• Title/Summary/Keyword: Stall Suppression

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A Suggested Mechanism of Significant Stall Suppression Effects by Air Separator Devices in Axial Flow Fans

  • Yamaguchi, Nobuyuki
    • International Journal of Fluid Machinery and Systems
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    • v.4 no.1
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    • pp.57-66
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    • 2011
  • Radial-vaned air separators show a strong stall suppression effect in an axial flow fans. From a survey of existing literature on the effects and the author's data, a possible mechanism for the significant effects has been proposed here. The stall suppression is suggested to have been achieved by a combination of the following several effects; (1) suction of blade and casing boundary layers and elimination of embryos of stall, (2) separation and straightening of reversed swirling flow from the main flow, (3) induction of the fan main flow toward the casing wall and enhancement of the outward inclination of meridional streamlines across the rotor blade row, thus keeping the Euler head increase in the decrease in fan flow rate, and (4) reinforcement of axi-symmetric structure of the main flow. These phenomena have been induced and enhanced by a stable vortex-ring encasing the blade tips and the air separator. These integrated effects appear to have caused the great stall suppression effect that would have been impossible by other types of stall prevention devices. Thus the author would like to name the device "tip-vortex-ring assisted stall suppression device".

Investigation on the Off Design Performance of a Transonic Compressor with Circumferential Grooves

  • Zhu, Jianhong;Piao, Ying;Zhou, Jianxing;Qi, Xingming
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.03a
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    • pp.66-71
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    • 2008
  • Two cases with circumferential grooves were designed for a transonic compressor, and 3-D numerical simulations were conducted for stall mechanism at three representative speeds. A conclusion can be drawn from the comparison between compressors with or without casing treatment that: with the rising of rotation speed, stall margin increases dramatically under the help of casing treatments, and the case with middle grooves has reasonable compromise between stall margin increment and efficiency cutting. At lower speed, the increment reduces, and grooves at the back of blade tip have more influence on stall margin. Further investigation shows there is a transition in mechanism of compressor stall with the decline of rotational speed: at high rotation speed, the expansion of stall margin mainly results from the suppression of tip leakage vortex by casing treatments, yet it benefits more from the depression of boundary layer separation from suction surface of blade tip.

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Effect of Diffuser Width on Rotating Stall in Centrifugal with Vaneless Diffuser (원심형 송풍기에서 베인리스 디퓨저의 폭변화가 선회실속에 미치는 영향)

  • Kim, Jin-Hyeong;Jo, Gang-Rae
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.10
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    • pp.1293-1302
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    • 2001
  • It is generally known that radial vane blowers with vaneless diffuser may generate mostly only a rotating stall but backward curved vane blowers may do both an impeller and a diffuser rotating stalls. In this study, it was found from the numerical and experimental results that the diffuser rotating stall does not appear in a radial vane because of the suppression for the diffuser stall appearance by occurring of impeller rotating stall in a large flow rate coefficient. The diffuser rotating stalls occurring when the width of diffuser is broaden fur a backward curved vane blower are classified definitely by the diffuser flow rate coefficient defined by adopting the varying diffuser width.

Numerical Study about the Effect of Continuous Blowing On Aerodynamic Characteristics of NACA 0015 Airfoil (연속적 블로잉에 따른 NACA 0015 익형 공력특성 변화에 대한 수치적 연구)

  • Choe, Seong-Yun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.5
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    • pp.1-11
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    • 2006
  • The effects of continuous blowing on flow control and stall suppression for flows over a NACA 0015 airfoil at low Reynolds numbers were numerically investigated through its parameter variation on unstructured meshes. The aerodynamic force and moment variations due to flow control were examined, along with the stall angle-of-attack change for stall suppression. The results showed that blowing with relatively strong jet increases lift at the cost of drag increment below stall angle. Continuous blowing delays flow stall when it is implemented near the leading edge. When the blowing jet was aligned along the flow direction on the airfoil, the favorable flow control effect was most significant below the stall angle of attack.

Flow Characteristics of a Paraglider Canopy with Leading-edge Tubercles (선단돌기가 적용된 패러글라이더 캐노피의 유동특성 연구)

  • Shin, Jeonghan;Chae, Seokbong;Shin, Yisu;Park, Jungmok;Song, Ginseok;Kim, Jooha
    • Journal of the Korean Society of Visualization
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    • v.19 no.3
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    • pp.106-114
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    • 2021
  • In the present study, we investigate the flow characteristics of a paraglider canopy with leading-edge tubercles by performing force measurement and surface flow visualizations. The experiment is conducted at Re = 3.3×105 in a wind tunnel, where Re is the Reynolds number based on the mean chord length and the free-stream velocity. The canopy model with leading-edge tubercles has flow characteristics of a two-step stall, showing an earlier onset of the first stall than the canopy model without leading-edge tubercles. However, the main stall angle of the tubercled model is much larger than that of the canopy model without tubercles, resulting in a higher aerodynamic performance at high angles of attack. The delay in the main stall is ascribed to the suppression of separation bubble collapse around the wingtip at high angles of attack.