this case, you can draw the temperature profile between the upper and the lower walls (vertical on the walls).
Question
Using Salome I made a mesh of a model with internal flow fluid phenomonen.I need help to know that to increase the number of nodes and make the aspect ration better I converted my triangular mesh overall to a bi-quadratic (using" Conver to/from biquadratic" option).This made Aspect Ratio near to 1 but I am worried that since the A.R changed in the boundary layer mesh as well(which was not my target region) will it behave abnormally and give bad results?Should boundary layer mesh be kept unmodified?
Thank you
Rani P Ramachandran
.A new way might be to see by converting it to and from quadratic and check Y+ value.Good strategy.
Question
All high-lift devices increase the value of the maximum lift coefficient (CLMAX). Two common ways to increase CLMAX are to increase the camber of the airfoil or to delay the boundary layer separation. The usual method of increasing the camber is through the use of trailing-edge flaps (DA'F, 1970). The deflection increase boundary layer energy only, slats increase boundary layer energy and increase the local camber, and leading edge flaps increase the local camber only (Kluga, 1985a). One main disadvantage of slots is the high stall angle created. The airplane must approa~h for a landing in an extreme nose-up attitude which promotes reduced visibility.
Twist is an aerodynamic feature added to aircraft wings to adjust lift distribution along the wing. Now by using twistable flaps could augment aerodynamic efficiency during critical flight paths i.e. take off and landing where flaps play important role.
Question
I have watched videos about wall function on youtube but still confused about understanding viscous sublayer, logarithmic region, and wall functions. I couldn't find relevant material. Where do I find these topics? Can someone suggest some material regarding viscous sub-layer/logarithmic region and to understand y+ (wall functions)?
I would add that the meaning of y+ is very very simple. It is nothing but that the local Reynolds number measured along a normal-to-wall direction. That is, y+=0 is the wall position and then the value increases according to y+=(u_tau/vi)*y.
Question
Hi,
I am trying to set up WRF model and I would like to specify explicit eta levels. My study will primarily be focused on storms and the boundary layer, so ideally, I would like to have very high resolution upto 3 km altitude. I am using three domains of 9km, 3km and 1km resolutions, with two way nesting. I am unaware of any thumb rules we need to follow or factors we need to keep in mind while deciding the vertical levels. Can you please educate me about them and help me out?
Also, I was told that, in case we don't want to specify eta levels, the number of vertical levels needs to be
Height of model top/ (0.1*Resolution of innermost domain)
My model top will be around 20km (50 hPa), so if I go by this rule, I will end up using 200 vertical levels. Please help me understand why it is necessary to have these many levels.
Thankyou.
A related issue is the consistency between vertical & horizontal spacings. A paper was written by Mahrer in the 90s and another by by Fox-Rabinovich & Lindzen
All the best
Question
Do not be used from the boundary layer mesh in structured mesh (ansys meshing), when the fluid flow is turbulence ?
Because it is important in the turbulent flow checking the amount Y+
Are the correct simulation results without a boundary layer mesh in structured mesh?
Thank you
In unstructured mesh, you can set the first layer height using the inflation option.
Also, in a structured mesh, you can set that using edge sizing and proper "number of divisions" and "bias factor."
Question
I am trying to answer this question to round up a table on safety and hazard characteristics of H2 for homes (completed the information on odorless nature of H2 and near-invisible flame.
For flame flashback, I find no clear prevention measures; only analysis of certain factors (e.g. combustion induced vortex breakdown and wall boundary layer flashback)
Thus, the boundary layer fluid injection is to some degree capable of preventing the flame from entering the tube, however, it cannot stop the flashback process once it has started and the flame is confined inside the tube.
Thus, boundary layer flashback is prevented more effectively when the injection takes place closer to the tube exit.
Thanks a lot Sven. This is good to hear about.
Question
The boundary layer formation over a circular cylinder when it is submerged in unidirectional flow is a well-established phenomenon. However, I am looking for the phenomena and characteristics of the boundary layer formation over the cylinder when placed in circulating fluid flow.
I believe it would still be the same. Laminar boundary-layer flows occur when a moving viscous fluid comes in contact with a solid surface and a layer of rotational fluid, the boundary layer, forms in response to the action of viscosity and the no-slip boundary condition on the surface.
My reference is: Pijush K. Kundu, Ira M. Cohen, David R. Dowling,
Chapter 10 - Boundary Layers and Related Topics,
Editor(s): Pijush K. Kundu, Ira M. Cohen, David R. Dowling,
Fluid Mechanics (Sixth Edition),
2016,
ISBN 9780124059351,
Question
It is well established when a circular cylinder is submerged into a polymer layer, a thin polymer is formed over the cylinder. My question is what is the mechanism of the formation of the polymer layer over the cylinder. Moreover, Is there any relation between the adsorbed polymer layer and boundary layer formation based on the fluid mechanics? If you have any suggestions please let me know.
