The compressor plays a key role in the development of new jet engines. The development of aerodynamically stable compressors with low blade vibrations is a difficult task, due to high aerodynamic loading, strong secondary flows, and high susceptibility to blade vibrations. Especially close to the stall limit, the fundamental aerodynamic and aeroelastic effects are not fully understood and remain a focus of current research activities.

For that reason, the aerodynamic and aeroelastic behavior of an engine-like transonic compressor is investigated in this paper. Simulations were carried out for the transonic compressor at the Technische Universität Darmstadt using the AU3D flow solver. A validation with experimental data shows close agreement between simulation and measurement for both steady and transient data. The simulations enable a detailed flow analysis during stall inception and non-synchronous vibrations (NSV) at operating points close to the stall limit.

During the initial phase of stall inception, fluctuations of the shear layer between main flow and a blockage zone in the passage, caused by the tip clearance flow, occur in the rotor tip region. The shear layer fluctuations are responsible for the emergence of vortical structures, as well as high and low pressure areas, which propagate relative to the rotor against the direction of rotation. As the fluctations continue to grow, large scale stall cells are formed. Also before stall inception, shear layer fluctuations can occur and their structure is very similar to the fluctuations leading to the onset of stall. In this case, the fluctuations remain small in size and the compressor continues to operate on the stable characteristic. The high and low pressure areas caused by the fluctuations yield an unsteady blade force when passing the rotor blades. NSV can occur as a result. Even though the flow field in the rotor tip region is highly complex, the shear layer fluctuations during stall inception and NSV can be explained by the basic flow principles of the Kelvin-Helmholtz-Instability.


On the Mechanism of Spike Stall Inception and Near Stall Non-Synchronous Vibration in an Axial Compressor

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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