Random Sunday Project

Hi! I’m trying to run a CFD simulation of airflow over a bicycle helmet in ANSYS fluent and i’m not sure where i’m going wrong? The quality of my cells is fine I think and I used y+sqrt(74)*re^(-13/14) for my y_1 value using last ratio on my walls. I think the issue is with the y1 value though?

my results are SO wrong getting 0 velocity anywhere in the system (set inlet to 10m/s) pressure is whack and getting 0 y+ values for my entire system. setting my residuals to converge at 1e-03 which i know is a bit high? also using standard k epsilon turbulence model

This is my first time trying a proper 3D model, usually for class we’ve just extruded the cross section. Maybe I should go back to that?

I’m really a beginner at this so any help at all would be so appreciated thank you!!

Hey everyone! 👋

I’m a C++ developer with a CAD internals background (previously implemented the QDIM command from scratch in IntelliCAD — worked heavily with tolerances, and geometric heuristics).

I'm spending the next 2 months dedicated to writing a focused, high-performance open-source C++ library for mesh generation / geometry cleanup.

Since you guys are pushing FreeCAD FEM to its limits: Where does the meshing pipeline (Gmsh / Netgen / internal tools) break down most painfully for you?

What specific CAD edge-cases (thin-sheet solids, dirty non-manifold faces, micro-gaps, complex fillets) routinely fail to mesh or crash your workflow?

Drop your most annoying issues — I'm looking for the ugliest real-world bottlenecks to solve and benchmark.

I am simulating an enclosed parking garage in Autodesk CFD.

- Garage area: approximately 1,974 m2
- Mechanical exhaust: 4,200 m3/h
- Natural make-up air through wall openings and the garage door
- Clean incoming air: scalar = 0
- Required CO emission: 247 g/h
- Target: below 100 ppm at 1.7 m height

I use a scalar transport model where scalar 0 represents clean air and scalar 1 represents pure CO.

Initially, I modelled the entire driving area as one large Internal Fan region with a flow rate of 0.02 m3/s. I calculated the source scalar using:

Scalar = CO mass flow / (air density x source volume flow)

This resulted in a source scalar of approximately 0.0027. However, the scalar at the exhaust was approximately 0.0012, which seems too high.

I am now considering several long rectangular source regions along the driving lanes. Each source would be 0.6 m wide, and the CO emission would be distributed according to the source lengths.

What is the correct way to model a known CO emission rate of 247 g/h in Autodesk CFD?

- Should I use Internal Fans, volumetric sources, or another source type?
- Can the scalar be calculated from CO mass flow divided by air density and source volume flow?
- How can I ensure that the model injects exactly 247 g/h?
- How should I verify this with a mass balance at the mechanical exhaust?
- Does anyone have experience in these kinds of simulations?

Any advice on modelling contaminant sources in Autodesk CFD would be appreciated.

Hi, I'm quite new to CFD and I'm having major problems with meshing. I'm studying the drag coefficient on an elliptical and tangent ogive nose cone and I'm using a 2D axisymmetric geometry. From what I read on literature it's important to have y+ close to 1 on the first layer near the wall, because with this setup the model (k-omega SST in this case) doesn't need to use wall functions. I don't understand from what criteria I need to subdivide the edges or what element size to use to have an accettable mesh; then in ansys meshing if I use a general mesh element size to small (and I don't know what is too small for it) the meshing process get's stuck at 5% when converting triangular elements to quads. Is there any literature, videos or piece of knowledge I should read or watch to really understand meshing? I feel like I'm walking in the dark. If needed I will upload the domain I was trying to mesh.

I posted this post here a while ago:
https://www.reddit.com/r/CFD/s/ynCa0b4g8i

Since then, I’ve been trying to improve my mesh, I switched from a tetrahedron to a poly hex-core and also started using fluent meshing. (Attached is my current mesh). Currently it has orthogonal minimum of 0.3 and skewness maximum of 0.48.

But despite my efforts on trying to improve my mesh. The residuals still almost look the same from before. Could it be a setting issue? Or is my mesh still really that bad?