The thickness of a diffusion boundary layer around a cylinder can be estimated for short times, by considering the growth of a thin unsteady boundary layer on a flat plate. The thickness d will scale as d=1.7 sqrt(D t) with D the diffusion coefficient of the polymer in the solvent. Assuming the concentration of the polymer on the surface to be unity, one can calculate the flux of mass towards the cylinder, which decreases as 1/sqt(T). The integral of this mass flux provides an indication for the thickness of the polymer layer (taking into acount the density of the polymer). This should yield some order of magnitude estimate and insight into relevant control parameters. This is analogous with heat transfer. This very crude model has been used for a viscous boundary layer on a rotating cylinder in order to estimate the onset of centrifugal instability. Onset of centrifugal instability at a rotating cylinder in a stratified fluid . The model does not assumes any effect of the rotation of the cylinder on the boundary layer thickness and is still quite succesful.
Question
Is temperature gradient at wall proportional to thermal boundary layer thickness or not?
If you can understand my question, please find attached figure.
If they are proportional to each other or not, please explain.
When calculating the heat transfer Colburn factors were used.
Question
Hello everyone, I would need some help with a calculation that I am trying to do.
Let's suppose I am trying to understand the the diffusion limitations of oxygen in the burning of a solid fuel.
I would like to get the concentration of the oxygen at the surface of the fuel, and understand the thickness of the boundary layer.
The data I have available is the flow of air in the combustion chamber, as well as the particle size distribution of the fuel.
Does anybody know how to proceed?
Thank you!
You will have to calculate the diffusivity, yes, and be able understand the boundary layer theory. The diffusivity in this case solid-gas interface. There are alots of analogies that are made available to this extreme. The concentrations and pressure data and mass transfer coefficients must be made available to clearly understand this concept. I recommended you consult materials Transport Phenomenon. You may also check review material on Mass transfer coefficients, and boundary layer theories.
Question
Hello experts, as part of the control of the separation of the turbulent boundary layer on an aerodynamic profile, by a synthetic jet such as this jet has been modeled by an oscillating membrane. the displacement of this is done by a sinusoidal function using (UDF).
what values should I use in the boundary conditions (specification method) to model this synthetic jet?
Best regards,
Dear Obayes
The pdf attached by you is a master thesis which is just a preview of the work, not the entire thesis. If possible kindly attached the full thesis.
Thanking You
Question
In Engineering, Science, and Fluid Dynamics, there are many unitless numbers very useful for effective simulation. However, is there any parameter you analyze recently and you just appreciate your observation?
Which dimensionless parameter have you analyzed and deeply appreciate it's significance?
The Reynolds number (Re) helps predict flow patterns in different fluid flow situations.
Question
Dear researchers, I want to simulate a flow (air) in a wind tunnel, and I want to integrate a fluidic actuator inside it in order to control the separation of the boundary layer. At the blower inlet a velocity of 30m / s is imposed and at the inlet of the fluidic actuator of 0.3 MPa is imposed. My question are:
should I use Pressure Based Solver or a Density-Based Solver?
Dear Prashant, thank you so much for your help
Question
Dear researchers, I want to simulate a flow (air) in a wind tunnel, and I want to integrate a fluidic actuator inside it in order to control the separation of the boundary layer. At the blower inlet a velocity of 30m / s is imposed and at the inlet of the fluidic actuator of 0.3 MPa is imposed. My question are:
should I use Pressure Based Solver or a Density-Based Solver?
The pressure-based approach was developed for low-speed incompressible flows, while the density-based approach was mainly used for high-speed compressible flows. However, recently both methods have been extended and reformulated to solve and operate for a wide range of flow conditions beyond their traditional or original intent." "In both methods, the velocity field is obtained from the momentum equations. In the density-based approach, the continuity equation is used to obtain the density field while the pressure field is determined from the equation of state." "On the other hand, in the pressure-based approach, the pressure field is extracted by solving a pressure or pressure correction equation which is obtained by manipulating continuity and momentum equations." The pressure-based solver traditionally has been used for incompressible and mildly compressible flows. The density-based approach, on the other hand, was originally designed for high-speed compressible flows. Both approaches are now applicable to a broad range of flows (from incompressible to highly compressible), but the origins of the density-based formulation may give it an accuracy (i.e. shock resolution) advantage over the pressure-based solver for high-speed compressible flows."
I hope this answer helps you
Question
To keep surface relative humidity constant at 77%, when the potential temperature increases from 288K to 300K, we must increase specific humidity of boundary layer from 8g/kg to 16,7g/kg and soil temperature from 285K to 297K. What is the equation from which these values can be derived?
Following
Question
Simply a fluid is flowing over a flat plate.
#Fluid mechanics
#Boundary layer
The pressure across the boundary layer does not change. The pressure is impressed on the boundary layer it value can be calculated by hydrodynamic consideration.
Question
I want to ask how the displacement and momentum thickness can be calculated from CFD results?
should I plot the velocity profile at the location I want to calculate the displacement or momentum thickness, then from the data point I have to predict an equation relating the velocity with normal distance from the wall. Then finally integrate the equation?
I am not sure how it can be calculated, can anyone help?
Dear Zein
I hope you are doing well.
what you suggested is fine and Dr Han approach is very typical
Good luck
Osama
Question
The intraparticle diffusion model, introduced by Weber and Morris, is one of the most commonly used techniques to identify the diffusion mechanism. Where kint is the intraparticle diffusion rate constant and C is a constant, related to the thickness of the boundary layer. In the phenomenon of adsorption, a multilinearity expressing the existence of multiple sequential steps is given in several works.
