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Influence of Surface Roughness on Heat Transfer and Effectiveness for a Fully Film Cooled Nozzle Guide Vane Measured by Wide Band Liquid Crystals and Direct Heat Flux Gauges

[+] Author Affiliations
S. M. Guo, C. C. Lai, T. V. Jones, M. L. G. Oldfield

University of Oxford, England

G. D. Lock

University of Bath, Bath, England

A. J. Rawlinson

Rolls-Royce plc, Derby, England

Paper No. 2000-GT-0204, pp. V003T01A012; 11 pages
doi:10.1115/2000-GT-0204
From:
  • ASME Turbo Expo 2000: Power for Land, Sea, and Air
  • Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration
  • Munich, Germany, May 8–11, 2000
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7856-9
  • Copyright © 2000 by ASME

abstract

The influence of surface roughness on heat transfer coefficient and cooling effectiveness for a fully film cooled 3D nozzle guide vane (NGV) has been measured in a transonic annular cascade using wide band liquid crystal and direct heat flux gauges (DHFGs). The liquid crystal methods were used for rough surface measurements and the DHFGs were used for the smooth surfaces. The measurements have been made at engine representative Mach and Reynolds numbers and inlet freestream turbulence intensity. The aerodynamic and thermodynamic characteristics of the coolant flow have been modelled to represent engine conditions by using a heavy “foreign gas” (30.2% SF6 and 69.8% Ar by weight). Two cooling geometries (cylindrical and fan-shaped holes) have been tested. The strategies of obtaining accurate heat transfer data using a variety of transient heat transfer measurement techniques under the extreme conditions of transonic flow and high heat transfer coefficient are presented.

The surfaces of interest are coated with wide-band thermochromic liquid crystals which cover the range of NGV surface temperature variation encountered in the test. The liquid crystal has a natural peak-to-peak roughness height of 25 μm creating a transitionally rough surface on the NGV. The time variation of colour is processed to give distributions of both heat transfer coefficient and film cooling effectiveness over the NGV surface. The NGV was first instrumented with the DHFGs and smooth surface tests preformed. Subsequently the surface was coated with liquid crystals for the rough surface tests. The DHFGs were then employed as the means of calibrating the liquid crystal layer. The roughness of 25 μm, which is the typical order of roughness for the in service turbine blades and vanes, increases the heat transfer coefficient by up to 50% over the smooth surface level. The film cooling effectiveness is influenced less by the roughness.

Copyright © 2000 by ASME

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