Active suppression of aerodynamic instabilities in turbomachines

Abstract

In this paper, we advocate a strategy for controlling a class of turbomachine instabilities, whose primitive phases can be modeled by linear theory, but that eventually grow into a performance-limiting modification of the basic flow. The phenomena of rotating stall and surge are two very different practical examples in which small disturbances grow to magnitudes such that they limit machine performance. We develop a theory that shows how an additional disturbance, driven from real-time data measured within the turbomachine, can be generated so as to realize a device with characteristics fundamentally different than those of the machine without control. For the particular compressor analyzed, the control increases the stable operating range by 20% of the mean flow. We show that active control can also be used to destabilize a compressor in an undesirable state such as nonrecoverable stall. Examination of the energetics of the controlled system shows the required control power scales with the square of the ambient disturbance level, which can be several orders of magnitude below the power of the machine. Brief mention is also made of the use of structural dynamics, rather than active control, to enhance stability.