ANSYS Fluent: Turbulent Backward Facing Step

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ANSYS Fluent: Turbulent Backward Facing Step | Tutorial

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CFDKareem

Күн бұрын

Пікірлер: 29

@vijethanchalkar5340 Ай бұрын

Thanks!

@abhishekbenny7930 4 ай бұрын

Hi Kareem, when you calculated the wall distance why did you put 0.01 as the boundary length and also, why is the wall distance you calculated on the website different to the one you put into Ansys. Thank You.

@cfdkareem 4 ай бұрын

Hello, the characteristic length used to calculate the Y+ is the step height, 0.01 m. Good catch on the wall distance! The one calculated on the website should have been used as the first layer height of the inflation. It looks like I forgot to paste the value!

@abhishekbenny7930 4 ай бұрын

@@cfdkareemyh that was really baffling me, but thanks for clarifying

@LCucumidesC 3 ай бұрын

Dear Kareem, I would like to know what the analytical equation is for the velocity profile. Thank you.

@cfdkareem 3 ай бұрын

There are numerous equations for estimating the turbulent velocity profile. The most common for industrial flows is known as the Prandtl one seventh power law which takes the form: u/Umax=(y/R)^1/7. You can plug in Umax and R to solve for u over the range of y.

@joaquinbarawed9016 3 ай бұрын

Hi, I can’t seem to find where to download the experimental data, and the link I’m pressing only opens up a new tab with the data

@cfdkareem 3 ай бұрын

Hello Joaquin, near the bottom of the NASA page there are two links to the Cf and Cp data. Clicking the links will open a new tab with the data displayed in text format. You can then copy the data and paste it into excel or a text document.

@haiderh2052 6 ай бұрын

Hi, can I just extend the upstream length for this case instead of creating a secondary simulation for inlet profile ? will that works the same

@cfdkareem 6 ай бұрын

It will! You just have to make sure you extend it far enough for the flow to fully develop. It will also increase your solving time as the mesh will get much larger.

@benguerichezah4676 Ай бұрын

I have problem i want to fill this geometry with fluid ,i try your vedio but i have problem in velocity contour is empty don't fill with fluide

@cfdkareem Ай бұрын

Hello, are you trying to change the flow from air to water? Or trying to do a multiphase simulation with air and water?

@aliakbas7387 3 ай бұрын

hello sir, im trying to simulate a similar case but with small inlet lenght to see the vorticies at the top wall. However, nomatter which methods or solvers i use i can not get the same results with published articles."E. Ertürk, Numerical solutions of 2-D steady incompressible flow over a backward-facing step, Part I: High Reynolds number solutions, Computers & Fluids 37 (2008) ". Can you give me any hints to handle this simulation. Laminar case is easy but i can only get top vorticies with DES method but it is still not accurate. I can not get the 3third vortex for Re = 3000 and the other x/h values doesnt match with the reference.

@aliakbas7387 3 ай бұрын

Our teacher said u can use k-epsilon for turbulence but with that method you can only get the first vortex others only appears for the initial iterations then dissappear.

@aliakbas7387 3 ай бұрын

also, with very fine mesh (i have uniform 150k grids) DES methods takes almost 2k iterations to hit 10^-3 criteria and oscillations never stops as i see.

@ratuldas5352 11 ай бұрын

Hello, just a simple question, why did you divide x/0.1? I can't get my head around it.

@cfdkareem 11 ай бұрын

Hello, in our analysis we divided the x variable by our step height, .01. This will make our variable "non-dimensional" since we divided X, with units meters, by the step height, also with units meters. It is common to report data as non-dimensional values so the output is not dependent on the size of the domain. In other words, we could use the reattachment point from our simulation and compare it directly to a simulation domain twice as big. It is similar to normalizing data in a statistical analysis which allows us to compare two data sets with a common ratio. Let me know if that answered your question!

@marstokrom Жыл бұрын

Hey! could you describe how to make the secondary simulation for defining the fully developed turbulent flow inlet condition in a bit more detail? what size does the mesh need to be etc? How do i know if the flow is fully developed? Thanks! this video is excellent

@marstokrom Жыл бұрын

my apologies, i see youve linked it already! legend!

@JamesAGBAJE-wg1yo 4 ай бұрын

Hi Kareem, please I’m having issues with the secondary simulation can you share the file of the velocity profile?

@cfdkareem 4 ай бұрын

Hey James, I've added the inlet velocity profile to the video description! Copy it to a .txt file. It can then be read in as a profile for the velocity inlet.

@aiwithhamzanaeem Жыл бұрын

Looking for topic "Backward step flow in transonic regime"

@cfdkareem Жыл бұрын

Hey Muhammad, thanks for the suggestion! I will add it to my list for future videos!

@marstokrom Жыл бұрын

Hi again kareem! just wondering, why opt for the coupled solution approach rather than SIMPLE or SIMPLEC? many thanks!

@cfdkareem Жыл бұрын

The coupled solver is more robust then the SIMPLE or SIMPLEC numerical approach, most of the time. SIMPLE is good for giving quick simulations if the boundary conditions are well defined and the pressure-velocity coupling is low. When in doubt I would always recommend the coupled solver, even if it may be a bit slower to compute.

@tomfindlay5652 Жыл бұрын

I can’t seem to find the data you have linked , I can only find data for skin friction coefficient and not wall shear stress

@cfdkareem Жыл бұрын

Hey Tom, the wall shear stress is a scalar multiple of skin friction coefficient, Cf = tao/(.5*rho*U^2). In this case we are looking at the second zero crossing of the graph. This point will be equivalent for wall shear and skin friction coefficient. You can plot either the wall shear stress or the skin friction coefficient to compare to the experimental data to simulation.

@tomfindlay5652 Жыл бұрын

@@cfdkareem my simulation data seems quite off, I didn't do the developed flow simulation for the inlet conditions, would this likely be the reason for the large difference or something else fundamentally wrong

@tomfindlay5652 Жыл бұрын

@@Syrsylo The X/h values on the graph are much lower than the experimental data, but the shape of the graph is the same