When a sphere moves through the air it first compresses the air at the center point in front of the moving sphere. Then this air accelerates around the sides of the sphere and exhibits laminar flow (streamlined non-turbulent flow) until it reaches approximately the middle of the side of the sphere ( a plane perpendicular to the plane of motion). And then, as the air wraps around the back side of the sphere it develops a turbulent flow characterized by little whirlies and eddies, which creates drag on the sphere.

Although my understanding of German is very limited, I hope that this should help you decide the correct translation.

Regards.
Luis Luis

Verdünnungsverhältnins in einer By-Pass-Turbine (aeronaut.)= dilution ratio
Verdünnung bei Flüssigkeiten=dilution
Fächer=fan

rarefaction wave

>>Dense Gas Dynamics …. The unusual behavior of these fluids stems from the fundamental derivative of gas dynamics. For most everyday fluids (like air) the sign of this parameter is essentially constant and positive, giving the classical behavior of compression shock waves and expansion rarefaction waves. <<
http://rintintin.colorado.edu/~fergason/text.html
AltaVista (English) :
[+aerodynamics +"compression shock”] 7 hits
[+aerodynamics +”dilution wave”] zero hits
[+aerodynamics +"rarefaction"] 44 hits
[+aerodynamics +"rarefaction wave"] 2 hits:
http://www.sci.kcn.ru/imm/group-gil.html
http://utias.utoronto.ca/test/tnotes.htm

For some basic terminology:

Advanced Topics in Aerodynamics -- Shock Waves
http://www.aerodyn.org/HighSpeed/shock.html