• Title/Summary/Keyword: Taylor Vortex

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A Proposal for Diesel Spray Model Using a TAB Breakup Model and Discrete Vortex Method

  • Yeom, Jeong-Kuk;Lee, Myung-Jun;Chung, Sung-Sik;Ha, Jong-Yul;Jiro Senda;Hajime Fujimoto
    • Journal of Mechanical Science and Technology
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    • v.16 no.4
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    • pp.532-548
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    • 2002
  • A hybrid model consisting of a modified TAB (Taylor Analogy Breakup) model and DVM (Discrete Vortex Method) is proposed for numerical analysis of the evaporating spray phenomena in diesel engines. The simulation process of the hybrid model is divided into three steps. First, the droplet breakup of injected fuel is analyzed by using the modified TAB model. Second, spray evaporation is calculated based on the theory of Siebers'liquid length. The liquid length analysis of injected fuel is used to integrate the modified TAB model and DVM. Lastly, both ambient gas flow and inner vortex flow of injected fuel are analyzed by using DVM. An experiment with an evaporative free spray at the early stage of its injection was conducted under in-cylinder like conditions to examine an accuracy of the present hybrid model. The calculated results of the gas jet flow by DVM agree well with the experimental results. The calculated and experimental results all confirm that the ambient gas flow dominates the downstream diesel spray flow.

Application of a discrete vortex method for the analysis of suspension bridge deck sections

  • Taylor, I.J.;Vezza, M.
    • Wind and Structures
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    • v.4 no.4
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    • pp.333-352
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    • 2001
  • A two dimensional discrete vortex method (DIVEX) has been developed to predict unsteady and incompressible flow fields around closed bodies. The basis of the method is the discretisation of the vorticity field, rather than the velocity field, into a series of vortex particles that are free to move in the flow field that the particles collectively induce. This paper gives a brief description of the numerical implementation of DIVEX and presents the results of calculations on a recent suspension bridge deck section. The predictions for the static section demonstrate that the method captures the character of the flow field at different angles of incidence. In addition, flutter derivatives are obtained from simulations of the flow field around the section undergoing vertical and torsional oscillatory motion. The subsequent predictions of the critical flutter velocity compare well with those from both experiment and other computations. A brief study of the effect of flow control vanes on the aeroelastic stability of the bridge is also presented and the results from DIVEX are shown to be in accordance with previous analytical and experimental studies. In conclusion, the results indicate that DIVEX is a very useful design tool in the field of wind engineering.

Simulation of viscous and inviscid rayleigh-taylor instability with surface tension by using MPS

  • Kim, Kyung Sung;Kim, Moo Hyun
    • Ocean Systems Engineering
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    • v.8 no.2
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    • pp.167-182
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    • 2018
  • RTI (Rayleigh-Taylor instability) is investigated by a multi-liquid MPS (Moving Particle Semi-implicit) method for both viscous and inviscid flows for various density differences, initial-disturbance amplitudes, viscosities, and surface tensions. The MPS simulation can be continued up to the late stage of high nonlinearity with complicated patterns and its initial developments agree well with the linear theoretical results. According to the relevant linear theory, the difference between inviscid and viscous fluids is the rising velocity at which upward-mushroom-like RTI flow with vortex formation is generated. However, with the developed MPS program, significant differences in both growing patters and developing speeds are observed. Also, more dispersion can be observed in the inviscid case. With larger Atwood (AT) number, stronger RTI flows are developed earlier, as expected, with higher potential-energy differences. With larger initial disturbances, quite different patterns of RTI-development are observed compared to the small-initial-disturbance case. If AT number is small, the surface tension tends to delay and suppress the RTI development when it is sufficiently large. Interestingly, at high AT number, the RTI-suppressions by increased surface tension become less effective.

