This paper presents the Large Eddy Simulation (LES) of a low pressure turbine nozzle guide vane (NGV) for different Reynolds and Mach number. The analysis is based on a slice of the blade that may be representative of midspan flow where secondary flows, hub and shroud contributions are lower. The original configuration from which has been extracted the mid-span blading profile is a linear cascade including hub, shroud and cavities representative of a low-pressure turbine extensively studied numerically and validated against experiments in previous studies. The spanwise blade extent is 1 cm to ensure uncorrelated signal at top and down spanwise conditions due to periodic boundary conditions applied on these surfaces. The mesh is designed to provide requirements for wall-resolved LES including wake refinement and the use of accurate numerical schemes to properly resolve flow structures. In low-pressure turbine, the variation of the Reynolds number during the mission of the gas turbine is a well-known effect since its value can vary of a factor four between take-off and cruise due to ambient conditions variation. This can induce performance variations due to various phenomena with among them suction side boundary layer separation on the aft portion of the blade due to adverse pressure gradient and laminar boundary layer that can be maintained due to the relatively low Reynolds number in low-pressure turbine. Similarly, the Mach number in the low-pressure turbine may vary depending on the thrust required from the gas turbine at the considered mission phase and ambient conditions for which flow behavior and component performance can also occur similarly to the Reynolds number effect. The current paper investigates through numerical simulation the flow representative of a medium-sized low-pressure turbine with three different Reynolds number Re = 175'000 (cruise), 280'000 (mid-level altitude) and 500'000 (take-off) keeping the same characteristic Mach number Ma = 0.2 and three different Mach number Ma = 0.2, 0.5 and 0.8 keeping the same Reynolds number Re = 500'000. The study focuses on different flow characteristics including pressure distribution around the blade, near-wall flow behavior, the generation of losses and the effect of Reynolds and Mach numbers on these different phenomena. A special emphasis is given to the generation of loss based on an entropy approach and the redistribution of mean kinetic energy towards turbulent kinetic energy. This analysis shows the modification of the loss generated depending on the Mach and Reynolds number and the redistribution towards turbulent kinetic energy.

 

This analysis shows the modification of the loss generated depending on the Mach and Reynolds number and the redistribution towards turbulent kinetic energy.


Reynolds and Mach Number Effects on the Flow in a Low-Pressure Turbine

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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