i want to know which of the above is better for cfd and why and what exactly these two differ from. im a student whos got solidworks but only ansys student and i wanna know the difference in detail. help me please

Hi!! I am trying to simulate flow inside an air purifier using ansys fluent. I have not been able to achieve satisfactory results so far. Can anyone please help?

TIA!!

Want to test mpi performance across a few compute nodes. Each node has 256 cpus.

All the tutorials models I test run in just a few seconds on one cpu...

For engineers who have to compare many possible design variations, I'm curious how you actually handle it in industry.

For example, if you have hundreds or thousands of possible geometry/parameter combinations:

• How do you decide which designs are worth simulating?
• Do you actually run simulations for all of them, or use some kind of screening/optimization method?
• What tools do you use for this?
• What part of the process takes the most time?
• Is computational cost the main limitation, or is setting up/running/post-processing the simulations the bigger bottleneck?
• Do you use surrogate models, reduced-order models, optimization software, custom Python scripts, etc.?
• What happens when the design space becomes too large to explore practically?

I'm particularly interested in how this is handled in industry and what the biggest bottleneck is in practice.

https://preview.redd.it/2i0w758jl4kh1.png?width=1441&format=png&auto=webp&s=6d00de476c18d9603db522fb6fe930835d285b01

Previously I have modelled big cylinder at end of the pipe or screen. Now I have seen some paper where outlet is at some upstream distance from pipe end, I am doing that now. The problem I am facing is when I drew sketch as above and extrude(add frozen), cylinder is created but there are some overlapping volumes between small and big cylinder. Due to this, when I do setup, I got to know that,

https://preview.redd.it/d40bcaotl4kh1.png?width=1072&format=png&auto=webp&s=0393db163b8cb844da05432397dac18287200b08

This is how outlet should look like, you can see hole in the middle. I hope it is right. If it is right, then see what outlet it was showing for me below,

https://preview.redd.it/vinanzgxl4kh1.png?width=1078&format=png&auto=webp&s=4c265eaf20525c31e2bff3ac79b0b8d5bfbdd3bc

I hope you understood. This blue circle shouldnt come.

One more thing, when I merge these bodies to make it one body, screen gaps are not visible since it got merged into big cylinder body. I dont want this to happen, I need to see screen gaps like below,

https://preview.redd.it/hnh3drrcm4kh1.png?width=1437&format=png&auto=webp&s=b25ceacb77deea54bbf5895b6763f8c0369e7a18

Note all are fluid modelled regions, there is no solid anywhere, so gaps represents walls of distortion screen.

2. I have tried one more thing, I have created small cylinder in that same plane and tried "Boolean subtract" and got outlet face like below,

https://preview.redd.it/kitliwmjm4kh1.png?width=1037&format=png&auto=webp&s=704e836c1b757cb4061eb46751f406e8285b266d

But I got to have 3 different bodies as shown below, and when I merge them together, then I cant find screen walls since it got merged into big cylinder volume. I need screen walls so that I can apply inflation and face sizing in that region particularly.

https://preview.redd.it/tk1wj1zqm4kh1.png?width=1195&format=png&auto=webp&s=5cb1e71f7fecad7c1b2d66ebc8dcf50cfd21eb2a

Keeping all these in mind, any other alternative or better way to model this big outer cylinder and merge. Any suggestions would help, thanks in advance.

See below single body merged together when big cylinder was drawn at end of the screen, screen gaps are visible here,

https://preview.redd.it/r2qcj7c9n4kh1.png?width=1434&format=png&auto=webp&s=2e5d1eed3caaea020bd4f082af22141c82f5abe3

Hey guys, I've got about a year of experience with OpenFOAM. I've run different types of simulations — SIMPLE, PIMPLE, incompressible, compressible, laminar, turbulent — on 2D airfoils and 3D aircraft, like the NASA N2A HWB model, with decent mesh quality and case setup. The post-processed results matched the reference data pretty well. Just sharing this to give some context on where I'm at with OpenFOAM, but I'm still learning and exploring more of it.

Lately I've been seeing AI/ML being used in CFD, and since I come from a non-coding background (I'm a Mechanical Engineer), AI/ML and neural networks still feel like a black box to me. I don't really know how they work under the hood.

So I wanted to ask — how can I actually use AI/ML and neural networks in aviation-related CFD work?

For context, my future work will mostly revolve around optimization studies, detailed aircraft analysis, and static/dynamic stability analysis of aircraft. So I'm hoping to understand how AI/ML can help speed things up, and ideally how to align with whatever the industry is currently doing in this space.

I am involved in an hypersonic CFD case with a good emphasis on combustion modelling and with the instabilities in fluent , honestly it's frustrating . Looking for some better options to learn from scratch and diversify my profile for a beginner , what are the options and how viable are they ?

I’m trying to understand the derivation from Navier–Stokes → Euler → Bernoulli. My confusion is about where the incompressibility assumption enters.

I start with the incompressible Navier–Stokes equation. After assuming inviscid flow, I get Euler’s equation. Then, taking the equation along a streamline and integrating gives the Bernoulli equation.

