forces and force coefficient

maddy11 · January 24, 2019, 06:33

I'm running a 2D turbulent compressible rae2822 airfoil simulation at mach no 0.6 using rhoCentralFoam solver.
The simulation ran fine and i got accurate pressure and velocity contours as well as able to plot Cp vs x/c using paraview.
But the wallShearStress and the values of the coefficients are way off than the standard results.
To calculate forces and force coefficients i used the standard code in the controlDict.

Another thing i want to know is whether y+ values effect the forces.because im getting different values of forces coefficient for different y+ values.

controlDict.txt

yambanshee · January 25, 2019, 02:34

To get accurate drag, it is necessary to resolve the boundary layer as a wall function will not give a good enough velocity gradient to accurately determine wall shear. As such, y+ is a very important metric for determining wall shear, and by extension, drag. If you can afford it, I would ensure that the y+ along the entire wall is at or less than 1, and that minimal to no cell grading is used for the first couple of cells. But it is also a difficult task to get accurate drag coefficents for aerofoils, and I struggled correlating numerical and experimental in my undergrad thesis when investigating a naca foil in transitional conditions.

January 24, 2019, 06:33	forces and force coefficient	#1
maddy11 Member madz Join Date: Sep 2018 Posts: 34 Rep Power: 9	I'm running a 2D turbulent compressible rae2822 airfoil simulation at mach no 0.6 using rhoCentralFoam solver. The simulation ran fine and i got accurate pressure and velocity contours as well as able to plot Cp vs x/c using paraview. But the wallShearStress and the values of the coefficients are way off than the standard results. To calculate forces and force coefficients i used the standard code in the controlDict. Another thing i want to know is whether y+ values effect the forces.because im getting different values of forces coefficient for different y+ values. controlDict.txt

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January 25, 2019, 02:34		#2
yambanshee Senior Member Zander Meiring Join Date: Jul 2018 Posts: 125 Rep Power: 9	To get accurate drag, it is necessary to resolve the boundary layer as a wall function will not give a good enough velocity gradient to accurately determine wall shear. As such, y+ is a very important metric for determining wall shear, and by extension, drag. If you can afford it, I would ensure that the y+ along the entire wall is at or less than 1, and that minimal to no cell grading is used for the first couple of cells. But it is also a difficult task to get accurate drag coefficents for aerofoils, and I struggled correlating numerical and experimental in my undergrad thesis when investigating a naca foil in transitional conditions.