Compressor Stability Enhancement Using Discrete Tip Injection

Abstract

Mass injection upstream of the tip of a high-speed axial compressor rotor is a stability enhancement approach known to be effective in suppressing stall in tip-critical rotors. This process is examined in a transonic axial compressor rotor through experiments and time-average Navier-Stokes CFD simulations. Measurements and simulations for discrete injection are presented for a range of injection rates and distributions of injectors around the annulus. The simulations indicate that tip injection increases stability by unloading the rotor tip and that increasing injection velocity improves the effectiveness of tip injection. For the tested rotor, experimental results demonstrate that at 70% speed the stalling flow coefficient can be reduced by 30% using an injected massflow equivalent to 1% of the annulus flow. At design speed, the stalling flow coefficient was reduced by 6% using an injected massflow equivalent to 2% of the annulus flow. The experiments show that stability enhancement is related to the mass-averaged axial velocity at the tip. For a given injected massflow, the mass averaged axial velocity at the tip is increased by injecting flow over discrete portions of the circumference as opposed to full-annular injection. The implications of these results on the design of recirculating casing treatments and other methods to enhance stability will be discussed.

Effects of injection frequency on the rotor stall margin

“…V x,Max is injection velocity, whose value ( refer to ref. [6]) is Finite differential method was used in this code to solve the Reynolds-averaged NS equations. The turbulent viscosity was computed with one equation model of BL.…”

“…After that, Weigl [5] investigated the effects of steady and unsteady injection on the rotor stability enhancement, and indicated that the steady injection was the most effective factor, moreover, the active injection could improve the stability further. Suder [6] and Khaleghi [7] studied the effects of injection parameters on the rotor stability enhancement, and it was found that the injection velocity and angle influenced the stability obviously.…”

Flow instability and its control in compression systems

“…Unlike the traditional empirical design approach of passive control by trade-off for the improvement of compressor performance, detailed study was performed in Ref. [45], both experimentally and using steady flow CFD simulation, for the blade passage flow parameters, e.g. the redistribution of the incidence and blade loading towards decreasing at the tip under various injection configurations.…”

Injection profile effects on low speed axial compressor stability enhancement

“…Consequently, the axial compressor can be operated at a lower flow rate with injection. Day [1], Weigl et al [2] and Suder et al [3], demonstrated enhancement of compressor stability with tip injection. In these investigations, the injection air mass flow rate varied between 1 and 6% of the design point or stall onset mass flow rate.…”