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The crossflow, one of the most important flow structures in the turbine endwall, has significant effects on the endwall film cooling. However, there is a lack of quantitative analysis on it due to the complexity of the endwall flow field. In the current study, a turning channel is utilized to generate the crossflow free from vortex structures. Experiments are conducted and numerical results are utilized to supplement flow-field details. Effects of the momentum ratio (I), crossflow intensity, and main-flow Reynolds number (R e D) are analyzed. Theories of three-dimensional boundary layer flow are introduced to help reveal underlying mechanisms. It is observed that coolant trajectories obey linearity in the cylindrical coordinate. Then, the deflection of coolant can be quantified using the straight-line slope, and I is demonstrated to well scale the coolant migration under the crossflow, which guides predictions on coolant trajectories. Reversely, the disturbance of cooling injections on the crossflow is non-negligible, mainly suppressing the crossflow development. Besides, the crossflow enhances the coolant spreading, and improves the cooling performance. R e D has non-negligible effects on the cooling performance by altering the crossflow profile in the boundary layer. Lower R e D leads to a distorted coolant spatial distribution, resulting in a severer main gas/coolant mixture. [ABSTRACT FROM AUTHOR]

Film cooling is an important cooling method for the high-temperature components of modern aero-engines. There have been many previous studies on the influences of compound angle on film cooling performance, most of which are conducted in the ideal flat plate environment with zero pressure gradient, and the results indicate that at high blowing ratios, a large compound angle tends to improve the film cooling performance. However, in this work, it is found that a large compound angle tends to decrease the film cooling performance significantly with the influences of endwall lateral pressure gradient. A curved tunnel with constant width is employed to generate lateral pressure gradient similar to that in the endwall region of real turbine blade. It is shown that the crossflow near the endwall surface is the most obvious flow characteristic in this flow environment. Based on this discovery, we further conduct research on the influences of compound angles on film cooling performance in a curved tunnel both with numerical and experimental approaches. A well-designed laidback fan-shaped film cooling hole is used in this work. The experimental results show that for a film cooling hole with a large compound angle under blowing ratios ranging from 1.0 to 3.0, film cooling performance is reduced significantly under the environment of endwall lateral pressure gradient compared with zero pressure gradient environment. Detailed numerical results further indicate that due to the interaction between endwall crossflow and the strong single kidney vortex created by the large compound angle hole, large amounts of coolant are lifted away from endwall surface, which results in poor cooling performance. A topological model on the interaction between endwall crossflow and kidney vortices is proposed to help illustrate this phenomenon. The results of this work suggest that turbine cooling designers carefully consider the negative influence of large compound angles on endwall film cooling due to the lateral pressure gradient. [ABSTRACT FROM AUTHOR]

The strong secondary flow and the interaction between multiple vortices result in substantial aerodynamic losses in the endwall region of the highly-loaded turbine. Accurate predictions of complex turbulence characteristics propose severe challenges to the widely used Reynolds-Averaged Navier-Stokes (RANS) approach. This work adopts a high accuracy hybrid RANS/Large Eddy Simulation (LES) method on a highly-loaded turbine blade for which the Reynolds number is 611,000 and the exit Mach number is 0.8. Results verify that, in contrast with the RANS method, the hybrid method can provide more accurate predictions and detailed small-scale flow structures than the RANS simulation. Analysis of the Reynolds stresses predicted by the hybrid method reveals the complex turbulence characteristics in the endwall region and highlights shortcomings of Reynolds stresses predictions existing in the RANS method in the highly-loaded turbine blade environment. To analyze turbulence characteristics near the blade endwall, the Lumley triangle method is applied to quantify the turbulence anisotropy degree. Based on fine flow field structures, the proper orthogonal decomposition (POD) method is used to extract the dominant flow structures from the unsteady hybrid method results. The turbulence kinetic energy budget is employed to study dominant terms in turbulent flow. The total pressure loss coefficient based on the first law of thermodynamics and the entropy generation rate (EGR) based on the second law of thermodynamics are both used to study the loss generation mechanism in the endwall region. Predicted turbulence characteristics and flow mechanism can provide guide towards low loss design and flow control of the turbine blade. [ABSTRACT FROM AUTHOR]