Integral methods in compressible laminar boundary layers and their application to hypersonic pressure interactions

Method for properties of laminar boundary layer with heat transfer and arbitrary pressure gradients - application to hypersonic pressure interactio

Investigations into the mechanism and rates of atmospheric mixing in the lower thermosphere Semiannual status report

Investigating mechanism and rates of atmospheric mixing in lower thermospher

Escaping the trap of complication and complexity in multiscale microkinetic modelling of heterogeneous catalytic processes

In this feature article, the development of methods to enable a hierarchical multiscale approach to the microkinetic analysis of heterogeneous catalytic processes is reviewed. This methodology is an effective route to escape the trap of complication and complexity in multiscale microkinetic modelling. On the one hand, the complication of the problem is related to the fact that the observed catalyst functionality is inherently a multiscale property of the reacting system and its analysis requires bridging the phenomena at different time and length scales. On the other hand, the complexity of the problem derives from the system dimension of the chemical systems, which typically results in a number of elementary steps and species, that are beyond the limit of accessibility of present-day computational power even for the most efficient implementation of atomistic first-principles simulations. The main idea behind the hierarchical approach is to tackle the problem with methods of increasing accuracy in a dual feed-back loop between theory and experiments. The potential of the methodology is shown in the context of unravelling the WGS and r-WGS catalytic mechanisms on Rh catalysts. As a perspective, the extension to structure-dependent microkinetic modelling is discussed

Effects of direction decoupling in flux calculation in finite volume solvers

In a finite volume CFD method for unsteady flow, fluxes of mass, momentum and energy are exchanged between cells over a series of small time steps. The conventional approach, which we will refer to as direction decoupling, is to estimate fluxes across interfaces in a regular array of cells by using a one-dimensional flux expression based on the component of flow velocity normal to the interface between cells. This means that fluxes cannot be exchanged between diagonally adjacent cells since they share no cell interface, even if the local flow conditions dictate that the fluxes should flow diagonally. The direction decoupling imposed by the numerical method requires that the fluxes reach a diagonally adjacent cell in two time-steps. In order to evaluate the e®ects of this direction decoupling, we examine two numerical methods which differ only in that one uses direction decoupling while the other does not. We examine a generalized form of Pullin's Equilibrium Flux Method (EFM) [J. Comput. Physics, v34, 1980, pp 231-244] which we have called the True Direction Equilibrium Flux Method (TDEFM). The TDEFM fluxes, derived from kinetic theory, flow not only between cells sharing an interface, but ultimately to any cell in the grid. TDEFM is used here to simulate a blast wave and an imploding flow problem on a structured rectangular mesh and is compared with results from direction decoupled EFM. Since both EFM and TDEFM are identical in the low CFL number limit, differences between the results demonstrate the detrimental e®ect of direction decoupling. Differences resulting from direction decoupling are also shown in the simulation of hypersonic flow over a rectangular body. The computational cost of allowing the EFM fluxes to flow in the correct directions on the grid is minimal

Some aspects of chemical non-equilibrium in high speed high temperature flows

Imperial Users onl

Direct Simulation of Hypersonic Transitional Flows Over Blunt Slender Bodies

Hypersonic transitional flow has been studied using the Direct Simulation Monte Carlo method. The cylindrically blunted wedge and spherically blunted cone were examined for body half angles of 0°, 5° and 10°, at a flight velocity of 7.5 km/s, zero angle of incidence and altitudes of 70 to 100 km. Those geometries and flow conditions are important considerations for hypersonic vehicles currently under design. Surface chemistry was examined for diffuse, finite-catalytic surfaces. Nonequilibrium chemistry and nonequilibrium thermodynamics were considered for both configurations at all altitudes. Numerical simulations showed that rarefied gas effects, such as surface temperature jump and velocity slip, exist. Slip conditions were more significant for the axisymmetric cases and the onset of chemical dissociation occurred first for the two-dimensional configuration at 96 km. Comparisons between the numerical simulation and viscous shock-layer calculations at the higher altitudes show significant differences in the calculated heat-transfer rate, body drag and flowfield structure. A comparison with hypersonic wind tunnel heat-transfer rate data showed good agreement

Nongrey radiation effects on the boundary layer of an absorbing gas over a flat plate

Nongrey radiation effects on boundary layer of absorbing gas over flat plat

Shock tunnel studies of scramjet phenomena, supplement 6

Reports by the staff of the University of Queensland on various research studies related to the advancement of scramjet technology are presented. These reports document the tests conducted in the reflected shock tunnel T4 and supporting research facilities that have been used to study the injection, mixing, and combustion of hydrogen fuel in generic scramjets at flow conditions typical of hypersonic flight. In addition, topics include the development of instrumentation and measurement technology, such as combustor wall shear and stream composition in pulse facilities, and numerical studies and analyses of the scramjet combustor process and the test facility operation