• Title/Summary/Keyword: vortex

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THE FUNDAMENTAL SHOCK-VORTEX INTERACTION PATTERNS THAT DEPEND ON THE VORTEX FLOW REGIMES

  • Chang, Keun-Shik;Barik, Hrushikesh;Chang, Se-Myong
    • Journal of computational fluids engineering
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    • v.14 no.3
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    • pp.76-85
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    • 2009
  • The shock wave is deformed and the vortex is elongated simultaneously during the shock-vortex interaction. More precisely, the shock wave is deformed to a S-shape, consisting of a leading shock and a lagging shock by which the corresponding local vortex flows are accelerated and decelerated, respectively: the vortex flow swept by the leading shock is locally expanded and the one behind the lagging shock is locally compressed. As the leading shock escapes the vortex in the order of microseconds, the expanded flow region is quickly changed to a compression region due to the implosion effect. An induced shock is developed here and propagated against the vortex flow. This happens for a strong vortex because the tangential flow velocity of the vortex core is high enough to make the induced-shock wave speed supersonic relative to the vortex flow. For a weak shock, the vortex is basically subsonic and the induced shock wave is absent. For a vortex of intermediate strength, an induced shock wave is developed in the supersonic region but dissipated prematurely in the subsonic region. We have expounded these three shock-vortex interaction patterns that depend on the vortex flow regime using a third-order ENO method and numerical shadowgraphs.

The Ultimate Pattern of Shock-Vortex Interaction

  • Chang, Keun-Shik;Barik, Hrushikesh;Chang, Se-Myong
    • 한국전산유체공학회:학술대회논문집
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    • pp.337-339
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    • 2008
  • As a shock impinges into a vortex of variable strength, complex shock diffraction can occur. Since a vortex has a fixed rotating direction, the shock wave travelling in one direction creates strong asymmetry in the vortex flow field. The process is that first the shock is divided into two parts by the vortex. One part is moving in the adverse direction opposite to the vortex flow which is captured by the vortex center. The other part is moving in the favorable direction, namely, in the direction same as the vortex flow; it is swung around the vortex, accelerating the vortex flow. In this paper we have investigated numerically using ENO scheme how and why the shock-vortex interaction patterns appear so different for different parametric values. Conclusion is that there are three different types of shock-vortex interaction depending on two related parameters: shock Mach number and vortex Mach number. We present a parameter map by which we can discern what type of interaction pattern appears as a shock impinges into a vortex.

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The Ultimate Pattern of Shock-Vortex Interaction

  • Chang, Keun-Shik;Barik, Hrushikesh;Chang, Se-Myong
    • 한국전산유체공학회:학술대회논문집
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    • pp.337-339
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    • 2008
  • Abstract: As a shock impinges into a vortex of variable strength, complex shock diffraction can occur. Since a vortex has a fixed rotating direction, the shock wave travelling in one direction creates strong asymmetry in the vortex flow field. The process is that first the shock is divided into two parts by the vortex. One part is moving in the adverse direction opposite to the vortex flow which is captured by the vortex center. The other part is moving in the favorable direction, namely, in the direction same as the vortex flow; it is swung around the vortex, accelerating the vortex flow. In this paper we have investigated numerically using ENO scheme how and why the shock-vortex interaction patterns appear so different for different parametric values. Conclusion is that there are three different types of shock-vortex interaction depending on two related parameters: shock Mach number and vortex Mach number. We present a parameter map by which we can discern what type of interaction pattern appears as a shock impinges into a vortex.

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Simulation of the Vortex Shedding from a Circular Cylinder by Means of the Vortex Cloud Model (Vortex Cloud Model에 의한 추상체 주위의 Vortex 유출 Simulation)

  • D.K. Lee
    • Journal of the Society of Naval Architects of Korea
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    • v.30 no.3
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    • pp.62-74
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    • 1993
  • The vortex shedding from a circular cylinder placed in a steady uniform stream is simulated by the vortex cloud model of the discrete vortex method. The vorticity created at the cylinder surface is discretely represented by a number of nascent vortices at each time step and the motion of these cumulative vortices is monitored to produce the evolution of the vortex distribution pattern. Convection of vortices was traced by the vortex-in-cell technique and the force coefficients were calculated by both Sarpkaya's formulae and Lee's formulae for comparison. Discussions concerning the interrelation between the computational parameters and some principles for choosing the suitable values are included.

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The Effect on Wake Flow and Vortex Shedding Frequency by Vortex Stabilizer in Karman Vortex Type Air Flow Sensor (칼만와류식 공기유량센서의 와안정판이 후류유동장과 와유출주파수에 미치는 영향)

  • 임성원;류병남;이종춘;부정숙
    • Journal of Advanced Marine Engineering and Technology
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    • v.25 no.4
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    • pp.846-856
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    • 2001
  • An experimental study has been made to investigate the effect on wake flow and vortex shedding frequency by vortex stabilizer in Karman vortex type air flow sensor. The conditions investigated include 3 types of shapes and 3 types of separation distances of the vortex stabilizer. The phase averaged technique and smoke-wire flow visualization method are used to understand the detail information. The rolling up position of shear layer is fixed by the influence of the vortex stabilizer. Especially, the convex type vortex stabilizer has shown the more stable repeatability and linearity regarding the vortex shedding frequency compared to the other types.

