CUED Publications database

Aerodynamics of low reynolds number axial compressor sections

Maffioli, A and Hall, CA and Melvin, S (2015) Aerodynamics of low reynolds number axial compressor sections. In: UNSPECIFIED.

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© 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Compact axial compression systems are of interest to the domestic appliance indus- try. The associated low Reynolds number leads to high losses compared to large-scale compressors due to a transitional flow field with large regions of separation. However, if these regions of separation could be minimised and the losses reduced then the efficiency of low-Re compressors would be significantly improved. In this paper we explore the avail- able design space for compact axial compressor blade sections using a coupled free-stream and boundary layer solver. The sections we consider represent a rotor in a single-stage compressor with axial flow at inlet and chord-based Reynolds number Re = 50, 000. We first vary the inlet angle and camber of a conventional airfoil and find that the amount of turning such blades can impart increases with increasing flow coefficient, but this is always considerably lower than in high-Re blades. We then move to section designs with thickness distributions defined by a shape function and discover that moving the maximum thickness towards the front encourages early transition over the thickness "bump" leaving the turbu- lent flow downstream with a mild adverse pressure gradient. Hence turbulent separation on such front-thickened blades is delayed leading to lower loss and deviation. For this style of section, we produce a map of rotor efficiency as a function of design flow coefficient and stage loading. Peak efficiency is found to occur at higher stage loading values than for the conventional airfoil designs. Design stage loadings above 0.4 are predicted to be achievable at design flow coefficients above 0.5, while peak efficiency is obtained at lower stage loadings of about 0.3 with peak efficiency increasing with increasing flow coefficient. We also study the effect of pitch-to-chord ratio and observe that there is a trade-off be- tween design efficiency and operating range as the blade spacing is increased. A Lieblein diffusion factor DF = 0.45, leads to a good compromise and this is a comparable value to that used in conventional large-scale compressor designs. Finally experiments with linear cascades created from the blade designs confirm the complex flow patterns over low-Re sections. The measurements also demonstrate the challenge in accurately capturing the laminar separation bubble on the suction surface, and suggest a move towards high-fidelity numerical simulations for future research.

Item Type: Conference or Workshop Item (UNSPECIFIED)
Divisions: Div A > Turbomachinery
Depositing User: Cron Job
Date Deposited: 17 Jul 2017 19:37
Last Modified: 19 Jul 2018 07:31