ROUTE TO SURGE FOR A THROTTLED COMPRESSOR — A NUMERICAL STUDY

Abstract

Aerodynamic instabilities of axial compressors are investigated numerically and compared with experimental results. The compressor flow in the interblade-row spaces is simulated by means of 2-D Euler equations while the blade rows are modelled as quasi-steady actuator disks. The coupling of different unbladed regions of the compressor by actuator disks, which is characterized by the influence of stator and rotor, is captured in terms of conservation laws and source terms by means of compressor characteristics. At inflow and outflow nonreflecting boundary conditions are used in order to avoid any nonphysical reflections at the boundary. Numerically simulating this model for selected initial and boundary conditions, we observe that for increasing values of the imposed exit pressure the compressor flow undergoes several qualitative changes. At some critical value of exit pressure a primary stable steady state losses stability to several coexisting time-periodic states with a number of rotating stall cells. While for these time-periodic states the mass flow does not depend on time, all solution branches lead finally to surge, i.e., to states with an oscillation of mass flow in time if the exit pressure is sufficiently large. In addition, the numerical results are compared with experimental measurements.