But I’ve also seen a more general Bernoulli equation for compressible flow(last equation in image). If I started from the incompressible Navier–Stokes equation, where density is already assumed constant, how can the derivation lead to the compressible form?

Also, is the differential equation along a streamline valid for both compressible and incompressible flow, with the difference appearing only when we integrate it?

https://preview.redd.it/r4z53kqw5vjh1.png?width=592&format=png&auto=webp&s=e705b4dab5db04af8456097e162c2c97f371ed6a

I am studying fluid mechanics. Right now I am on inviscid flow and I am having some difficulties in understanding certain aspects of flow past solid objects. I have tried to sketch my understanding so far along with the particular issues I have below.

So the setup is that we have uniform flow at infinity and a solid non moving finite object in the way. Now from Kelvin's theorem we can show that on streamlines which go from infinity to infinity the vorticity vanishes. If these are the only streamlines the vorticity vanishes everywhere and the flow is a potential flow. However if we solve the problem under the assumption of potential flow we encounter d'Alembert's paradox. There is no drag on the body and the solution is unphysical.

There is a loophole in the argument that shows the flow is potential namely it does not apply for streamlines which hug the solid surface. Since these don't start from infinity they also don't affect the boundary conditions at infinity. So we can create additional solutions by superimposing potential flow solutions with these ones. But we then have to relax the potential flow criteria. Here are my questions:

1. These solutions, that include streamlines that hug the surface, have the phenomenon of separation. The streamlines lines only follow the surface partly and then partway from it. Why is speration necessary? I mean what about streamlines that go all the way around the surface of the solid body.

2. Also there is in these cases the formation of a surface of tangential discontinuity where the tangential component of the velocity field suffers a discontinuity. I can't seem to visualize this surface. Like where is this formed on the body itself or in the fluid bulk surrounding the body. My book says the discontinuity on the surface causes part of the fluid to have vorticity. I don't understand this and I don't understand why is the formation of said surface a necessary consequence of seperation.

3. There are multiple different solutions corresponding to the above problem if you take into account the multiple possible surfaces of discontinuities.

4. These solutions are unstable owing to the discontinuity in velocity.

Please help me answer these questions.

Hi all

I have now used fluent meshing which has organised workflow and convenient to use. Quality is much better compared to tetra, it has maximum skewness of 0.84 and minimum orthogonal quality is 0.15. See mesh below,

https://preview.redd.it/ywihz933kkjh1.png?width=935&format=png&auto=webp&s=d3804c3510cae43c19c94d10dbd27b23461b5c56

I have tried two cases

1. Incompressible case- velocity inlet and pressure outlet

2. Subsonic compressible case- total pressure inlet and static pressure outlet

See below, flow goes via pipe and screen is there and then it expands into ambient air. Downstream length is 15D, bigger cylinder diameter is 14D, where D is diameter of smaller pipe.

https://preview.redd.it/nqie3678kkjh1.png?width=1229&format=png&auto=webp&s=15121000fc24c33bf19edca3794e72a2487c2cb5

1. For incompressible case with velocity inlet of 1m/s and outlet absolute pressure as 101325Pa, see residuals below,

I used coupled solver with second order upwind for all turbulence, pressure and momentum and reduced URF for pressure with 0.3 and 0.5 for momentum. Note energy equation is turned off and constant fluid properties were used. I am doing it for steady RANS simulation, k-e realizable is used.

https://preview.redd.it/kx8kaw0dmkjh1.png?width=1298&format=png&auto=webp&s=ab4522d8bdc11642f0703f11282468054a8c47e8

It was good upto 200 iterations but later it got diverged. I dont know why.

2. For subsonic compressible case,

I used total pressure of 110250Pa and pressure at outlet is same 101325Pa. Residual are even more high here, energy equation is turned on, density is ideal gas, viscosity follows sutherland law, k-e is used. I used coupler solver here also.

https://preview.redd.it/0qrp0yjumkjh1.png?width=1148&format=png&auto=webp&s=229f003facea6dcba3719ddf3f0add743017ce15

For 2nd case, I just tried finding velocity range or statistics using cell register, it was showing literally all cells having very high unrealistic values, I dont know why it is happening. See below for example,

https://preview.redd.it/j602koe0nkjh1.png?width=653&format=png&auto=webp&s=e4306db2f1bd309c4424f360303b0a36aaccc4de

So my question what is the actual problem here?

(i) Mesh quality is good here-I used polyhexa in fluent meshing, it is much better than tetra, max skewness is 0.84 and min orthogonal quality is 0.15.

(ii) I tried reducing URF, then also it is not working.

(iii) Initially I tried with very less downstream length and radius, now I have increased that- I have referred paper for this.

What else are there to try? I cant find correct reason why solution is not converging and residuals are highly unstable. Is there anything wrong with boundary conditions and schemes. I hope there is no problem with mesh, since I have good quality mesh. It was any way diverging for both tetra also before. But current mesh quality is much better than tetra one. Thanks in advance. I hope I told all information required to diagnose this issue!