Reduction of bleed valve rate requirements for control of rotating stall using continuous air injection

Actuation of the compressor characteristic, via the use of continuous air injection, has been experimentally verified on a single-stage, low-speed axial compressor, to provide a method of reducing the rate requirement of bleed valve control of rotating stall. The experiments show that the bleed valve rate requirement is reduced from approximately 145 Hz to below 10 Hz when the amount of compressor characteristic actuation is increased. Theoretical tools based on a low order model (1-3 states) and simulations based on a reduced order distributed model (37 states) have been developed to estimate the gain and rate requirements of the bleed controller. All of the analytical formulas and simulations share the same qualitative trends with respect to the experiments. This qualitative agreement indicates that bleed valve control of rotating stall depends crucially on the rate limit of the bleed valve, and the theoretical tools indicate that the rate limit requirement depends on both the stable and the unstable part of the compressor characteristic. By combining compressor characteristic identification tools and the analytic relations, insights for designing a compressor-bleed pair are provided.