As fuel prices rise and environmental awareness becomes an increasingly important topic,udthe efficiency of engines used for power production and transport must be increased whilstuddecreasing exhaust gas emissions and noise levels. From results obtained during this researchudproject, in combination with work being produced at other research facilities, it isudhoped that a greater understanding of how the leading edge region of compressor bladesudreact to changes in engine operating points in a steady and unsteady environment is gained.udThis thesis investigates the boundary layer development at the leading edge of a controlleduddiffusion stator blade with a circular arc leading edge profile. Steady flow measurementsudwere made inside a large scale 2D compressor cascade at Reynolds numbers of 260, 000udand 400, 000 over a range of inlet flow angles corresponding to both positive and negativeudincidence at a level of freestream turbulence similar to that seen in an embedded stage ofudindustrial axial flow compressor.udThe instrumented blade of a large scale 2D cascade contained a series of very high resolutionudstatic pressure tappings and an array of hot-film sensors in the first 10% of surfaceudlength from the leading edge. Detailed static pressure measurements in the leading edge regionudshow the time-mean boundary layer development through the velocity over-speed andudfollowing region of accelerating flow on the suction surface. The formation of separationudbubbles at the leading edge of the pressure and suction surfaces trigger the boundary layerudto undergo an initial and rapid transition to turbulence. On the pressure surface the bubbleudforms at all values of incidence tested, whereas on the suction surface a bubble only formsudfor incidence greater than design. In all cases the bubble length was reduced significantlyudas Reynolds number was increased. These trends are supported by the qualitative analysisudof surface flow visualisation images.udQuasi-wall shear stress measurements from hot-film sensors were interpreted using a hybridudthreshold peak-valley-counting algorithm to yield time-averaged turbulent intermittencyudon the blade’s suction surface. These results, in combination with raw quasi-walludshear stress traces show evidence of boundary layer relaminarisation on the suction surfaceuddownstream of the leading edge velocity over-speed in the favorable pressure gradientudleading to peak suction. The relaminarisation process is observed to become less effectiveudas Reynolds number and inlet flow angle are increased.ududThe boundary layer development is shown to have a large influence on the blade total pressureudloss. Initial observations were made without unsteady wakes and at negative incidenceudloss was seen to increase as the Reynolds number was decreased and, in contrast, at positiveudincidence the opposite trend was displayed. The cascade’s rotating bar mechanism wasudused for unsteady tests where the influence of changing reduced frequency was investigatedudand compared to the performance of the cascade in steady operation. Results showedudthat increasing the stator reduced frequency brought about an increase in total blade pressureudloss. The proportion of total loss generated by the suction surface increased linearly asudthe reduced frequency was increased from 0.47
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