Large-Eddy Simulation of Shaped Hole Film Cooling With the Influence of Cross Flow

Abstract

In the modern highly-loaded gas turbine, due to the large pressure difference between the suction side and the pressure side of the turbine blade, strong cross flow is formed and it strongly affects the aerodynamic and cooling performances in the end-wall region. The film cooling behavior in the environment of strong cross flow is different from the straight channel environment widely studied in the literature. In this research, the effect of cross flow on film cooling is investigated by Large Eddy Simulation (LES) using subgrid-scale (SGS) model. Numerical simulation is carried out in a curved passage to simulate the turbine blade passage. Shaped cooling hole with blowing ratio 1 is studied. The time-averaged friction line results are compared with existing experimental ink trace results. The vortex structures, both time-averaged and instantaneous, are analyzed to study the effect of cross flow on film cooling. At the exit of the cooling hole, the hanging vortices with negative y-vorticity are more flat in shape and closer to the wall in position in contrast to hanging vortex with positive y-vorticity, which is caused by cross flow and results in the asymmetry of hairpin vortices downstream as well as the asymmetry of the distribution of coolant. It has been shown that the vortices from mainstream have a significant impact on the field near the exit of the cooling hole. Those vortices interact with the hairpin vortices from the cooling hole and directly lead to the asymmetry of the hairpin vortices. Proper Orthogonal Decomposition (POD) analysis is further conducted to extract the dominant flow structures and the physical mechanisms of primary POD modes are given to explain the distribution of film cooling effectiveness affected by cross flow. Based on the specific situation in this work, a fast incremental POD (iPOD) approach is adopted since the rank of the field matrix is far less than the rows, which is caused by the tall and thin character of the matrix, which makes the analysis less costly and more effective. This research helps to understand the cooling performance in the real turbine blade passage and to explain the coolant mixing process based on the instantaneous flow field obtained using high precision LES simulation and powerful iPOD.

Film-cooling hole optimization and experimental validation considering the lateral pressure gradient

“…In order to select the appropriate turbulence model for the film cooling simulations, three different turbulence models: realizable k−ϵ model (Shih et al, 1995), shear stress transport (SST) model (Menter, 1994), and transitional SST model (Langtry and Menter, 2009), are initially selected and employed to obtain the numerical simulation results, respectively. The numerical simulation results of the laterally averaged film cooling effectiveness are further validated with the experimental results obtained from our previous works (Li et al, 2018;Wang et al, 2019), as shown in Figure 7. It can be seen that the realizable k−ϵ model performs the best compared with the experimental results and thus is selected as the turbulence model for the following numerical simulations.…”

“…In order to address this difficulty, a curved tunnel is designed to solely provide the lateral pressure gradient for film cooling, as shown in Figure 1B. A curved tunnel with a constant width is adopted (Li et al, 2018;Wang et al, 2019), which is determined from the real dimension of the experimental facility. Compared with the ideal flat plate, the lateral pressure gradient is one of the most significant characteristics in the curve tunnel environment.…”

“…FIGURE 7Numerical simulation results of the laterally averaged film cooling effectiveness curves obtained from three selected turbulence models, together with the experimental results obtained fromLi et al (2018) andWang et al (2019).…”

Large Eddy Simulation of Film Cooling with Forward Expansion Hole: Comparative Study with LES and RANS Simulations

“…They stated that the reason for the decrease in the effectiveness at high Mach numbers was the separation and large-scale oscillation of the coolant in the hole. Furthermore, Wang, Su, and Yuan (2020) studied the effect of the cross-flow on the film cooling process on an end wall and the flow fields of a 7-7-7 shaped hole with the LES Smagorinsky-Lilly model [17]. The cross-flow caused the counter-rotating vortex pair (CRVP) to be asymmetric.…”