One can also use the description based on the analogy to catalytic non-stationary processes. However, solving the inverse problem for partial differential equation/s is difficult.
Question
I am trying to validate the experimental results from a paper but I am not able to replicate the profile of turbulence intensity in the domain. I have explained the entire problem statement in the following word documents and also attached the relevant UDF and papers. It would be really helpful if anyone could give some insights as to how I could change my UDF/simulation setup in order to get accurate results. Thank you.
There are a few parameters missing from your udf,
You can get it from the udf attached below.
This worked with the test condition I have used.
Cheers
Question
Hello, I'm a graduate student at UNIST, South Korea.
I have a question after reading your recent paper, "Urbanization in an Underdeveloped City—Nanning, China and its Impact on a Heavy Rainfall Event in July".
How did you get output variables of heating rate induced by boundary layer (BL), radiation scheme (RA), cumulus scheme (CU), and microphysical scheme (MP) in Figure 8?
It would be very helpful for my research if you let me know.
Different materials heat up at different rates, and calculating how long it will take to raise an object’s temperature by a specified amount is a common problem for physics students. To calculate it, you need to know the specific heat capacity of the object, the mass of the object, the change in temperature you’re looking for and the rate at which heat energy is supplied to it. See this calculation performed for water and lead to understand the process and how it’s calculated in general.
Calculate the heat (Q) required using the formula:
Q = mcT
Where m means the mass of the object, c stands for the specific heat capacity and ∆T is the change in temperature. The time taken (t) to heat the object when energy is supplied at power P is given by:
t = Q ÷ P
1. Calculate the Change in Temperature in Celsius or Kelvin
The formula for the amount of heat energy required to produce a certain change in temperature is:
Q = mcT
Where m means the mass of the object, c is the specific heat capacity of the material it’s made from and ∆T is the change in temperature. First, calculate the change in temperature using the formula:
T = final temperature starting temperature
If you’re heating something from 10° to 50°, this gives:
T = 50° – 10°
= 40°
Note that while Celsius and Kelvin are different units (and 0 °C = 273 K), a change of 1 °C equals a change of 1 K, so they can be used interchangeably in this formula.
Question
Hi, all.
We know boundary layer thickness of flat plate (Blasius solution) as 0.99 U.My question is can we apply the same phenomena to airfoil (flat plate approximation) or is there any formulae or terminology/relation to estimate boundary layer thickness of an airfoil.Please, someone, explain and also the influencing parameters. Thanks all
Question
I want to use standard sandpapers of different grit sizes to impart flow resistance to a surface. I am wondering how to convert the roughness of sandpaper to an equivalent sand-grain roughness. Is there any established correlation between grit size and equivalent sand-grain roughness?
Question
I have found that someone has posted kind of criteria for Near wall functions to solve boundary layers. The five types of wall functions are :
1. Standard wall functions (30 < Y+ < 300)
2. Scalable wall functions (Y+ > 11.225)
3.Non-Equilibrium wall functions (30 < Y+ < 300)
4.Enhanced wall treatment (Y+ < 5)
5. User-defined
A problem was solved with converged solution by taking Y+ <5, and using Standard wall function instead of Enhanced wall treatment as refered above. Because the model in this problem has small gaps and impossible to put first layer with Y+ between 30-300.
So, is this solution correct ?
"
However i am not sure to understand what you mean when saying you model has small gaps. "
There are narrow channels within the geometry, then it is not good to create coarse mesh.
Question
Hi all,
I hope you all are doing well. I am working on the simulation of airfoils with boundary layer suction. I found a reference to validate my CFD results, as shown below.
"Stanewsky E, Délery J, Fulker J, de Matteis P, editors. Drag Reduction by Shock and Boundary Layer Control: Results of the Project EUROSHOCK II. Supported by the European Union 1996-1999. Springer Science & Business Media; 2002 Apr 24."
They used RAE 5225 and DRA-2303 airfoils, but their coordinates were not given explicitly. Kindly share it with me if anybody has the coordinates.
Also, please feel free to suggest any other references which contain detailed experimental data of boundary layer suction on airfoil shapes.
Dear all,
Ahmad K. Sleiti and Ahmed Ramadhan Al-Obaidi, I could not find the coordinates of RAE 5225 or DRA 2303 airfoils on the website. Please correct me if I am wrong.
Faraz Ahmad, As I mentioned, I could not find the coordinates anywhere given explicitly.
Question
Hi
I am trying to model an impeller rotating at a certain angular speed using MRF technique in Ansys fluent. Overall i expect clean attached flows and I am not really interetsted in resolving the boundary layer as I am more interested in studying the mixing of 2 liquids by the impellers. As i understand K-omega reliazable model is computationallly expensive and more for resolving the boundary layers. Which turbulence model is better for my flow as I want to keep my model light weight so that it is easier for convergence and computationally less expensive. Your advise will be really appreciated
Thanks/Regards
You can begin by trying different k-epsilon models (standard, RNG, realisable ) and compare it with experimental data.
Question
I am currently working on a project involving shock / boundary layer interactions using experiments and CFD. I am looking for some books / papers where I can get the theoretical understanding of such interactions.
I plan to model the flow using RANS if possible, but I'm not counting LES or DNS out just yet.
