• Title/Summary/Keyword: boundary condition

Search Result 1,995, Processing Time 0.213 seconds

A Study on the Effect of Inlet Boundary Condition on Flow Characteristics of a Supersonic Turbine

  • Shin, Bong-Gun;Kim, Kui-Soon;Kim, Jin-Han
    • International Journal of Aeronautical and Space Sciences
    • /
    • v.6 no.1
    • /
    • pp.1-7
    • /
    • 2005
  • The inlet boundary condition of computations about the supersonic turbine flow is commonly applied as far-field inlet boundary condition with specified velocity. However, the inflow condition of supersonic turbine is sometimes affected by the shocks or expansion waves propagated from leading edges of blade. These shocks and expansion waves alter the inlet boundary condition. In this case, the inlet boundary condition can not be specified Therefore, in this paper, numerical analyses for three different inlet conditions - fa-field inlet boundary condition, inlet boundary condition with a linear nozzle and inlet boundary condition with a converging-diverging nozzle - have been performed and compared with experimental results to solve the problem. It is found that the inlet condition with a linear nozzle or a converging-diverging nozzle can prevent changing of inlet boundary condition, and thus predict more accurately the supersonic flow within turbine cascade than a far-field inlet boundary condition does.

On the Reconstruction of Pinwise Flux Distribution Using Several Types of Boundary Conditions

  • Park, C. J.;Kim, Y. H.;N. Z. Cho
    • Nuclear Engineering and Technology
    • /
    • v.28 no.3
    • /
    • pp.311-319
    • /
    • 1996
  • We reconstruct the assembly pinwise flux using several types of boundary conditions and confirm that the reconstructed fluxes are the same with the reference flux if the boundary condition is exact. We test EPRI-9R benchmark problem with four boundary conditions, such as Dirichlet boundary condition, Neumann boundary condition, homogeneous mixed boundary condition (albedo type), and inhomogeneous mixed boundary condition. We also test reconstruction of the pinwise flux from nodal values, specifically from the AFEN [1, 2] results. From the nodal flux distribution we obtain surface flux and surface current distributions, which can be used to construct various types of boundary conditions. The result show that the Neumann boundary condition cannot be used for iterative schemes because of its ill-conditioning problem and that the other three boundary conditions give similar accuracy. The Dirichlet boundary condition requires the shortest computing time. The inhomogeneous mixed boundary condition requires only slightly longer computing time than the Dirichlet boundary condition, so that it could also be an alternative. In contrast to the fixed-source type problem resulting from the Dirichlet, Neumann, inhomogeneous mixed boundary conditions, the homogeneous mixed boundary condition constitutes an eigenvalue problem and requires longest computing time among the three (Dirichlet, inhomogeneous mixed, homogeneous mixed) boundary condition problems.

  • PDF

AN UNSTRUCTURED STEADY COMPRESSIBLE NAVIER-STOKES SOLVER WITH IMPLICIT BOUNDARY CONDITION METHOD (내재적 경계조건 방법을 적용한 비정렬 격자 기반의 정상 압축성 Navier-Stokes 해석자)

  • Baek, C.;Kim, M.;Choi, S.;Lee, S.;Kim, C.W.
    • Journal of computational fluids engineering
    • /
    • v.21 no.1
    • /
    • pp.10-18
    • /
    • 2016
  • Numerical boundary conditions are as important as the governing equations when analyzing the fluid flows numerically. An explicit boundary condition method updates the solutions at the boundaries with extrapolation from the interior of the computational domain, while the implicit boundary condition method in conjunction with an implicit time integration method solves the solutions of the entire computational domain including the boundaries simultaneously. The implicit boundary condition method, therefore, is more robust than the explicit boundary condition method. In this paper, steady compressible 2-Dimensional Navier-Stokes solver is developed. We present the implicit boundary condition method coupled with LU-SGS(Lower Upper Symmetric Gauss Seidel) method. Also, the explicit boundary condition method is implemented for comparison. The preconditioning Navier-Stokes equations are solved on unstructured meshes. The numerical computations for a number of flows show that the implicit boundary condition method can give accurate solutions.

