Heat transfer, transition, and aerodynamic loss in a linear vane cascade at low Reynolds numbers in high speed flows.

摘要

Low pressure turbine research is essential for improving the efficiency of the modern gas turbine engine. At high altitude cruise conditions, the low pressure turbine experiences low Reynolds number flow, which produces a laminar boundary layer on airfoil surfaces. The integrity of the laminar boundary layer is highly susceptible to flow disturbances resulting from blade wakes and freestream turbulence. This susceptibility often leads to enhanced profile and secondary losses, which reduces turbine efficiency. Previous research conducted on low pressure turbine flow conditions, has investigated heat transfer, boundary layer separation bubbles, and secondary flows subjected to varying levels of freestream turbulence. This research is often conducted with low velocity wind tunnels, which are unable to produce engine relevant Mach numbers. Facilities that are able to produce engine relevant velocities are restricted to high Reynolds numbers and face difficulties acquiring well resolved flow data from restricted run times. Due to the limited abilities of current ground test facilities, new methodologies and facilities are needed to produce detailed heat transfer and flow loss data pertinent to the low pressure turbine operating conditions.;The Mechanical Engineering Department at the University of North Dakota has designed and developed a new facility able to conduct low Reynolds number research at engine relevant velocities, which is applicable to low pressure turbines. The facility is comprised of a sealed, closed loop wind tunnel, which operates at steady state conditions. The facility is able to create flow conditions with a Reynolds number between 50,000 and 1,000,000 at Mach numbers up to 0.9.;The work of this thesis documents, in detail, the low Reynolds number transonic facility and the research conducted within it. The research includes vane surface heat transfer and pressure distributions along with exit surveys acquired using a five-hole cone probe documenting total pressure loss, secondary velocity vectors, turning angle, and loss distributions over a range of Reynolds numbers between 90,000 and 720,000 at Mach numbers between 0.7 and 0.9 under low and aero-combustor turbulence conditions.;The experimental results of this research indicate as Reynolds number decreases, secondary losses increase. In addition, for a given Reynolds number, secondary losses decrease as Mach number increases. Secondary loss structures such as the passage/horseshoe vortex weaken with enhanced turbulence but overall losses increase. Heat transfer measurements show a scaling factor on Stanton number as Reynolds number increases, which is augmented under aero-combustor turbulence.