Chapter 6 Compressible flow Introduction
1 Chapter 6 Compressible flow Introduction
When is a flow compressible? A compressible flow differs from an incompressible one in that significant change happens in the density dp Pathline dt xo Fluid element Pressure
2 When is a flow compressible? Pressure Fluid element Pathline A compressible flow differs from an incompressible one in that significant change happens in the density. 0 dt d
Density of a fluid element increases or decreases as the pressure does in compressible flow P= pRT =50m/s =100m/s I=300m/s 4=P-p=p12 =1.54% =6.17% =55.5 100 Pa/00 k
3 Density of a fluid element increases or decreases as the pressure does in compressible flow V = 50m/s V =100m/s V = 300m/s 2 2 1 p = pa − p = V 1.54% 50 = pa p 6.17% 100 = pa p 55.5% 300 = pa p p = RT C p k =
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 Number
4 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
Examples of high speed flow Ma=085 Ma=2.35 Ma4 Ma=25
5 Examples of high speed flow Ma=0.85 Ma=2.35 Ma=4 Ma=25