The Experimental Method to Identify The Boundary Condition of Vibrating Structure (진동 구조물의 경계조건을 실험적으로 구하는 방법)

  • Kim, Young-Ju;Kim, Yang-Hann
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
    • /
    • /
    • pp.525-530
    • /
    • 2000
  • The vibration shape of the structure with arbitrary boundary condition under excitation is determined by the governing equation and the boundary condition and driving force. In this paper, driving point impedance that is defined by the ratio of the driving force at one point to the velocity of that point is selected as a measure to identify the boundary condition. First, this paper deals with a string with arbitrary boundary condition. It is selected because of its simplicity, but generality of which exhibits the desired physical phenomena. Particularly the relation among the driving point impedance, the boundary condition and the vibration shape is dealt as a primary step to identify the boundary condition by using the driving point impedance.

  • PDF

Effect of Boundary Condition History on the Symmetry Breaking Bifurcation of Wall-Driven Cavity Flows

  • Cho, Ji-Ryong
    • Journal of Mechanical Science and Technology
    • /
    • v.19 no.11
    • /
    • pp.2077-2081
    • /
    • 2005
  • A symmetry breaking nonlinear fluid flow in a two-dimensional wall-driven square cavity taking symmetric boundary condition after some transients has been investigated numerically. It has been shown that the symmetry breaking critical Reynolds number is dependent on the time history of the boundary condition. The cavity has at least three stable steady state solutions for Re=300-375, and two stable solutions if Re>400. Also, it has also been showed that a particular solution among several possible solutions can be obtained by a controlled boundary condition.

Numerical Simulation of Thermal Lattice Boltzmann Model with a Modified In-Ternal Energy Non-Equilibrium First-Order Extrapolation Boundary Condition (수정된 내부 에너지 비평형 1차 외삽 경계조건을 적용한 열 유동 격자 볼츠만 모델에 관한 수치적 연구)

  • Jeong, Hae-Kwon;Kim, Lae-Sung;Lee, Hyun-Goo;Lee, Jae-Ryong;Ha, Man-Yeong
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.31 no.7
    • /
    • pp.620-627
    • /
    • 2007
  • In this paper, we adapt a modified internal energy non-equilibrium first-order extrapolation thermal boundary condition to the thermal lattice Boltzmann model (TLBM). This model is the double populations approach to simulate hydrodynamic and thermal fields. The bounce-back boundary condition which is a traditional boundary condition of lattice Boltzmann method has only a first order in numerical accuracy at the boundary and numerical instability. A non-equilibrium first-order extrapolation boundary condition has been verified to be of better numerical stability than the bounce-back boundary condition and this boundary condition is proved to be of second-order accuracy for the flat boundaries. The two-dimensional natural convection flow in a square cavity with Pr=0.71 and various Rayleigh numbers are simulated. The results are found to be in good agreement with those of previous studies.

Numerical Analysis of the Slip Velocity and Temperature-Jump in Microchannel Using Langmuir Slip Boundary Condition (미소채널내의 Langmuir 미끄럼 경계조건을 통한 미끄럼 속도 및 급격한 온도변화에 관한 수치해석)

  • Kim, Sang-Woo;Kim, Hyun-Goo;Lee, Do-Hyung
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.33 no.3
    • /
    • pp.164-169
    • /
    • 2009
  • The slip velocity and the temperature jumps for low-speed flow in microchannels are investigated using Langmuir slip boundary condition. This slip boundary condition is suggested to simulate micro flow. The current study analyzes Langmuir slip boundary condition theoretically and it analyzed numerically micro-Couette flow, micro-Poiseuille flow and grooved microchannel flow. First, to prove validity for Langmuir slip condition, an analytical solution for micro-Couette flow is derived from Navier-Stokes equations with Langmuir slip conditions and is compared with DSMC and an analytical solution with Maxwell slip boundary condition. Second, the numerical analysis is performed for micro-Poiseuille flow and grooved microchannel flow. The slip velocity and temperature distribution are compared with results of DSMC or Maxwell slip condition and those are shown in good agreement.