Double wall cooling, consisting of internal impingement cooling and external film cooling, is believed to be an advanced cooling technique in turbine blades. In this paper, in order to improve the uniformity of temperature distribution, a flat plate double wall cooling model with gradient diameter of film and impingement holes is proposed, and the steady three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations are solved to study its heat transfer and flow characteristics. In double wall cooling schemes, film holes of 30 deg inclined angle have the same diameter D with staggered array impingement holes of 90 deg for uniform pattern. Both the spanwise and streamwise pitches are 5D. The thickness of film plate and impingement plate are 2.5D and 1.25D respectively, and the impingement gap is 2.5D. The +10% and -10% film and impingement jet patterns are compared with a uniform pattern in detail. By comparing the results of four broadly used turbulence models with experimental data, SST k-ω turbulence model is finally selected, and the grid-independent solution can be achieved with 6 million grids after comparing the laterally averaged cooling effectiveness of different grids. All simulations are performed under four blowing ratios ranging from 0.5 to 2.For gradient diameter of film hole patterns, results show that -10% film pattern always has the lowest film flow non-uniformity coefficient. The laterally averaged overall cooling effectiveness of uniform pattern lies between that of +10% and -10% film patterns, but the intersection of three patterns moves upstream from half middle of flow direction with the increase of blowing ratio. Therefore, the -10% film pattern exerts the highest area averaged cooling effectiveness, which is improved by up to 1.6% and 1% at BR=0.5 and 1 respectively compared with uniform pattern. However, at higher blowing ratio, the +10% film pattern maintains higher cooling effectiveness and lower total pressure loss. For gradient diameter of impingement hole patterns, the intersection of laterally averaged overall cooling effectiveness in three patterns is almost located near the middle of flow direction under all blowing ratios. The uniform pattern exists the highest area averaged cooling effectiveness and the smallest non-uniform coefficient, but -10% jet pattern has advantages of reducing pressure loss, especially in laminated loss.

Conjugate Heat Transfer Characteristics of Double Wall Cooling With Gradient Diameter of Film and Impingement Holes

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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