Top: Rotor-wake facility. Bottom: Computed blade surface temperature
and stream-surface entropy.
Through a combination of experimental and computational studies,
researchers at the NASA Lewis Research Center investigated the
effect of upstream blade-row wake passing on the showerhead (leading
edge) film cooling of a downstream turbine. The experiments were
performed in a steady-flow annular turbine cascade facility equipped
with an upstream rotating row of cylindrical rods to produce a
periodic wake field similar to that found in an actual turbine.
Spanwise, chordwise, and temporal resolution of the blade surface
temperature were achieved through the use of an array of nickel
thin-film surface gauges covering one unit cell of a showerhead
film hole pattern. Film effectiveness and Nusselt numbers were
determined for a test matrix of various injectants, injectant
blowing ratios, and wake Strouhal numbers (
St
).
Results indicate a demonstrable reduction in film effectiveness
with increasing Strouhal number, as well as the expected increase
in film effectiveness with blowing ratio. An equation was developed
to correlate the span-average film effectiveness data. The primary
effect of wake unsteadiness was found to be correlated well by
a chordwise-constant decrement of 0.094
St
. Measurable
spanwise film effectiveness variations were found near the showerhead
region, but meaningful unsteady variations and downstream spanwise
variations were not found. Nusselt numbers were less sensitive
to wake and injection changes.
Computations were performed with a three-dimensional turbulent
Navier-Stokes code that had been modified to model wake passing
and film cooling. Unsteady computations were found to agree well
with steady computations when the proper time-average blowing
ratio and pressure/suction surface flow split were matched. The
remaining differences were found to be due to enhanced mixing
in the unsteady solution caused by the wake sweeping normally
on the pressure surface. Steady computations were found to be
in excellent agreement with experimental Nusselt numbers but to
overpredict experimental film effectiveness values. This is likely
due to the inability of the code to match actual hole exit-velocity
profiles and the absence of a credible turbulence model for film
cooling.
Heidmann, J.D.: A Numerical Study of the Effect of Wake Passing on Turbine Blade Film Cooling. AIAA Paper 95-3044 (Also NASA TM-107077), 1995.
Heidmann, J.D.; Lucci, B.L.; and Reshotko, E.: An Experimental Study of the Effect of Wake Passing on Turbine Blade Film Cooling. Accepted for ASME Paper, ASME TURBO EXPO, Orlando, FL, June 1997.
Heidmann, J.D.: The Effect of Wake Passing on Turbine Blade Film
Cooling. Ph.D. Dissertation, Case Western Reserve University (Also
NASA TM-107380), 1996.
Previous articleLast updated May 5, 1997
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