Stall recovery process for performance enhancement of an axial compressor has been experimentally carried out using air injection at its rotor blade row tip region. Twelve air injectors had been mounted evenly spaced around the compressor casing upstream the rotor blade row. Instantaneous flow velocities at various radial and circumferential positions were measured simultaneously utilizing hot wire anemometry. These unsteady results, separately presented in frequency and time domains, provided to distinguish stall inception process and consequent flow induced fluctuations. Time-dependent responses of the flow field properties within the compressor passage and progressive alleviation of stall cells are demonstrated during the tip injection process. Blade tip air injection worked effectively and enhanced the compressor stall margin about 9%. This attractive result occurred for the case where the total mass flow rate passing through the air injectors was as small as 0.8% of the compressor main flow rate. In addition, this augmentation in the stall margin was accompanied by increase in the compressor delivery total pressure. Air injection at the blade row tip region caused its beneficial effects to extend throughout the blade whole span, especially while working at the near-stall conditions.

Abstract.Responses of an axial compressor isolated rotor blade row to various inlet distortions have been investigated utilizing computational fluid dynamic technique. Distortions have been imposed by five screens of different geometries, but with the same blockage ratio. These screens were embedded upstream of the rotor blade row. Flow fields are simulated in detail for compressor design point and near stall conditions. Performance curves for distorted cases are extracted and compared to the undisturbed case. Flow simulations and consequent performance characteristics show that the worst cases belong to non-symmetric blockages, i.e., those of partial circumferential configurations. These cases produce the largest wakes which can disturb the flow, considerably. Superior performances correspond to the inner and outer continuous circumferential distortion screens. Since, they produce no significant disturbances to the main flow in comparison to the non-symmetric screens.

An effective new formulation is developed for simulation of transitional flows. This formulation is based on modifications made to the latest numerical model utilizing vorticity and momentum thickness Reynolds numbers concepts. In this respect, rigorous experiments were conducted in a wind tunnel to modify the existing formulation to a more reliable form suitable for modeling of transitional flows. Test model was a linear cascade of axial compressor blades. Wind tunnel tests consisted of measurements of surface pressure distributions and velocity profiles utilizing hot film anemometry. Different freestream turbulence intensities, flow incidences, and Reynolds numbers were examined. New correlations were imposed to a commercial numerical flow solver; applying them to some standard objects produced more reliable results than those obtained from other formulations, presented so far. This attribution is more emphasized especially while dealing with modeling laminar separation bubbles, where transition occurs within the free shear layer.