Unsteady Forces in Jet Engine 7.5 Compressor Stage

Abstract

This paper analyzes unsteady forces acting on rotor blades in a 7.5-stage compressor with full admission. An in-house code was used to calculate 3D-unsteady non-viscous flow of ideal gas through a 7.5-stage compressor, using the Godunov–Kolgan method. The numerical analysis included blade vibrations and aerodynamic multistage coupling. All the stator blade rows in front of R1, R2, R3, R4, R5, R6, and R7 rotor blades as well as one stator row behind these rotor blades experienced excitation and multistage coupling occurred. This means that the first stator can influence not only the first rotor blades, but also other blades. For compressor rotor blade design, as previously only one stator cascade with high excitation frequencies was included in the equation of blade resonance margin: Hk = 〈0.9 b N1 n, 1.1 b N1 n〉, where N1 is the number of stator blades behind rotor blade row, b is the engine order excitation, and n is the rotation speed. We suggest applying several resonance mergions.