Session: 32-01 Flow Control

Paper Number: 152993

Aerodynamic Performance Evaluation of Leading Edge Tubercles on Low Pressure Turbine Blades at Very Low Reynolds Numbers and Higher Turbulence 

The performance of the turbine section of an aircraft gas turbine engine plays a major role in the overall efficiency of the engine. The low-pressure turbine (LPT) section of the turbine is a crucial component for power extraction and also one of the heaviest. Increasing LPT efficiency can potentially lead to a reduction in the number of blades, stages, and overall turbine weight. LPT losses depend on blade profile and associated secondary flows, and incoming flow condition. At higher altitude, the LPT is susceptible to a substantial decrease in performance due to Reynolds Lapse. This phenomenon is manifested by suction surface boundary layer state variation and separation. Alleviating these negative aspects could lead to safer high-altitude operations. In an effort to enhance LPT performance, aerodynamic work-load enhancement and various methods of flow control, both passive and active, have been employed over the years. This paper presents results and recommendations from an experimental application of leading edge tubercles as passive flow control devices for a purpose-designed, aft-loaded LPT profile.  These bio-inspired geometric features have been shown to delay stall and improve post-stall operability of airfoils and wings. In the present study, tubercle geometry was designed  with guidance provided by a neural network technique called Self-Organizing Maps, trained by available published data. In addition to low turbulence tests, the performance of the baseline and tubercled blade were also investigated at higher turbulence, representative of engine operation. The experimental LPT performance evaluation took place in a cascade and included measurement of mid-span surface pressure, signal variance on blade surface using hot-film, cascade-exit mixed-out losses, and suction surface flow visualization. The higher turbulence level at the cascade inlet was produced using a passive turbulence-generating grid. Conclusions were drawn after consideration of wake traverses, exit losses, surface pressure measurements, and flow visualization at various axial-chord Reynolds numbers between 15,000 and 90,000.  The suction-surface pressure provided information on blade loading and flow separation and hot-film provided information on the state of boundary layer. The flow visualization helped in observing the effectiveness of tubercle in modifying the suction surface flow. Some reduction in exit losses and increased performance at lower Reynolds numbers was noted.  Valuable insight has been gained on the challenges associated with very low Reynolds number testing and recommendations have been made for sustained future work.

Presenting Author: Asad Asghar Royal Military College of Canada

Presenting Author Biography: Asad Asghar is a Research Associate and Adjunct Associate Professor at the Royal Military College of Canada in the Department of Mechanical and Aerospace Engineering. He teaches thermo-fluid courses and conducts research in the aeronautical engineering field. His research interest and publications are in supersonic and subsonic aerodynamics, flow control, wind tunnel testing, propulsion, aero-engine component testing, inlets, compressors, fans, and turbine. He has published research papers in ASME and AIAA journals and conferences and presented papers in CASI conferences. Asghar holds a B.Sc. in Mechanical Engineering. He holds a M.Sc. in Aerospace Engineering and a Ph.D. in Mechanical and Aerospace engineering from the University of Notre Dame.

Authors:

Benjamin D. Frosst Royal Military College of Canada
Asad Asghar Royal Military College of Canada
William D. E. Allan Royal Military College of Canada
Kyle T. Kavanaugh Air Force Research Lab/RQTT
John Clark Air Force Research Lab / RQTT