2 nd International Conference “From Scientific Computing to Computational Engineering” 2 nd IC-SCCE Athens,5-8 July, 2006 ©IC-SCCE FINITE ELEMENT –BASED SIMULATION OF HIGH FREQUENCY PULSATING-FLOW IN PUMP SYSTEMS Yannis Koveos 1 , Efthymios Kolyvas 1 , Anthony Tzes 1 , and Demosthenes Tsahalis 2 1 University of Patras, Dept. of Electrical & Computer Engineering, 26500 Patras, Greece 2 Laboratory of Fluid Mechanics and Energy (LFME) University of Patras P.O.BOX 1400, 26500 Patras, Greece e-mail: tsahalis@lfme.chemeng.upatras.gr , web page: http://www.lfme.gr Keywords: CFD, pulsating flow, fluid - structure interaction Abstract. This paper focuses on the modeling and simulation of pulsating fluid-flow and its interaction with the surrounding structure in high performance pump systems. The employed idealized-model of the pump corresponds to that of a flexible pipe (cylinder). The fluid enters through an ideal on/off valve, compressed by a piston in the pump chamber, and exits via an on/off valve. The modeling of this system, when the pump frequency increases, demands an investigation of the underlying fluid mechanics and the fluid-structure interaction. FEM-based simulation studies were performed, and related results are presented, for the purpose of determining the effect of the pulsating frequency, the length of the pump’s chamber, and the relative opening/closure of the valves, on the performance of the pump. I. INTRODUCTION Electro-hydraulic pump systems operating at high frequencies have become quite feasible due to the utilization of piezoelectric materials ([1]-[6]) as the actuating elements (pistons, valves). These systems offer high energy output in a compact size and have reduced weight. The need to operate at high frequencies is due to the limited stroke generated by these piezo-actuators and the necessary hydraulic based stroke amplification with the same force level. In order to maintain the efficiency of power transformation at an accepted high level, challenging hydraulic aspects like limited pressure propagation, hydraulic inductivity and valve flow aspects need to be taken under into account at the early design stages of the hybrid electro-hydraulic system. Despite the simplicity of the hydraulic amplifier’s model, the analysis of the underlying fluid dynamics and its interaction with the pump’s structure needs to be investigated. The schematic model of the amplifier setup is similar to the one provided in Figure 1. The complexity in the analysis of such a system dictates a lumped system analysis for the fluid dynamics. The existing simulation models [4] utilize lumped parameters and investigate the effects of the fluid compressibility and energy losses, limited pressure propagation and hydraulic inductivity. A straightforward implication of the lumped parameterization is the inability to calculate the pressure losses, caused by line friction and turbulent flow, thus resulting in the incorporation of statistical means. Additional drawbacks of the current approaches are the unrealistic differential pressures calculated and the simplification that the fluid assumes constant density along the pipe. Despite these simplifications, the developed models are in agreement with the experimental data for the case of low frequencies. The inability of the lumped models to predict the behavior of the fluid is revealed at higher frequencies (>200Hz), where the behavior of the pulsating fluid cannot be captured without a more detailed modeling. In the current study, a Finite Element Analysis (FEA) approach is adopted in order to incorporate the distributed nature of the phenomenon and examine the behavior of the pulsating fluid inside the pipe and the piston chamber. The performance of the pump system is investigated, in terms of ‘normalized’ outflow and compared to the one obtained by the lumped case. A parametric study reveals that the extracted pressure propagation effects at different pipe lengths justify the divergence of the experimental results from the theoretical ones (calculated via the lumped parametrization method). It is shown that the present fluid dynamics, are not only affected by the transmission line length (which