• Title/Summary/Keyword: Compressible Flow

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Unstructured Pressure Based Method for All Speed Flows (전 속도영역 유동을 위한 비정렬격자 압력기반해법)

  • Choi, Hyung-Il;Lee, Do-Hyung;Maeng, Joo-Sung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.11
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    • pp.1521-1530
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    • 2002
  • This article proposes a pressure based method for predicting flows at all speeds. The compressible SIMPLE algorithm is extended to unstructured grid framework. Convection terms are discretized using second-order scheme with deferred correction approach. Diffusion term discretization is based on structured grid analogy that can be easily adopted to hybrid unstructured grid solver. This method also uses node centered scheme with edge based data structure for memory and computing time efficiency of arbitrary grid types. Both incompressible and compressible benchmark problems are solved using the above methodology. The demonstration of this method is extended to slip flow problem that has low Reynolds number but compressibility effect. It is shown that the proposed method can improve efficiency in memory usage and computing time without losing any accuracy.

Calculation of Rotor-Stator Interactions Using a Low Reynolds Number Turbulence Model (저레이놀즈수 난류모델을 사용한 정익-동익 상호작용 해석)

  • Choi, Chang Ho;Yoo, Jung Yul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.10
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    • pp.1229-1239
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    • 1999
  • A computational study on unsteady compressible flows has been performed by adopting a low Reynolds number $k-{\omega}$ turbulence model in conjunction with dual time stepping scheme. An explicit four-stage Runge-Kutta scheme for the Navier-Stokes equations and an approximate factorization scheme for the $k-{\omega}$ turbulence model equations are used. Computational results obtained for blade surface pressure distributions in the process of rotor-stator interaction in a turbine stage are in good agreement with extant experimental data. The effects of the wake from the stator on the boundary-layer transition over the rotor blade surface are discussed by showing that high intensity turbulence of the stator wake induces an early transition.

A Study of Convergence Enhancement Using Preconditioning Methods at Two Dimensional Compressible Low Speed Flows (저속 압축성 유동에서 예조건화 방법을 이용한 수렴성 증진에 대한 연구)

  • Lee J. E.;Park S. H.;Kwon J. H.
    • 한국전산유체공학회:학술대회논문집
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    • 2004.10a
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    • pp.7-14
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    • 2004
  • It is well known that preconditioning methods are efficient for convergence acceleration at compressible low Mach number flows. In this study, the original Euler equations and three preconditioners nondimensionalized differently are implemented in two dimensional inviscid bump flows using the 3rd order MUSCL and DADI schemes as flux discretization and time integration respectively. The multigrid and local time stepping methods are also used to accelerate the convergence. The test case indicates that a properly modified local preconditioning technique involving concepts of a global preconditioning one produces Mach number independent convergence. Besides, an asymptotic analysis for properties of preconditioning methods is added.

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Numerical Investigation of Sound Generation in the Flow Past a Cavity (공동을 지나는 비정상 유동에 의한 소음 방사 해석)

  • Heo, Dae-Nyoung;Lee, Duck-Joo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2000.06a
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    • pp.104-109
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    • 2000
  • The modes of oscillation and radiated acoustic fields of compressible flows over open cavities are investigated computationally. The compressible Navier-Stokes equations are solved for two-dimensional cavities with laminar boundary layers upstream. The high-order and high-resolution numerical schemes are used for the evaluation of spatial derivatives and the time integration. Physically correct numerical boundary conditions are implemented to produce time-accurate solutions in the whole computation domain. The computational domain is large enough to directly resolve a portion of the radiated acoutic field. The results show a transition from a shear layer mode, for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear layer mode is well characterized by Rossiter modes and these oscillations lead to intense upstream acoustic radiation dominated by a single frequency. The wake mode is characterized instead by a large-scale vortex shedding. Acoustic radiation is more intense, with multiple frequencies present.

