Has anyone here been working on those gigs where you can do CFD for AI training? I know it's kind of digging my own grave thinking long-term, but has anyone earned decent money from it? I lost my job and have been looking into different alternatives until I find something

Top left: velocity. Top right: vorticity
Bottom left: velocity mag. Bottom right: density

Simulation:
grid: 200x200
lid velocity: CFL 0.45, wave speed: CFL 0.09 (at time zero)
walls: free slip
approximate Re: ~ 1e6 (from comparing its turbulence intensity against other simulations)
pressure function: shallow water
runtime: around 20 - 25 minutes (around 47,000±2,000 Δt) (35Δt/s)

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After I've done that mach 2.1 simulation, I wanted to see what would happen at higher mach number, so I did it with this water (compressible Euler) solver.

This simulation was started right after I've done the previous test simulation. I've simulated this far, so I didn't bother redoing the simulation.

Stay tuned for the part 3 where I've got ideal gas pressure function and energy equation working properly. It'll have better visualization than this too with proper physical scale.

Here's Part 1 of Supersonic Lid-Driven Cavity Flow Series

I'm working on a multiphase CFD simulation in ANSYS Fluent, and I'm having trouble setting up the interfaces between my fluid regions. I've attached images of my 3D geometry to make the problem easier to understand.

1. Geometry and physical setup

My model consists of three regions:

• 🔵 Blue region – Air: The incoming airflow region.
• 🟢 Green region – Fluid: A separate fluid region that interacts with the incoming air.
• 🟫 Brick-coloured region – Solid: The solid workpiece region.

The physical process I'm trying to simulate involves the incoming air interacting with the green fluid region first, followed by the fluid interacting with the solid workpiece.

Both fluids should remain within their intended regions while interacting across their shared interface. I want to capture the fluid–fluid interaction and the subsequent interaction between the fluid and the solid workpiece.

2. The problem I'm facing

After importing my geometry into ANSYS Fluent, the interfaces between the different regions appear as wall boundaries with a no-slip condition.

The main problem is that I cannot change these boundaries to fluid interfaces. Even when I try changing their types in the Boundary Conditions panel, the changes do not persist, and the boundaries revert to their original wall type when I reopen the panel.

I'm unsure whether this behaviour originates from my geometry setup in SpaceClaim, the way the bodies or cell zones were created, or the interface configuration in Fluent.

3. What I'm trying to achieve

I want to configure the model so that:

1. Air and the second fluid can interact across their shared interface.
2. Both fluids remain within their intended regions, rather than simply mixing throughout the entire computational domain.
3. The second fluid interacts with the solid workpiece through the appropriate fluid–solid boundary condition.
4. The interfaces are configured correctly for a multiphase simulation, rather than unintentionally behaving as impermeable solid walls.

I'm considering a VOF-based multiphase approach, but I'm unsure whether my current geometry and interface configuration are appropriate for this setup.

4. My questions

I'd really appreciate some guidance on the following:

• Geometry: Should I create the fluid regions using shared topology and conformal meshing, or should I keep the bodies separate and create mesh interfaces in Fluent?
• Boundary conditions: Why are the fluid–fluid interfaces automatically appearing as walls, and why can't I change their types?
• Interface setup: Should these boundaries be configured using coupled wall/shadow pairs, mesh interfaces, or another approach? How do I determine which is appropriate for my geometry?
• Multiphase modelling: Is VOF suitable for this setup if both fluids occupy predefined regions initially but must interact across their interface?
• Fluid–solid interaction: How should I configure the interface between the second fluid and the solid workpiece?

sorry for long text, i have generated my text form AI for better understanding of my problem.

Since yesterday, when I finished setting up my simulation, something weird has been happening with the solver. Pressure in a whole area of the building keeps rising linearly, even though the building is split into over- and under-total-pressure areas. The weird thing is that both my inlets and outlets are matched exactly, and so I thought that maybe it could be the difference in air temperature between the inlet and outlet affecting the density of the air and thus creating an imbalance in the system. So I switched one outlet to a pressure outlet, and yet again, pressure kept going up linearly well above atmospheric pressure.

Another thing: my initial conditions are set to 24.1°C, and for some reason, the solver starts at cca 68°C; God knows why :(

Thank you very much if you find a second to help me!

Here is a link to a copy of the project:

https://www.simscale.com/projects/STAN1119/help_1728548534

Hi everyone! I’m working on my first external aerodynamics study to learn CFD. I’m trying to predict the drag and lift coefficients of a vehicle prototype using ANSYS Fluent Student, with a mesh limit of around 1 million cells. I’ve been having trouble with convergence and choosing an appropriate near-wall treatment.

From what I’ve read, k–ω SST is commonly used for external aerodynamic simulations, often with a mesh targeting y+ ≈ 1 or lower to resolve the near-wall region. However, achieving this while adequately refining the rest of the domain is challenging within my cell limit.

I’m also considering realizable k–ε with a wall-function approach targeting y+ > 30. My understanding is that this could reduce the near-wall mesh requirements, although predicting separation under adverse pressure gradients may be more challenging. I’m unsure which near-wall treatment would be appropriate: standard wall functions, scalable wall functions, non-equilibrium wall functions, or enhanced wall treatment.

The vehicle uses narrow bicycle-type wheels, and the rear wheel is enclosed by a fairing. One geometry-related question is whether I should include the air cavity between the rear tire and its fairing, or simplify that region. What level of detail is appropriate for this type of simulation?

My current setup is:

• Steady-state RANS with k–ω SST.
• Inlet velocity: 8 m/s.
• A symmetry plane.
• Rotating-wall boundary conditions for both wheels.
• A moving ground.
• No rear tire cavity volume (fully closed).

As for the mesh:

• 1M cells.
• Minimum orthogonal quality 0.12
• Body of influence regions and local sizing.
• Last Ratio method and 15 boundary layers (first cell height adjusted)

I estimated the first-layer height to target y+ < 1 and ran the simulation, but the drag and lift coefficients did not settle to constant values.

I’d appreciate some advice on the following:

1. Are there any obvious problems with my mesh or near-wall approach?
2. How can I distinguish numerical convergence problems from flow behavior that may require a transient simulation? Or perhaps it is a geometry issue.
3. Within the cell limit, would you prioritize an SST mesh targeting y+ ≈ 1, or consider realizable k–ε with wall functions?

I’ve attached the drag and lift coefficient histories, a mesh view, a y+ contour, and a velocity plot.

Any feedback would be appreciated. Thanks!

Y+ Contour seems to be fine without going in between de 5-30 region.