Publication Cover
Numerical Heat Transfer, Part A: Applications
An International Journal of Computation and Methodology
Volume 69, 2016 - Issue 5
345
Views
9
CrossRef citations to date
0
Altmetric
Original Articles

Prediction of film cooling effectiveness over a flat plate from film heating studies

, , , &
Pages 529-544 | Received 03 Mar 2015, Accepted 26 Jun 2015, Published online: 30 Nov 2015
 

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

Reprints and Corporate Permissions

Please note: Selecting permissions does not provide access to the full text of the article, please see our help page How do I view content?

To request a reprint or corporate permissions for this article, please click on the relevant link below:

Academic Permissions

Please note: Selecting permissions does not provide access to the full text of the article, please see our help page How do I view content?

Obtain permissions instantly via Rightslink by clicking on the button below:

If you are unable to obtain permissions via Rightslink, please complete and submit this Permissions form. For more information, please visit our Permissions help page.