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Graduate Seminar Series, Dr. Christopher R. Marks

Christopher-Marks.jpgChristopher R. Marks, Ph.D.

U.S. Air Force Research Laboratory, Wright-Patterson AFB, OH

Friday, November 17, 2023, 3:00 - 4:00 PM
Zoom projection in JH-109

Title: The Onset of Low Reynolds Number Separation in High-lift High-Work LPT Passages


ABSTRACT: The low-pressure turbine section of aircraft engines accounts for a large portion of the overall engine weight. The engine size, weight, and part count can be reduced by increasing the blade lift and work coefficients while maintaining high efficiency. However, achieving these gains is far from trivial. Low Reynolds number conditions that exist over portions of the operating envelope result in a reduced efficiency due to laminar boundary layer separation. The resulting “Reynolds-lapse” can greatly influence the performance of high-lift high-work low-pressure turbine blades. While the mid-span Reynolds-lapse phenomena has attracted much attention in the literature, the focus of the presentation is on the evolution of separation across the blade span. Rather than solely focusing on the 2D separation phenomena at fixed Reynolds numbers, the current study describes the onset and decline of separation along the blade span when the Reynolds number is varied through the knee of the Reynolds-lapse curve. Extensive experimental measurements were obtained in a low-speed linear cascade arrangement of low-pressure turbine research profiles. Two different high-lift (Zw = 1.78 and Zw = 1.88) high-work profiles were considered. A unique four camera composite velocimetry measurement of the suction surface flow was used to capture the progression in separation over a half-span. A difference in the onset of separation between the two blade profiles was observed. In one case the separated flow region progressed from the endwall toward the mid-span, and in the other blade set it progressed from the mid-span toward the endwall. The findings provide a new and deeper understanding of the separation development across the passage of high-lift high-work turbine blades at low Reynolds number.

BIO: Dr. Christopher R. Marks is a Senior Aerospace Engineer for the Aerospace Systems Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio. Dr. Marks manages fundamental research related to the aerodynamics of internal flows in turbines. He has authored more than 40 research publications in the area of aerodynamics related to aircraft and turbomachinery.