Engineering topics
Publications and source records attributed to Chang, James L. C..
Algebraic approximation developed for use in calculating turbulent flow in duct with sharp 180 degree turn. Sharp curvatures of surfaces at turn increase complexity of flow and equations describing it. Approximation simplifies mathematical modeling of complicated turbulent flows, particularly those in air-breathing engines.
Three-dimensional, incompressible flow simulated on computer. Report discusses mathematical basis of IN3SD computer code and application of code to several test problems. Relies heavily on use of pseudocompressibility to solve numerically three-dimensional Navier-Stokes equations of viscous, incompressible flow. With further study and some modification, valuable computational tool for solution of engineering problems in fluid dynamics.
This paper presents a simple algebraic turbulence model developed for internal flows which is based on the vorticity length and magnitude. The length scale is defined using the distance between the maximum and the minimum points of the absolute vorticity. This model is numerically tested in a turbulent internal layer flow through an axisymmetric U-duct with very sharp curvature; the ratio of the boundary layer thickness to the radius of curvature of the duct is of order 1. In this U-duct flow, strong adverse and favorable pressure gradients coexist and interact with each other. Satisfactoy agreement with experimental results is obtained.
The method of pseudocompressibility has been found to be an efficient method for obtaining a steady-state solution to the incompressible Navier-Stokes equations. Recent improvements to this method include the use of a diagonal scheme for the inversion of the equations equations at each iteration. The necessary transformations have been derived for the pseudocompressibility equations in generalized coordinates. The diagonal algorithm reduces the computing time necessary to obtain a steady-state solution by a factor of nearly three. Implicit viscous terms are maintained in the equations, and it has become possible to use fourth-order implicit dissipation. The steady-state solution is unchanged by the approximations resulting from the diagonalization of the equations. Computed results for flow over a two-dimensional backward-facing step and a three-dimensional cylinder mounted normal to a flat plate are presented for both the old and new algorithms. The computing efficiency of these algorithms are compared. Identical solutions are obtained from both algorithms which compare well with experimental results.
The purpose of this study is to examine in detail incompressible laminar and turbulent flows inside the oxidizer side Hot Gas Manifold of the Space Shuttle Main Engine. To perform this study, an implicit finite difference code cast in general curvilinear coordinates is further developed. The code is based on the method of pseudo-compressibility and utilize ADI or implicit approximate factorization algorithm to achieve computational efficiency. A multiple-zone method is developed to overcome the complexity of the geometry. In the present study, the laminar and turbulent flows in the oxidizer side Hot Gas Manifold have been computed. The study reveals that: (1) there exists large recirculation zones inside the bowl if no vanes are present; (2) strong secondary flows are observed in the transfer tube; and (3) properly shaped and positioned guide vanes are effective in eliminating flow separation.
The purpose of this study is to examine in detail incompressible laminar and turbulent flows inside a turnaround duct with and without guide vanes and to investigate the effects of vanes on the flow characteristics. To perform this study, an implicit finite difference code cast in general curvilinear coordinates is further developed. The code is based on the method of pseudo-compressibility and utilize ADI or implicit approximate factorization algorithm to achieve computational efficiency. Method of segmental sweeping is developed to overcome the multiple-zone problem due to imposition of guide vanes. In the present study, several test cases have been computed. These test cases include laminar and turbulent flows inside a turnaround duct without and with two or three guide vanes. The study reveals that: (1) there exists large recirculation zones inside the duct if no vanes are present; (2) properly shaped and positional guide vanes are effective in eliminating flow separation; and (3) laminar and turbulent flows have similar flow features. But turbulent flow has less total pressure drop.
Incompressible viscous flow inside the turnaround duct, the fuel bowl, the transfer duct and the racetrack of the Space Shuttle Main Engine (SSME) Hot Gas Manifold (HGM) has been computed using the method of pseudo-compressibility together with an implicit, approximate-factorization algorithm. A multiple-zone method is used to make solution of flows in complex geometries easy. A model which predicts the pressure loading for the shield and the injector post arrangement without solving the complex flow field in the main injector region is proposed. The computed results show good qualitative agreement with experimental data.