• Title/Summary/Keyword: $k-{\varepsilon}$ turbulence model

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Numerical Design and Performance Prediction of Low Specific Speed Centrifugal Pump Impeller

  • Yongxue, Zhang;Xin, Zhou;Zhongli, Ji;Cuiwei, Jiang
    • International Journal of Fluid Machinery and Systems
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    • v.4 no.1
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    • pp.133-139
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    • 2011
  • In this paper, Based on Two-dimensional Flow Theory, adopting quasi-orthogonal method and point-by-point integration method to design the impeller of the low specific speed centrifugal pump by code, and using RANS (Reynolds Averaged N-S) Equation with a standard k-${\varepsilon}$ two-equation turbulence model and log-law wall function to solve 3D turbulent flow field in the impeller of the low specific speed pump. An analysis of the influences of the blade profile on velocity distributions, pressure distributions and pump performance and the investigation of the flow regulation pattern in the impeller of the centrifugal pump are presented. And the result shows that this method can be used as a new way in low speed centrifugal pump impeller design.

A Study on the Nozzle-Rotor Interactions of Partial Admission Supersonic Turbines

  • Seong, Young-sik;Han, Seong-hoon;Kim, Kui-soon;Park, Chang-kyu
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2004.03a
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    • pp.391-397
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    • 2004
  • The performance characteristics of partial admission supersonic turbines are analyzed by using the commercial CFD program FLUENT6.0. The governing equations were discretized with Euler implicit method in time and 2nd-order upwind scheme of FVM in space. The k-$\varepsilon$ turbulence model was utilized to describe the turbulent flow field. In order to investigate the nozzle--rotor interactions and the effect of partial admission, the flows in supersonic turbine rotor cascades with a nozzle are computed. Extensive computations of partial admission supersonic turbines provide the shock structures and flow patterns in the nozzle and rotor. It is clearly shown that the nozzle flow is highly affected by the shocks or expansion waves propagated from the rotor leading edge. And the rotor flow is also affected by the shocks or wakes originated from the nozzle.

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Effectiveness of Ventilation Control in a Dry Room with a Heat and Moisture Source

  • Lee, Kwan-Soo;Lim, Kwang-Ok;Ahn, Kang-Ho;Jung, Young-Sick
    • International Journal of Air-Conditioning and Refrigeration
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    • v.9 no.4
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    • pp.1-9
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    • 2001
  • The temperature and moisture distributions in a dry room with a heat and moisture source -i.e., workers- are studied numerically by using a standard $k-\varepsilon$ turbulence model. In order to evaluate the effectiveness of heat and moisture ventilation inside the room, the heat removal capacity and the moisture exhaust efficiency are introduced. The effectiveness of ventilation control is analyzed by evaluating the temperature and humidity distributions in the room quantitatively. It is found that the mean absolute humidity inside the room is almost constant regardless of the models and the heat generation rates in this study range. This results from the fact that the moisture generation by the workers was relatively small. Through the modification of the design, 40% improvement in critical decay time was achieved.

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A Computational Study of the Vortical Flows over a Delta Wing At High-Angle of Attack (고영각의 델타익에서 발생하는 와유동에 관한 수치해석적 연구)

  • Kim Hyun-Sub;Kweon Yong-Hun;Kim Heuy-Dong;Shon Myong-Hwan
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.795-798
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    • 2002
  • This paper dispicts the vortical flow characteristics over a delta wing using a computational analysis for the purpose of investigating and visualizing the effect of the angle of attack and fee stream velocity on the low-speed delta wing aerodynamics. Computations are applied to the full, 3-dimensional, compressible, Navier-Stokes Equations. In computations, the free stream velocity is changed between 20m/s and 60m/s and the angle of attack of the delta wing is changed between $16^{\circ}\;and\;28^{\circ}$. For the correct prediction of the major features associated with the delta wing vortex flows, various turbulence models are tested. The standard $k-{\varepsilon}$ turbulence model predict well the vertical flows over the delta wing. Computational results are compared with the previous experimental ones. It is found that the present CFD results predict the vortical flow characteristics over the delta wing, and with an increase in the free steam velocity, the leading edge vortex moves outboard and its streangth is increased.

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Conceptual design and numerical simulations of a vertical axis water turbine used for underwater mooring platforms

  • Wenlong, Tian;Baowei, Song;Zhaoyong, Mao
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.5 no.4
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    • pp.625-634
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    • 2013
  • Energy is a direct restriction to the working life of an underwater mooring platform (UMP). In this paper, a vertical axis water turbine (VAWT) is designed to supply energy for UMPs. The VAWT has several controlled blades, which can be opened or closed by inside plunger pumps. Two-dimensional transient numerical studies are presented to determine the operating performance and power output of the turbine under low ocean current velocity. A standard k-${\varepsilon}$ turbulence model is used to perform the transient simulations. The influence of structural parameters, including foil section profile, foil chord length and rotor diameter, on the turbine performance are investigated over a range of tip-speed-ratios (TSRs). It was found that turbine with three unit length NACA0015 foils generated a maximum averaged coefficient of power, 0.1, at TSR = 2.

