# Turbulent boundary layer on a flat plate

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 January 16, 2009, 09:40 Hi everyone, I am running s #1 New Member   Sébastien Bocquet Join Date: Mar 2009 Posts: 21 Rep Power: 17 Hi everyone, I am running some 2D calculations over a flat plate, and comparing the openFOAM results with flu3m (Navier-Stokes CFD code from ONERA), Fluent and experimental/theoretical data. I am using 2 meshes. Here is a description of the case : Application : simpleFoam Kinematic viscosity nu=1.57e-5 mē/s Plate length L=1m Re (end of plate) = 4.4e6 divScheme : Gauss upwind Turbulence model : Spalart Allmaras First mesh : 0.15 < Y+ (first node) < 0.2 Second mesh (identical to first mesh with 35 first cells close to the plate removed) : 20 < Y+ (first node) < 23 Boundary conditions : Inlet : inlet Top : pressureOutlet Exit : extrapolatedOutlet Plate : wallFunctions U(inlet)=69.177m/s nut(inlet)=1.5e-5 mē/s nuTilda(inlet)=1.5e-5 mē/s p(inlet)=p(top)=pref=0 Initial conditions = boundary conditions at inlet For the first mesh : Plots of U+=f(y+) : At x=0.12 : At x=0.94 : For the second mesh : Plots of U+=f(y+) and mut/mu=f(y+) : At x=0.12 : At x=0.94 : Comments : The mesh with y+ around 20 gives satisfying results especially on the velocity profile at x=0.94 and the local friction Cf. At x=0.12, we have an offset on the U+ velocity profile in the log region and a smaller turbulent viscosity compared to flu3m and Fluent The finer mesh (y+ around 0.15) induces a significant offset on the U+ profile in the log region, with a smaller turbulent viscosity than the other calculations and an underestimated local friction (2.5e-3 compared to 3e-3 for the theoretical/experimental results at the end of the plate). If someone encountered a similar problem... Thanks in advance

 January 17, 2009, 03:30 Hi Sebastien, I'm working on #2 Senior Member   Ivan Flaminio Cozza Join Date: Mar 2009 Location: Torino, Piemonte, Italia Posts: 210 Rep Power: 18 Hi Sebastien, I'm working on a similar case, a RANS over a flat plate at Mach 0.06 and Re 1.3x10^5. If you choose a wall-function treatment, you have to put your first cell at y+ around 30, if you want to use a y+ less than 1, you have to use a lowRe model, so if find some lowRe model suitable for a flat plate you can use it! Ivan