An experimental investigation of the performance of a contra-rotating stage is reported. The influence of factors such as speed ratio of the two rotors, rotor stagger, pitch-chord ratio and axial spacing between the rotors is examinedfrom tests on a 0.66 hub-tip ratio compressor. The study reveals that the performance of a contra-rotating stage is affected by all these factors. Axial spacing between the rotors and the speed ratio of the rotors both exhibit a strong influence on the stalling behaviour of the stage. It has been f i n d that in a stage with close axial gap, rotating stall on the first rotor is suppressed i f the second rotor is contra-rotated at a speed 50 per cent faster than the first rotor. This unique advantage of contra-rotation is not obtained if the axial gap is large.Measurements of sound pressure level are also reported to highlight the high noise problems associated with a contra-rotating stage.

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The paper reports the results of an experimental investigation into the aeroacoustic performance of a contra-rotatingaxial flow compressor stage having a hub-tip ratio of 0.66. Aerodynamic superiority of a contra-stage is examined from the point of view of higher pressure rise, increased through flow and rotating stall suppression. Measurements of sound pressure level and real-time analysis of the noise signals is reported for different speed combinations for clean and distorted inlet flow for two axial gaps between the contra-rotors. The effect of pitch chord ratio and axial gap between the rotors on the aeroacoustic performance is discussed. The study reveals that the axial gap between the rotors significantly affects the aeroacoustic performance of a contra-stage.

The paper reports the results of an experimental investigation on the effect of casing treatment on aerodynamic performance of a low-speed contrarotating axial compressor stage having a hub-tip ratio of 0.667. Three types of casing treatments, namely axial slots, axial skewed slots and circumferential grooves, have been examined. Flow structure downstream of the rotors is examined for treated casing and compared with solid casing. The results show a significant improvement in stall margin and efficiency during off-design operation of a contra stage.

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