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# Boundary Layer - Science topic

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Questions related to Boundary Layer

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.

Thank you in advance for your suggestion

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?

I appreciate your comments.

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??

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.

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.

Planetary Boundary Layer Height and its diurnal change

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

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?

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?

Thanks in advance,

Nikos.

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??

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.

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?Its a

**steady state Analysis****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.**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.

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 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?

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?

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.

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)?

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)

Can you please help me understand why this is the case?

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.

Hi to ladies and gentlemen

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

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)

In the literature: https://www.mw.tum.de/fileadmin/w00btx/td/Forschung/Dissertationen/baumgaertner15.pdf

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.

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.

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.

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.

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!

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,

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?

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 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?

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?

Simply a fluid is flowing over a flat plate.

#Fluid mechanics

#Boundary layer

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?

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.

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.

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.

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

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?

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 ?**

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.

I appreciate any help you can provide.

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

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.

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.

Hello everyone, I am confused about whether the boundary layer formation takes place in case of ideal fluids?

I will appreciate your help

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.

Your suggestions are appreciated.

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.

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

I am looking at a specific namelist.input tailored for urban areas.

Thanks.

p.s. WRF version 4.0

- In near-wall region, to what degree is the rough-wall boundary layer confined?
- On which occasion to use the roughness height h and the ratio of height and boundary layer thickness h/δ, respectively?
- 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.
- 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?
- 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?

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?

GMSH program, how we define boundary layer on airfoil to solve more converge?

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?

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

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.

Thanking you in advance .

Regards,

Ramesh Bhoraniya

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?

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

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.

Thanks in advance

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 ?

Your kind suggestions in this regard will be really helpful .

Aamir

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?

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?

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?

Guys,

I'm reading this Article:

You can download it from here:

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.

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 !

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.

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 ?

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.

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?

Hi

I want to evaluate thickness of boundary layer on the whole surface of an airfoil by ANSYS Fluent.

Do you have any suggestion?

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?

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.

What is the drag coefficient for rectangular pile cap if Cd for cylindrical piles connected witht the rectangular pile cap is 0.53

if there is please help me to do so. thanks

**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