If the value does not change from Mach 0 to 4, the direction of the force does not seem to be a problem.nFluentBatavia, have you checked that you have selected the whole surface of your body?nAnother way to detect the error is to plot contours of pressure, velocity and density at different flow speeds. Mach 0.5, 0.8, 1.2 and 1.5, for example. With these simulations you will able to detect the shock waves, as well as the pressure distribution in the wake region. In the proposed cases, the variation in the drag force should be important. n