Browsing by Author "Mrosla, Edward"
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Item Flow Establishment and Initial Entrainment of Heated Water Surface Jets(St. Anthony Falls Hydraulic Laboratory, 1975-01) Stefan, Heinz; Bergstedt, Loren; Mrosla, EdwardMathematical models to predict water temperature distributions resulting from heated water surface discharges usually consider three subregions of the flow field: (a) an outlet region or zone of flow establishment (ZFE), (b) a zone of fully established jet flow, and (c) a far field with mostly passive dispersion. Of these three regions, zone (b) can be treated mathematically most readily using integral techniques; zone (c) requires input specifying mean flow and turbulence of the ambient flow field; and zone (a) depends essentially on the geometry of the outlet and the discharge characteristics in terms of the velocity and temperature of the water. The results of an experimental study dealing with zone (a) are reported. The discharge channel had a rectangular cross section and led into a deep, wide reservoir. The aspect ratio (width-to-depth ratio) of the channel, the volumetric discharge rate, and the discharge temperature were varied. A cross-flow was imposed in some of the experiments. The length of the zone of flow establishment, Xo or So, was measured in terms of mean excess temperature, mean velocity, and turbulence intensity along the trajectory. The length, Xo or So, was related to channel aspect ratio A, outlet densimetric Froude number Fo, and cross-flow-to-jet velocity ratio R. Total volumetric flow rates during flow establishment were established as a function of distance along the jet axis and related to A and Fo. The results are useful either for extension of existing mathematical models of fully developed heated water surface jets or for verification of mathematical models of the zone of flow establishment.Item The Use of Standard Bodies to Measure the Cavitation Strength of Water(St. Anthony Falls Hydraulic Laboratory, 1973-09) Silberman, Edward; Schiebe, Frank; Mrosla, EdwardResearch has been conducted to evaluate a technique for measuring the cavitation strength of water. The technique is based on counting cavitation events as a function of cavitation number on a standard body, thereby producing cavitation characteristic curves. It is assumed that water cavitates because of nuclei carried in the water and that the measured characteristic curves must therefore be related to the nuclei which are present. In this research it was hypothesized that the nuclei, whatever their real nature, could be represented by a distribution of equivalent gas bubbles of neutral density. The standard bodies were designed according to potential flow theory so that the bubble trajectories, along with their cavitation rates, could be calculated. By calculating cavitation characteristic curves for various bubble numbers and size distributions and comparing the calculated curves with measured curves for the same body, it was possible to infer the specifications for the equivalent bubble nuclei that were present in any test. The equivalent nuclei can be described using N, the number of cavitatable bubbles per unit volume of water (a number far smaller than the total number of nuclei per unit volume); rmax, the likeiy radius of the largest bubbles in the distribution; and a, a parameter of the exponential size distribution assumed for the bubbles. As a consequenoe, given (N,rmax,a) and an experimental realization whose flow field can be calculated by potential flow theory, it should be possible to predict incipient cavitation. The experiment devised for verifying this statement proved to be faulty, and experimental verification has not yet been accomplished. An alternative for future study has been proposed which calls for abandoning the hypothesis of equivalent bubble nuclei and determining the relative cavitation strength of water by direct comparison of a measured cavitation characteristic curve obtained on a standard body in a specific test configuration with a catalogue of such curves kept on file for a family of standard bodies.