Abstract
In this paper, we compare using computational fluid dynamics the aero-thermal performance of two candidate casing manifolds for supplying an impingement-actuated active tip clearance control system for an aero-engine high-pressure turbine. The two geometries are (a) single-entry: an annular manifold fed at one circumferential location; (b) multiple-entry: a casing manifold split into four annular sectors, with each sector supplied separately from an annular ring main. Both the single-entry and multiple-entry systems analysed in this paper are idealised versions of active clearance control systems in current production engines. Aero-thermal performance is quantitatively assessed on the basis of the heat transfer coefficient distribution, driving temperature difference for heat transfer between the jet and casing wall and total pressure loss within the high-pressure turbine active clearance control system. We predict that the mean heat transfer coefficient (defined with respect to the inlet temperature and local wall temperature) of the single-entry active clearance control system is 77% greater than the multiple-entry system, primarily because the coolant in the multiple-entry case picks up approximately 40 K of temperature from the ring main walls, and secondarily because the average jet Reynolds number of impingement holes in the single-entry system is 1.2 times greater than in the multiple-entry system. The multiple-entry system exhibits many local hot and cold spots, depending on the position of the transfer boxes, while the single-entry case has a more predictable aero-thermal field across the system. The multiple-entry feed system uses an average of 20% of the total available pressure drop, while the feed system for the single-entry geometry uses only 2% of the total available pressure drop. From the aero-thermal results of this computational study, and in consideration of holistic aero-engine design factors, we conclude that a single-entry system is closer to an optimal solution than a multiple-entry system.
Highlights
The aviation industry has identified the accelerated development of active clearance control (ACC) systems as key to delivering the European Aviation Advisory Council’s2020 targets of increased efficiency, reduced emissions and increased flight cycles [1]
We investigate the effect of single-entry vs. multiple-entry feed on the performance of an High-pressure turbine (HPT) ACC system
Aero-thermal performance is quantitatively assessed on the basis of the heat transfer coefficient (HTC) distribution, driving temperature difference for heat transfer between the jet and casing wall and total pressure loss within the HPT ACC system
Summary
The aviation industry has identified the accelerated development of active clearance control (ACC) systems as key to delivering the European Aviation Advisory Council’s. 2020 targets of increased efficiency, reduced emissions and increased flight cycles [1]. ACC reduces turbine tip leakage flow, irreversible mixing, diffusion and instabilities, which increases stage efficiency [2] and lengthens engine service life—a considerable advantage given that a major engine overhaul can cost upwards of USD 1 M [3]. High-pressure turbine (HPT) ACC has been shown to improve net specific fuel consumption (SFC) by. NOx and CO emissions are reduced by 10% and. 16%, respectively, with the implementation of HPT ACC in short haul aircraft [6].
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