Experiments are reported concerning turbulent separated flow downstream of a backward-facing step in a two-dimensional channel that was rotated at a steady rate about a spanwise axis. Reattachment distance is reported as a function of Reynolds number, rotation direction and number and passage aspect ratio. Extensive flow visualization films have been produced. It is demonstrated that turbulent motions in a free shear layer may be suppressed or enhanced by system rotation according to the sense of the rotation. Two-dimensional, spanwise vortices which have been observed in the free shear layer are found to be relatively insensitive to system rotation in the stabilizing direction. These vortices are believed to be important contributors to the high rates of free shear layer entrainment, even in stationary systems at moderate Reynolds numbers.
Experiments with incompressible flow are reported concerning the effects of Coriolis acceleration on flow separation and on separated flow in plane-wall diffusers of rectangular cross section. The diffusers were rotated about an axis perpendicular to the plane of the nearly two-dimensional flow in order to simulate some features of the blade-to-blade flow distribution in the radial portion of the centrifugal impeller. Various stall regimes are mapped on coordinates of rotation number and diffuser area ratio (at fixed wall length). Diffuser pressure-recovery coefficient is reported as a function of area ratio and rotation number. These data demonstrate that, by suppressing turbulent mixing and shear stress in the suction-side boundary layers, the Coriolis acceleration field greatly enhances the tendency for stall to appear in a diffuser. This effect causes a corresponding reduction in the throat-to-exit pressure recovery as compared to that of nonrotating diffusers of the same geometry and inlet flow blockage.
This paper presents the results of an empirical study undertaken to assess the appropriateness and applicability of a simple, analytical model of pump-piping system flow instability. The analysis is used to describe behavior actually observed in a well defined, simple, pump-piping system. The frequency and amplitude of the flow oscillations observed during pump surge and the range of the pump-piping system characteristic parameters for which unstable flow oscillations occurred are in good agreement with the behavior predicted by the analysis. The results of this work provide a quantitative basis for investigating modifications to the lumped-parameter model in order to make it also appropriate for the analysis of more complex pump or compressor system. Although the analytical model displayed here is not new, a direct comparison of model predictions against similar measurements of first-order pump surge has not been published prior to this work.
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