Drag estimation on wedge-shaped protuberances in high-speed flows

A semi-empirical method is developed to estimate drag on wedge-shaped projections in hypersonic flow. Force balance measurements from gun tunnel tests directly measure total drag on blunt wedges, where the boundary layer and the entropy layer are weakly coupled. Detailed flowfield analysis from numerical simulations provides estimated locations of peak pressure ratio and skin friction. Schlieren images are used for detecting incipient separation in incoming flows with laminar and turbulent boundary layers. Test results indicate the presence of local hotspots at reattachment points of strong detached shocks on the wedge compression ramp, and of primary and secondary vortical structures around lateral faces. Total drag is found to decrease with decreasing bluntness but increasing slenderness in wedges tend to increase skin friction drag

Electric and Hybrid Vehicle System Research and Development Project: Hybrid Vehicle Potential Assessment. Volume IV. Series systems

In the Hybrid Vehicle Potential Assessment Task three major powertrain configurations (parallel, parallel with flywheel, and series) were studied. An evaluation of the series configuration is presented. The series configuration has the advantage that the engine is mechanically uncoupled from the wheels and can be operated at its best economy point much of the time. The mechanical energy produced by the engine is converted through a generator into electrical energy which is used to drive the motor or charge the batteries. This configuration offers a good degree of flexibility. It has the disadvantage that substantial losses of energy occur since the mechanical energy from the engine passes through several components before being used to drive the wheels. The energy produced by the engine is reduced by the product of efficiencies of components connected in series. Trade-offs involved in the study of the series configuration were directed toward establishing the size of the engine, motor and generator to meet vehicle acceleration performance; determining what level to operate the engine, and determining when to use the battery. These results were then used in the electric range simulation

Computational methodology for investigating the transient interaction between a reaction control jet and a hypersonic crossflow

A computational methodology has been developed to investigate the transient start of a Reaction Control (RC) jet into a hypersonic cross flow. The method uses the rhoCentral-Foam solver, which forms part of the OpenFOAM Computational Fluid Dynamics (CFD) package. Results have been compared to analytical solutions and previous simulations of a one-dimensional shock tube, a two-dimensional wedge, a diamond airfoil and a forward step. Further evidence of validation has been gained by comparing results with experimental data for a two-dimensional jet issuing into a quiescent atmosphere, and the steady interaction between a three-dimensional RC jet and a hypersonic cross flow. This work extends the scope of validation data available for rhoCentralFoam in open literature. Results show that the rhoCentralFoam solver performs well, and is able to capture all relevant flow structures. Shock properties, velocity and density fields were well predicted, but accuracy was decreased in some cases when predicting temperature and pressure fields. Overall, the numerical scheme is suitable for investigating the transient interaction between an RC jet and a hypersonic cross flow