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Numerical analysis of cavitation phenomena with variable speed centrifugal pump

Rakibuzzaman M., Kim K., Suh S.-H.

Journal of Power Technologies

2016

Vol. 96, nr 4

306--311

Cavitation is an abnormal physical phenomenon which can be generated in relatively low pressure regions in centrifugal pumps. In predicting and understanding cavitation in the pumps, it is important to secure their efficiency and reliability. The purpose of this study is to analyze the cavitation flows in centrifugal pumps with variable speeds through numerical methods. The Rayleigh–Plesset cavitation model was adapted as the source term for inter-phase mass transfer in order to predict and understand the cavitation performances. The Reynolds-average Navier-Stokes (RANS) equations were discretized by the finite volume method. The two-equation SST turbulence model was accounted for turbulent flows. The numerical analysis results were validated with experimental data and it was found that both results were in good accordance. The cavitation performances were obtained for variable speeds with different temperatures and the effects on cavitation were described according to different cavitation numbers. Cavitation performances were also observed for different centrifugal pump stages (1st and 2nd). The performances of cavitation decreased with the increase of rotational speed. In addition, the development of cavitation is elucidated according to the different temperatures, and the effects of water vapor volume fraction are discussed.

Estimation of mean speed and speed standard devation from CFD prediction

Popiołek Z.

Architecture Civil Engineering Environment

2008

Vol. 1, no. 1

141-146

Mean velocity field predicted by CFD simulations on the basis of RANS equations differs from the mean (in time) magnitude of the velocity, i.e. the mean speed, existing in rooms and measured by low velocity thermal anemometers with omnidirectional (spherical) sensors. Similarly, velocity standard deviation differs from the standard deviation of the speed. In this paper the discrepancies are identified and discussed. A new method for estimation of mean speed and standard deviation of the speed based on CFD predictions of mean velocity and kinetic turbulence energy is suggested. Uncertainty of mean speed and standard deviation of the speed estimation is determined. A significant improvement can be expected in the determination of the PMV and DR indices by further processing of mean velocity and standard deviation of velocity, as predicted by CFD simulations.

Średnia prędkość będąca wynikiem obliczeń CFD bazujących na równaniach RANS różni się od uśrednionego w czasie modułu wektora prędkości tj. od średniej szybkości, która mierzona jest w pomieszczeniach za pomocą termoanemometrów z czujnikami wielokierunkowymi (sferycznymi). Podobnie, odchylenie standardowe prędkości różni się od odchylenia standardowego szybkości. W artykule różnice te zostały zidentyfikowane i przedyskutowane. Nowa metoda estymacji średniej szybkości i odchylenia standardowego szybkości na podstawie uzyskanej z obliczeń CFD średniej prędkości i energii kinetycznej turbulencji została zaproponowana. Wyznaczona została niepewność takiej estymacji. Można oczekiwać znaczącej poprawy dokładności wyznaczania wskaźników komfortu termicznego PMV i wskaźnika dyskomfortu wywołanego zjawiskiem przeciągu DR z wyników obliczeń CFD.