The number and distribution of reverse-tangent injectors can be tailored to match the expected stall/surge characteristics of the compressor and the space available for installation. Reverse-tangent injection can be implemented in any of three operating modes:

  1. Continuous operation, in which the working fluid is injected continuously;
  2. Open-loop operation, in which injection is initiated by on-off valves upon detection of compressor instability or conditions known to precede compressor instability and the injection is terminated when stable compressor operation returns; or
  3. Closed-loop or feedback-controlled operation, in which compressor stability is monitored and the number of active injectors and the injection rate are continually adjusted, using a dynamic control model and controlled valves.

In each of these operating modes, the injected working fluid can be supplied from an external source or from a downstream compressor stage where the total pressure is sufficient to produce the injected stream(s).

This work was done by Gary J. Skoch of the U.S. Army Research Laboratory for Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Commercial Technology Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-17560-1.