Louver and effusion cooling heat transfer for a double wall effusion plate with impingement jet array coolant supply

Abstract

Louver slot cooling is employed, which consists of an aligned collection of film cooling holes, contained within a specially-designed device which concentrates, and directs the coolant from a slot, so that cooling air then advects as a layer downstream along the test surface. This louver-supplied coolant is then supplemented by coolant which emerges from different rows of downstream film cooling holes. Coolant for both cooling arrangements is supplied using an array of impingement jets. Experimental data are provided for a mainstream Reynolds number Re_ms range of 168,000–181,000. Full-coverage film cooling initial blowing ratio values are 2.5, 3.2, 4.4, and 5.2, with respective louver slot blowing ratios of 1.2, 1.5, 2.1, and 2.4. Measured lateral-averaged adiabatic effectiveness results show that, with impingement supply cooling only, for blowing ratios of 4.4 and lower, the louver and effusion cooling arrangement generally provides higher effectiveness, relative to an effusion cooling only arrangement. For all blowing ratios considered, another advantage of the louver slot is more uniform values of increased effectiveness along the entire test surface, including locations which are just downstream of the slot. Relatively weak dependence on blowing ratio is present for the louver and film cooling arrangement, in contrast to the effusion only configuration, where effectiveness data generally increase progressively and substantially (at most x/d_e locations) as the blowing ratio becomes larger. Lateral-averaged heat transfer coefficient values for the effusion cooling only arrangement, and for the louver and effusion cooling arrangement, are approximately quantitatively similar when the blowing ratio is 4.3 to 4.4. Data for blowing ratios BR of 5.2 to 5.5 show that the louver and effusion cooling gives much lower lateral-averaged heat transfer coefficients, compared to the effusion cooling only arrangement. This is a result of reduced local turbulent thermal transport levels within the wake flows which are present downstream of the louver leap device.

Introduction

The present investigation considers the use of louver slot cooling to provide thermal protection of gas turbine engine components, especially combustor liners. Note that very little information is available within archival and conference literature on this subject. Of the few existing studies, Juhasz and Marek [1] use a variety of slot arrangements within a simulated combustor segment of a gas turbine, with a rectangular cross-section. A mixing model for local flow turbulence is employed for the development of correlation equations, which provide results which match experimental data. Lefebvre [2] indicates that slot arrangements with axial injection paths are an efficient means of providing enhanced thermal protection to the inner wall of a combustor liner. Both experimental and numerical tools are employed by Jia et al. [3] to investigate angled film cooling slots. Results at different blowing ratios show that numerically-predicted velocity profiles are altered by different boundary condition arrangements. Using both experimental measurements and numerical predictions, Ceccherini et al. [4] investigate the effects of slot, effusion, and dilution holes. According to these researchers, cooling effectiveness magnitudes and distributions are affected in a significant manner by values of the exit velocity associated with effusion cooling. Andreini et al. [5] employ numerical prediction tools to investigate heat transfer coefficient characteristics with the same liner cooling configurations as are considered by Ceccherini et al. [4]. Andreini et al. [6] investigate heat flux reduction, heat transfer coefficient, and film cooling effectiveness downstream of louver slots. Velocity ratio and blowing ratio effects are addressed for experimental configurations which model combustor components within different types of gas turbine engines.

Inanli et al. [7] investigate different slot configurations in combination with different effusion cooling arrangements. Each louver device is referred to as a leap geometry, with investigation of both flat and angled leap configurations. Of these different arrangements, the straight leap geometry generally provides better film cooling effectiveness performance relative to the angled arrangement, provided results are compared at the same blowing ratio. Associated values of mean cooling effectiveness range from 0.60 to 0.70. Kiyici et al. [8] use numerical predicted tools to study the same arrangements and experimental conditions which are employed by Inanli et al. [7]. Considered are three different blowing ratio values, and three different slot heights [8]. Numerical and experimental results show that spatially-averaged effectiveness changes by only small amounts as either streamwise location or blowing ratio is altered. Da Silva et al. [9] describe film cooling effectiveness and local velocity variations associated with a louver combined scheme. Centerline film cooling effectiveness values range from magnitudes near 1.0, with decreasing values with streamwise development, such that values eventually approach 0.2 to 0.5, depending upon the magnitude of blowing ratio.

Within the present experimental study, a louver slot is employed upstream of an array full coverage film cooling holes. The louver is unique because it produces a layer of coolant, which is approximately spanwise uniform along the test surface downstream of the associated slot. The results provided are different from those associated with previous investigations, because of the particular louver slot and full-coverage film cooling holes configurations which are utilized, and because of the method of coolant supply. Here, an impingement jet array is employed to provide coolant to both the louver slot and to the full coverage holes. Louver and film cooling mass flow rates and blowing ratios are then determined by different hole diameters for the two different types of cooling holes. Full-coverage film cooling initial blowing ratio values are 2.5, 3.2, 4.4, and 5.2, with respective louver slot blowing ratios of 1.2, 1.5, 2.1, and 2.4. The mainstream Reynolds number Re_ms range is 168,000 to 181,000. Along the mainstream side of the test plate, given are local blowing ratio and normalized pressure distributions, in addition to measured distributions of local and spanwise-averaged heat transfer coefficients, and local and spanwise-averaged adiabatic effectiveness values.