Session: 11-14-01 Heat Transfer in Gas Turbines

Paper Number: 73135

Start Time: Wednesday, 01:50 PM

73135 - Effect of Inlet Geometry on Flat Plate, Film Cooling Effectiveness From Shaped Holes 

ABSTRACT

Modern gas turbine engines require a sophisticated cooling system design to achieve higher power output and efficiency. Film cooling is an indispensable part of the turbine external cooling mechanism. In this study, systematic tests were carried out to evaluate the potential effect of non-cylindrical inlet geometries on the performance of laid back, fan-shaped film cooling holes using the steady state pressure sensitive paint (PSP) measurement technique.

“Racetrack” shaped inlet geometries with aspect ratios of 2:1 and 4:1 were selected as the subjects of this study, due to their possible potential of improving the film cooling effectiveness. A laid-back, fan-shaped hole with a cylindrical inlet studied in open literature was selected as control. The outlets of the tested film cooling holes share the same geometric parameters of the prescribed fan-shaped hole design, while the inlet geometry varies. Additionally, basic cylindrical holes were also tested to benchmark the experimental setup. The coolant flow conditions range from blowing ratios of M=0.3-1.5 and density ratios DR=1 and 2. The mainstream turbulence intensity is fixed at 6%.

Test results show that the shaped inlets can provide a higher area-averaged film cooling effectiveness, , over the traditional cylindrical inlet design using the same amount of coolant, but the performance varies with flow conditions. For the 2:1 inlet, an advantage of 20% higher  could be maintained for DR=1, while for DR=2 this advantage is reduced to 10%. For the 4:1 inlet, when the coolant momentum flux ratio, I<0.5, a similar or slightly higher improvement can be obtained, but when I>1, the advantage diminishes with the growing momentum flux ratio to approximately 5%, at I=2.25. The coolant coverage for the 2:1 inlet is better than the other two inlet geometries downstream at higher momentum flux ratios (I>1). While the 4:1 inlet enjoys a more concentrated film coverage in regions closer to the hole (X/D_h<5) when I<0.5. When compared with existing correlations predicting film cooling performance of a 2D slot or a shaped hole with a cylindrical inlet, coolant ejected from the fan-shaped hole with shaped inlets behave more akin to being ejected from a continuous slot in the near hole regions.

In addition, the discharge coefficients, C_d, were measured for all the geometries investigated. Results show that the 2:1 inlet geometry is similar to the cylindrical inlet in terms of discharge coefficients under most flow conditions. For the 4:1 inlet, its discharge coefficient is 0.02-0.04 lower than the fan-shaped holes with a cylindrical inlet under the same flow condition.

To conclude, if the manufacturing cost and turbine structural strength is not taken into consideration, the 2:1 inlet is an overall better alternative to the existing cylindrical inlet for laid-back, fan-shaped cooling holes.

Keywords: flat plate film cooling, inlet geometry, shaped holes, film cooling effectiveness, discharge coefficient, pressure sensitive paint.

Presenting Author: Hanlin Wang Texas A&amp;M University

Authors:

Hanlin Wang Texas A&M University
Lesley M. Wright Texas A&M University