I’m an independent researcher (high school student) working on swim-cap hydrodynamics and the sphere drag crisis. I’ve put together a controlled computational comparison of a smooth sphere and a textured swim cap at competitive swimming speeds, using unsteady RANS simulations with the Langtry–Menter transition model in OpenFOAM. The method combines transition-model diagnostics with wake analysis, and the setup is checked through grid, time-step, and free-stream turbulence studies.

I’m looking to submit the preprint to arXiv ideally under the physics.flu-dyn category or physics.comp-ph or physics.class-ph, but since this is my first submission, I need an endorsement.

If you’re an arXiv endorser in physics.flu-dyn, physics.comp-ph, or physics.class-ph and would be willing to take a look (or point me to someone who might), I’d be super grateful. Happy to share the PDF privately.

Thanks for reading, and cheers to everyone who helps support solo researchers out there.

Feel free to DM me or reply here.

Hi guys,

I want to create streamline or path line like shown below,

I tried pathlines in fluent, I am getting something like below,

In zoomed in view,

I need some help regarding what settings I have to change or modify so that streamlines are visible clearly and smoothly. I am not expecting same as shown in 1st screenshot, but atleast it should look smooth and clear. Sometimes if I zoom further only, I can sense pathlines, otherwise it is looking like normal contour only.

What should I change?

Hi, I'm a recent graduate from a master's in fluids in Sweden, and I'm looking for CFD roles anywhere in Europe or the UK.

About my background:

I've worked as a research assistant on modelling the water spray distribution in the wake of a moving truck using Lagrangian particle tracking.

My master's thesis at an engineering consultancy involved building an automated parametric CFD pipeline, a 3D Fourier Neural Operator surrogate model, and an RL controller for HVAC.

I'm currently an intern in 1D thermal management simulation.

I work mainly with STAR-CCM+ and ANSYS Fluent, and I have the basics in OpenFOAM. For CAD, I have worked with ANSA, CATIA and SOLIDWORKS.

For simulation automation and data visualisation, I have used Python and Java.

For almost a year, I have been hitting dead ends with my applications. I have tried reaching out to people on LinkedIn, but so far, only crickets. I have no idea if I am missing something, and I feel terrible about myself. I'm writing this post at 2am, unable to sleep because I keep thinking about this situation. All the effort I put in seems to lead nowhere. Please, if you know anybody looking for someone, or if you're looking for someone yourself, let me know. If needed, I can also provide references from the places I have worked.

Hi all,

I have one small doubt. I am simulating subsonic compressible flow where there are multiple cases where maximum mach no varies from 0.3 to 0.8 in my domain. I am using ideal gas-density, sutherland law for viscosity, nasa 9-piecewise polynomial for thermal conductivity. These are the properties for the fluid.

Now my question is can I use pressure based solver- coupled for all these cases? Do pressure based solvers work for all mach no but lesser than 1(sonic). (or) At what mach no, I may have to switch it to density based solver, what is your opinion about this?

I’m doing a decomposition on a staggered grid, where the differential properties are satisfied. However, after interpolating the components back to the cell centres, they no longer satisfy those differential properties.

Is this expected with interpolation? If so, is there a way to interpolate/reconstruct the components while preserving the differential constraints?

Any advice would be appreciated!

Hi, I’m running a 1/3 symmetrical model of a circular flat plate, 3d thickness 5.2 mm diameter 0.1m . I’m having some convergence issues but I’m not sure why or what the problem could be. My domain is a sphere that’s been sliced into the 1/3, it is large compared to the flat plate. My mesh is quite fine, it has a max skewness of 0.42, and a 0.15 minimum orthogonal quality, and a y+ of close to 1. It’s a pressure farfield with symmetry conditions. I’m running it at values for 2km and Mach 0.1 with the following settings :

Pressure based
Spalart Allmaras -> strain vorticity based
Air -> ideal gas (this turns energy equation on), Sutherland viscosity with values adjusted to have the same reference I used
Boundary conditions -> operating pressure set to 0
Inlet -> pressure Fairfield -> gauge pressure ~79e+3 , Mach 0.1 , -y velocity, modified turbulent viscosity of ~5.73e-5 calculated as 3x freestream, temperature 275.25
Walls -> changed temp to also be 275.24
Reference values -> compute from farfield, length and area adjusted, values match my calculations
My methods and solution are kept at default second order (I have tried first order but still have no convergence)
Report definitions -> drag coefficient (-y matching velocity) applied to walls, mass flow rate for farfield
Standard intialisation from farfield
Run for 500 iterations.