Analysis on Characteristic of Pressure Fluctuation in Hydraulic Turbine with Guide Vane

  • Shi, FengXia;Yang, JunHu;Wang, XiaoHui
    • International Journal of Fluid Machinery and Systems
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    • v.9 no.3
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    • pp.237-244
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    • 2016
  • An unsteady three-dimensional simulation based on Reynolds time-averaged governing equation and RNG $k-{\varepsilon}$ turbulence model, was presented for pump-as-turbine, the pressure fluctuation characteristic of hydraulic turbine with guide vane was obtained. The results show that the time domains of pressure fluctuation in volute change periodically and have identical cycles. In volute tongue and inlet pressure fluctuations are light, while in dynamic and static coupling interface pressure fluctuations are serious; In impeller blade region the pressure fluctuation of pressure surface are lighter than that of suction surface. The dominant frequencies of pressure fluctuation concentrate in low frequency region, and concentrate within 2 times of the blade passing frequency.

A Numerical Study of the Effects of Piston Head Configurations on Stratified Mixture Formation in Gasoline Direct-injection Engines

  • Cha, Kyung-Se;Park, Chan-Guk;Tomoyuki Wakisaka
    • Journal of Mechanical Science and Technology
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    • v.16 no.4
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    • pp.557-563
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    • 2002
  • In this paper, the characteristics of flow and spray motions affected by from piston head configurations were investigated numerically. Calculations were carried out from intake process to the end of compression. GTT (Generalized Tank and Tube method) code, which includes a third order upwind Chakravarthy-Osher TVD scheme and k-$\varepsilon$ turbulence model with fuel spray analysis was used for the calculations. As a results, piston heads with smaller radii of curvature were found to give stronger reverse tumble than those with larger radii of curvature. Similar results are shown in the convection and diffusion of fuel sprays.

Numerical Simulation of Chemically Reacting Shock Wave-Turbulent Boundary Layer Interactions (화학반응이 있는 난류경계층과 충격파의 상호작용에 대한수치해석)

  • Mun, Su-Yeon;Lee, Chung-Won;Son, Chang-Hyeon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.3
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    • pp.375-383
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    • 2002
  • The flowfield of transverse jet in a supersonic air stream subjected to shock wave turbulent boundary layer interactions is simulated numerically by Generalized Taylor Galerkin(GTG) finite element methods. Effects of turbulence are taken into account with a two-equation (k-$\varepsilon$) model with a compressibility correction. Injection pressures and slot widths are varied in the present study. Pressure, separation extents, and penetration heights are compared with experimental data. Favorable comparisons with experimental measurements are demonstrated.

Flow Control Analysis of S-duct Diffuser Inlet

  • Lian, Xiaochun;Zhang, Lifen;Wu, Dingyi
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2008.03a
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    • pp.157-159
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    • 2008
  • An numerical investigation of the flow characteristics inside a diffusing S-duct inlet with and without vortex generators(VGs) was conducted. The primary discussion herein focuses on development of secondary flow in the S-duct with and without VGs, pressure recovery and distortion at the exit are also discussed. Full three-dimensional Navier-Stokes equations are solved using finite volume method and $k-\varepsilon$ turbulence model is employed. In order to validate the credibility of the numerical methods, predicted results of surface pressure are compared with flight test for the S-duct inlet without VGs, and it shows fairly good agreement. The result shows that VGs alter the flow characteristics in the S-duct and are effective in reducing distortion and ineffective in improving pressure recovery.

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A Numerical Study on Flows Over Two-Dimensional Simplified Vehicle-Like Body (단순화된 2차원 자동차형 물체주위 유동에 관한 수치해석적 연구)

  • 강신형;이영림;유정열;이택시;김응서
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.2
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    • pp.277-286
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    • 1989
  • Turbulent flows around two-dimensional vehicle-like bodies in ground proximity are numerically simulated. The Reynolds averaged Navier-Stokes equations with a k-.epsilon. turbulence model are numercally solved, and a body-fitted coordinate system is used. It is shown that the simulation is acceptable in comparison with limitted data measured in the wind-tunnel. According to numerical simulations, drag coefficients are under-estimated and lift coefficients are over-estimated during the model test in the wind-tunnel if the ground is fixed. Such ground effects are reduced as Reynolds number is increased. Reducing the gap between the vehicle and the ground make drag coefficients smaller and lift coefficients larger. The changes in static pressure distributions on the bottom and the rear surface play dominent roles in determination of the drag and the lift of the body in ground proximity. Drag component less than 10% of the total amount is contributed by skin-frictions. When the slant-angle of the body is reduced, the drag shows its minimum value and the lift shows its maximum value at about 22 degree.