Film cooling performance and flow field of compounded double jet holes with trench
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ORIGINAL
Film cooling performance and flow field of compounded double jet holes with trench B. Koushi Priyatham1 · P. S. B. Pratyush1 · S. R. Shine1 Received: 8 July 2019 / Accepted: 1 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Film cooling performance of a novel double jet configuration is numerically analysed. The proposed scheme has a primary compound angle hole along with a secondary hole compounded in the laterally opposite direction. The primary hole is provided with a trench at the coolant hole exit. Numerical analysis is performed using RANS equations along with standard k-ω turbulence model. The numerical scheme is validated through the excellent agreement between the available experimental data for tangential, compound, and crater designs having similar primary hole geometric parameters. It is seen that the proposed compounded double jet trench design (DJT) combines the advantages of compound angle, double jet and trenched configurations and provides better lateral and uniform coolant distribution, reduced jet lift off, and higher coolant attachment in the stream wise direction. The vortex mechanisms responsible for the coolant spread in near-hole and down stream regions are identified. The various flow structures that are responsible for higher effectiveness are compared with other configurations. The effect of free stream turbulence at various blowing ratios is studied and found that the increase of turbulence produced significant increase in lateral effectiveness at higher blowing ratios. This effect is predominant at far downstream locations of the coolant exit plane. Abbreviations D Primary coolant hole diameter, mm Di,m Diffusion coefficient of species i d Secondary hole diameter, mm Ji Diffusion flux arises out of concentration gradients of species i h Trench depth, mm L Length of the primary hole, mm M Blowing ratio, uc ρc /u∞ ρ∞ P Pitch, mm Turbulent Schmidt number Sct T Temperature, K Tu Turbulent intensity, % t Time, s V Velocity, ms −1 x Distance in the mainstream direction Mass fraction of ith component Yi z Distance in the lateral direction
S. R. Shine
Greek α γ η η η μ ρ
Tangential angle with respect to the mainstream Compound angle with respect to Vertical in Ydirection (deg) Film cooling effectiveness, η(x/D) = [Tw (x/D) − T∞ ]/[Tc − T∞ ] Average film cooling effectiveness Spatially averaged film cooling effectiveness Dynamic viscosity, kgm−1 s −1 Density, kgm−3
Subscripts 1 Primary hole 2 Secondary hole c Coolant i Species Lat Lateral direction w Wall ∞ Mainstream
1 Introduction
[email protected] 1
Department of Aerospace Engineering, Indian Institute of Space Science and Technology, IIST, Thiruvananthapuram, India
Secondary coolant fluid injected along a surface is often referred as film cooling and is being used in gas turbine blades to protect it from the elevated temperature environment. Numerous studies have been available in open
Heat Mass Transfer
literature which investigates various parameters that affect film cooling performanc
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