Transient behavior of a centrifugal pump during starting period Issa Chalghoum ⇑ , Sami Elaoud, Mohsen Akrout, Ezzeddine Hadj Taieb Research Laboratory ‘‘Applied Fluid Mechanics, Process and Environment Engineering”, National Engineering School of Sfax, BP’W’3038 Sfax, Tunisia article info Article history: Received 17 March 2015 Received in revised form 17 February 2016 Accepted 29 February 2016 Available online 15 March 2016 Keywords: Transient behavior Centrifugal pump Valve Startup period Method of characteristics abstract A theoretical analysis on transient flow inside a centrifugal pump was carried out, building on unsteady and incompressible fluid equations applied to the impeller during the starting periods. The transient flow behavior is governed by two hyperbolic partial differential equations; namely continuity and motion equations. The characteristics method of the specified time intervals was used to analyze the dynamic characteristic of the pump. To follow the dynamic behavior of the pump during startup periods, a numerical study was performed on the pump impeller with different openings of the discharge valve. The comparison between the numerical and experimental results of the pump characteristic curve has shown a good concordance. The results have also revealed that the pressure increase is important in the case of a short starting period of the pump and a large mass of water in the pipelines. In this study, the effect of the impeller diameter and number of blades on the pressure evolution was also analyzed. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Centrifugal pumps are fundamental elements that are com- monly encountered in turbomachinery applications. Transient flow behavior through centrifugal pump during the starting and stop- ping periods was object of several experimental and theoretical studies. Experimental studies have shown that the impulsive pres- sure and lag in circulation formation around the impeller vanes are the main reasons for the difference between dynamic and quasi- steady characteristics of turbo pump during its starting period [1–3]. During this period, it has been shown that three factors are responsible for the departure of the dynamic characteristics of a pump during startup from the normal steady-state performance [4]. These factors are the mass of water in the pipeline, the valve opening percentage and the starting time. The theoretical and pre- dictive models have been carried out on the transient characteris- tics of a centrifugal pump during starting and stopping periods [5,6]. Both models were experimentally validated. Unfortunately, the authors did not focus on the startup time and pump geometry effects on the pump characteristic and the dynamic pressure curves. By solving transient angular momentum and energy equations, a theoretical expression of the instantaneous head, including terms of angular acceleration, flow acceleration, and velocity profile vari- ation, is presented [8]. In addition, it has been demonstrated that instantaneous velocity profile variation is another important factor determining transient characteristics. Added to that and through experiments on the hydrodynamic performance of a centrifugal pump during transient operation [7], neat differences between transient and quasi-steady characteristics are found. In fact, quasi-steady assumptions were not valid for transient (accelerat- ing or decelerating) applications. A study on the transient pump startup [9] has shown the effect of the inertia of the pump impeller on the head and the discharge during the starting period. In this study, it has been deduced that for a pump with a high moment of inertia, an extended time for the fluid is needed to reach the steady-state flow. The transient effect was investigated by performing fast star- tups of the pump in cavitating and non-cavitating conditions [11,12]. In cavitating conditions, different types of unsteady behav- iors were obtained. Besides, the cavitation effects on the pump head evolution at constant rotation speed have been studied. Moreover, to explain the evolution of the pump head during the startup phase, a physical analysis was proposed. Nevertheless, for a pump having a small impeller moment of inertia, the steady state operating speed will be approached much more rapidly than the fluid which would reach steady-state flow. Building on the characteristic method, the transient flows in quasi-rigid pipelines caused by starting pumps has been investi- gated [14]. In this work, the authors studied different pump start- ing times and their effect on the dynamic behavior of the flow. The obtained results have revealed that the transient pressure rise in the case of a slow startup is more significant than that in the case of a rapid startup. Furthermore, the steady-state operating point is http://dx.doi.org/10.1016/j.apacoust.2016.02.007 0003-682X/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: chalghoumissa@yahoo.fr (I. Chalghoum), elaoudsa@yahoo.fr (S. Elaoud). Applied Acoustics 109 (2016) 82–89 Contents lists available at ScienceDirect Applied Acoustics journal homepage: www.elsevier.com/locate/apacoust