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Development of a novel film cooling hole geometry

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Sargison, JE (2001) Development of a novel film cooling hole geometry. PhD thesis, University of Oxford.

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Abstract

This thesis presents the design, development and testing of a new film cooling hole
geometry, the converging slot-hole or console. Both the thermal and aerodynamic
performance were measured, using the adiabatic effectiveness and heat transfer
coefficient, and aerodynamic loss respectively, to quantify performance. Comparative
measurements were made, by testing conventional film cooling hole shapes in parallel
with the console experiments. The CFD code, Fluent, was used to predict the performance
of the initial design concept before it was manufactured.
Initial performance measurements in incompressible flow were performed in a low speed
wind tunnel at an engine representative Reynolds number based on mainstream flow and
hole diameter. For these experiments, the coolant to mainstream density ratio was
approximately unity, and the cooling performance was measured over a flat plate. The
console was tested in parallel with cylindrical holes, a slot and fan-shaped holes, all of
which had equal throat area per unit width. The heat transfer performance was measured at
steady state using thermochromic liquid crystals sprayed onto a flat plate heater. The
aerodynamic performance of the holes was measured by traversing the boundary layer 50
cylindrical hole diameters downstream of the injection location with a pitot probe.
Engine representative measurements of the console performance were made in a transonic
annular cascade that simulates the three-dimensional flow in the gas turbine. The
Reynolds and Mach numbers were representative of engine conditions, and the coolant
flow was made aerodynamically and thermodynamically similar to engine conditions by
matching both the momentum flux and density ratios. This was achieved by using a heavy
foreign gas with the composition of 30.2% SF6 and 69.8% Ar by weight, which simulates
the coolant to mainstream density ratio of 1.78, and has a ratio of specific heats of 1.4. The
performance of a nozzle guide vane with rows of fan-shaped holes was compared with an
NGV with a film cooling configuration designed with rows of consoles replacing rows of
fan-shaped holes. The heat transfer performance was measured using a modified step
change transient liquid crystal technique. The aerodynamic performance was measured
using a four hole probe traverse downstream of the NGV.
The heat transfer performance of the console was found to be similar to or slightly lower
than the performance of fan-shaped holes. The most significant benefit of the console was
found to be the aerodynamic performance, with a loss due to film cooling of only 20% of
the loss due to film cooling of the rows of fan-shaped holes measured at engine
representative conditions.

Item Type: Thesis (PhD)
Date Deposited: 29 Feb 2008 01:02
Last Modified: 11 Mar 2016 05:54
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