Incipient Shock Waves
Usually The Shock Wave Forms When Supersonic Flow Changes Into Subsonic Flow. I.e At Mach 1.but Incipient Shock Wave Starts From M>0.8 To M 1.this Happens When There Is A Sudden Increase Of Pressure And Density,fall In Velocity Over The Aerofoil.u Can See This Wave At The Centre Of The Aerofoil Than The Shock Wave At The 3/4 Of The Aerofoil.