Any additional info on this topic will also be highly appreciated.
Several researchers in this field: Zheltovodov, Bushnell, Borovoy.
Question
Any software that you recommend which can help in obtaining precise PBL (Planetary Boundary Layer) structure/height using the raw ceilometer data as an input.
Thank you.
Hi Nakul,
In most of the ceilometer, aerosol topmost layer (seibert et al., 2000, Munkel et al., 2007) is consider as PBL (most of the time it referred as mixing layer height during windy day time period/residual layer during stable night period).
As you mentioned that you want to retrieve PBL directly from a software. So, I would like to suggest you that based on manufacturer of ceilometer, software available.
CHM viewer -Lufft CHM Ceilometer
Lab View - Vaisala ceilometer.
Hope so this information is useful for you.
Question
Hello everyone, I am confused about whether the boundary layer formation takes place in case of ideal fluids?
The boundary layer appears when there is a no-slip condition at the interface between the fluid and its wall. You may assume the no-slip condition just for the real fluid, not for ideal fluid. As you know, when you assume the fluid is ideal, then it means that the fluid has no viscous effect or inviscid (non-viscous). In other words, the no-slip assumption is valid when you consider that the fluid has its viscosity effect. With this assumption then you may have the boundary-layer flow.
Thank you and have a nice Saturday night at home.
Best regards.
Nazar
Question
Hi, everyone.
I‘m studying on the properties of the boundary layer with different free-stream velocity, and I'm wondering how to determine its thickness.
@Lifeng Tian,
I did it for turbulent BL. Anyways, I don't know whether it will work in your case or not. However, if it doesn't work, then PIV is only option, I think!
Thanks.
--Arnab.
Question
I have two non-linear coupled pdes which are basically non-similar boundary layer equations.Is there anyone who can tell me the numerical technique by which I can solve it easily. Here I'm attaching the equations.
Your notation is questionable, I see explicitly the independent variable "csi" but then you use the prime for the derivatives of f. What about the other independent variable, is that the vertical direction "eta"?
Generally, other than using the FD method, a third order PDE is converted in three first order ODE, as illustrated here
You can find a lot of literature about the numerical methods for such equations.
Question
Also i need to know how to exactly calculate the roughness element height
I have attached the required details and formula
any helping material or method or insights will be great for my master thesis research
For compressible flows because the airfoil is curved there is a transverse pressure gradient near the surface. In such cases it is necessery to compute the theoretical (ideal) velocity profile first (by taking total pressure equal to stagnation pressure of the inflow and using isentropic flow equations to get velocity which is not a constant value as in case of a flat plate flow). In the next step you need to find a point at which the velocity in your flow is reaching e.g. 99.5% of this theoretical (ideal) profile. This way you will find your boundary layer edge on a convex surface and be able to compute for example integral parameters, such as displacement or momentum thickness.
Check any Myring's publications for details...
Regards
Oskar
Question
I am looking at a specific namelist.input tailored for urban areas.
Thanks.
p.s. WRF version 4.0
Thanks a lot Ravindra!
Question
1. In near-wall region, to what degree is the rough-wall boundary layer confined?
2. On which occasion to use the roughness height h and the ratio of height and boundary layer thickness h/δ, respectively?
3. It seems that when h/δ is limited to 0.2, the Townsend's hypothesis is valid from which the roughness elements won't affect outer layer in near-wall region. Whereas h/δ larger than 0.2 has impact on the entire boundary layer (inner-layer and outer-layer) so the Townsend's hypothesis won't be applicable.
4. Quote the numerical work done by Leonardi and Bhaganagar for turbulence channel flow, the roughness effect can be observed in outer layer. Seems like a paradox to Townsend's hypothesis. Could anyone give a reasonable explanation?
5. Research on wall similarity hypothesis is mainly focused on the collapse of mean velocity profiles, structural changes, Reynolds stresses and their contribution, is that right? what else should be included?
Dear Yuna,
much depends on the Reynolds number and on the type of fluid we are talking about (gas, Newtonian or non-Newtonian fluid ...). In general, these topics are not of binary character, they are continuous. Although I did not read Leonardi and Bhaganagar, I am not surprised from their result as for me it is absolutely clear that Townsend's ideas stem from a futher past and cannot simply applied today, when a simple cook-book like approach is no longer applicable.
I attach couple of papers which underline that you touched a serious problem: the task to overcome simple empiricism which today is still very common. We measure "turbulent things" mostly very nicely, but we do not UNDERSTAND them.
Here is a paper which makes a first attempt to change that:
For me it would be a great joy to cooperate with people who are intersted in wall turbulence, e.g. around the superpipe/Princeton or CICLOPE and other facilities. Then one could improve or extend existing approaches. E.g., if you come from the oil world, then please are aware that oil is no standard fluid like e.g. water, it is of non-Newtonian character so that the turbulent boudnary layer with non-zero roughness challenges the brain.
Question
Hi all. I am doing a simple CFD simulation flow past over spherical body to understand the concept of y+ and boundary layer.
I have a simple question related to log-law layer. I read that for this region the value should be in between the range of 30 to 300. Now, how I should know that for my simulation y+ value 35 is good enough or 60 or some high value?
This question is somehow often not well formulated by people.
