Generation Mechanisms of Rotating Stall and Surge in Centrifugal Compressors.


Type
Article
Change log
Authors
Sundström, Elias 
Semlitsch, Bernhard  ORCID logo  https://orcid.org/0000-0001-7715-863X
Mihăescu, Mihai 
Abstract

Flow instabilities such as Rotating Stall and Surge limit the operating range of centrifugal compressors at low mass-flow rates. Employing compressible Large Eddy Simulations (LES), their generation mechanisms are exposed. Toward low mass-flow rate operating conditions, flow reversal over the blade tips (generated by the back pressure) causes an inflection point of the inlet flow profile. There, a shear-layer induces vortical structures circulating at the compressor inlet. Traces of these flow structures are observed until far downstream in the radial diffuser. The tip leakage flow exhibits angular momentum imparted by the impeller, which deteriorates the incidence angles at the blade tips through an over imposed swirling component to the incoming flow. We show that the impeller is incapable to maintain constant efficiency at surge operating conditions due to the extreme alteration of the incidence angle. This induces unsteady flow momentum transfer downstream, which is reflected as compression wave at the compressor outlet traveling toward the impeller. There, the pressure oscillations govern the tip leakage flow and hence, the incidence angles at the impeller. When these individual self-exited processes occurs in-phase, a surge limit-cycle establishes.

Description
Keywords
Centrifugal compressor, LES, Rotating stall, Surge
Journal Title
Flow Turbul Combust
Conference Name
Journal ISSN
1386-6184
1573-1987
Volume Title
100
Publisher
Springer Science and Business Media LLC