My current configuration has energy equation on, viscous laminar model, pressure based, steady time, gravity off. Mass flow inlet at 0.06kg and 293K with pressure outlet 0Pa gauge and 293K. Heat flux at 20000 is applied at the bottom outer face.

The solver settings are currently on coupled, least square based gradient, second order on pressure, second order upwind on momentum, and second order upwind on energy. I tried to change momentum to first order a while ago, and that actually made it go down by a lot, but I heard that it’s less accurate so I switched back to second order upwind.

My control settings are currently on default which are pressure and momentum at 0.5, density and body forces at 1, and energy at 0.75. I tried lowering this values before, but nothing changed so I just reverted them back to the original.

I tried to see if there is a mass imbalance and got. Mass flow rate inlet at 0.06 and outlet at -0.06004121. So I don’t think there’s much of at imbalance.

I also tried comparing my results from a paper I’m basing this baseline geometry to and got 139.18Pa for the area weighted average of my inlet compared to his 139.59. And 311.9588K for my Area weighted average of my heated wall compared to his 314K(I also need help possibly bringing this closer). I think it’s also good to note that from improving my mesh, I did get a better inlet pressure, because before I was getting 134Pa.

Any advice would be greatly appreciated 😊.

I’ve just got my first potential customer, and I’m willing to compromise on the money for some brand visibility. I wonder generally what’s the pay?

They have a small electronics box and want to run the analysis on it.

I’m an employed fresher engineer with a BSc in Mech engineering if this is relevant

Hello everyone.

I’m trying to replicate some experimental analysis with Ansys Fluent. Particularly I’m trying to simulate a Wells turbine on different airflow conditions (same RPM, different inlet velocities).
The goal is to plot torque and pressure coefficients over time/flow coefficient.
I’m getting very bad torque values, about 50% of the experimental results (more on that below).

Here’s the setup:

I created a CAD with same exact geometry features of the tested turbine.

I imported it into Ansys, considered just the duct in which the air flows (just like the OWC simulator in the real test). Divided the domain into 3 zones, two stationary and 1 MRF. (I considered no tip gap to avoid strange behavior there, since 1mm of gap it could be hard to simulate). Also, only simulated 1/6 of the turbine, a single blade passage (6 blades in tot)

Meshed and open fluent.

The solver is Ansys Fluent, I set up the air conditions (viscosity and density). I set up the MRF rotational speed and inlet velocity on 9m/s (i want to get one condition right before analyzing more intel speed values). Used k omega.

I initialized and run 500/1000 iterations.

Data obtained:

CFD (Torque on a single blade):

Pressure: 0.016280575 Nm
Viscous: 0.0025203426 Nm
Total: 0.018800917 Nm

Experimental results at 65Hz and 9m/s of inlet speed vel:

0.206 Nm, which divided by 6 give me: 0.0343 Nm

That's about 54% of the exp data

Thanks everyone:)

Hello, I've almost completed my master degree in aerospace engineering focused on fluid dynamics an CFD.

I was wondering and I want to ask to the people that work in this field, how is you job changed since the AI became very popular in the last 2 years?

Do you use it a lot? Do you code and still write solvers?

Thanks in advance to everyone

Hi

Fire safety of battery energy storage systems, and I would love advice on which software to invest in learning.

What I want to simulate:

Thermal runaway in prismatic LFP cells and how it propagates cell → module → rack → neighbouring racks

I am interested in getting the heat release rate (HRR) and total heat release (THR) of a burning rack.

Effect of rack spacing and of insulation layers (between cells, modules and racks) on propagation

Later: a full battery room (~10 MWh, 40 racks) thermal runaway simulations

Options I'm considering: Ansys Fluent, STAR-CCM+, FDS (with PyroSim), OpenFOAM.

Which GUI tool would you pick to do runaway + venting + combustion + HRR in one workflow?

Thanks a lot.

