Hi!
Drag forces and drag coefficients are related to each other based on a formula that requires some user input, most notably the reference area A and the freestream velocity V:
Since these values are ‘arbitrary’ to some extent, I sometimes find users having difficulties to compare data. As you can infer from the equation, forces will vary with velocity and, if they are not linearly correlated, Cd will also change with velocity.
Suggestion: compare forces rather than coefficients, because forces do not rely on user-defined parameters. Furthermore, when comparing simulation tools, take extreme caution so that both runs are set as close as possible and so that both are fully converged.
Remember to sum up both viscous and pressure forces, as both of them should be accounted for when it comes to lift & drag.
Cheers