1) First of all, the definition of y+=y*u_tau/ni says that it is a local Reynolds number evaluated from y=0 at the wall. That variable is similar to the Re_x along a flat plate. Therefore, the wall law U+(y+) is defined in terms of a continuous variable in the physical space, that is theory not a numerical results. There is not discretization in the physical meaning of the log-law.
2) When you talk about a numerical simulation, the grid in normal-to-wall direction defines a set of discrete values y+, starting from y+= for the node on the wall, y+=hy*u_tau/ni is the first discrete value corresponding to the node at the space h+ from the wall. So on for the other nodes in the vertical direction.
3) The presence of u_tau means that this function depends on the averaged stress at the wall, that is you should evaluate y+ after that the solution is known.
4) The log law is in a physical range of y+, the numerical simulation can be twofold, a) resolving the BL that is you have at least 3-4 nodes distributed at y+<1 in such a way to resolve the viscous laminar sublayer b) wall model condition, you do not solve the BL but you prescribe the stress you have at y+ in the log law.
In conclusion, the evaluation of the grid distribution of y+ requires to use the solution (that is to compute tau_wall) and, eventually, refine the grid and repeat the simulation.
Question
GMSH program, how we define boundary layer on airfoil to solve more converge?
Define boundary layer: Mesh->Define->Size fields->Boundarylayer
Refine mesh: Mesh->Transfinite
Question
Hello all.
I am simulating a centrifugal pump. Before I started simulating, I ran few test cases on a simple setup to look into the y+. In the test case (which is a simple pipe flow), I could see that the yplus value specified for inflation matches the post-processing results. I am using SST turbulence model with automatic wall treatment.
When I am taking the same yplus to pump, which consists of rotating flows, the yplus fails. Now, as I did the sensitivity analysis using (10-15 layers in the boundary layer), y+ <1 and yplus 20-200 (where SST behaves like k-epsilon),l. However, I could not find the yplus specified for inflation to be matching with that of the post processing results. The difference is atleast an order near the blade walls. Now, I assume that it might be due to the large separation zone in the pressure side. Besides, the effect of y+ variation is not significant to compute the performance for the pumps.
My question is: Has any researcher found yplus value to be fully satisfied in case of turbomachines in CFX? Is it important to verify yplus (for Journal Papers) value even when we know that the wall function is not affecting our parameters of study?
Hi,
from my perspective this is rather logical. The estimates calculated for y+ in the meshing process for specifying the inflation layer parameters are based on correlations for a fully developed turbulent boundary layer. For a long pipe this is a pretty valid assumption, since the flow has enough length along the wall to develop from the inlet boundary conditions to fully turbulent flow conditions, so that after some pipe length the postprocessing y+ is in pretty good agreement with what was used during the generation of the inflation layers in the mesh.
For a more complicated geometry like your centrifugal pump the cord length of the blades of the centrifugal pumps is rather much too short to develop a fully developed turb. boundary layer. Furthermore flow development over the blade surfaces is disturbed by flow separation and so forth. Consequently the underlying assumption of a fully developed turb. boundary layer is violated (for this assumption being taken into account for mesh property estimates) and you end up with differing y+ values in the postprocessing. But the values in the postprocessing are the physically valid values. Consequently you need to carry out a few iterations between mesh generation --> flow simulation --> postprocessing --> mesh generation in order to find good mesh properties and consequently tolerable y+ values. If for example you encounter a wide-spread y+~10 in the first results, than you might to reduce the 1st layer height in the inflation layers by approx. the same factor (10) in order to end up with y+~1 in your next flow simulation in the same place.
And regarding your last question: over wide parts of the blade surfaces it is possible to have reasonable low y+ in the order of 1. But in front stagnation points, where the flow hits the front of a blade or other parts of the geometry it is usually not possible with reasonable efforts to reduce y+ to 1, but this concerns usually only very minor part of the overall surface areas.
Best regards,
Dr. Th. Frank.
Question
Hello Everyone
I am simulating an airfoil at Low Reynolds Number flow Regime Re=10^5 , in this particular case a laminar boundary layer separates , forming a laminar separation bubble , then transition to turbulent and reatching to the airfoil . Is SA model capable of simulating such kind of flow in which three 'different behavior of flow exists ?
Regards
Question
I am solving axisymmetric boundary layer developed on a rotating circular cylinder using Fluent code. In a model, I modeled only fluid domain which have inlet, outlet, no-slip and free-stream conditions. Left and right planes are given symmetric boundary condition. (homogeneous in the circumferential direction). I prepared three dimensional model with circumferential direction is homogeneous, so only two cells generated in this direction. Then I applied rotation on the wall of cylinder ( No-slip also) to give rotation.
It is necessary to used moving mesh in this solution ? The solution file is attached at a single streamwise location with different rotation rate. I think the solution is not right. How one can validate it. Expecting a quick response.
Please comment on attached velocity profile.
Regards,
Ramesh Bhoraniya
Why do you get a boundary layer in case of Omega=0 ? In your case, if I understood it right, there should be no flow under these circumstances, and therefore no boundary layer as well. So why do you see an almost constant U of approx. 2.2m/s in the free stream with no respect to the rotational velocity of the cylinder?
Best regards,
Dr. Th. Frank.
