Autodesk Simulation CFD NACA0012 Benchmark Test

[WolfgangFischer4396]

We have been conducting our own attempt to validate Simulation CFD 2015 by modelling the well researched and documented NACA0012 aerofoil section in 2D. We have been very disappointed with our results and would be interested if anybody else has attempted a similar test. Following the advice in the Autodesk help files, we have the following settings:

• Section: naca0012 (Have tried both sharp point and blunted TE profiles)
• AOA : 10 deg (Have also looked at 8deg but has similar problems)
• Reynolds Number : 1e6 (Match to data)
• Mach Number : 0.15 (Match to data)
• Farfield : 30chords (have tried ranges 10c to 100c, only about 1% different)
• Mesh : Four concentric zones, mesh size =1/300th chord near section, increasing upto about 1 chord in farfield. Mesh growth rate reduced to 1.01 to smooth transitions. Typically produces mesh with more than 100000 fluid nodes.
• BL Mesh Enhancement : ON (BL Layers : 10).
• Physics : Compressible & incompressible (compressible is often unstable)
• Turbulence Model : SST K-omega
• Free stream turbulence intensity : 0.01 (reduced from default of 0.05 as this is external flow, all other turbulence settings default).
• Advection Scheme : ADV2 (ADV5 is not significantly better and more often unstable).
• Convergence Tolerances : Tight

Over a range of settings we have never achieved an error in lift force lower than 15%, and computed drag is typically 6x higher than published data for these conditions. I have seen considerably better results published on-line from Fluent and Cosmol simulations.
Is this really the best we can expect for this software, or am I doing something wrong ?

I have sent this also to Autodesk Support, with relevant files included.

[OmkarJ]

Don't have much in external aerodynamics but I have few suggestions/questions...

• A word on future plans to incporporate the Eddy viscosity transport model (one equation model), that has proved comparable to SST, less grid sensitive and inexpensive for external aerodynamic analysis? (Ref: A One-Equation Turbulence Model for Aerodynamic Flows. AIAA-Paper 92-0439, 1992)
• Any comment on how to tackle the transition? In most airfol cases, the boundary layer is laminar near the leading edge and turbulent near trailing edge, with transition happening somewhere in between. Since typical 2-equation turbulence models do not capture this distinction, they simulate the turbulent layer everywhere, generating unphysical eddy viscosity nearby leading edge. Hence overall viscous forces and consequently drag are overpredicted. In the benchmarking I have done in the past, I found lift coefficients spot-on with respect to data because they are pressure driven, but drag coefficeints were typically overpredicted.
• A word on how to ensure the boundary layer is "resolved" (integrated through). SST doesn't use wall functions but blending functions so not only having smaller Y+ values (ideally of the order of 1~3?) is useful but also it is preferable to actually have enhrancement layers to cover the thickness of entire boundary layer. On first run, while Y+ can be seen on the wall, it will be interesting to have some guidelines on how to judge the boundary layer thickness versus total enhancmenet thickness to make sure the steep velocity gradients are captured. 
• Recommendations for simulating 3D wings (say Onera-M6)?
• Guidelines for transonic compressible flows that are not covered in doco?
• Project Ventus

Thanks.

[IDBateman]

I agree with OmkarJ on his third point regarding Y+ assement of the whole boundary layer enhancement region. Exactly my current problem !

[Royce_adsk]

I do see this benefit, but there is no easy workflow currently.

Add a kudos to this request:

http://forums.autodesk.com/t5/simulation-cfd-ideastation/display-y-values-for-entire-domain-and-not-...

[IDBateman]

The current display of Y+ appears to be designed for 3D representation, but in a 2D view there is some scope for improvement.

I've attached an imagine that may help explain my point.