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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

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2019

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Vol. 57 nr 3

617--629

EN

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.

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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

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2018

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Vol. 56 nr 4

1083--1095

EN

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.

3

Source term model for streamwise Rod Vortex Generator modelling

Kwiatkowski T., Flaszyński P.

Journal of KONES

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2016

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Vol. 23, No. 4

261--268

EN

In the article, the new method of modelling of Rod Vortex Generators (RVGs) was proposed. RVGs are inclined rods, mounted in boundary layer used to flow control. RVGs were intensively investigated in Institute of Fluid-Flow Machinery in Gdansk, Poland. The research results indicate high potential of RVGs to flow control in wide range of Mach numbers (Mach 0.3-1.45) in the main flow. Due to the flow structure details generated by RVG, it is required to create fine grids in the vicinity of RVGs, which increase the computational cost. In order to overcome this difficulty and reduce computational cost the new numerical models of RVGs are proposed, which use the modification of BAY model. Using BAY model it is not needed to resolve the shape of RVG in detail and it is possible to use orthogonal meshes. The BAY model was originally proposed to predict flows behind thin-plate vortex generators. This model works by adding momentum source term to Reynolds-Averaged Navier-Stokes equations in ANSYS Fluent. The BAY model spatial vectors orientation was modified and some simplifications were performed. The model was calibrated and simulations were carried out for the single rod. The results and effectiveness of modified BAY model were compared with wind-tunnel experiment results and grid-resolved model.