The wave pattern generated by a model of a Porsche 944 in a Mach 3 wind
tunnel is made visible using schlieren with a microsecond exposure time. The
flow is from left to right. The wind tunnel is the 8" by 8" tunnel at the
Princeton University Gasdynamics
Laboratory, operating at a stagnation pressure of about 100 psia,
resulting in a Reynolds number of 63x10^6/m (a length Reynolds number of
The boundary layers on the floor and ceiling of the tunnel
are clearly visible. A shock forms in front of the vehicle, and another
shock forms at the junction of the hood and the windshield. These shocks
interact with the boundary layer on the ceiling, producing a separation
shock that forms well ahead of the point where the other shocks impinge,
demonstrating the upstream influence of this interaction.
The photograph was taken by John Donovan and Michael Selig in about 1987.