Flow Visualization of Multi-Hole Film-Cooling Flow under Varying Freestream Turbulence Levels

Abstract

A flat plate film cooling flow from a multi-exit hole configuration has been numerically simulated using both steady and unsteady Reynolds Averaged Navier Stokes (RANS and URANS) Computational Fluid Dynamics (CFD) formulations. This multi-exit hole concept, the Anti-Vortex Hole (AVH), has been developed and studied by previous research groups and shown to mitigate or counter the vorticity generated by conventional holes resulting in a more attached film cooling layer and higher film cooling effectiveness. The film cooling jets interaction with the free stream flow is a long studied area in gas turbine heat transfer. The present study numerically simulates the jet interaction with the multi-exit hole concept at a high blowing ratio (M = 2.0) and density ratio (DR = 2.0) in order to provide a more detailed, graphical explanation of the improvement in film cooling effectiveness. This paper presents a numerical study of the flow visualization of the interaction of film cooling jets with a subsonic crossflow. The contour plots of adiabatic cooling effectiveness were used to compare the multi-exit hole and conventional single hole configurations. The vortex structures in the flow were analyzed by URANS formulations and the effect of these vortices on the cooling effectiveness was investigated together with the coolant jet lift-off predictions. Quasi-Instantaneous Temperature Isosurface plots are used in the investigations of the effect of turbulence intensity on the cooling effectiveness and coolant jet coverage. The effect of varying turbulence intensity was investigated when analyzing the jets' interaction with the cross flow and the corresponding temperatures at the wall. The results show that as the turbulence intensity is increased, the cooling flow will stay more attached to the wall and have more pronounced lateral spreading far downstream of the cooling holes.

Analytical Modelling of the Effects of Different Gas Turbine Cooling Techniques on Engine Performance = Analytische Modellierung der Wirkungen von verschiedenen Kuhlungskonfigurationen der Turbinenschaufeln auf der Gasturbinenleistung

“…The literature on analyzing film cooling flow for conventional holes under different flow conditions is very broad both in experimental [33,38,42,43] and numerical aspects [35,40,41], which allows researchers to use these resources to validate their numerical tools that they developed for advanced cooling hole configurations. Anti-Vortex Hole configuration also has a developing literature in both experimental [39,44] and numerical analysis [36,37,45].…”

“…Numerical simulations for film cooling methods uses different solution techniques involving steady Reynolds Averaged Numerical Solver (RANS) [37,46], unsteady RANS [37], Detached Eddy Simulations (DES) [35,41] and Large Eddy Simulations (LES) [40]. Among these numerical solution techniques, DES and LES simulations are proven to be more successful over the other techniques for conventional holes [41], but do not have broad applications for AVH holes yet due to their increased numerical cost.…”

“…Boundary conditions were set in accordance with similar other CFD studies using conventional and AVH film cooling configurations ( [33], [35]- [37]). The boundary types used in the simulations are given in Table 28.…”

“…The flow physics models and flow conditions were selected in accordance with several numerical ( [35] and [37]) and experimental [38] studies. Unsteady, 3D, turbulent flow with ideal gas properties was used in all simulations.…”

“…According to Bons et al [48], increasing the turbulence intensity of the main flow increases the effectiveness distribution in the midline region between adjacent single holes. For the AVH hole geometry, Repko et al [37] showed that the orientation of the vortices generated from the main hole and the side holes of the AVH configuration will be the same with the case of adjacent single holes.…”