Effect of Taylor Vortex on Cake Formation in Membrane Filtration (막여과에서 테일러 와류가 케이크 형성에 미치는 영향)

  • 박원철;김현우;최창균;박진용;김재진
    • Proceedings of the Membrane Society of Korea Conference
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    • 1997.04b
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    • pp.52-55
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    • 1997
  • 여과가 진행됨에 따라 막의 표면에서 발생하여 여과선속을 저하시키는 케이크층의 형성은 막을 이용한 고-액 분리공정에서 발생하는 가장 큰 문제점의 하나로서 이는 막 분리공정의 경제성을 좌우하는 중요한 인자가 된다. 이러한 문제점을 극복하기 위하여 유체와 막 사이의 상대속도를 증가시켜 여과속도를 향상시키는 십자흐름 여과, 즉 CFF(crossflow filtration)에 대한 연구가 활발히 진행되어 왔다. 그러나 이러한 심자흐름 여과에서도 막과 유체 사이의 상대속도의 증가에 한계가 있고 또한, 막의 기공보다 작은 입자가 막의 기공 내에 침투하여 막을 오염시키는 현상을 예측하기 어렵기 때문에 여과기의 설계에 있어서 많은 문제점이 발생하고 있다. 이에 오염된 막을 재생시키기 위하여 기계적.화학적인 여러 가지 방법들이 개발되고 여과선속을 향상시키는 방법이 꾸준히 연구되어 분리막 기술의 경제성을 향상시켜 왔다. 본 연구에서는 매우 안정된 유동의 하나로서 막 표면의 전단력을 향상시키는 데에 효과가 있다고 알려진 Taylor와류를 응용한 회전막 여과기를 사용하여 여러 가지 크기의 입자에 대한 여과실험을 수행함으로써 이러한 유동이 케이크의 형성에 미치는 영향을 살펴보았다. 또한 여과선속에 영향을 미치는 여러 매개인자를 알아보고 실험결과를 간단한 모델식에 적용해 봄으로써 막의 저항을 예측할 수 있는 모델식으로의 개선 방향을 제시하고자 한다.

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A study on temporal accuracy of OpenFOAM

  • Lee, Sang Bong
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.9 no.4
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    • pp.429-438
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    • 2017
  • Cranke-Nicolson scheme in native OpenFOAM source libraries was not able to provide 2nd order temporal accuracy of velocity and pressure since the volume flux of convective nonlinear terms was 1st accurate in time. In the present study the simplest way of getting the volume flux with 2nd order accuracy was proposed by using old fluxes. A possible numerical instability originated from an explicit estimation of volume fluxes could be handled by introducing a weighting factor which was determined by observing the ratio of the finally corrected volume flux to the intermediate volume flux at the previous step. The new calculation of volume fluxes was able to provide temporally accurate velocity and pressure with 2nd order. The improvement of temporal accuracy was validated by performing numerical simulations of 2D Taylor-Green vortex of which an exact solution was known and 2D vortex shedding from a circular cylinder.

Flow Characteristics of Inclined Turbulent Jet Issuing into Turbulent Boundary Layer Developing on Concave and Convex Surfaces (오목면 및 볼록면에 존재하는 난류경계층유동과 경사지게 분사되는 난류제트의 유동특성)

  • 이상우;이준식;이택식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.2
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    • pp.302-312
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    • 1992
  • Three dimensional velocity measurements of a 35.deg. inclined jet issuing into turbulent boundary layer on both concave and convex surfaces have been conducted. To investigate solely the effect of each curvature on the flow field, streamwise pressure variations are minimized by adjusting the shape of the opposite wall in the curved region. From the measured velocity components, streamwise mean vorticities are calculated to determine jet-crossflow interface. The results on convex surface show that the injected jet is separated from the wall and the bound vortex maintains its structure far downstream. On concave surface, the secondary flow in the jet cross-sections are enhanced and in some downstream region from the jet exit, the flow on the concave surface has been developed to Taylor-Gortler vortices

Experimental Study on the Vortex Flow in a Concentric Annulus with a Rotating Inner Cylinder

  • Kim, Young-Ju;Hwang, Young-Kyu
    • Journal of Mechanical Science and Technology
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    • v.17 no.4
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    • pp.562-570
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    • 2003
  • This experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and of 0.4% aqueous solution of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0~600 rpm. Also, the visualization of vortex flows has been performed to observe the unstable waves. The results of present study reveal the relation of the bulk flow Reynolds number Re and Rossby number Ro with respect to the skin friction coefficients. In somehow, they show the existence of flow instability mechanism. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and. then, it gradually approach to zero for the turbulent flow regime. Consequently, the critical (bulk flow) Reynolds number Re$\_$c/ decreases as the rotational speed increases. Thus, the rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.