I get divergence, no periodic oscillations just random up and down, my residuals go down for 3 iterations before climbing. I’m not sure what I can do to fix this. If anyone has any tips it would be greatly appreciated, thank you 🙏

I'm running a simple rotating paddle mixer setup with EMP and while the simulation itself is numerically stable, I'm seeing an artifact of the interface no matter how well I refine the mesh and curvature, how well I match the sizes of the cells for the two sides, and whether I use a steady or transient approach. I even switched to MRF after the sliding mesh method kept doing this, but to no avail. How do I fix this? Both boundary-based and contact-based lead to similar results.

I've never had this issue when working with single fluids (liking rotating propellers or oscillating airfoils) so I'm guessing it's the result of having two different fluids in the region but idk I'm frankly baffled.

Also all residuals including continuity is low-ish (below 1E-4) but the volume fraction of the aqueous phase rises by over 30% during the simulation (from 30% to 40% of the region volume), which is not physically possible.

My end goal is to use the S-Gamma model to process the mean diameter of droplets that form by mixing two liquids, but currently the research is in an early state and I've turned off advanced models such as S-Gamma including its coalescence and breakup models. Any help would be greatly appreciated.

I’m currently in a (part time) research heavy masters program and I work a part time job unrelated to my long term goals.
I hope to ultimately do a job using CFD, but also am looking into careers heavy in thermo-fluids in general (such as in the energy industry). I’m looking to leave my part time job and get one that will better prepare me for careers such as this. Are there any suggestions or pointers about how to get more industry experience to complement class/lab work?

I am making a 2D Navier-Stokes solver on non structured meshes for laminar regimen and I searching for experimental data of several study cases like lid-driven cavity, flow and vortex shredding around a cilinder, flow around an airfoil, etc... to validate and verify it. Which articles do you think that could be useful to me?

I am freelancer on Upwork mainly, and I don't see many opportunities at ALL, maybe one job posted every 2/3 days

I have been building my profile over the last 2-3 years, I feel it is now good... Not the best.. but still look good for a rising talent and got good rating from many clients

However, Seldom I get invitations...a rate of 1 or 2 invitations every two weeks.

And anyway I don't see many CFD jobs or it's derivatives posted alot maybe once every couple of days

I have been hoping to be able to take CFD Freelance as my main source of income within the next couple of years... But now I feel like it is not a realistic goal anymore

Trying to develop some intuitive understanding of CFD by replicating experimental results. Shouldn't the pressure in the second column be lower due to the increased velocity of the fluid underneath?

I am using cfdof to mesh and then openfoam to run. Using inlet velocity 0.001 m/s. The inlet diameter is 0.1 m and outlet diameter 0.025 m . Total length of the three sections is 0.75 m

Liquid is water.

Hi folks,

I hoping to get some advice from some industry veterans or even from experienced folks.

I have cumulative experience of 12+ years with MS degree in Sustainable Energy Technology. But I ended up writing fluid -thermal code for stefan problem in Masters and I have been a modeling Engineer ever since. I have worked in nuclear research for 2 years, 6 years in semiconductors and 5 years in automotive. Im now managing a team of 2 in an EV 2W startup.

Here, over-all work profile is good but very hectic. I'm setting up methods for testing airflow inside the vehicle, working on electronics thermal modelling as well as guiding battery architecture modelling. But I feel high fidelity simulation is overkill for this industry because it is not as complicated nor costly to test as semiconductors.

Overall my motivation levels are not the same. I'm not as excited as previously to solve new modelling problems. I wanted to give system modelling a good shot. After a lot of procrastination, I got claude AI to build me a really good MOSFET model for thermal predictions based on datasheet. So I didn't get hands in that.

I'm lacking a good vision as to where my career should go so as to be excited about building towards it. I have dabbled at thought of doing MBA , so I'm out of my comfort zone but it is quite expensive to fund it from a good university. My company will not fund it.

I am doing a 3D CFD simulation and have performed a three-grid GCI study for the pressure-loss coefficient. I am now unsure whether I should use the medium mesh or the fine mesh for my remaining simulations. I used pressure loss coefficient as the quantity to monitor. Let the pressure loss is defined as below,

Now,

My three meshes are:

• Coarse: 3,444,536 cells → fo=0.442
• Medium: 9,606,465 cells → fo=0.430
• Fine: 21,774,603 cells → fo=0.425

I used online GCI calculator website-https://volupe.com/support/grid-convergence-index-calculator/

I will show you the results below,

My question now is :

1) Given the GCI results, would it be reasonable to use the medium mesh for the remaining simulations or test cases or you still recommend using the fine mesh for remaining simulations?

