The ow in the volute of a low speciÿc-speed pump was studied both experimentally and numerically near its design point. Measurements included time-averaged values of velocity and static pressure at a large number of locations in the volute. The numerical computations were based on the unsteady three-dimensional potential ow model for the core ow. Viscous losses were quantiÿed using additional models that use the potential ow as input. It is shown that near the design point of this pump, the core ow behaves like a potential ow, provided that no boundary layer separation occurs. Explanations are given for the presence of local deviations due to secondary ow. These local deviations do not in uence the overall potential ow characteristics signiÿcantly.
An unwanted side effect of pumping stations is that fish suffer from injury and mortality when passing through the pumps and that fish migration is hampered. In recent years, the development of so-called fish-friendly pumping stations has received increasing attention from European governmental institutions and pump manufacturers. In the Netherlands, many field studies have been conducted over the last decade to assess the chances of survival for fish passing through pumps. A clear correlation between observed injury or mortality and, for example, flow rate, shaft speed, or pump type could not be established. This paper presents a new analysis of these field studies. It uses American studies on the biological criteria for fish injury, the most important of which are pressure changes, shear forces, and mechanical injury. A blade strike model is adapted to fish passing through centrifugal pumps of radial, mixed-flow, and axial type. It reveals the relation between fish injury and the type of pump, its size, shaft speed, and pressure head. The results correlate fairly well with experiments. The flow through a typical mixed-flow pump is calculated using computational fluid dynamics (CFD). The results show that pressure fluctuations and shear forces are not likely to add much to fish mortality. Guidelines for the design and selection of fish-friendly pumps are given with the introduction of two new dimensionless numbers: the blade strike probability factor and the blade strike velocity factor. It shows that fish-friendliness of pumps decreases with increasing specific speed value.
Many centrifugal pumps have a suction velocity profile, which is nonuniform, either by design like in double-suction pumps, sump pumps, and in-line pumps, or as a result of an installation close to an upstream disturbance like a pipe bend. This paper presents an experimental study on the effect of a nonuniform suction velocity profile on performance of a mixed-flow pump and hydrodynamic forces on the impeller. In the experiments, a newly designed dynamometer is used, equipped with six full Wheatstone bridges of strain gauges to measure the six generalized force components. It is placed in between the shaft of the pump and the impeller and corotates with the rotor system. A high accuracy is obtained due to the orthogonality of bridge positioning and the signal conditioning electronics embedded within the dynamometer. The suction flow distribution to the pump is adapted using a pipe bundle situated in the suction pipe. Results of measurements show the influence of the suction flow profile and blade interaction on pump performance and forces. Among the most important observations are a backward whirling motion of the rotor system and a considerable steady radial force.
A total of 1253 live cyprinids and eel were exposed to a centrifugal pump to study fish damage rates in a wide operating range. The observed types of injuries were consistent with a mechanical cause of damage. The measured mortality rates for cyprinids show a fair agreement with a blade strike model based on empirical data by Electric Power Research Institute. Analysis of the experiments with eel led to a new correlation for the blade mortality ratio for this species; lethal injury rate is shown to be zero up to a strike velocity of 8 m·s -1 and increases linearly to 42% for a strike velocity of 15 m·s -1 . Use was made of video recordings that provided valuable information on the orientation and distribution of fish approaching the impeller. Results are presented using a new method to visualize fish mortality from a pump in its entire operating range using graphs of pressure head versus flow rate. The theory of pump hydrodynamics is used to derive a method to scale results of fish damage rate, obtained either by a model or by experiments, to different pump sizes, shaft speeds, or fish lengths. This will prove essential for a valid interpretation of pump experiments with fish.
The hydraulic performance of an industrial mixed-flow pump is analyzed using a three-dimensional potential flow model to compute the unsteady flow through the entire pump configuration. Subsequently, several additional models that use the potential flow results are employed to assess the losses. Computed head agrees well with experiments in the range 70 percent–130 percent BEP flow rate. Although the boundary layer displacement in the volute is substantial, its effect on global characteristics is negligible. Computations show that a truly unsteady analysis of the complete impeller and volute is necessary to compute even global performance characteristics; an analysis of an isolated impeller channel and volute with an averaging procedure at the interface is inadequate.
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