Question
What information does the intraparticle diffusion model provide? When it is expected to be valid and when invalid? pleas explain in a simple manner with example if possible. And what is the diffusion boundary layer in such cases?
I'm not sure exactly what your model describes, but I can tell you the story of a huge expensive blunder that arose from not considering the difference between inter- and intra-particle diffusion. I came along afterward and fixed the modeling error. I am intentionally vague about who did what and where, but the mathematics are described: http://dudleybenton.altervista.org/publications/Contaminant%20Transport%20in%20Granular%20Media.pdf If I knew more about what you were investigating, I might be able to locate some free software.
Question
Could someone please recommend me how to calibrate a differential pressure sensor for a pitot tube that will be used in a boundary layer wind tunnel, I bought a Pitot tube 160E Dwyer and a Honeywell HSCMRRN005NDAA5 sensor, with a pressure range of + / - 5 inH2O.
Thank you
It's a good question! You may think of another measuring device, hot wire! or to use this tube in measuring known flow data. Good luck,,,
Question
Dear all,
I have coated MnCO3 microparticles with different biopolymers through Layer-by-layer approach.
I am not sure how to analyze the sample under SEM.
I fear sputtering might damage the coating.
My sample is in powder form.
If you use KBr pellet you might have scattering problem using IR if you have microparticles but not if you use a micro-Raman. You can always use ATR-FTIR to avoid the problem. This would tell you if you have polymer in the sample (not necessary if that polymer is where you want it to be).
Maybe you could use backscattering SEM to check if you have organic on the Mn particle surface or use a transmission technique (TEM or optic microscopy if both particles and shell are tiny or big enough).
Also an Mn quantification might help to know how mich of your final mass is MnCO3 and how migh is possibly polymer.
Question
Hello Everyone ,
Hope you are doing fine . I have this question about the reference values , that which length should one use while doing external aerodynamic CFD simulation of a full aircraft . The main objective of the simulation is to get the aerodynamic coefficients values at different angle of attacks . Should I be using full length of the aircraft as the resulting boundary layer will be formed over whole of the aircraft length ?
Aamir
I do go with Dear François Morency for his answer.
Question
In turbulent boundary layer, the transition and turbulent regions could be clearly known by seen the Cf plot and averaged velocity profiles via transformation. However, how can I know where the flow enters streamwise fully-turbulent region in supersonic mixing layer by numerical simulation ? As I learn from open literature , combined with my own work, I get three ideas
1. Some empirical equation to ensure a sufficient length of the computational domain. For example, the criterion for xeff/dm1 > 500 proposed by Papamoschou and Roshko (1988).
2. Velocity power spectrum. Calculate the spectrum of a point and get the -5/3 and -7 slope.
3. The Reynolds stress profiles, which should be self-similar. However, the Urms profiles are hard to overlap, so what is the criterion to define 'self-similar'?
Actually, which one or more are rational? Do you have more answers?
Well, you could perform several analyses. For example you can compute the TKE over several planes normal to the streamwise direction and associate the evaluation of the energy spectra.
A qualitative approach could be the identification of the vortical structures.
I don't think it exists a unique approach.
Question
When I tried grid sensitivity analysis for both supersonic boundary layer and mixing flow, I found that a more refined wall normal grid scale near solid surface would cause the spatial transition in advance than a coarse one, but in mixing region in mixing layer flow, more refined grid scale would cause the transition later in stream-wise position. All the cases I mentioned above could well match the Reynolds stress distribution compared with experiments and other simulation results. As I think, a finer grid would reduce the dissipation so that transition should be earlier, but why does it fail to work in mixing flow?
This is a quite interesting discussion that reminds me of Professor Moin Lecture at DOE CSGF 2011: Turbulence: V&V and UQ Analysis of a Multi-scale complex system.
The following questions may arise. Are you comparing two numerical computations? Are you using experiments to assess which computation is more accurate? Are you refining in the spanwise direction as well?
Professor
Tapan K. Sengupta
answer is right on the money, I have seen that myself on some numerical experiments. That makes perfect sense based on numerical methods discussions.
Are you using LES? if so, are you "updating your BC?" something I have always had is there is a temporal-space relation for LES. indeed, for any numerical methods where you are really interested in temporal-spatial high accuracy. Professor Tapan also have great paper in that field too.
Question
When I mesh the profile with boundary layers, it works fine except at the trailing edge. Therefore, there would be problem after simulation. Is there any methods to solve trailing edge mesh problem in gmsh?
Don't cut the trailing edge like that. Make it a smooth half circle (or just slightly less, to get the tangents right). Put about 10 mesh points on that small half circle.
Question
Guys,
Please take a look at Fig. 8. I'm trying to export the exprimental data of the velocity profiles in this graph. Both X and Y axises are normalized(non-dimensionalized). Y is normalized by H and there is no problem to me(just need to multiply it by H) but X axis is strange to me. Anybody could explain it to me that how is this graph drawed? I just want to export the exprimental data but don't know how to dimensionalize the X axis.
You can use the software of xy extract
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Hello, I need the equations that show the coefficient of the matrix that solves the velocity contours of the boundary layer over a flat plate. I have the explicit discretization equations but I need the equations that are used for TDMA.
Vielen Dank !
