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2 Journal of Theoretical and Applied Mechanics

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Study on the behavior of streamwise vortices formed between leading edge tubercles in a compressor cascade

Zheng Tan, Qiang Xiao-Qing, Teng Jin-Fang, Feng Jin-Zhang

Journal of Theoretical and Applied Mechanics

2019

Vol. 57 nr 3

617--629

A study has been carried out to investigate the formation mechanism and development of streamwise vortices induced by leading edge tubercles in a high speed compressor cascade. The preliminary assessment of the cascade performance in terms of the total pressure loss coefficient shows that the loss reduction is achieved at high incidence angles. A smaller wavelength leads to higher additional losses at the design point, but gives rise to a greater loss reduction at high incidence angles. The modified cascade with a tubercle wavelength of 4% chord achieves the maximum loss reduction of 36.1% at i = 10◦ , as well as the stall angle improvement of 27.6%. The formation mechanism of streamwise vortices is elaborated on the basis of the streamwise vorticity equation, in which the streamwise turning terms may be responsible for the generation of streamwise vortices. Slices of streamwise vorticity at various streamwise locations, combined with vorticity strength distributions, have been presented to study the development of streamwise vortices. The counter-rotating vortices are divided into the crest-induced streamwise vortices (CSVs) and trough-induced streamwise vortices (TSVs). A streamwise vortex pair formed from a part of the CSV sheets behind troughs, is gradually entrained by the TSV pair along the streamwise direction. In addition, the tubercles with a smaller wavelength result in higher streamwise vorticity strength with which the streamwise vortices interact with the flow separation more sufficiently and delay the separation to a greater extent.

Numerical loss analysis in a compressor cascade with leading edge tubercles

Zheng T., Qiang X.-Q., Teng J.-F., Teng J.-Z.

Journal of Theoretical and Applied Mechanics

2018

Vol. 56 nr 4

1083--1095

A numerical analysis of loss has been carried out to explore the loss mechanism of leading edge tubercles in a high speed compressor cascade. Taking the lead from flippers of the humpback whale, tubercles are passive structures of a blade for flow control. Evaluation of the overall performance in terms of entropy increase shows that the loss reduction is achieved both at high negative and high positive incidence angles, while a rise in the loss is obtained near the design point. And a smaller wave number as well as a smaller amplitude results in lower additional losses at the design point. Spanwise and streamwise distributions of pitchwise-averaged entropy increase combined with flow details have been presented to survey the loss development and, subsequently, to interpret the loss mechanism. The tubercle geometry results in the deflection flow and the consequent spanwise pressure gradient. This pressure gradient induces formation of counter-rotating streamwise vortices, transports away the low-momentum fluid near wall from crests towards troughs and leads to local high loss regions behind troughs as well as loss reduction behind the crests in comparison to the baseline. The interaction between these vortices and flow separation by momentum transfer leads to separation delay and the consequent loss reduction at the outlet.