When is compressibility important? When a fluid moves at high speed, density changes become significant Change in density only about 5% 0.8 flow speed c-sound speed 0.6 0,4 Ma<0.3 incompressible 0.2 Ma>0.3 compressible Mach Number4 When is compressibility important? When a fluid moves at high speed, density changes become significant c V Ma = - flow speed - sound speed Ma<0.3 incompressible Ma>0.3 compressible