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Abstract
The current investigation clarifies the key factor on the film cooling effectiveness, which is the fundamental of the film cooling research. Conventionally, the momentum flux ratio is thought as the most critical factor on the film cooling effectiveness, and the counterrotating vortex pair (CRVP) also has significant impact. A new scheme named the nozzle scheme has been created to separate the momentum flux ratio and control the CRVP intensity. Three configurations of the nozzle scheme and the baseline have been simulated numerically under density ratio of 2 and blowing ratios that varied from 0.5 to 2. The results demonstrate that the CRVP intensity, instead of the momentum flux ratio, is the most critical factor governing the film-cooling effectiveness, and the mainstream direction component is its main component. Therefore, its two compositions, which are the corresponding velocity gradients, naturally become the key parameters considered in the design of new film cooling geometry.
NOMENCLATURE
| A | = | area (m2) |
| Br | = | blowing ratio (ρjUj/ρmUm) |
| CRVP/CVP | = | counterrotating vortex pair |
| D | = | diameter of cooling hole (0.0127m) |
| Dr | = | density ratio (ρj/ρm) |
| I | = | momentum flux ratio |
| JICF | = | jet in cross flow |
| JF | = | jet flow subdomain |
| L | = | length of cooling hole (1.5D) |
| = | mass flow rate (kg/s) | |
| MF | = | mainstream flow subdomain |
| p | = | cooling hole pitch (3D) |
| RANS | = | Reynolds-averaged Navier–Stokes |
| RSM | = | Reynolds stress model |
| RKE | = | realizable k-ϵ model |
| T | = | temperature (K) |
| U | = | local velocity perpendicular to a specific surface (m/s) |
| u, v, w | = | Cartesian coordinate velocities (m/s) |
| x, y, z | = | Cartesian coordinates |
| X, Y, Z | = | coordinate values (m) |
Greek Symbols
| η | = | adiabatic film cooling effectiveness ((Tw – Tm)/ (Tj – Tm)) |
| ρ | = | density (kg/m3) |
| θ | = | normalized temperature ((T – Tm)/ (Tj – Tm)) |
| ω | = | vorticity (m2/s2) |
Subscripts
| A | = | area average |
| c | = | centerline |
| j | = | jet |
| l | = | lateral |
| m | = | main stream |
| ov | = | overall |
| x | = | X component |
| w | = | wall conditions |
Superscripts
| * | = | the value before normalization |
| - | = | average value |
Additional information
Notes on contributors
Hao Ming Li
Hao Ming Li is a Ph.D. student at the Energy and Heat Transfer Laboratory, Department of Mechanical Engineering, Concordia University, Montreal, Canada. He received his M.A.Sc. degree from Concordia University in 2012. Now he is working on the film cooling heat transfer numerically and experimentally.
Ibrahim Hassan
Ibrahim Hassan is a professor of mechanical engineering at Concordia University. His research interests include heat transfer, micro fluids, thermal microelectromechanical systems (MEMS), multiphase flow, and computational fluid dynamics (CFD) applications. The research conducted by Dr. Hassan present the state-of-the-art solutions to applications found in industries such as aerospace, nuclear power, and solar energy. He has published over 200 articles in refereed journals, conference proceedings, and book chapters. He recently received the prestigious NSERC “National Science and Research Council of Canada” Discovery Accelerator Supplement (DAS) Award in 2010.