SIMULATION OPTICS

This paper is concerned with the simulation of the flow in a flat, `two-dimensional' laboratory centrifugal pump. The main concern of the study is the calculation of the flow-induced noise. The aim of the present paper is to develop a computationally simple and fast method which is capable of giving a useful estimate of the noise-generating `background-flow'. A companion paper describes the hydroacoustic part of the analysis. In the numerical flow model of the pump, the inlet is modelled by a point source and the blades of the impeller are covered with vortex elements with discrete, bound vortices. The casing is covered with source panels. Vortices are shed from the trailing edges of the impeller blades and convected with the streaming fluid in order to satisfy Kelvin's theorem. After computation of the velocity field, the fluid forces acting on the impeller blades are calculated by application of the unsteady Bernoulli equation. Some case studies of pump flows are presented. The acoustic properties of these flows is the subject of the second part of the paper.

With extensively using of centrifugal pumps, noise generation in these pumps is increasingly receiving research attention in recent years. The noise sources in centrifugal pumps are mainly composed of mechanical noise and flow-induced noise. And the study of flow-induced noise has become a hotspot and important domain in the field. The flow-induced noise closely related to the inner pressure pulses and vibration of volute in pumps, therefore, it is necessary to research the interaction and mechanism among them. To investigate the relationships, a test system is designed which includes a test loop and a measurement system. The hydrophones and pressure sensors are installed on the outlet of the pump and vibration acceleration sensors are disposed on the pump body. Via these instruments, the signals of noise, pressure pulses and vibration are collected and analyzed. The results show that the level of flow-induced noise becomes smaller as the flow increment during low flow rate operations, and it is steadily close to the design point, then it increases with the growing of flow rate in high flow rate conditions. Furthermore, there are some similar peak points in the power spectrum charts of noise, pressure pulses and vibration. The broadband noise at low flow rate is mostly focused on the region of 0-40 times shaft frequency, which is mostly made by rotating stall and vortex; while the noise at high flow rate conditions is focused on the region of 60-100 times shaft frequency, which may be mostly made by cavitations. The proposed research is of practical and academic significance to the study of noise reduction for centrifugal pumps.

Pressure pulsations excited by a centrifugal turbomachinery such as compressor, fan or pump at the blade passing frequency may cause severe noise and vibrations in piping system. Therefore, the practical evaluation method of pressure pulsations is strongly recommended. In particular, the maximum pressure amplitude under the resonant conditions should be appropriately evaluated. In this study, a one-dimensional excitation source model for a compressor or pump is introduced based on the equation of motion, so as to incorporate the non-linear damping proportional to velocity squared in the total piping system including the compressor or pump. The damping characteristics of the compressor or pump are investigated by using the semi-empirical model. It is shown that the resistance coefficient of the compressor or pump depends on the Reynolds number that is defined using the equivalent velocity of the pulsating flow. The frequency response of the pressure amplitude and the pressure distribution in the piping system can be evaluated by introducing the equivalent resistance of the compressor or pump and that of piping system. In particular, the relation of the maximum pressure amplitude in piping system to the location of the excitation source under resonant conditions can be evaluated. Finally, the reduction of the pressure pulsations by use of an orifice plate is discussed in terms of the pulsation energy loss.

Centrifugal pumps represent the primary source of acoustic energy in industrial piping. For hydraulically similar pumps, the amount of emitted energy …

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Novobiocin ノボビオシン; Molecular FormulaC31H36N2O11 Average mass612.624 Da (3R,4S,5R,6R)-5-hydroxy-6-(4-hydroxy-3-(4-hydroxy-3-(3-methylbut-2-enyl)benzamido)-8-methyl-2-oxo-2H-chromen-7-yloxy)-3-methox…

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