SimScale CAE Forum

Not getting correct drag coefficient

To start here’s a link to my project: https://www.simscale.com/projects/premalp/flow_around_sphere_higher_flow_rate_pt_2/

Hi all! I am very new to SimScale (and CFD in general) and am trying to create a simple setup of water flowing past a sphere. When I run this simulation, I find that the drag coefficient does not match up with what is expected (I have tried flow rates that correspond to Re values ranging from 0.1 to 100000). Right now, I am using Re = 100, and I have tried making some modifications to the mesh but those changes have not changed the results. Does anyone have suggestions for things I should try modifying to get the correct drag coefficient?

For reference, with the current input flow rate, the expected drag coefficient is 0.993, but the simulation converges at about 1.10.

If anyone is curious, here is my source for expected drag coefficient : https://www.sciencedirect.com/science/article/abs/pii/S0032591007006225

Any help would be greatly appreciated! Thank you!

Hi!

There should be two main factors here:

  • For a Re = 100, external flow is laminar, however the turbulence model is currently set to k-epsilon:

  • Especially for validation cases, it’s always recommended running mesh sensitivity studies. You mentioned you have already tested different meshes, however 900k cells is definitely not the limit. Mesh convergence varies quite a bit from problem to problem.

I’d recommend running some tests, applying additional refinement around the sphere (including here the region downstream from the sphere).

Cheers

1 Like

Great I’ll try those suggestions. Thank you!