Numerical Simulations of Flow in Axial Compressor System, Preparatory Steps for Active Control

For most compressor flows, the existence of turbulent shear stresses is essential to compensate and overcome the adverse pressure gradients without separation. The performance of compressor improves as the turbulent stresses get stronger relative to the laminar viscous stresses, which become significant as the Reynolds number increases. The methods used to design subsonic axial flow compressors and fans are based on correlations such as deviation angle vs. incidence angle to obtain the expected performance for a particular blade profile. In this paper, compressor models that are used frequently in controller designs are described and the effect of the assumptions on the prediction capability of these models is explained. The control concepts used to maintain and therefore grant the stable operation are presented and monitored, as well as an outline of sensors, actuators and automatic controllers is given. The survey concludes that the behavior of a compressor system subsequent to instability onset is reasonably understood but the considered models can not describe all types of instabilities encountered. There comes the recommendation that for a better understanding of the mechanisms behind the onset of such instabilities, refinements as new improvements of the existing models are require, which may give insights into new automatic control methods