Assessment of Higher-Order RANS Closures in a Decelerated Planar Wall-Bounded Turbulent Flow

A reference DNS database is presented, which includes third- and fourth-order moment budgets for unstrained and strained planar channel flow. Existing RANS closure models for third- and fourth-order terms are surveyed, and new model ideas are introduced. The various models are then compared with the DNS data term by term using a priori testing of the higher-order budgets of turbulence transport, velocity-pressure-gradient, and dissipation for both the unstrained and strained databases. Generally, the models for the velocity-pressure-gradient terms are most in need of improvement

Application of Computer Simulation in a Design Study of a New Concept of Pulverized Coal Gasification

The paper presents some results of the mathematical simulation of a new concept of direct gasification of pulverized coal in a stream reactor. The new method method presumes that gasification of pulverized coal will occur in the. annular region of a cylindrical reactor during the co-current flow of coal-oxidant mixture in the peripheral zone and hot combustion products—serving as a heat source—in the core region of the reactor. Part I. of the paper outlined the rationale of the gasification concept and described the model of hydrodynamics and of radiative heat transfer in the particle-laden gas flow. The process was modelled as a reactive, multi-component, two-phase mixture flow with simultaneous combustion in the core and coal gasification in the peripheral annular region of the reactor, with radiative heat exchange between the two co-current streams. The gas phase was described in the Eulerian frame and the discrete phase in the Lagrangian frame with an account for mutual mass and heat exchange between the two phases. Radiation heat exchange was modelled by the six-flux model. Part II deals with coal chemical reactions relevant to the considered gasification concept and presents some results of computation by the complete model of the process. Heterogeneous chemical reactions of coal were treated in a kinetic-diffusion regime. The model, verified in an example of pulverized coal combustion, showed that the concept is feasible and yielded basic information for the design of an experimental rig for a final verification of the new gasification technique. © 1994, Taylor & Francis Group, LLC. All rights reserved