Flow Over UAV - Question about FLUENT Solver and Y+
 

Dear All,

I have been trying to model turbulence on a mini-UAV as part of a project for my school. The problem is that I don't quite understand how to assess if the use of Y+ in my model has been correctly implemented.

I have used the Y+ Wall Distance Estimation for Y+ values of 30 and 1, getting 3.5e-4 m and 1.2e-5 m respectively for the estimated wall distance.

My objective is to accurately capture the CD coefficient for the entire UAV, I've read that the Y+ value depends on type of model, what I have is: Re = 2.1e+5, V = 25 m/s, Chord Line = 0.1255 m.

I have used K-epsilon Standard and Realizable Models with enhanced wall treatment for Y+=30 and K-omega SST for Y+=1 and I basically get the same drag and lift coefficients for both models, I don't know if instead of resolving the viscous sub-layer I should use wall functions.

Also, I had checked the velocity profile on my models and saw that the velocity doesn't rapidly change normal to the surface of the wing. Does that mean the model is grid independent?

Below I attach some images for the k-omega SST Model (Y+=1):

1.- Contours of Y+ from Post in Fluent

2.- XY Plot of Y+ for the UAV

Any help is greatly appreciated!

Wall Yplus
 

The values for are in the expected range. So, you can trust the model as far as the mesh resolution is concerned. Accuracy depends on other aspects as well, such as, material properties, boundary conditions, discretization order, etc. But mesh is good.