Yen-Sen Chen

PREDICTION OF RADIATIVE TRANSFER IN GENERAL BODY-FITTED COORDINATES

The discrete ordinates method (DOM) and the finite-volume method (FVM) are employed to simulate two-dimensional and three-dimensional radiation problems in general body-fitted coordinates. Numerical analyses of these two methods indicate that the discretized equations for the DOM and the FVM are very similar. However, the FVM uses the averaged direction and scattering phase function over a control angle rather than the discrete direction and scattering phase function as in the DOM. To examine the accuracy and computational efficiency of the DOM and FVM in general body-fitted coordinates, five two-dimensional and three-dimensional benchmark problems with transparent, absorbing, emitting, and scattering media are considered. The solutions from both methods are found to be in good agreement with other available solutions. In some cases, the results from the FVM seem slightly better than those from the DOM. The required CPU time and iterations for the DOM and FVM are essentially the same for each problem. Thi...

Parallel simulation of radiative heat transfer using an unstructured finite volume method

A spatial domain-based parallel algorithm is developed for simulating radiative heat transfer in a distributed computing environment. The radiative transfer equation is solved using an unstructured finite-volume method that is applicable for any 2D planar, axisymmetric, and 3D problems with structured, unstructured, or hybrid grids. The domain decomposition is carried out by equally partitioning the spatial domain into many subdomains along the longer geometric dimension. Communication among the subdomains on each processor is performed through a message-passing interface library. In order to examine the parallel performance of the unstructured radiation code, two benchmark problems are investigated for different absorption coefficients, scattering coefficients, and grid sizes in a parallel computer. To help us understand the change of parallel performance, a new parameter, the total inner iteration number, is introduced to analyze the results. For all the cases examined, as expected, the parallel perform...

Investigation of chemical kinetics integration algorithms for reacting flows

A numerical investigation was conducted for integrating the chemical kinetics in computation of chemical reacting flows when an operator-splitting (point implicit) procedure was used to couple the chemical kinetics source term and fluid dynamics. The stiff initial value problems of ordinary differential equations were solved by an implicit formulation over a characteristic time scale of fluid. Analytical Jacobian has been derived to improve the numerical efficiency. Numerical test was first conducted for simplified one-dimensional ignition delay problem. It was then applied to a two-dimensional shockinduced combustion using both uniform and adapted grids. Some important issues have been addressed when the operator-splitting procedure is employed. It was found that evaluation of the kinetics source terms had a significant effect to combustion phenomena such ignition delay time. The current prediction was compared well with the experimental shadowgraph.

COMBINED EULERIAN-VOF-LAGRANGIAN METHOD FOR GENERAL GAS-LIQUID FLOW APPLICATIONS

This article summarizes the technical development and validation of a multiphase computational fluid dynamics (CFD) numerical method using a combined volume-of-fluid (VOF)/Lagrangian tracking model to analyze general dispersed multiphase-flow problems with free surfaces. The gas-liquid interfacial mass, momentum, and energy transfer are modeled by continuum surface mechanisms. A high-order TVD scheme is also implemented for capturing sharp interfaces between immiscible phases. The objectives of the present study are to develop and verify the fractional volume-of-fluid cell partitioning approach into a predictor-corrector algorithm, which is suitable for solving fluid flows at all speeds regimes, and to demonstrate the effectiveness of the present approach by simulating benchmark problems including coaxial jet atomization.

Numerical investigation of the slag behavior in the aft-end cavity of solid rocket motors

The 2-D RSRM geometry at 67 seconds is used for the analysis of the slag behavior in the aft-end cavity using the FDNS (Finite Difference Navier-Stokes) code to obtain a better understanding of the relationship between slag behavior and SRM performance. The FDNS flow solver is a finite difference method for solving NavierStokes equations using non-staggered curvilinear grid system with multi-zone multi-block option for multiple species to simulate the complex flow problems. A Lagrangian-Eulerian particle tracking method is employed in the FDNS to provide effects of momentum and energy exchanges between the gas phase and the particle phase. The particle trajectories are calculated using a one-step implicit method. The VOF (Volume of Fluid) method is employed to investigate the slag behavior in the aft-end cavity of the solid rocket motors. The obtained results reveal the potential impact of the particles on the operation of the motor as well as its performance. It is believed that the heat flux and the pressure distributions in the aft-end cavity will cause recirculation and influence the design requirements. The influence becomes more serious due to the accumulation of the slag in the aft-end cavity. In the present study, the particulate phase is assumed to be aluminum oxide (A1203) only. The accumulated slag changes the shape of the aft-end cavity and influences the flowfield. The obtained analyses of the flowfield and the slag behavior in the aft-end cavity using the FDNS code in the present study could provide necessary assistance for the designers to improve the performance of solid rocket motors.

Particulate multi-phase flowfield analysis for advanced solid rocket motor

Particulate multi-phase flowfield with chemical reaction for a 2D advanced solid rocket motor (ASRM) is analyzed using the finite difference Navier-Stokes (FDNS) code. The flowfield in the aft dome cavity of the ASRM is examined and its significant impact on the motor operation and performance is demonstrated. Chemical reaction analysis is performed for H2O, O2, H2, O, H, OH, CO, CO2, Cl, Cl2, HCl, and N2. The turbulent dispersion effect is calculated with the Monte Carlo method. Result show that a recirculation zone exists at the entry of the aft-dome cavity. The particle impingement could cause the erosion and damage nozzle wall. Accumulating in the impingement area the particles change the wall shape and affect the motor performance.