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VORTEX STRUCTURE IN THE SCOUR HOLE BY GATE OPENING OF HYDRAULIC STRUCTURE

  • Kim, Jin-Hong;Choe, Jae-Wan
    • Water Engineering Research
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    • v.1 no.1
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    • pp.83-92
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    • 2000
  • Jet flow can occur by gate opening at downstream of a hydraulic structure such as weir of drainage gate. If the stream bed is not hard or the bed protection is not sufficient, vortex erosion occurs and a resulting scour hole will be formed due to the high shear stress of the jet flow. Once the scour hole is formed, a vortex occurs in ti and this vortex causes additional erosion. If this erosion continues and reaches to the hydraulic structure, it can undermine the bottom of the hydraulic structure and this will lead to failure of the structure itself. Thus, it is necessary to define the physical features of the vortex structure in the scour hole for the design of the bed protection. This study presents the turbulent vortex structure in the scour hole by the gate opening of the hydraulic structure. Characteristics of vortex motion, circulation, vortex scale and vortex were analyzed through experiments. Experimental results of the vortex velocity were compared with theoretical ones. From these, circulation and vortex scale were obtained with known values of inflow depth, inflow velocity and scale of scour hole

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Numerical Analysis of Tip Vortex Cavitation Behavior and Noise on Hydrofoil using Dissipation Vortex Model and Bubble Theory (소산이 고려된 보오텍스 모델과 버블 이론을 이용한 수중익 날개 끝 보오텍스 캐비테이션 거동 및 소음의 수치적 해석)

  • Park, Kwang-Kun;Seol, Han-Shin;Lee, Soo-Gab
    • Journal of the Society of Naval Architects of Korea
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    • v.43 no.2
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    • pp.177-185
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    • 2006
  • Cavitation is the dominant noise source of the marine vehicle. Of the various types of cavitation , tip vortex cavitation is the first appearance type of marine propeller cavitation and it generates high frequency noise. In this study, tip vortex cavitation behavior and noise are numerically investigated. A numerical scheme using Eulerian flow field computation and Lagrangian particle trace approach is applied to simulate the tip vortex cavitation on the hydrofoil. Vortex flow field is simulated by combined Moore and Saffman's vortex core radius equation and Sculley vortex model. Tip vortex cavitation behavior is analyzed by coupled Rayleigh-Plesset equation and trajectory equation. The cavitation nuclei are distributed and released in the vortex flow result. Vortex cavitation trajectories and radius variations are computed according to nuclei initial size. Noise is analyzed using time dependent cavitation bubble position and radius data. This study may lay the foundation for future work on vortex cavitation study and it will provide a basis for proper underwater propeller noise control strategies.

Numerical Calculation of the Far Field Acoustic Pressure from the Unsteady Motion of the Three-dimensional Vortex Filament (삼차원 와선의 비정상 거동에 의한 원거리 음압의 수치해석)

  • Ryu, Ki-Wahn;Lee, Duck-Joo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.6
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    • pp.942-950
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    • 1997
  • Far field acoustic pressure from the evolution and interaction of three-dimensional vortex filament is calculated numerically. A vortex ring is a typical example of the three-dimensional vortex filament. An elliptic vortex ring emits a strong sound signal due to significant distortion and stretching of the vortec filament. The far field acoustic pressure is linearly dependent on the third time derivatives of the vortex positions. A numerical scheme of high resolution is employed to describe in detail the elliptic vortex ring motions which ar highly nonlinear. Descretized vortex filaments are interpolated by using a parametric blending function to remove a possible numerical instability. The distorted vortex filament, owing to the self-induced and the induced velocity from the other vortex segments, is redistributed at each time step. The accuracy and efficiency of the scheme are validated by comparisons with the analytic solution of circular vortex ring interaction.

Vortex Interaction Characteristics of a Delta Wing/LEX (삼각날개/LEX에서의 와류 상호작용 특성)

  • 이기영;손명환
    • Journal of the Korea Institute of Military Science and Technology
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    • v.5 no.3
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    • pp.77-86
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    • 2002
  • An experimental study of the vortex interaction characteristics of a delta wing/LEX configuration was conducted in a wind tunnel using the micro water droplet and laser beam sheet visualization technique. The main focus of this study was to analyze the effect of the angle of attack and sideslip angle on the vortex interaction and vortex breakdown. These tests were accomplished at angles of attack between $16^{\circ}$ and $28^{\circ}$ and sideslip angle between $0^{\circ}$ and $-15^{\circ}$ at free-stream velocity of 6.2 m/s. Flow visualization data provide a description of the vortex interaction between LEX and wing vortices, and of the vortex breakdown. The introduction of LEX vortex stabilized the vortical flow, and delayed the vortex breakdown up to higher angle of attack. The vortex interaction and breakdown was promoted on the windward side, whereas they are suppressed on the leeward side.

VORTEX SHEAR VELOCITY AND ITS EROSION IN THE SCOUR HOLE

  • Lee, Hong-Sik;Kim, Jin-Hong;Lee, Sam-Hee
    • Water Engineering Research
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    • v.1 no.4
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    • pp.259-266
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    • 2000
  • Scour hole is formed due to the high shear stress of the jet flow at the outlet of a hydraulic structure and vortex erosion occurs in the scour hole. It is important to determine the amount of vortex erosion occurs in the scour hole. It is important to determine the amount of vortex erosion for the design of bed protection. If the vortex erosion continues and reaches to the hydraulic structure, it causes the deformation of the structure itself. To obtain the amount of the vortex erosion, it is necessary to determine the shear velocity of the line vortex in the scour hole was derived by the theory of energy conservation and found to be related to the upstream overflow velocity. The amount of vortex erosion from the scour hole was obtained using entrainment equation for given value of shear velocity. For a design purpose, if the flow velocity at the end of an apron and the properties of bed material are given, the amount of vortex erosion was obtained.

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