Abstract
In order to explore the effect of blowing ratio on film cooling over a convex surface, the present study adopts the transient liquid crystal thermography for the film cooling measurement on a straight circular hole configuration. The test piece has a strength of curvature(2r/D)of 92.5, pitch to diameter ratio(P/D)of 3 and streamwise injection angle(γ)of35∘All measurements were conducted under the mainstream Reynolds number(Red)of 1700 with turbulence intensity(Tu)of 3.8%, and the density ratio between coolant and mainstream(ρc/ρm)is 0.98. In current study, the effect of blowing ratio(M)on film cooling performance is investigated by varying the range of blowing ratio from 0.5 to 2.0. Two transient tests of different injection flow temperature were conducted to obtain both detailed heat transfer coefficient and film cooling effectiveness distributions of measured region. The present measured results show that both the spanwise averaged heat transfer coefficient and film cooling effectiveness increase with decreased blowing ratio.
Highlights
Film cooling is a technique of cooling gas turbine blades to protect them from high temperature gases
Lin et al (1998) used a low-Reynolds number turbulence model to investigate film cooling of flat and convex surfaces. They showed that the injection flow lift-off phenomenon depends not just on the momentum flux ratio and on the profile of boundary layer and the ratio of boundary layer thickness to hole diameter
Close to the result of Schwarz et al The lower values in the result of Goldstein et al might be due to the larger injection angle of 45 Goldstein et al stated that shallower injection angles have the better effectiveness near injection holes on a convex surface, as show in the comparison result of Figure 3
Summary
In order to explore the effect of blowing ratio on film cooling over a convex surface, the present study adopts the transient liquid crystal thermography for the film cooling measurement on a straight circular hole configuration. The effect of blowing ratio (M) on film cooling performance is investigated by varying the range of blowing ratio from 0.5 to 2.0. Two transient tests of different injection flow temperature were conducted to obtain both detailed heat transfer coefficient and film cooling effectiveness distributions of measured region. The present measured results show that both the spanwise averaged heat transfer coefficient and film cooling effectiveness increase with decreased blowing ratio
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