Great Mysteries of Engineering Fluid Dynamics
The Extra Shock Wave
by G.D. Stubley
Synopsis
One of the features of supersonic flows is that the flow field adjusts suddenly to downstream disturbances. For example, when the flow approaching the two-dimensional wedge shown below is supersonic there is no physical mechanism for the flow field to adjust to the presence of the wedge before reaching the wedge.
Therefore, the flow adjusts by turning suddenly over the oblique shock wave which radiates from the tip of the wedge. Across the shock, the flow angle changes suddenly and there is a corresponding jump in pressure, temperature, and density.
Shown below is a fringe plot of the relative pressure field for supersonic flow of air over a 10± wedge. The oblique shock radiating upwards from the tip of the wedge can be clearly seen.
Notice that there is also an oblique shock wave radiating downwards from the tip even though the bottom surface is parallel to the approach flow. What causes this second oblique shock wave?
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