Perkins, SCT and Henderson, AD, The effect of stator reduced frequency on transition and separation at the leading edge of a compressor stator, Proceedings of the 18th Australasian Fluid Mechanics Conference, 3-7 December, Tasmania, Australia, pp. 1-4. ISBN 978-0-646-58373-0 (2012) [Refereed Conference Paper]
Copyright 2012 Leishman Associates
Official URL: http://www.proceedings.com/17862.html
Studies on the effect of stator reduced frequency in low pressure turbines have shown that periodic wake-induced unsteadiness can increase blade element circulation and reduce losses by up to 15% when compared to steady flow operation. This is primarily due to suppression of a large separation bubble that forms downstream of peak suction under steady conditions, and this is periodically suppressed by wake passing events resulting in significantly reduced losses generated within the boundary layer.
This research examines the effect of wake induced unsteady flow on a controlled diffusion (CD) compressor stator blade with circular arc leading edge. The blade profile is tested inside a large scale two-dimensional cascade, which is fitted with a traveling bar mechanism to produce wakes similar those generated by an upstream rotor blade row. The flow is seen to experience flow separations and subsequent transition at the leading edge on both the pressure and suction surfaces due to a velocity overspeed caused by discontinuities in surface curvature.
Testing was carried out at reduced frequencies of 0, 0:47, 0:94 and 1:88 at the design inlet flow angle of 45.5o. The Reynolds number based on chord was 230;000 and the average freestream turbulent intensity was 4:0%.
A range of experimental measurements were used to study the stator’s performance: high resolution time-averaged blade surface static pressure measurements; inlet and exit 3-hole probe traverses and triggered data acquisition from an array of surface mounted hot-film sensors. Results from the hot-film sensors were subsequently interpreted to yield quasi-wall shear stress (QWSS) and turbulent intermittency, and ensemble averaged statistics are presented.
Results show that increasing stator reduced frequency from 0 to 1:88 increases the overall blade pressure loss. The losses generated on the pressure surface and suction surfaces differ significantly. The pressure surface demonstrate a clear reduction in loss with an increase in reduced frequency whereas the opposite trend was seen on the suction surface.Wake-induced turbulent strips were observed to suppress the formation of a leading edge separation bubble that forms under steady flow conditions on the suction surface, and also between wake passing events. These strips reduced in width and level of turbulent intermittency through the favorable pressure gradient leading to peak suction and grew in the adverse pressure gradient of the velocity overspeed. The flow between wakeinduced turbulent strips partially relaminarises through the favorable pressure gradient leading to peak suction.
|Item Type:||Refereed Conference Paper|
|Keywords:||axial, compressor, stator, leading edge|
|Research Group:||Fluid mechanics and thermal engineering|
|Research Field:||Aerodynamics (excl. hypersonic aerodynamics)|
|Objective Group:||Energy transformation|
|Objective Field:||Energy transformation not elsewhere classified|
|UTAS Author:||Perkins, SCT (Mr Sam Perkins)|
|UTAS Author:||Henderson, AD (Associate Professor Alan Henderson)|
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