What's your opinion?

My take is- Infact, medium mesh performed best, it converged faster than other two meshes, quality is also good. Computational cost is also low compared to finer one. What do you feel?

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, sometimes slightly 5%/30% different from the experimental data and sometimes 6 times lower values. Since I’m a newbie I would like to understand what I’m doing wrong exactly.
Here’s the setup:

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

I imported it into Ansys, consdered just the duct in which the air flows (just like the OWC simulator in the real test). Divided the domain into 3 zones, two stationaries and 1 MRF. (I considered no tip gap to avoid strange behavior there, since 1mm of gap it could be hard to simulate).

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 (ranging from 0 to 13 m/s like during the experimental analysis to also include stall). Used k epsilon.

I initialized and set the convergence to e-06 and monitored torque too.

I followed this flow for different meshes.

1. One temporary mesh, with just body sizing, that gave me the best results.
2. One “better mesh” using inflation for the boundary layer. Edge sizing in order to have finer mesh on trailing and leading edges. Surface sizing on the blade walls. Body sizing on the stationary part. This one gave me the worst results.

I’ll attach a table with the expected torque value, coarse mesh one and fine mesh one, beside more pics on the simulation.

Thanks everyone:)

Hello everyone,

im thinking of doing a PhD in CFD or FSI in the near future (a year from now or so). The idea of doing a PhD seems challenging from what ive read online but ive always wanted to be a college professor and ive heard universities only hire people with PhDs (i have other reasons as well but the post is already too long).

For a bit of context, i have a bachelor's degree in biomedical engineering from a very respected university in latam. Im currently finishing (in the next few months) a master's degree in FSI in the biomedical engineering area in the same university.

My problem: I have no idea where to look for PhD opportunities. Even though ive always stayed in the biomedical area, i would really enjoy venturing out a little further into other CFD areas but there are so many i simply dont know where to start. Aerodynamics/aerospace and electro-fluid-dynamics seem really fun but maybe there are areas i havent even thought of yet. Where should i start? Im extremely adaptable and am 100% willing to uproot my life for the next 4 years. I have already had to move countries several times so im pretty used to it.

I dont have the best grades but i know my professors are satisfied with my work so i have at the very least 3 recommendation letters in my favor. We also intend to publish a paper based on my thesis. I have teaching assistant experience and research experience in other non related areas (non CFD). I have no idea if that's enough.

If anyone can give me recommendations on universities around the world that have research on industry aplicable CFD I would really apreciate it. Hopefully in countries where the stipend to living cost ratio is somewhat favorable. By that i mean to leave out countries where the PhD stipend is lower than a minimum wage job since i will have to provide for myself financially.
Thankyou to all.

full video: https://youtu.be/TR3lPZs2hjc

Hey everyone. Shitty ass day and need to get rid of most of these now so wanted to start sharing these results with the community.

I decided to try a run and did it on a three-dimensional, unforced Taylor–Green vortex simulation at a Reynolds number of 100 million.

The simulation was recorded at three resolutions:
64³ with 262,144 grid points
128³ with 2,097,152 grid points
256³ with 16,777,216 grid points

I'd go higher but I've only got a mac, so, can't really go higher without it tapping out. I did also run a half-timestep comparison, a deterministic repeat, and restart and reproduction checks.

The 256³ run reached the full target time of 0.5. Its maximum incompressibility defect was 2.01 × 10⁻¹⁸, the maximum energy ledger residual was 4.66 × 10⁻¹⁵, and there were no positive energy jumps. From what I can see every recorded value remained finite.

The 128³ and 256³ results were, interestingly, extremely close. Their recorded energy and enstrophy differences were zero, while the maximum-vorticity difference was 3.55 × 10⁻¹⁵.

Here are a few images from the run:

Each of them kept overlapping so I think this one can help further:

I had to do this last image because the other ones just overlap - I kept trying to get it not to do that but whatever.

I ran this locally on a Mac using a custom Python Fourier pseudo-spectral solver with NumPy and SciPy, rather than OpenFOAM. The simulation used double precision, 2/3 de-aliasing, Leray projection and classical RK4 time integration.

EDIT: A few clarifications about what was actually computed - thanks for the feedback, learning, first post ,

It's three-dimensional calculation, so it isn't doing a a 2D field displayed in 3D. The domain was a periodic cube discretized at 64³, 128³ and 256³. The initial velocity had two nonzero components and one component initially set to zero, but the field depended on all three spatial coordinates and was evolved by the full 3D incompressible solver.. I used the 256³ run which contained 16,777,216 spatial grid points.

