Applied Mechanics and Materials Submitted: 2014-06-05 ISSN: 1662-7482, Vols. 599-601, pp 230-236 Accepted: 2014-06-05 doi:10.4028/www.scientific.net/amm.599-601.230 Online: 2014-08-11 2014 Trans Tech Publications, Switzerland Cavitation Effect to the Hydraulic Piston Pump Flow Pulsation Zhang Huan 1, a 1 Department of Electromechanical, Chengdu Technological University, Chengdu 611730, China a yyyhhhlll2013@126.com Key words: water hydraulics; axial piston pump; flow pulsation; cavitations; CFD Abstract: The flow pulsation is one of the main factors, which affect the performance of water hydraulic piston pump, and cavitation also has importance effect on flow pulsation. In this paper, CFD technology is used to simulate visually the porting process,which causes the flow pulsation in water hydraulic axial piston pump. As a result, the flow pulsation rates and other parameters on fluid-field corresponding to different rotary speed and different loading are obtained respectively when cavitation is considered and not, which can present theoretic references for the development of water hydraulic pump. Introduction Along with the enhancement of people s environmental protection consciousness and requirements of the sustainable development. As the key working medium of system 0f natural water, hydraulic has gradually become the research hotspot of the hydraulic industry. As the key element of hydraulic pressure system, the performance of hydraulic pump affects the performance of the whole hydraulic system directly. It can reduce the noise of hydraulic system and improve the stability of the system by reducing the pump flow and pressure pulsation of the water pressure. Because the pressure pulsation that caused by the flow pulsation will cause the vibration and noise of hydraulic system, so the flow pulsation has become one of the key indicators of pump performance. The reason is that the main cause of flow pulsation produced as follows: 1) Cylinder and piston s relative movement speed will have sin( ϖ t + α) pulse ingredients; 2) the number of drainage plunger alternate periodically. Cavitation is an extremely complex phenomenon of fluid. It has an important influence on hydraulics parameters, such as the flow pulsation of hydraulic pump. The reason why cavitation occurs is that when the liquid internal pressure is lower than the saturated vapor pressure of water, liquid will carburate to accelerate the formation of air bubbles and generate cavitation in low pressure area. Because when air bubble breaks it will produce very big pressure, the high pressure cavity that caused by air bubbles that breaks constantly in the water flow can destroy the solid surface, forming a "empty". Cavitation phenomenon is prominent and have influence on the engineering. And cavitation is complicated.both at home and abroad, cavitation is undertook a large number of studies [1-6].But the result is not satisfactory. Many problems remains to be further explored. Therefore, reducing the process of the hydraulic piston pump with flow pulsation of the flow and reduce the generation of air pockets, have big significance of reducing pressure impact and noise. By using CFD technology to the axis of water to the plunger pump with flow visualization simulization process and analysis to the location produced by flow pulsation and cavitation in the match flow process, provides the theory basis for the improving water finale plunger pump, and helps to improve the work performance. Computational modeling and calculation conditions Computational modeling. Fig.1 is a typical schematic diagram of quantitative axial plunger pump. Due to sliding boots parts have little impact on the flow pulsation, geometric model can be simplified to a certain extent, the main parameters of the geometric model of simplified geometric model is shown in Table 1. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 130.203.136.75, Pennsylvania State University, University Park, USA-06/03/16,23:03:32)
Applied Mechanics and Materials Vols. 599-601 231 Fig. 1 Structure diagram of the hydraulic pistontion pump Table 1 Main parameters of the geometric model of water hydraulics axial piston pump Arguments for value Take the value Plunger number z 9 Plunger diameter d (mm) 22 Enclosed initial length l0 volume (mm) 40 Plunger distribution circle radius R (mm) 37 Match flow window inner r1 (mm) 32 Match flow window diameter r2 (mm) 42 Water inlet big end diameter d1 (mm) 32 Small water inlet end diameter d2 (mm) 16 Drain the big end diameter d3 (mm) 22 Drain the small end diameter d4 (mm) 12 Llet suction drain length (mm) 60 Valve plate thickness z1 (mm) 5 Swash plate Angle ( ) 15.8 In this paper, in the form of valve plate seal water for opening "negative", opening Angle of 1 hydraulic pump as an example for analysis. Fig. 2 Calculation model and its meshing Due to the use of CFD software, analysis of the fluid only need to consider the flow of the fluid part, only take fluid field to establish water finale to the plunger pump model. In this case by using finite volume method, the model is divided into 74820 hexahedron units, 89247 nodes, the model grid structure as shown in Fig.2. In the figure nine of the same diameter cylindrical part on the top of the waist shape tank represents the inclosed work volume in the plunger cavity of the cylinder block. Big waist shape groove represents the valve disc shaped groove on the waist. Other cavity fluid flow channel, one of the larger diameter represents the suction cavity flow, the smaller diameter represents the pressurized water chamber flow.
