Abstract
Experimental investigations in a single-stage low speed axial research compressor are presented. The influence of four different rotor tip clearances on the overall compressor performance and on the rotor tip flow field is investigated in configurations with and without circumferential groove casing treatments. Piezo-resistive pressure transducers are used to capture the unsteady flow field in the rotor tip region. The investigated casing groove is effectively working at the three largest investigated tip clearance sizes. The largest achieved operating range increase by the groove is 6.9%. The groove can delay the upstream movement of the flow interface between leakage flow and main flow and thus increase the stable operating range. Rotating instabilities are shown to exist at large tip clearance sizes in throttled operating conditions. Their amplitudes can be damped by the casing groove. No modal activities could be detected in the current single-stage compressor build.
Highlights
The relative motion between blades and casing dictates the necessity of radial clearances in an axial compressor
The use of wide-chord blades is not able to totally compensate for this effect. These observations underline the fact that axial compressors at least partially run with tip clearances that are greater than favored by aerodynamic, which lead to the above-mentioned performance penalties
One possible means to recover a loss in operating range due to a tip clearance increase is the use of circumferential groove casing treatments
Summary
The relative motion between blades and casing dictates the necessity of radial clearances in an axial compressor. The use of wide-chord blades is not able to totally compensate for this effect These observations underline the fact that axial compressors at least partially run with tip clearances that are greater than favored by aerodynamic, which lead to the above-mentioned performance penalties. One possible means to recover a loss in operating range due to a tip clearance increase is the use of circumferential groove casing treatments. Their simplicity and ease of installation put them in the focus of research for several decades. The influence of tip clearance increases and casing groove on the rotor tip flow field is shown. Their influence on rotating instabilities and modal oscillations will be addressed to increase understanding of these phenomena
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