Impact of High Freestream Turbulence on LPT Endwall Flow: Part I – Loss Development and Time-Averaged Flow Field

Abstract Realistic turbomachinery conditions include high levels of freestream turbulence; however, this aspect of the flow is typically overlooked in both low-pressure turbine (LPT) simulations and experiments. A better understanding of the impact of high freestream turbulence intensity (TI) on the endwall region of LPT blades is imperative. To fully assess the impact of elevated turbulence, three different incoming turbulence levels were examined at three different Reynolds numbers. Three planes of total pressure loss were measured downstream of the cascade mapping loss development. Surface pressure measurements were collected along the blade surface at midspan. Three planes of high-speed Stereoscopic Particle Image Velocimetry (SPIV) were acquired to investigate the impact varying incoming turbulence levels have on the endwall flow structures. Increasing the turbulence to the highest level was found to reduce the overall loss at the exit of the passage. The greatest impact of elevated freestream turbulence was observed at the lowest Reynolds number investigated. The time-averaged velocimetry measurements in the endwall region demonstrated that increasing the freestream turbulence intensity altered the locations of vortices throughout the endwall. Freestream turbulence levels must be increased, better matching real engine conditions, to get a more accurate prediction of pressure losses and flow topology when simulating the flow surrounding LPT blades.