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Improvement of Cooled Turbine Airfoils by Special Cutback

[+] Author Affiliations
Boris I. Mamaev, Mikhail M. Petukhovskiy, Alexander V. Pozdnyakov

Siemens LLC, Moscow, Russia

Marat R. Valeev

FGUE “SME” Motor Design Office, Ufa, Russia

Paper No. GT2010-22056, pp. 1081-1087; 7 pages
doi:10.1115/GT2010-22056
From:
  • ASME Turbo Expo 2010: Power for Land, Sea, and Air
  • Volume 7: Turbomachinery, Parts A, B, and C
  • Glasgow, UK, June 14–18, 2010
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4402-1 | eISBN: 978-0-7918-3872-3
  • Copyright © 2010 by ASME

abstract

A substantial reduction in high temperature turbine efficiency due to a thickening trailing edge on the blades can be compensated by ejection of cooling air on the airfoil pressure side near the edge, which is made thinner at the expense of a pressure-side contour bend. A blade-row midspan section of the aircraft high-pressure turbine was chosen for investigations. Flow parameters of the section: inlet and outlet angles were 36° and 65°, respectively (axial reference), outlet isentropic Mach number was 0.94. Four linear cascades were examined. They differed mainly in the airfoil trailing edge geometry. Three airfoils had the same thin trailing edges and contour bend angles ε = 10, 15 and 20°; one airfoil with a thick round edge had no bend. Widths of the slot for cooling air ejection were the same for all airfoils tested. Measurements were made for exit Mach numbers from 0.6 to 0.95 and relative cooling mass flows from 0 to 1.5%. The respective Reynolds numbers varied from 7.5·106 to 9·106 . The incidence value was 2°. Pressure distributions along profiles, outlet total and static pressures, back pressures for cooling air with gas-outlet angles were measured. The experiments showed streamlining of all cascades were favorable. For the airfoils with ε = 10 and 15° the profile losses were low and normal for uncooled cascades with thin trailing edge. Hence, for such bends losses due to a step on the airfoil pressure side were negligible. As expected, the losses in the cascade with the thick rounding edge were significantly higher. The losses in the cascade with ε = 20° were the greatest. The coolant exit had no distinct influence on streamlining airfoils. The back-pressure for cooling air was approximately equal to the outlet static pressure. For cascades with ε = 10 and 15° the ejection of coolant led to a small increase of losses due to additional mixing losses. Thus, the airfoil contour bend is a powerful tool for the aerodynamic improvement of cooled turbines. It may lead to gains in stage efficiency of 1[[ellipsis]]1.5%. It should be noted that this tool has already been used successfully for several aircraft and industrial turbines of recent design.

Copyright © 2010 by ASME
Topics: Turbines , Airfoils

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