Discussion

We discovered from these results that lift and drag forces are both functions of air velocity. Furthermore they are both affected in some way by the transition from laminar to turbulent flow due to increasing air velocity.

The drag on our model is much greater for low velocity flows. This could possibly be due to the fact that the flow is still laminar. As the flow velocity increases and begins to turn turbulent the drag coefficient on the car drops dramatically then increases slightly as the flow becomes fully turbulent (as shown on our C_D vs velocity graph). We found that as the velocity of the flow increased the drag coefficient converged around .6. This is because the flow started out laminer, but changed to turbulent when the flow speed was high enough. The C_D magnitude first fell .6 at about 14 m/s, presumebly where the transition to turbulence began. By 17 m/s, the flow seemed to have become fully turbulent and the drag coefficient stabilized at 0.6.

The C_L vs velocity graph shows that the shape of the General Lee model creates a small amount of lift at lower speeds, but after the model car speed reaches about 19 m/s the lift force drops to zero, then starts to become negative. This is beneficial as one would want the car to create some down force as it sped up so that it could corner better. We also saw that as the flow goes from laminar to turbulent flow around the model the lift coefficient drops and, as the flow becomes fully turbulent the lift coefficient converges around -0.01 which is a subtle down force. However the error on our lift coefficients suggest that it is possible that the car never produces any down force. More importantly, this model never produces a significant amount of positive lift at a high velocity. The Charger can therefore maintain reasonable control at high speeds since the wheels are never being pulled off the ground.

The benefit to finding these lift and drag coefficients is that they can be used for any sized model of the car including a full scale model as long as the Reynolds number of the flow is the same in each case.