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This paper describes an experimental study of the starting process in a reflected-shock tunnel, and compares the results with numerical calculations reported previously (Smith 1962). It is shown that an unsteady expansion wave dominates the transient flow, and the shock-wave system plays a minor role. The effects of initial pressure in the nozzle were investigated, and the behaviour of the secondary shock wave was noted. It was found that initial pressures larger even than the steady-flow static pressure can be tolerated without prolonging the starting process, despite the presence of a strong secondary shock wave. Other analyses, based on the ‘steady-state’ model of the starting process, are discussed and shown to give an unrealistic description of the flow field.

A Solar fuel injector that provides lean premixed combustion conditions has been studied in a combined experimental and numerical investigation. Lean premixed conditions can be accompanied by excessive combustion driven pressure oscillations which must be eliminated before the release of a final combustor design. In order to eliminate the pressure oscillations the location of fuel injection was parametrically evaluated to determine a stable configuration. It was observed that small axial changes in the position of the fuel spokes within the premix duct of the fuel injector had a significant positive effect on decoupling the excitation of the natural acoustic modes of the combustion system. In order to further understand the phenomenon, a time-accurate 2D CFD analysis was performed. 2D analysis was first calibrated using 3D steady-state CFD computations of the premixer in order to model the radial distribution of velocities in the premixer caused by non-uniform inlet conditions and swirling flow. 2D time-accurate calculations were then performed on the baseline configuration. The calculations captured the coupling of heat release with the combustor acoustics, which resulted in excessive pressure oscillations. When the axial location of the fuel injection was moved, the CFD analysis accurately captured the fuel time lag to the flame-front, and qualitatively matched the experimental findings. [S0742-4795(00)01103-0]

This article discusses improvements made to the methodology of the Housing and Urban Development (HUD) point-in-time (PIT) homeless census. HUD’s PIT results are presented to Congress as official data for policy consideration. Yet, PIT methodology focuses on visible street homeless individuals and those in shelters while neglecting the “marginally housed” or less visible homeless who live in automobiles or temporarily stay with friends and extended family. Being a hidden population, the marginally housed has been a traditionally difficult population to study. We replicated HUD’s PIT count but additionally targeted the marginally housed to improve traditional methods of counting the homeless. We improve the PIT count in two ways: (1) by extensively training counters, and (2) by using the personal networks of hundreds of counters to seek out the marginally housed. Student researchers from a local university located 333 more homeless individuals than the local PIT, of which 153 were marginally housed. We do not claim this to be an exhaustive count of all the marginally housed in the region, but it is an initial step in developing methodologies to include this hidden population when calculating the total homeless population. This approach can also improve traditional homeless counts in other cities.