Hi all, I’m a PhD student working on corrosion and erosion-corrosion of steels in liquid lead. I’m designing a test rig and using CFD to work out what flow the samples actually see. I’d appreciate input from people with more turbulence modelling experience than me.

Setup

• Horizontal disk, radius 140 mm, submerged in a pool of liquid lead (ρ ≈ 10,500 kg/m³) at around 700 °C under argon. It’s driven by a vertical shaft through the lid.
• The vessel is only slightly larger than the disk, so the radial gap at the rim is narrow.
• Samples are flush-mounted on the disk and rotate with it.
• Stationary radial baffles on the vessel wall suppress the bulk swirl. Without them, the free surface would dip to the floor at a few Hz, well below the design speed.
• Design speed is 28 Hz (1680 rpm), so Re = ΩR²/ν ≈ 2×10⁷. Only the inner ~16 mm of the disk is below the transition Reynolds number.
• Tool: COMSOL CFD Module.

Outputs I care about

1. Wall shear stress on the sample faces (the main one)
2. Residual swirl as a function of baffle geometry
3. Loads on the baffles and the rotor torque
4. Pool turnover and mixing

The route I’m planning

A 3D transient with an ALE free surface is out of reach computationally, so I want to avoid it entirely.

1. 2D axisymmetric, unbaffled, at low speed. The ALE free surface works here (surface tension off, Bo ≫ 1). I’ll take the ALE surface shape h(r), freeze it as a rigid slip lid, and re-solve stationary. If the velocities match the ALE run and the residual Δh = (p − p̄)/ρg along the lid is close to zero, I’ve shown that “rigid lid plus pressure check” reproduces the exact free surface.
2. 3D baffled sector at 28 Hz with a flat slip lid. This is a periodic 360°/N wedge solved as stationary RANS. Steady should be valid because the disk is a surface of revolution and the baffles are fixed, so nothing in the geometry moves in the lab frame. A sliding-wall condition on the disk is enough, with no rotating domain. I’ll read Δh on the lid, and if it’s within about 2% of the depth, the flat lid is justified.
3. Only if Step 2 fails: iterate the lid shape stationary, using h_new = h + (p − p̄)/ρg imposed as a prescribed mesh displacement, until Δh is small.

Questions

1. Does this route hold up? The weak point I can see is that the 2D validation happens at low speed and without baffles. That’s a different flow regime from the 3D design case, so the validation may not transfer. How would you close that gap?
2. Turbulence model. The reference facility I’m comparing against used standard k-ε with wall functions. My main output is τ_w on the samples, and there’s separated flow off the baffles, so I’m leaning towards SST with a wall-resolved mesh (y⁺ ≈ 1) at the samples. Is that right, or is something like realizable k-ε, v2-f or RSM better suited to rotor-stator flow with strong swirl and curvature?
3. Narrow gap. The gap between the disk rim and the wall is small, and the baffles sit in or near it. That flow is somewhere between rotor-stator and Taylor–Couette, with bluff bodies in the way. Does that change your model recommendation, or how fine the mesh needs to be there?
4. Steady vs transient. The baffle wakes will shed. Is steady RANS with stalled residuals acceptable for mean τ_w, or should I go to URANS on the fixed geometry?
5. Verification. Beyond the route above, my plan is:
   • a three-level mesh convergence study on the baffled case, not the easy unbaffled one
   • k-ε with wall functions compared against wall-resolved SST
   • 90° vs 180° sector, plus one full 360° run to rule out an m = 1 mode
   • the unbaffled moment coefficient compared against rotor-stator cavity correlations (Daily & Nece)
   • motor torque vs speed measured on the real rig

Am I missing anything? Are there better benchmarks for a disk in an enclosed, baffled tank, for example from the stirred-tank literature?

I’m open to any other suggestion, including “your whole approach is wrong because…”. I’m happy to share more details or plots.

Hi everyone,

I’m a 3rd-year aerospace engineering undergrad, and I’m an international student. I have to choose my specialization right now, and I’m really stuck. I’d appreciate some honest advice.

