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

Abstract

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. NomenclatureC vane true chord length, m Cp specific heat ratio, (J/kg/K) h surface heat transfer coefficient, (W/m 2 /K) Lu energy scale, Lu = 1.5 u' 3 / Ma Mach number Re C Reynolds number based on true chord and exit conditions S surface distance from stagnation point, m St Stanton number, h/V EX Cp Tu turbulence intensity, Tu = |u'|/U IN u' rms fluctuation velocity, m/s U IN ideal cascade inlet velocity, m/s V EX ideal cascade exit velocity, m/s Y Normal distance from the wall, m Y + normal distance in wall units, Y + = Y (/)/ Greek Letter Symbols  turbulent dissipation rate, m 2 /s 3  kinematic viscosity, m 2 /s  density, kg/m 3  surface shear stress, N/m 2 Subscripts EX refers to conditions at the nozzle exit plane IN refers to conditions at the nozzle inlet plane INTRODUCTIONUnmanned aerial vehicles (UAVs) have a growing mission in supporting military engagements abroad as well as ensuring domestic security in the US. UAV's have been engaged to help assess the damage of natural disasters, patrol borders and assess crop health. The yearly market for unmanned aerial vehicles (UAV's) is expected to grow to at a rate of 12% through 2018 to a value of $18.6 billion according to Market Research Media. A growing number of large to medium UAV's are being designed to use turbofan engines due to the ability to achieve high thrust to weight ratios and high thermal and propu...

Aerodynamic Effects of High Turbulence Intensity on a Variable-Speed Power-Turbine Blade with Large Incidence and Reynolds Number Variations

“…Given that the lower mission-relevant Reynolds numbers were not achievable in the NASA turbine cascade test facility, it remains for separate work 16,17 to assess transitional flow characteristics at combined high Tu and cruise-relevant Reynolds numbers. This is in strong contrast to the blade loading at low Tu which exhibited separation, transition, reattachment on both suction and pressure sides of the blade, depending on incidence angle.…”