The Effect of Airfoil Clocking on Efficiency and Noise of Low Pressure Turbines

Abstract

The effect of airfoil clocking (stator-stator interaction) on efficiency and noise of low pressure turbines (LPT) was investigated experimentally in a multistage turbine high-speed rig. The rig consisted of three stages of a state-of-the-art LPT. The stages were characterized by a very high wall-slope angle, reverse cut-off design, very high lift, and very high aspect ratio airfoils. The rig had identical blade count for the second and third stators. The circumferential position of the second stator was individually adjusted with respect to the third stator. Eight different circumferential clocking locations over one pitch were back-to-back tested. The rig was heavily instrumented with miniature five hole probes, hot wires, hot films, total pressure and temperature rakes, pressure tappings on the airfoil surface, two array of Kulites in a rotatory module, etc. Every clocking location was tested with the same instrumentation and at the same operating conditions with the intention of determining the impact of the clocking on the overall efficiency and noise. Due to the large amount of data, the results of this test will be reported in several papers. The present paper contains the impact on the overall efficiency, radial traverses, static pressure fields on the airfoils and averaged sound pressure levels in the duct. The comparison of the results suggests that the efficiency is weakly affected by clocking; however the effect on noise is noticeable for some acoustic tones at certain operating conditions.