Unsteady simulation of a 3.5 stage compressor using multi-frequency phase-lagged method

Multi-frequency phase-lagged boundary condition has the advantage of reducing the computational domain to one single blade passage per row in unsteady flow simulation of a multistage turbomachinery, which saves the requirement of computer memory and time. The first part of the paper presents the implementation process of this approach in CFD code to predict unsteady flow field in multi-stage turbo-machinery. Unsteady simulations and steady simulations are then performed on a 3.5 stage compressor. Compared with the steady results, the compressor performance predicted by unsteady calculation match much better with the experimental data. The flow field of neighboring blade passages per row in compressor appears different due to the unsteady interaction of rotor and stator. The blade surface pressure distribution of middle stators fluctuate in large amplitude especially at the trailing edge of the stator. The interaction between stator blades and forward shock wave of the downstream rotor under small axial gap is the key factor of stator blade pressure fluctuation.