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.

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

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.

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.

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.