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Analysis and control of the tip-leakage flow of an isolated and fixed blade

Abstract : To reduce the environmental footprint of aviation, it is essential to develop lighter and more fuel efficient turbojet engines. This can be achieved by increasing the efficiency of axial compressors and by extending their range of stable operation. The main limitations of axial compressors are caused by the flow going through the gap between the tip of rotor blades and the casing, also known as tip-leakage or tip-gap flow. This study aims at providing a detailed description of the tip-leakage flow, in order to analyze its sensitivity to design parameters and to control devices based on air injection from the casing. The setup is composed of a single blade, set orthogonal to a flat plate that plays the role of the casing wall. This simplification makes optical measurements easier and allows a fine tuning of the gap height, the incoming boundary layer thickness at the casing wall and the blade loading. The analysis is based on experiments conducted in a low-speed wind tunnel that are complemented by CFD calculations. The tip-leakage flow is primarily driven by the gap height. The incoming boundary layer thickness and the blade loading also have a notable effect on the lateral postion of the tip-leakage vortex. The distribution of local entropy creation rate has been used to identify areas of losses in the flow. Moreover, the total pressure losses have been decomposed in two terms identified as a vortex loss and a wake loss. This vortex loss drives the increase of total pressure losses with the gap height. An empirical model has been developped to predict the evolution of the tip-leakage vortex circulation and of the total pressure losses with respect to the gap height. A steady injection of air from the casing has been evaluated, using normal jets in the gap. With this control strategy, the tip-leakage vortex tends to be closer to the blade, which could lead to an extension of the range of stable operation for axial compressors. In addition to that, the control device smoothes out the axial vorticity field in the tip-leakage vortex, which could be interesting to reduce rotor-stator interactions. However, this control strategy leads to higher total pressure losses and is less effective with larger gaps.
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Submitted on : Friday, November 13, 2020 - 10:50:25 AM
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  • HAL Id : tel-03003331, version 1

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Benjamin Deveaux. Analysis and control of the tip-leakage flow of an isolated and fixed blade. Engineering Sciences [physics]. HESAM UNIVERSITE, 2020. English. ⟨tel-03003331v1⟩

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