My situation:

• I can do well in both CFD and structures/materials.
• I genuinely love CFD more.
• But I keep hearing that as an international, CFD/aerospace jobs in the US are very tough because of ITAR/export control and visa sponsorship issues.
• My goal is to go directly into a funded PhD in the USA after my bachelor’s.
• At my university, there is no aerodynamics/CFD professor. The only relevant professor is in structures/materials.
• The lecturer who supervises thesis students is very helpful, much better than the other teachers, but he only has a master’s degree.
• I’m worried that if i work with both the professor and have papers in both areas, it might make me look unfocused to PhD admissions committees.

My main questions:

1. Should I formally specialize in structures/materials because that’s where I can get proper supervision, while keeping CFD as a side skill?
2. Or should I still try to pursue CFD even though there’s no CFD professor to guide me?
3. For US PhD admissions, does formal specialization matter, or do research output and letters of recommendation matter more?
4. How should I present papers in both areas on my CV/SOP so I don’t look unfocused?
5. Any advice for an international aiming for a direct US PhD in aerospace/mechanical engineering?

I’d really appreciate advice from people who’ve been through US PhD admissions, especially internationals in aerospace or mechanical engineering.

Hello everybody,

I'm a PhD student who needs to simulate a supersonic gas discharging in a vacuum chamber, I already gave a look at the possible standard solvers which openfoam offers, and only dsmcFoam could be interesting for my case, however it would take very long to run a rarefied simulation, that is why I would prefer to simulate using a hybrid solver that couples standard cfd with montecarlo technique.

I found hybridDCFoam, very interesting solver but the authors do not answer me, and developing such a code all by myself is not feasible.

Does anyone have a solver that can suit my case by any chance? We can even get in touch and talk about it if there is any.

An unusual post maybe - looking for advice and ideas on how to solve a potentially harmful wind condition in a project of mine.

I have run a bunch of CFDs now testing different potential solutions, with not a lot of success.

Because this project is confidential I’ll attempt to explain with sketches for this:

I have a building that consists of two towers with a bridge connecting them forming a tunnel, under this tunnel is the dropoffs for both towers.

The Bridge is about 5 floors (20m ish) above the ground level.

The entire development is raised up about 10m from sea level on a big podium you drive up to.

In the center of the tunnel is a long pool with driveway wrapping it for the dropoffs

the tunnel could not be more perfectly aligned with the 3 primary wind directions.

There are a couple of big issues:

1. The climate is very rainy, and with this wind, there is a real concern for a ton of wind driven rain into the drop-off area given how high the bridge is
2. The architecture perfectly increases wind speed via venturi effect and downwash, and you end up with 8-11m/s wind in the drop off area when the ambient wind speed outside is the average for the climate, around 4m/s. the 90th percentile wind for this climate is like 9m/s and then the wind under the tunnel is 20m/s+
3. The problem is two fold - you get downwash and a vortex off the corner of the tall tower that dives between the two buildings, and you get downwash off the side of the bridge that dives under and accelerates
4. If you remove the bridge, you exasperate the corner downwash from the tall tower because some of it is not hitting the top of the bridge now
5. I’ve tried numerous potential solutions, all with some success but certainly not enough to warrant doing them:
   1. A lower canopy that covers the drop off areas at only one floor height, under the bridge - this gets some of the wind from the bridge downwash and keeps it above, but it accelerates the wind down-washing from the corner of the building. I’ve tried various extents in plan and heights / shape canopies.
   2. A bunch of trees around the corner of the building, and within the drop-off center area - this helps in the immediate area, but not around it at all.
   3. Chamfering the corner of the tower helps a little bit mitigate the downwash, but this is very against the design language, and does not help at all the bridge issue.
   4. The bridge cannot get higher, but it could maybe go a floor lower - not ideal - but this also does not help, it squeezes the wind more.

So I am hoping for some solution ideas, from some of you that are not as tired ;). thank you.

