The red curves give the Cx of the sphere to a certain number of Mach. For the incompressible flows (up to Mach 0.3 included), the yellow, fuchsia and red curves are almost mixed up: They draw together the classic curve of the Cd crisis of the sphere versus its Reynolds (see [CX_SPHERE.png]): it is the lower red curve. But when, for a certain sphere diameter, the flow velocity is increased (in order to increase the Reynolds), the later increases very slightly, but especially the Cd increases vertiginously (blue curves for each diameter).We are forced, to sweep all possible Reynolds, to increase the diameter of the sphere (and therefore of the wind tunnel).
<a href="//commons.wikimedia.org/wiki/User:Bernard_de_Go_Mars" title="User:Bernard de Go Mars">Bernard de Go Mars</a>
<span class="int-own-work" lang="en">Own work</span>