Why does Cd increase until Mach1 while drag force increases?

[AielloJ]

When I was looking a project that included Mach vs Cd and Mach vs drag Force for a grid fin at different altitudes with different mach numbers, I saw that as Cd approached Mach 1, it increased but after passing Mach 1, it started to decrease but the drag force kept on increasing.

I initially thought that as it approaches trans sonic speed, shockwaves start to form inside the lattice (choked flow), which starts to create a little more drag. As it nears M1, a bow shock will form which would start diverting air away from the lattice and at the same time would create significant drag. A normal shock wave and oblique shockwave should form at this time, further increasing drag as speed increases and the bow shock eventually disappears. Yet as the fins start to go past M1, the oblique angle increases which would be associated with lower temp/pressure drops which would explain why the Cd decreases ? Wouldn't this contradict the Mach vs Force graph where the drag force keeps increasing?

This feels wrong but I did the best I could. I'd love to hear the flaws in this attempt.

 

[FactChecker]

Drag force is proportional to $V^2$, so it can keep increasing while $C_d$ remains constant or even decreases. In fact, if the real drag force does not increase as fast as $V^2$, then $C_d$ must decrease to make the drag equation correct: $D = C_d \frac {\rho V^2}{2}A$.

You may be correct about why the force increase does not keep up with $V^2$, but $V^2$ grows very fast. It wouldn't surprise me if it's just that more of the plane becomes "shadowed" as the speed increases and the drag force does not keep up with $V^2$.