This chapter contains sections titled: Introduction Basics Solving the Equations for Conduction Considerations for Convective Flows Nomenclature References
A differential approach for analysis of turbulent, axisymmetric, buoyant jets and plumes issuing nonvertically into a quiescent, uniform ambient is presented, in which the governing differential equations for conservation of mass, momentum, and energy, derived in a curvilinear, orthogonal coordinate system, are solved by a finite-difference method of the Dufort-Frankel type. This jet configuration is of interest with regard to the design of submerged, offshore outfalls from power plants. The analysis includes consideration of the transverse momentum equation as the jet follows a curved trajectory under the influence of buoyancy forces. The turbulent shear stress and heat flux terms in the governing equations are evaluated through a relatively simple turbulence model which accounts for the effect of buoyancy on the apparent turbulent viscosity through the gradient Richardson number. Predictions for buoyant jets discharging horizontally and at 45 deg to the horizontal are compared with recent experimental data and the results of other prediction methods.
The development of a two-dimensional time-accurate dual time step Navier-Stokes flow solver with time-derivative preconditioning and multigrid acceleration is described. The governing equations are integrated in time with both an explicit Runge-Kutta scheme and an implicit lower-upper symmetric-Gauss-Seidel scheme in a finite volume framework, yielding second-order accuracy in space and time. Issues concerning the implementation of multigrid for preconditioned, dual time step algorithms are discussed. Steady and unsteady computations were made of lid driven cavity flow, thermally driven cavity flow and pulsatile channel flow for a variety of conditions to validate the schemes and evaluate the effectiveness of multigrid for time-accurate simulations. Significant speedups were observed for steady and unsteady simulations. The speedups for unsteady simulations were problem dependent, a function of how rapidly the flow varied in time and the size of the allowable time step.
A variable property finite-difference calculation procedure is used to predict turbulent flow and heat transfer parameters in annular passages. Predictions from several turbulence models are compared with measurements over a range of flow and thermal conditions. Of the models considered, one utilizing transport equations for turbulence kinetic energy and characteristic mixing length scale gave the best overall performance. The inclusion of turbulence kinetic energy in the turbulence modeling was found not to be crucial for predicting isothermal flows or for predicting all parameters except the temperature distribution for flows with heat transfer at Reynold numbers greater than 110,000.
Background: The ultimate goal of the study is the improvement of predictive methods for safety analyses and design of Generation IV reactor systems such as supercritical water reactors (SCWR) for higher efficiency, improved performance and operation, design simplification, enhanced safety and reduced waste and cost. The objective of this Korean / US / laboratory / university collaboration of coupled fundamental computational and experimental studies is to develop the supporting knowledge needed for improved predictive techniques for use in the technology development of Generation IV reactor concepts and their passive safety systems. The present study emphasizes SCWR concepts in the Generation IV program.
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