Incompressible & Compressible Aerodynamics

Consider a centered Prandtl-Meyer expansion fan at a 𝜃 = 4° corner in a Mach 1.78 air flow, as shown in the figure below. The angle ψ (see figure) made by the ending wave of the fan with respect to the incoming stream is ________ degrees (rounded off to 1 decimal place). An excerpt from the table of Prandtl-Meyer function for air is provided below. M ν [deg] M ν [deg] M ν [deg] 1.72 18.40 1.82 21.30 1.92 24.15 1.74 18.98 1.84 21.88 1.94 24.71 1.76 19.56 1.86 22.45 1.96 25.27 1.78 20.15 1.88 23.02 1.98 25.83 1.80 20.73 1.90 23.59 2.00 26.38