Large Eddy Simulation of Film Cooling Involving Compound Angle Holes: Comparative Study of LES and RANS

Seung Il Baek,Joon Ahn

doi:10.3390/pr9020198

Abstract

A large eddy simulation (LES) was performed for film cooling in the gas turbine blade involving spanwise injection angles (orientation angles). For a streamwise coolant injection angle (inclination angle) of 35°, the effects of the orientation angle were compared considering a simple angle of 0° and 30°. Two ratios of the coolant to main flow mass flux (blowing ratio) of 0.5 and 1.0 were considered and the experimental conditions of Jung and Lee (2000) were adopted for the geometry and flow conditions. Moreover, a Reynolds averaged Navier–Stokes simulation (RANS) was performed to understand the characteristics of the turbulence models compared to those in the LES and experiments. In the RANS, three turbulence models were compared, namely, the realizable k-ε, k-ω shear stress transport, and Reynolds stress models. The temperature field and flow fields predicted through the RANS were similar to those obtained through the experiment and LES. Nevertheless, at a simple angle, the point at which the counter-rotating vortex pair (CRVP) collided on the wall and rose was different from that in the experiment and LES. Under the compound angle, the point at which the CRVP changed to a single vortex was different from that in the LES. The adiabatic film cooling effectiveness could not be accurately determined through the RANS but was well reflected by the LES, even under the compound angle. The reattachment of the injectant at a blowing ratio of 1.0 was better predicted by the RANS at the compound angle than at the simple angle. The temperature fluctuation was predicted to decrease slightly when the injectant was supplied at a compound angle.

Highlights

Published: 21 January 2021Gas turbines, which are composed of compressors, combustors, and turbines, are mainly used as aircraft engines and prime movers for natural gas power generation
The time-averaged flow and thermal fields obtained by the large eddy simulation (LES) and Reynolds averaged Navier–Stokes simulation (RANS) in a values
When the orientation angle was 0°, a kidney vortex occurred symmetriof the characteristics of the high velocity in the streamwise direction from the kidney vortex cally in the film cooling jet and both the LES and RANS predict this phenomenon well, as position is more similar to the experiment values than those obtained using the RANS

Summary

Introduction

Published: 21 January 2021Gas turbines, which are composed of compressors, combustors, and turbines, are mainly used as aircraft engines and prime movers for natural gas power generation. Ensuring cycle efficiency is critical in both these applications. Additional devices such as reheaters or regenerators can be installed to increase cycle efficiency, this technique cannot be adopted in the case of aircraft engines due to the limitations of the weight and frontal area. In general, to increase cycle efficiency, the turbine inlet temperature is raised above the allowable temperature limit of the materials by cooling the blade through the air from the compressor [1]. After cooling the inside of the blade, the air, injected through the blade surface, flows on the surface, thereby creating an insulating film to protect the blade from the hot combustion gases. To generate a uniform insulation film, it is advantageous to inject the coolant through a slot. To ensure the mechanical strength, cylindrical holes are usually arrayed in the spanwise direction, as shown in Figure 1a [2]

Methods

Results

Conclusion