The Effect of Area Ratio Change via Increased Hole Length for Shaped Film Cooling Holes with Constant Expansion Angles

[+] Author and Article Information
Shane E. Haydt

Mechanical and Nuclear Engineering Department, The Pennsylvania State University, University Park, PA 16802, USA

Stephen Lynch

Mechanical and Nuclear Engineering Department, The Pennsylvania State University, University Park, PA 16802, USA

Scott D. Lewis

Turbine Durability, United Technologies—Pratt & Whitney, 400 Main Street, East Hartford, CT 06108, USA

1Corresponding author.

ASME doi:10.1115/1.4038871 History: Received October 04, 2017; Revised October 19, 2017


Shaped film cooling holes are used as a cooling technology in gas turbines to reduce metal temperatures and improve durability, and they generally consist of a small metering section connected to a diffuser that expands in one or more directions. The area ratio of these holes is defined as the area at the exit of the diffuser, divided by the area at the metering section. A larger area ratio increases the diffusion of the coolant momentum, leading to lower average momentum of the coolant jet at the exit of the hole and generally better cooling performance. Cooling holes with larger area ratios are also more tolerant of high blowing ratio conditions, and the increased coolant diffusion typically better prevents jet liftoff from occurring. Higher area ratios have traditionally been accomplished by increasing the expansion angle of the diffuser while keeping the overall length of the hole constant. The present study maintains the diffuser expansion angles and instead increases the length of the diffuser, which results in longer holes. Various area ratios have been examined for two shaped holes: one with forward and lateral expansion angles of 7° (7-7-7 hole) and one with forward and lateral expansion angles of 12° (12-12-12 hole). Each hole shape was tested at numerous blowing ratios to capture trends across various flow rates. Adiabatic effectiveness measurements indicate that for the baseline 7-7-7 hole, a larger area ratio provides higher effectiveness, especially at higher blowing ratios.

Copyright (c) 2017 by ASME
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