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Verifying Accuracy of CFD Results

Question asked by Tom Quinlan on Jun 14, 2013
Latest reply on Jun 14, 2013 by Jared Conway

     For a school project, I am going to be running simulations comparing drag forces against a car model with varying external accesories. Before I move to complex geometries, I am trying to prove the validity of the CFD results with known values. Since there is no way to use hand calculation/known drag force coefficents on anything but the most basic of shapes, thats what I have started with.


     I have been using a smooth sphere, with varying diameters and flow velocities. I am calcuating reynolds number based on these parameters, and also the drag force coefficent based on the drag force experianced by the model. I have plotted the different Cd Vs. Re values on a graph, and have been comparig them to text book values for smooth spheres. I am attaching an excel with the data I have gathererd so far and a plot of accepted values. My results are quite different than what they should be and I am trying to figure out what parameters in my model/calculation error which could be casuing this error.


Current Setup:


V= 0.1 to 30 m/s

D= .0625 to 1 m

Boundary condition of a real wall with 0 roughness

Air at 293K,  1.2041 kg/m3,  0% humidity,  0.1% turbulence

Computational Domain Size: 5D downstream, 2D upstream, 1.5D Surrounding


Surface Goal: normal force in direction of flow