Flow visualisation and heat/mass transfer in a linear turbine cascade with tip clearance

Abstract

Flow visualisation and heat/mass transfer measurements in a linear turbine cascade with tip/casing clearances ranging from 0.60% to 6.90% of chord show the influence of blade tip geometry for a standard flat tip, a squealer tip and a geometry with a winglet on the pressure side and a squealer on the suction side of the blade. Oil-lampblack and oil-dot techniques show the surface flow on the blade endwall and tip while a laser light-sheet and a smoke wire indicate the three-dimensional flow in the tip clearance and blade passages. Local heat/mass transfer from the blade tips is measured using the naphthalene sublimation technique. Experiments with the standard flat tip blade clearly show that a separation bubble exists at the pressure side edge of the tip surface at all tip clearance levels. The effect of the tip leakage vortex on the secondary flows in the blade passage is also evident: with an increase of tip clearance, the horseshoe vortices disappear while the passage vortex is weakened and pushed away from the suction surface by a strengthened leakage vortex. The flow in the gap changes significantly for the squealer tip and the winglet-squealer tip cases. The surface flow visualisation identifies reattachment and recirculation regions on the blade tips. Photographic images, compared to detailed convective heat/mass transfer measurements, provide an interpretation of the heat/mass transfer results.

Keywords:

• Gas turbine heat transfer
• flow visualization
• naphthalene sublimation
• tip leakage
• blade tip

Additional information

Notes on contributors

R J Goldstein

Richard J Goldstein is Regents’ and James Ryan Professor of Mechanical Engineering at the University of Minnesota, a member of the U.S. National Academy of Engineering and a Foreign Member of the Royal Academy of Engineering. He is a Past President of the American Society of Mechanical Engineering, the International Center for Heat and Mass Transfer, and the Assembly for the International Heat Transfer Conferences. At the University of Minnesota, he teaches and does research related to fluid mechanics, heat transfer and energy systems.

P Jin

Peitong Jin graduated from University of Minneasota with a PhD degree in Thermodynamics and Heat Transfer. He is now a senior engineer with Caterpillar, Inc working on analysis and design of engine cooling systems.

M Papa

Marco Papa completed a PhD degree in Mechanical Engineering at the University of Minnesota. He has earned a Doctorate Degree in “Energy and Environment Engineering” and a Laurea Degree in Mechanical Engineering at the University of Rome “Tor Vergata”. His research has focused on experimental and numerical gas turbine heat transfer and on probes for measurement of thermophysical properties. He is currently working with E.ON, following international construction projects of thermoelectric power plants.

F Gori

Fabio Gori is Professor of Heat Transfer at the University of Rome “Tor Vergata”. He is member of: ASME (American Society of Mechanical Engineers), Scientific Council of the International Centre of Heat and Mass Transfer, ATI and UIT, Italian societies related to Heat Transfer and Fluid Mechanics. He was chairman of the Department of Mechanical Engineering in Rome. He was academic visitor at the Universities of Minnesota, Illinois at Chicago and Imperial College of Science and Technology. He was Visiting Professor at Cornell University and University of New York at Stony Brook.