Question
I have a DNS data of thermal bouyancy driven flow in a closed channel. The boundary conditions are, one wall is isothermal and other is adiabatic. I want to classify the regions in the flow as laminar, turbulent and transitional using the instantaneous velocities. I have read about the conditional sampling method used for determination of intermittency function in transitional boundary layer but I would like to know that if there is any generic way to determine the intermittency function for closed channel flows.
Hi Indu,
You can identify turbulence according to the fluctuation of velocity of the history of a sampling point. If you see random fluctuations, then it is turbulence. You can also judge according the energy spectral.
Question
Hello everyone. I set up 2D model for battery cooling . Batteries have heat generation of 79686 W/m^3 . My fluid is the air. At inlet has a velocity of 0.3 m/s. I am using k-e model (Realizable and enhanced wall treatment ) . Batteries and air is the coupled wall. Also at this coupled wall has inflation of 5 boundary layer. However i took a low y+ the values of 0.003 minimum and of 0.2 maximum. Also i'm using transient solution.
Please can you help me abot this problem ?
For classical boundary layers it's no use setting such low values for y+, usually going down to y+#1 is enough, so your max value of 0,2 seems already small. In the boundary layer, we expect a behavior of the flow such as u+=y+, which means a linear growing rate in y+ for the scaled velocity u+, so you don't need so many mesh layers to reproduce a linear behavior. Nevertheless, layers in your mesh shouldn't grow too fast in size : a factor 5 between adjacent cells seems too high because you will get strong numerical errors with such ratios, a more acceptable value could be a ratio of 1,2 for two contiguous cells.
Hope it's useful...
Regards
J. Collinet
Question
To date, no comprehensive method of predicting boundary layer transition is available in the literature. The existence of the Tollmien-Schlichting wave could describe the transition from laminar to turbulent flow. This wave effect has not been implemented, so far, in the computational fluid dynamic calculations. If we have a theory that can be applied in the CFD method, then we will know the area of the laminar and turbulent flow field. Moreover, it can change the existing model to give a better results. I am sure that we need the new mathematical models that correlate the transition from laminar to turbulence flow.
So, let's discuss the turbulence transition theory.
T= 2 mu S -p I
This expression is always valid and account for the time-dependent velocity.
That's my question.
Question
From flat plate formula for first cell height, we can work out first cell height for streamlined bodies, but if I want to do CFD of a bluff body (for example flat plate rotated at 90 degrees)how will I decide first cell height and mesh density on boundary layer?
It's not clear if you are seeking steady RANS solutions or whether you will be using the URANS (unsteady RANS) approach that helps capture large scale unsteady structures within the flow (e.g., vortex shedding behind the bluff body).  There is evidence (see Ong et al., Marine Structures 22 (2009) 142–153) that the URANS method may provide reasonable engineering estimates in the context of bluff body flows.  URANS computations would be more expensive than the RANS computations because of the need to perform a time accurate simulation and to accumulate a long enough time series to compute flow statistics.  However, keep in mind that the RANS computations may or may not converge to a stationary flow for bluff body flows.
Back to your query, the grid resolution requirements would vary significantly from the front of the bluff body (where the flow is attached) from those in the rear (i.e., the "base" flow, where the flow is separated).  Even in the attached flow region, the flow in the vicinity of the stagnation point is bound to be laminar, although a quick transition to turbulent flow could ensue depending on the surface roughness, freestream turbulent intensity, and the flow Reynolds number. If the laminar region is small, and therefore, can be ignored for the purpose of your computation, then you may use a skin friction estimate based on van Driest (Van Driest, E. R., “On the Aerodynamic Heating of Blunt Bodies,” ZAMP, 17, Vol. 9, issue 5-6, pp. 233-248. 1958) to ensure that your near wall spacing (i.e., first cell height) is consistent with the requirements of the turbulence model.
However, assuming that you are interested in relatively high Reynolds numbers, I would suggest an iterative approach based on URANS that begins with a grid that is based on a preliminary knowledge of the flowfield.  After scrutinizing the computed flowfield on the preliminary mesh, you can refine the mesh to ensure that all "relevant" flow features are adequately resolved and that the flow metrics of interest have become insensitive (to the order of the desired accuracy) to further refinements and/or some degree of grid coarsening. This is also the most convenient approach for any new class of fluid flow simulations.
Question
Hi
I want to evaluate thickness of boundary layer on the whole surface of an airfoil by ANSYS Fluent.
Do you have any suggestion?
Hallo again
I do agree that drawing an isoline would be helpful. However, the boudary layer thickness for airfoil cannot be defined as U_loc = 0.99*U_inf like in a flat plate. The main reason is, that flow accelerates significantly near the airfoil contour. This holds for inviscid and viscous flows especially when the airfoil thickness is large or when the angle of attack is not zero. In contrast, the inviscid velocity for a flat plate remains U_inf along the streamwise direction. Therefore, the definition of the BL thickness shall be V_total_loc = 0.99*V_total_loc_inviscid. In this sense, one should obtain the inviscid distribution outside the boundary layer but still in the vicinity of the wall. This is not a straightforward task. Therefore, plotting an isoline directly for U_loc = 0.99*U_inf will introduce some errors.
