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Journal Cover CFD Letters     [SJR: 0.256]   [H-I: 2]
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  This is an Open Access Journal Open Access journal
   ISSN (Print) 2180-1363
   Published by ISSR Journals Homepage  [3 journals]
  • A High Order Numerical Scheme for Incompressible Navier-Stokes Equations

    • Authors: Hassan Khurshid, Klauss Hoffmann
      Abstract: To solve the incompressible Navier-Stokes equations in a generalized coordinate system, a high order solver is presented. An exact projection method/fractional-step scheme is used in this study. Convective terms of the Navier-Stokes (N-S) equations are solved using fifth-order WENO spatial operators, and for the diffusion terms, a sixth- order compact central difference scheme is employed. The third-order Runge-Kutta (R-K) explicit time-integrating scheme with total variation diminishing (TVD) is adopted for the unsteady flow computations. The advantage of using a WENO scheme is that it can resolve applications using less number of grid points. Benchmark cases such as, driven cavity flow, Taylor-Green (TG) vortex, double shear layer, backward-facing step, and skewed cavity are used to investigate the accuracy of the scheme in detail for two dimensional flow. The code is further extended to three dimensions thus increasing the utility of the developed code for more complex problems. A simple example of flow thorough infinite long pipe has been solved in order to validate the 3D code.    
      PubDate: 2014-09-27
      Issue No: Vol. 6 (2014)
  • Numerical simulation of double diffusive laminar mixed convection in a
           horizontal rotating annulus Part (II): Effect of Prandtl number and
           buoyancy ratio

    • Authors: Medhat Sourour, Mohamed Teamah, Wael El-Maghlany, Heba M. Abdel Aziz
      Abstract: A numerical study of double-diffusive mixed convection within a horizontal rotating annulus has been investigated. The outer cylinder is fixed but the inner cylinder is considered to rotate in clockwise and anti-clockwise directions to introduce the forced convection effect. In addition, the solutal and thermal buoyancy forces are sustained by maintaining the inner and outer cylinder at uniform temperatures and concentrations but their values for the inner are higher than the outer. The flow is considered laminar regime under steady state conditions. The transport equations for the continuity, momentum, energy and mass transfer are solved using the finite volume technique. The considered domains in this investigation are: -15 ≤ N ≤ 15, 0.01 ≤ Ri ≤ 100 and 0.01 ≤ Pr ≤ 100. While the thermal Grashof number, Lewis number and the radius ratio are kept constant at values equal to104, 1 and 2 respectively. The effect of the selected parameters on the local and average Nusselt and Sherwood numbers are presented and studied. Finally, this investigation concerned with selection the best direction of the inner cylinder rotation to enhance both heat and mass transfer. A comparison was made with the published results and a good agreement was found.
      PubDate: 2014-09-27
      Issue No: Vol. 6 (2014)
  • A BGK-based Two-Equation Turbulence Model Algorithm for Solving
           Compressible Navier-Stokes Equations

    • Authors: Jiunn Chit Ong, Ashraf Ali Omar, Waqar Asrar
      Abstract: The implementation and validation of the k-ε / k-ω SST (Shear-Stress-Transport) two-equation turbulence model into the existing BGK (Bhatnagaar-Gross-Krook) flow solver for compressible Navier-Stokes equations in two-space dimensions generalized coordinates are presented. In developing the desired algorithm, the convection flux terms are discretized by a semi-discrete finite difference method. Then, the resulting inviscid flux functions are approximated by the gas-kinetic BGK scheme based on the approximate collisional Boltzmann equation. For high-order spatial accuracy, the cell interface values required by the inviscid flux functions are reconstructed via the MUSCL (Monotone Upstream-Centered Schemes for Conservation Laws) variable interpolation method coupled with a minmod limiter. As for the diffusion flux terms, they are discretized with a second-order central difference scheme. An explicit-type time integration method known as the modified fourth-order Runge-Kutta method is used to march the solution to steady-state. Four test cases have been solved using the developed algorithm, namely turbulent flat plate, transitional flat plate, turbulent RAE2822 airfoil and turbulent Sajben diffuser flows. The accuracy of the solver is examined and results obtained from the computations are also compared with available experimental or analytical data that will demonstrate good agreement has been obtained.
      PubDate: 2014-09-27
      Issue No: Vol. 6 (2014)
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