Heat Transfer Measurements in a Compressible Flow Vane Cascade Showing the Influence of Reynolds Number, Mach Number, and Turbulence Level on Transition and Augmentation of Laminar Heat Transfer by Free-Stream Turbulence

摘要

This research is focused on the effects of large changes in Reynolds number that typically occurs during the flight of high altitude UAV's. This paper documents the influence of Reynolds number, turbulence level, and exit Mach number on the vane surface Stanton number. Reynolds number is based on true chord and exit conditions and ranges from 90,000 through 1,000,000. Low and high inlet turbulence levels were developed for the study and determined to be 0.8% and 9.0%. Tests were run at exit Mach numbers of 0.7, 0.8 and 0.9. These surface heat transfer measurements were acquired in the University of North Dakota's transonic cascade test facility. This facility uses a closed loop to allow the regulation of system pressure to control the test condition Reynolds number. The Mach number is adjusted using a "roots" blower driven by a variable frequency drive. Heat transfer measurements were acquired using a constant heat flux foil fabricated using a 0.023 mm Inconel foil backed with 0.05 mm of Kapton and adhered to the heat transfer vane using a high temperature acrylic adhesive. The linear cascade is configured in a four vane three full passage arrangement. The low turbulence condition is developed using the existing flow conditioning section coupled to a 4.7 to 1 area ratio nozzle. The high turbulence condition uses a mock aero combustor to generate a turbulence level of around 9.0%. These data show the influence of Mach number, Reynolds number and turbulence level on transition and heat transfer augmentation and are expected to be useful in grounding heat transfer predictive methods applicable to small or high altitude gas turbine engines.