The Analysis of Two-phase Flow in a Lean Direct Injection Gas-turbine Combustor (희박연료 직접분사(Lean Direct Injection) 가스터빈 연소기의 이상유동 분석)

  • Lee, Kyobin;Kim, Jong-Chan;Sung, Hong-Gye
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.47 no.3
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    • pp.204-211
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    • 2019
  • The analysis on two-phase flow in a Lean Direct Injection(LDI) combustor has been investigated. Linearized Instability Sheet Atomization(LISA) and Aerodynamically Progressed Taylor Analogy Breakup(APTAB) breakup models are applied to simulate the droplet breakup process in hollow-cone spray. Breakup model is validated by comparing penetration length and Sauter Mean Diameter(SMD) of the experiment and simulation. In the LDI combustor, Precessing Vortex Core(PVC) is developed by swirling flow and most droplets are atomized along the PVC. It has been confirmed that all droplets have Stokes number less than 1.0.

A Study on Numerical Modeling of the Induced Heat to Gaseous Flow inside the Mixing Area of Ammonia SCR System in Diesel Nox After-treatment Devices (디젤 NOx 후처리 장치에 있어서 암모니아 SCR 시스템 혼합영역 내 가스유동의 유입열 수치모델링에 관한 연구)

  • Bae, Myung-Whan;Syaiful, Syaiful
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.11
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    • pp.897-905
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    • 2008
  • Selective catalytic reduction(SCR) is known as one of promising methods for reducing $NO_x$ emissions in diesel exhaust gases. $NO_x$ emissions react with ammonia in the catalyst surface of SCR system at working temperature of catalyst. In this study, to raise the reacting temperature when the exhaust gas temperature is too low, a heater is located at the bottom of SCR reactor. At an ambient temperature, ammonia is radially injected perpendicular to the exhaust gas flow at inlet pipe and uniformly mixed in the mixing area after being impinged against the wall. To predict the turbulent model inside the mixing area of SCR system, the standard ${\kappa}\;-\;{\varepsilon}$ model is applied. This work investigates numerically the effects of induced heat on the gaseous flow. The results show that the Taylor-$G{\ddot{o}}rtler$ type vortex is generated after the gaseous flow impinges the wall in which these vortices influence the temperature distribution. The addition of heat disturbs the flow structure in bottom area and then stretching flow occurs. Vorticity strand is also formed when heat is continuously increased. Constriction process takes place, however, when a further heat input over a critical temperature is increased and finally forms shed vortex which is disconnected from the vorticity strand. The strong vortex restricts the heat transport in the gaseous flow.

An Experimental Study of Turbulent Uniform Shear Flow in a Nearly Two-Dimensional $90^{\circ}$ Curved Duct (I) - Mean Flow Field- (2차원 $90^{\circ}$ 곡관에서 균일전단류의 특성에 대한 실험적 연구 (1) -평균유동장-)

  • 임효재;성형진;정명균
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.3
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    • pp.834-845
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    • 1995
  • An experimental study is made in a nearly two-dimensional 90.deg. curved duct to investigate the effects of interaction between streamline curvature and mean strain on turbulence. The initial shear at the entrance to the curved duct is varied by an upstream shear generator to produce five different shear conditions ; a uniform flow (UF), a positive weak shear (PW), a positive strong shear(PS), a negative weak shear (NW) and a negative strong shear(NS). With the mean field data of the case UF, variations of the momentum thickness, the shape factor and the skin friction over the convex(inner) surface and the concave (outer) surface are scrutinized quantitatively in-depth. It is found that, while the pressure loss due to curvature is insensitive to the inlet shear rates, the distributions of wall static pressure along both convex and concave surfaces are much influenced by the inlet shear rates.