Question
Hello,
i'am trying to run a simulation to obtain the drag of a boat running on the surface of water. I set up the simulation as fine as I know. Concerning this kind of simulation, the prism layer is very important since they allows me to evaluate aspects like pressure, which is the main component of the drag of a boat. I read how the Boundaries Layer is analyse in star ccm, so I know the interval's value of Y+ and the different treatment that star ccm+ use. The difficulty for me is to settle the value that I want for y+ What I read, is that we do not know the value before running the simulation... we know at the end of it. okay... and from here it seems to me that we "play" with the options like strechct factor, number of prims layer to obtain the goal value. I also read the "good" practice to have the value that we want. Let's said, I use the good practice for it... since it is just a supposition i may not have can the value that i want at the end... Problem is I'am running simulations (evaluating the drag of boat) which take 6 to 8hrs to converge... so I guess that there is another way to evaluate the values of y+ before running the entire simulation... I have look the help.. but I didn't find it yet. Can you please help me solve this problem?
The thickness of the first prism layer Y can be estimated by Y=(Y+)*L/0.172/power(Re,0.9), where Y+ is what you want to set, for example 50; L is the ship length; Re is Reynolds number. The number of layers and strech factor can be chose according to the best practice provided by STAR-CCM+ or by ITTC CFD guide, such as 6~10 layers and 1.2 respectively for high Y+ model. Generally, some difference still exists between Y+ what you want and Y+ what you read. However, their ratio seems to be constant in my experience. In other words, if you want to set Y+=50, what you read will be 25. So you can use Y+=100 in the formula above to get Y+=50 in the software. You can do some tests to find similar relation in your settings. I hope this can help you.
Question
Hello Researchers,
I am doing a simulation based on an experiment in which an atmospheric boundary layer was used which followed log-law.The experimental domain is quite large for a single work station to handle. So I scaled the geometry down. My doubt is whether we should even scale down the inlet conditions and also the surface roughness, if so how can we do it?
Regards,
Raj Kiran.
Thanks for the earliest reply. I will look into it.
Question
What is the drag coefficient for rectangular pile cap if Cd for cylindrical piles connected witht the rectangular pile cap is 0.53
As your question is incomplete so I can't explain it in detail but below mention thesis is might be helpful in your case.
"DRAG FORCES ON PILE GROUPS By RAPHAEL CROWLEY A THESIS"
Question
thank you so much. I already tired using an airfoil with very small thickness (about 1 to 2 % of chord) and it did work somehow. Do you have any idea how to analyze the BL over a Cylinder ?
thanks
Question
just to update the community and people interested in the problem.
I read that if and only if when one apply porous jump as the boundary condition, FLUENT would only consider flows perpendicular to the actual surface. That is definitely not our case. In particular, our system doesn’t possess inlet and/or outlet flows (or it doesn’t have to be perpendicular specifically), since it will be a real earth model simulation which will be representing fluid dynamics and it’s chemical interactions through 3-layered marine sediment. So, we are interested in natural flow of the water liquid in the undermost body, chemical interactions and outcomes of it in the middle body, once again natural flow of the water liquid and products from the reaction in the uppermost body by time, i.e. we solve the system as transient. As you can see, it’s not like a flow through cylindrical objects etc., thus it’s totally different. Today, we conclude that we need to figure out another option for boundary condition, since porous jump seems a bit non-functional.Once again the main fault we encounter when we run the program is most likely arised from enforcing a chemical reaction just in the middle body. Now, I am searching for some answers regarding how to enforce a chemical reaction just in a specific region(in our case in the middle) of a body.
My system is composed of 3 bodies, and the middle body will be the host of a reaction. All those three systems have the porous zone option activated. I want the water liquid which flows through the undermost body and arriving the porous jump boundary, passing through this boundary, reacting with the chemicals I designated in the middle body, creating those other products, and finally once again those products for this time passing through the second porous jump boundary and reaching to the uppermost body.
I hope you could imagine the system. Now I created 2 cell zones just above these porous jump boundaries with a width of 1 grid cell which was 8 m for my case, and also set the Y velocities of those interior cell zones as 0. Logically, since they are just above the porous jump boundaries they are actually in-situ of the reaction area(the middle body). So, I did activate the porous zone and reaction options for my cell zones, and set '0' value for the Y velocities in the fixed values tab (A researcher who encountered the same problem proposed this method, so I wanted to give it a try.).
Now, as for porous jump boundaries, I still set them as porous jump boundaries which I believe where the problem arises. When I didn't create a namedselections for them in mesh section, ANSYS Fluent gives the error for example:
Error: Species are not solved in neighbor cell threads (14 and 16)\n of interior zone 6. \n
Error Object: #f
but when I set them as porous jump boundaries, this time it gives an error of segmentation fault, no flow detected at porous jump 7(exp.).
One more thing, the properties of the porous jump condition:
FACE PERMEABILITY: 1e+10(default) How do I set it, I have a mesh system of 5000x5000 m and 40000 elements(grids) in this system
POROUS MEDIUM THICKNESS: 0 it is.
PRESSURE-JUMP COEFFICIENT: 0(default) I saw some calculations for cylindirical studies but I don't know how to calculate it or what are the values for 2D planar structures(systems).
What is it that I'm doing completely wrong and/or fail to notice?
Any comment would be much appreciated. Thanks in advance.
Cheers,
Selvi