Stability management of high speed axial flow compressor stage through axial extensions of bend skewed casing treatment

This paper presents the experimental results to understand the performance of moderately loaded high speed single stage transonic axial flow compressor subjected to various configurations of axial extensions of bend skewed casing treatment with moderate porosity.The bend skewed casing treatment of 33%porosity was coupled with rectangular plenum chamber of depth equal to the slots depth.The five axial extensions of 20%,40%,60%,80%and 100%were used for the experimental evaluations of compressor performance.The main objective was to identify the optimum extension of the casing treatment with reference to rotor leading edge which results in maximum stall margin improvements with minimum loss in the stage efficiency.At each axial extension the compressor performance is distinctive.The improvement in the stall margin was very significant at some axial extensions with 4%–5%penalty in the stage efficiency.The compressors stage shows recovery in terms of efficiency at lower axial extensions of 20%and 40%with increase in the peak stage efficiency.Measurements of flow parameters showed the typical behaviors at near stall flow conditions.Hot wire sensor was placed at the rotor upstream in the tip region to capture the oscillations in the inlet axial and tangential velocities at stall conditions.In the absence of casing treatment the compressor exhibit abrupt stall with very high oscillations in the inlet axial and tangential velocity of the flow.The extents of oscillations reduce with bend skewed casing treatment.Few measurements were also performed in the plenum chamber and salient results are presented in this paper.

Design of a two spool contra-rotating turbine for a turbo-fan engine

Contra-rotating turbines offer enhanced performance over their conventional corotating configurations.In addition,vaneless contra-rotating turbine stages offer lesser stage length along with improved performance.Contra-rotating turbines with a vaned LP stages offer a controlled work-split between the stages over a wider range of operating conditions by maintaining inlet swirl to the second rotor.The objective of the present work is to design an equivalent vaned contra-rotating turbine for an existing co-rotating configuration of a two-spool turbo fan engine.The contra-rotating turbine is designed by retaining the existing flow path and HP turbine,and redesigning the LP turbine for fixed radial distributions of inlet total temperature,pressure and swirl.A comparative study between performance of the co-rotating and contra-rotating turbines is carried out for different speeds.Cascade testing of the LP stator and rotor mean sections was carried out to validate the analysis.The LP stage of contra-rotating turbine exhibits a performance improvement by 2%points at design point,as per flow predictions.The reduced flow deflection in stator row is the primary reason for significant reduction in profile and secondary losses in contra-rotating turbine,which contributed to the performance improvement.A significant reduction of 23%in blade weight and 45% in LP stator vane count is obtained.

ITTC COMPARATIVE TESTS ON PRESSURE FLUCTUATIONS

Pressure fluctuation induced by unsteady propeller cavitation is one of the most predominant vibration sources. Cavitation Committee of International Towing Tank Conference (ITTC) has been continuously reviewing the theoretical and experimental prediction methods. In this paper, the accuracy of the existing prediction methods and the parameters which affect the model test results are discussed, especial]y with referring to the results of the comparative tests on the 'Sydney Express' propeller, organized by Cavitation Committee.