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Multiple Unstable Modes in the Reacting Mixing Layer (반응혼합층의 복수 불안정성 모드)

  • Sin, Dong-Sin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.2
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    • pp.616-623
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    • 1996
  • This paper investigates the linear stability of reacting mixing layers with special emphasis on the existence of multiple unstable modes. The governing equations for laminar flows are from two-dimensional compressible boundary-layer equations. The chemistry is a finite rate single step irreversible reaction with Arrhenius kinetics. For the incompressible reacintg mixing layer with variable density. A necessary condition for instability has been derived. The condition requires that the angular momentum, not the vorticity, to have a maximum in the flow domain. New inflectional modes of instability are found to exist in the outer part of the mixing layer. For the compressible reacting mixing layer, supersonic unstable modes may exist in the abscence of a generalized inflection point. The outer modes at high Mach numbers in the reacting mixing layer are continuations of the inflectional modes of low Mach number flows. However, the generalized inflection point is less important at supersonic flows.

A Computational Study of the Mach Disk in Under-Expanded Moist Air Jet (부족팽창 습공기 제트의 마하디스크 거동에 관한 수치적 연구)

  • Baek, Seung-Cheol;Kwon, Soon-Bum;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.514-519
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    • 2003
  • A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

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A Computational Study of the Mach Disk in Under-Expanded Moist Air Jet (부족팽창 습공기 제트의 마하디스크 거동에 관한 수치적 연구)

  • Baek, Seung-Cheol;Kwon, Soon-Bum;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.562-567
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    • 2003
  • A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

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A Compression Behavior of Semi-Solid Material and Finite Element Analysis Considering Flow of Liquid Phase (반응용재료의 압축거동 및 액상의 유동을 고려한 유한요소해석)

  • Gang, Chung-Gil;Yun, Jong-Hun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.12
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    • pp.3715-3727
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    • 1996
  • Compression behavior of semi-solid aluminum alloys with controlled solid fractions was investigated in the present study. The stress and strain relationships were obtained from the compression test. Variations of the solid fraction distribution and the material behaviour were investigated for various friction coeffieiants and die speedsd. For a finite element analysis, the semi-solid material was described by a compressible regid viscoplastic model for the solid region and darcy's law for the liquid region. The computed results were compared with experimental data for the validity of the yield criteria.

A Numerical Simulation on the Process of Diaphragm Opening in Shock Tube Flows (충격파관 유동의 파막과정에 관한 수치 시뮬레이션)

  • Shin, Choon-Sik;Jeong, June-Chang;Suryan, Abhilash;Kim, Heuy-Dong
    • Journal of the Korean Society of Propulsion Engineers
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    • v.13 no.1
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    • pp.27-33
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    • 2009
  • Shock tube flow measurement has been often hampered a finite opening time of diaphragm, but there is no systematic work to investigate its effect on the shock tube flow. In the present study, both the experimental and computational works have been performed on the shock tube flows at low pressure ratios. The computational analysis has been performed using the two-dimensional, unsteady, compressible Navier-Stokes equations, based upon a TVD MUSCL finite difference scheme. It is known that the present computational results reproduce the experimental data with good accuracy and simulate successfully the process of diaphragm opening as a function of time. The concept of an imaginary center is introduced to quantify the non-centered expansion wave due to a finite opening time of diaphragm. The results obtained show that the diaphragm opening time is reduced as the initial pressure ratio of shock tube increases, leading to the effect of a finite opening time of diaphragm to be more remarkable at low pressure ratios.

Design Characteristics of Non-Contact Type Seal for High Speed Spindle (고속주축용 비접촉 시일의 형상설계 연구)

  • 나병철;전경진;한동철
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.4
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    • pp.56-63
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    • 1997
  • Sealing of lubricant-air mixture in the high performance machining center is one of most the important characteristics to carry out enhanced lubrication. High speed spindle requires non-contact type of sealing mechanism. Evaluating an optimum seal design to minimize leakage is concerned in the aspect of flow control. Effect of geometry and leakage path are evaluated according to variation of sealing geometry. Velocity, pressure, turbulence intensity of profile is calculated to find more efficient geometry and variables. This offers a methodological way of enhancement seal design for high speed spindle. The working fluid is regarded as two phases that are mixed flow of oil phase and air phase. It is more reasonable to simulate an oil jet or oil mist type high speed spindle lubrication. Turbulence and compressible flow model are used to evaluate a flow characteristic. This paper considers a design effect of sealing capability of non- contact type seals for high speed spindle and analyzes leakage characteristics to minimize a leakage 7 on the same sealing area.

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