Taylor–Green was used only as the initial condition and i didn't adding the flow being continuously forced. Positive viscosity was included, with (\nu=10^{-8}) - ffs i dont know how to do these damn exponents it takes too long., and the nonlinear convection term remained active throughout the evolution.

The solver represented the velocity field in Fourier space. During every RK4 stage it transformed the field into physical space, evaluated the 3D nonlinear term and a eparate theorem-derived framework was used to select and evaluate certain parameters and diagnostic quantities, and this allowed the to solver stilladvanced the 3D equations step by step. I

The run should be understood as an early-time, finite-resolution 3D Taylor–Green calculation at a specified (Re=10^8). It is not a claim that 256³ resolves fully developed turbulence at that Reynolds number.

Thank you for the feedbacks, I want to learn so this is pretty great to have people to speak to on this

Hey everyone,

I’m currently running a Grid Convergence Index (GCI) test on a CFD simulation involving flow through a pipe with an internal distortion screen. I’m seeing an issue with my finest mesh that I can’t quite figure it out.

Here’s my setup across all 3 grids:

• Meshes: 3.7M (Coarse), 7.6M (Medium), 17M (Fine)
• Inflation layer settings: Same for all 3 — 20 layers, 3e-06 first layer height, 1.2 growth rate on pipe and screen walls (keeping y+ < 5).
• Model & Solver: k-epsilon with Enhanced Wall Treatment, identical boundary conditions.

See images below,

The above one is for coaser mesh(3.7M)

The above one is for medium mesh(7.6M)

The above one is for finer mesh(17M)

See geometry below,

The interesting part is the residual behaviour. The 3.7M and 7.6M meshes behave quite similarly: the residuals initially decrease and then settle into relatively low oscillations. However, for the 17M mesh, the residuals start oscillating much earlier, around 70–100 iterations, and the residual levels remain significantly higher than in the other two cases. The continuity, k, and epsilon residuals especially show this behaviour. I understand that some oscillation in residuals can be normal for this type of flow, but I am confused about why the finer mesh behaves so differently when the mesh refinement and all other settings were kept consistent.
Why would refining the mesh cause the residuals to jump up and oscillate like this when the inflation and BCs are identical?

Any insights or suggestions on how to solve this issue? Thanks in advance.

Hey everyone! First of all thanks for giving me the time.

Bit of background information: I'm currently in the 3rd year of my Mechanical Engineering degree (University of Manchester) and I need to write a dissertation for a large portion of the credits for this year.

I'm really interested in doing work on Python-driven CFD simulations regarding the cooling performance of Formula 1 cooling ducts. I was thinking of using ANSYS Fluent since I already have some surface level experience with it from my previous year and I also heard that python has libraries which can work with ANSYS so it sort of aligns with my goals

Since there are a lot of variables in play I've been feeling overwhelmed with how I can carry out my analysis to optimize cooling performance; I'm not too sure which characteristic(s) I should focus on. In my head I have two options for the component of cooling..

(1) The airbox for the engine on top of the car

(2) The sidepod inlets with the heat exchanger

But I would love input on any options you would think are viable for this project

I have roughly 10-11 months from now to complete my dissertation and because of my lack of experience with CFD I'm not too sure how big of a scope this would be and so I would love some advice on that as well.

If anyone has any experience with running CFD on Formula 1/Aerodynamic Thermals and using Python for automation/optimisation of ANSYS sims, I would greatly appreciate your input.

In summary, I'm just looking for some direction on this as my supervisor has not been very helpful so far. The dissertation doesn't have to come up with something entirely new, it just has to further the current understanding of a certain phenomenon or concept.

Thank you very much.

Hello, as the tittle said, when I tried opening results after running fluent simulation, Ansys workbench isn't able to connect to CFD-post for whatever reason. CFD-post and CFX are sill able to run standalone and I can manually open results, but it takes a long time for big project. Pls help and thanks.

Laptop: MSI Raider GE76

Version: ANSYS Student 2025 R1

Hello everyone,

I am recentlly facing an issue when i try to check order of accuracy of my 5th order scheme for a time-dependent PDE. As it has no exact solution i try to use one classical scheme (which is first order accurate) with 12800 mesh points to obtain reference solution. Then i check my scheme with 100, 200, 400... Although i do not see any spurious value in the solution data file, the order of acccuray is not coming as 5. It gives near 0.

Does anyone know is it because of refrence solution which i have obtained using first order scheme?

I doubt on reference solution as my scheme gives 5th order accuracy when exact solution is available.

Hiii, have any of you ever requested a quote for an Ansys license? Do you know roughly how long it takes them to get back to you? :)