Entropy production analysis of hysteresis characteristic of a pump-turbine model

Cavitation is a challenging flow abnormality that leads to undesirable effects on the hydraulic behaviour of centrifugal pumps. This study analyses the cavitating flow at a normal flow rate using t...

Entropy generation analysis for the cavitating head-drop characteristic of a centrifugal pump:

A numerical study on mechanisms of energy dissipation in a pump as turbine (PAT) using entropy generation theory

Mechanism of high amplitude low frequency fluctuations in a pump-turbine in pump mode

Particle Image Velocimetry (PIV), pressure and noise measurements are used to study the effect of modifications to tongue and impeller geometries on the flow structure and resulting noise in a centrifugal pump. It is demonstrated that the primary sources of noise are associated with interactions of the non-uniform outflux from the impeller (jet/wake phenomenon) with the tongue. Consequently, significant reduction of noise is achieved by increasing the gap between the tongue and the impeller up to about 20% of the impeller radius. Further increase in the gap affects the performance adversely with minimal impact on the noise level. When the gap is narrow, the primary sources of noise are impingement of the wake on the tip of the tongue, and tongue oscillations when the pressure difference across it is high. At about 20% gap, the entire wake and its associated vorticity trains miss the tongue, and the only (quite weak) effect of nonuniform outflux is the impingement of the jet on the tongue. An attempt is also made to reduce the non-uniformity in outflux from the impeller by inserting short vanes between the blades. They cause reduction in the size of the original wakes, but generate an additional jet/wake phenomenon of their own. Both wakes are weak to a level that their impacts on local pressure fluctuations and noise are insignificant. The only remaining major contributor to noise is tongue oscillations. This effect is shown to be dependent on the stiffness of the tongue.Copyright © 1995 by ASME

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Effect of Modification to Tongue and Impeller Geometry on Unsteady Flow, Pressure Fluctuations and Noise in a Centrifugal Pump

Unstable or flat head-flow curves can cause problems in parallel operations or in flat systems. Despite the considerable efforts that have been devoted to the study of head-flow curve instability in single-stage centrifugal pumps with volute casing, the cause of such phenomenon is not sufficiently understood. In this study, we investigated the variation of hydraulic losses based on the relationship between velocity distribution and entropy generation fields. Steady-state and unsteady simulations were obtained for a pump with an impeller outlet diameter of 174 mm, and the unsteady results are more coincided with the experiments. Results showed that the losses mainly focused on the blade suction surface and volute tongue, as well as in the region of the volute discharge at high flow rates. The entropy generation rate of the pump casing at partial flow rates changed slightly with a decrease in flow rate, whereas the energy losses in the impeller increased steeply when the flow rate dropped to 35 m3/h (the de...

Chen Xiaoping

Papers

Experimental and numerical investigations of head-flow curve instability of a single-stage centrifugal pump with volute casing