I am conducting aerodynamic analysis on a land speed record vehicle. I have just compared the turulance models Spalart-Allamaras, K-epsilon and K-omega. They all give me pretty much the same Cd and Cl value so whick model should I chose and why?

k-epsilon is good for the flow in large open area Spalart-Allamaras is given credit in aerodynamic application, especially airfoil, turbomachinery, where the blade experiences large pressure gradient SST is a modified version of k-omega therefore superior over k-omega; which is also good for some flows where typical recirculations are anticipated.

not to overlook is their efficiency, k-epsilon is the most efficient one with acceptable accuracy; while the computation with the spalart and SST model takes usually longer and requires a little more computer power

use realizable k-e for accurate lift and drag prediction but check valid y+ in prism layer for wall function.

for accurate calculations you may want to try the RSM model which is a second moment closure model and is known to overcome the well known defeciencies of the other RANS models. you should also compare the results of the different turbulence models to experimental data and judge their performance according to their agreement with the data. in the absence of this data you can use large eddy simulation to assesst the performance of other models. this approach is used by many authors now but the computations will be very time consuming. the most important thing is that you have to check the y+ values to ensure appropriate near wall treatment as red lemon said