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.
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