We get the velocity potential equation 102|0 2 X 200、O =0 a ox In this equation, the speed of sound is also the function ofφ y( )( ) 0 2 ( ) 1 ( ) 1 1 1 2 2 2 2 2 2 2 2 2 2 =        −           + −           − a x y x y a x x a y y        We get the velocity potential equation: In this equation , the speed of sound is also the function of :          +  −  = − 2 2 2 0 2 ( ) ( ) 2 1 x y a a    (11.12)