Combined effects of Reynolds number, turbulence intensity and periodic unsteady wake flow conditions on boundary layer development and heat transfer of a low pressure turbine blade

摘要

Detailed experimental investigation has been conducted to provide a detailed insightinto the heat transfer and aerodynamic behavior of a separation zone that is generated as aresult of boundary layer development along the suction surface of a highly loaded lowpressure turbine (LPT) blade. The research experimentally investigates the individual andcombined effects of periodic unsteady wake flows and freestream turbulence intensity (Tu)on heat transfer and aerodynamic behavior of the separation zone. Heat transfer experimentswere carried out at Reynolds number of 110,000, 150,000, and 250,00 based on the suctionsurface length and the cascade exit velocity. Aerodynamic experiments were performed atRe = 110,000 and 150,000. For the above Re-numbers, the experimental matrix includesTus of 1.9%, 3.0%, 8.0%,13.0% and three different unsteady wake frequencies with thesteady inlet flow as the reference configuration. Detailed heat transfer and boundary layermeasurements are performed with particular attention paid to the heat transfer andaerodynamic behavior of the separation zone at different Tus at steady and periodicunsteady flow conditions. The objectives of the research are (a) to quantify the effect of Tuon the aero-thermal behavior of the separation bubble at steady inlet flow condition, (b) toinvestigate the combined effects of Tu and the unsteady wake flow on the aero-thermalbehavior of the separation bubble, and (c) to provide a complete set of heat transfer andaerodynamic data for numerical simulation that incorporates Navier-Stokes and energyequations. The analysis of the experimental data reveals details of boundary layer separationdynamics which is essential for understanding the physics of the separation phenomenonunder periodic unsteady wake flow and different Reynolds number and Tu. To provide acomplete picture of the transition process and separation dynamics, extensive intermittencyanalysis was conducted. Ensemble averaged maximum and minimum intermittencyfunctions were determined leading to the relative intermittency function. In addition, thedetailed intermittency analysis reveals that the relative intermittency factor follows aGaussian distribution confirming the universal character of the relative intermittencyfunction.