Introduction to Compressible Flow - Mechanical （介绍了可压缩流机械）.pdf

Introduction to Compressible Flow Dρ ≠ 0 Dt The density of a gas changes significantly along a streamline Compressible Flow Definition of Compressibility: the fractional change in volume of the fluid element per unit change in pressure p p + dp p p p + dp v v − dv p + dp p p + dp Compressible Flow 1. Mach Number: M = V = local velocity c speed of sound 2. Compressibility becomes important for High Speed Flows where M 0.3 • M 0.3 – Subsonic incompressible • 0.3 M 0.8 – Subsonic compressible • 0.8 M 1.2 – transonic flow – shock waves appear mixed subsonic and sonic flow regime • 1.2 M 3.0 - Supersonic – shock waves are present but NO subsonic flow • M 3.0 – Hypersonic Flow, shock waves and other flow changes are very strong 1 Compressible Flow 3. Significant changes in velocity and pressure result in density variations throughout a flow field 4. Large Temperature variations result in density variations. As a result we now have two new variables we must solve for: T ρρ ρρ We need 2 new equations. We will solve: mass, linear momentum, energy and an equation of state.