Hello! and Good day,

I’ve recently just started to learn how to mesh for CFD. I’ve been watching a few videos and I’m now proceeding to try and run a mesh independence test. I know the basic concept of going from coarse to fine mesh, and etc. I’ve also watched a few videos about it.

But I’m kinda confused as to what I am allowed to change when running one. Do I only alter global size? How about local sizing or inflation layers? And etc

Guys one small doubt,

To find static and total pressure at a point in 3d flow field, we should use vertex average or area weighted average?? Which one would be more appropriate??

Hi everyone! We are a student rocketry club working on a liquid rocket engine.

We are looking for someone experienced in CFD who can mentor us, as we currently lack expertise in this area.

If anyone is willing to guide us, please ping me personally. We would really love to learn and build our knowledge in this field. Thank you!

I’m writing a 2D finite-volume solver in MATLAB for the steady convection-diffusion equation for temperature (hybrid differencing, given velocity field and grid).

So far i have

• Non-uniform Cartesian grid with 25x25 interior cells. Cell-centre nodes plus boundary nodes that sit exactly on the boundary faces.
• The velocity field (u, v) comes from files, stored at the nodes. I don’t have the solver or discretisation that produced it.
• To build the convective coefficients I need mass fluxes, so i interpolate node velocity to faces.
• The resulting face fluxes don’t satisfy continuity, what is the usual way to get face fluxes that satisfy ΔF = 0, cuz this affects the Temperature field while solving differencing schemes right?

Hello, Good day!
Im new to CFD and learning to generate mesh. Initially I started using Ansys mesh, then was directed to Fluent meshing. But for some reason my boundary layers can’t seem to show up. Im quite sure that I selected the correct regions and places to grow on but they still won’t show. Here is an image

I am currently conducting a University project which requires me to simulate an accelerating Delta Wing. My model has been validated and verified under the limitations of my Student License in ANSYS Fluent. Validation was obtained by comparing the lift coefficient at a 10-degree AoA to experimental values. My first acceleration case is a 50 g acceleration at a 10-degree AoA. The steady-state case was run first. Initially, the residuals were converging well for each time step; however, some oscillations began later on. I decreased the Courant number from 200 to 50 and the Pressure and Momentum Explicit relaxation to 0.25 from 0.75. This dropped the residuals, but they still did not converge. The Lift Force during a particular time step is, however, showing convergence (imo, I am very inexperienced with CFD). I have attached some images. If anybody could advise on whether the solution can be considered converged for the particular time step, even if the residuals are oscillating, that would be greatly appreciated. The net flow is 0.51% of Total Inflow.

Edit: I have included an image of the residuals after making the changes mentioned above in the comments

Single H100. The same case takes 5 h 37 min with OpenFOAM v2412 on 26 cores.

Details: brae.sh/solvers/interfoam

I’m a beginner in CFD
I would like to learn how to conduct CFD simulations to investigate aircraft static and dynamic stability using ANSYS Fluent and OpenFOAM.
I would be grateful for any guidance you can provide.

Recently I’ve been working on a numerical project (more-so E&M related but this question is relevant to this community) and as a new PhD student want to get results fast. I’ve went through the entire formalism and know exactly what to implement but this step obviously has its own challenges and it’s inevitable you’ll run into something you didn’t originally consider (edge cases, etc).

After writing a small bit of code I’ll usually feed it into some AI and just ask it to double check. It’ll spot errors extremely quickly, stuff which would’ve taken me forever to even realize (stuff that would only ever get triggered on edge cases). It’ll automatically provide revised code which works much better than anything I could create. For reference, one part of my project involves a nasty integral with several branch points that get crossed, which results in many edge cases that I’ll only discover after tons of testing.

While in a way it’s nice to have such a tool at your disposal to double check your work, I’m becoming disheartened as I feel like trying to make my own code is a complete waste when AI realistically can do it better. A lot of people I know say they don’t write code by hand anymore so I’m unsure if I’m just wasting my time at this point.

I wanted to ask people with more experience what their outlook is—I don’t want to have my projects not contain my actual work but I also don’t want to fall behind my peers.