![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
ABSTRACT
Film cooling is widely used to protect surfaces exposed to gases at a high temperature in gas turbine engines. Film heating is the reverse of film cooling, where hot secondary fluid is injected onto the walls to protect against a relatively cold mainstream. In the literature, the latter has often been used as an experimental analogue of the former, since mainstream flow rates are substantially higher, and it is relatively simpler to heat the smaller stream of secondary fluid for experiments. In this paper, the results obtained from a numerical study of film cooling and film heating over a flat plate through single-slot injection are presented. Since the objective of the work is to evaluate the suitability of film heating as a proxy for film cooling, it was decided to keep computational simple, using two-dimensional simulations. The effect of a density ratio of injectant-to-mainstream in the range of 0.2–5 is studied numerically to cover film heating and film cooling. Numerical simulations were carried out for three blowing ratios, M = 1, 2, and 3 at a fixed mainstream Reynolds number of 1.5 × 105 for three injection angles, 30°, 45°, and 60°. Numerical simulations were also carried out for a wide range of momentum flux ratio for film heating and film cooling at an injection angle of 30°. The results show that film heating and film cooling are not equivalent, especially when the density ratio deviates from unity substantially. Based on numerical study, it appears possible to predict film cooling effectiveness from film heating effectiveness for a wide range of density ratios, even though the effectiveness values obtained in regard to film cooling and film heating differ significantly.
Nomenclature
| D | = | slot width, m |
| DR | = | density ratio, |
| FC | = | film cooling |
| FH | = | film heating |
| I | = | momentum flux ratio |
| M | = | blowing ratio, |
| P | = | pressure |
| Re | = | Reynolds number based on mainstream flow, |
| S | = | characteristic length, S = 32D |
| T | = | absolute temperature, K |
| TR | = | temperature ratio, |
| U | = | velocity, m/s |
| VR | = | velocity ratio, |
| X | = | streamwise coordinate, m |
| Y | = | spanwise coordinate, m |
| α | = | injection angle, in degrees |
| η | = | adiabatic effectiveness, |
| ρ | = | density, kg/m3 |
| µ | = | dynamic viscosity, Pa-s |
| Subscripts | = | |
| ad | = | adiabatic wall |
| avg | = | spanwise average |
| dyn | = | dynamic |
| ms | = | mainstream |
| sec | = | secondary |
| w | = | wall |
Nomenclature
| D | = | slot width, m |
| DR | = | density ratio, |
| FC | = | film cooling |
| FH | = | film heating |
| I | = | momentum flux ratio |
| M | = | blowing ratio, |
| P | = | pressure |
| Re | = | Reynolds number based on mainstream flow, |
| S | = | characteristic length, S = 32D |
| T | = | absolute temperature, K |
| TR | = | temperature ratio, |
| U | = | velocity, m/s |
| VR | = | velocity ratio, |
| X | = | streamwise coordinate, m |
| Y | = | spanwise coordinate, m |
| α | = | injection angle, in degrees |
| η | = | adiabatic effectiveness, |
| ρ | = | density, kg/m3 |
| µ | = | dynamic viscosity, Pa-s |
| Subscripts | = | |
| ad | = | adiabatic wall |
| avg | = | spanwise average |
| dyn | = | dynamic |
| ms | = | mainstream |
| sec | = | secondary |
| w | = | wall |