232 Frontiers of Manufacturing Science and Measuring Technology IV Calculation conditions. Due to the compressibility of water is very small, and when the bubble accounts for a relatively small volume, will have little impact on the fluid density, thus to make the following assumptions: model of fluid flow state: 1) fluid is incompressible, Newtonian fluid; 2) by calculating the youngest of Reynolds number, the model is greater than the critical Reynolds number cri (2000 ~ 3000), so we use the turbulence model[5]. Turbulent kinetic energy is:k=1.5 U 2 I 2 (1) 1.5 0.75 Turbulent energy dissipation is: k ε = C µ (2) l Eq.1: U water inlet velocity; I turbulence intensity; C µ the coefficient of turbulent model; 1/10 - mixing length (inlet height). In this paper, calculation of recommended value of 0.1, 0.09, from 0.001 (< 0.0032), the main characteristics of water parameters are shown in Table 2. Density ρ (kg/m 3 ) Table 2 Physical properties of water (temperature:20 ) Dynamic Viscosity Coefficient of thermal conductivity µ k (Pa s) (W/(m K)) Specific heat C v (J/(kg K)) 997.56 0.0008887 0.62027 4181.72 Mobile grid In most of the flow phenomenon, the relative motion between fluid is caused by the relative motion between solid element. In CFD calculation method, the relative motion between fluid is mainly achieved through mobile grid technology. In the Anchor the water to the plunger pump model, mobile grid is made up of cylinder body and valve disc, piston and cylinder block between the solid components caused by the relative motion between fluid flow region of the grid. In the calculation, the process of plunger cavity closed working volume changed by the rotating of cylinder body, is realized by using the ASI mobile grid technology. Because grid computing process is changing constantly, we select the transient PISO algorithm when we choose algorithms, the selected parameters are shown in Table 3. Cavitation model Table 3 Algorithm with difference scheme The transient calculation method PISO The biggest iteration steps 50 Residual correction coefficient 0.1 Stress relaxation factor 0.25 The momentum equation difference scheme LUD Cavitation is phenomena of the liquid change into a gas phase that occurred in the liquid phase in certain conditions. When the liquid pressure is lower than the saturated vapor pressure, it will produce bubbles. Air bubbles in the liquid will not only hinder the flow of fluid, but also reduce the volumetric efficiency of the pump, sometimes it will lead the phenomenon such as noise, vibration and cavitation of solid surface. And it will break when bubbles go into the high pressure area again, increasing the pitting corrosion of solid parts. The analysis of this example, we suppose the water medium is constant temperature (20 ), that means without the consideration of the heat transfer of fluid in the process of cavitation phenomenon, using the transient analysis of cavitation phenomenon.
Applied Mechanics and Materials Vols. 599-601 233 In this cavitation model, the scalar VOF (volume of fluid) is liquid volume ratioto in volume controlling, on behalf of cavitation region and the degree of cavitation. If C represent the value of the VOF, the control volume of gas in volume ratioto is1 C.Supposing when liquid pressure is lower than the standard vaporization pressure, it will produce bubbles in the modeling. This calculation using barotropic model, P crit = Pv, P v is saturated steam pressure in the local temperature. The physical characteristics of water vapor parameters in the temperature of 20 is shown in Table 4. Table 4 Physical properties of the water vapor (temperature:20 ) Density ρ (kg/m 3 ) 0.0173 The calculation results Dynamic viscosity µ 6 (Pas) 9.18 10 The speed of sound in the water C water (m/s) 1450.0 The speed of sound in Water vapour C vapour (m/s) 4181.72 The theory of approximate calculation. 1) The rate of flow pulsation The calculating formula rate of flow pulsation of odd plunger pump is formula[2] : Qmax Qmin 2 π δ = = 2tan ( ) 100% 1 ( Q 4 max + Q z min) 2 (3) In Eq.3: δ the rate of flow pulsation ; Qmax, Q min maximum, minimum flow; z number of hydraulic pump plunger. In fact, due to the number of plunger pump are greater than or equal to 3, therefore, the Eq. 3 can be simplified as: 2 π π 2 1.25 δ = 2tan ( ) 2( ) 100% 2 4z 4z z (4) In this article the plunger pump plunger number 9, the type of hydraulic pump flow pulsation rate can be calculated by Eq.4 is 1.54%. 2) Cavitation Theoretical analysis showed that the cylinder hole plunger movement in the process of water absorption rate and water flow area is changing. Inϕ = 3π / 2 place, the plunger movement speed is the biggest. And in ϕ = 2π place, flow area is the smallest. So the two generate cavitation easily[5]. CFD calculation results In this paper, through the adoption of mobile grid on three kinds of speed and turbulence model, we use visualization simulation analysis for the flow state in the hydraulic pump of nine kinds of working conditions of the combination of three kinds of load pressure, the analytical results is shown in Fig.3 and Fig.4. The flow curve of hydraulic pump is shown in Fig.5, and the flow pulsation rate data is shown in Table 5. Analysis of results In the usual count, we don t consider the influence of the rotational speed and load pressure of the flow pulsation, and believe that the flow fluctuation frequency of each cylinder body rotation taking a turn is z. The Fig.5 shows: (1) Water finale to the plunger pump has flow pulsation; (2) Under the condition of the same revolutions, the average flow is basically a constant;
234 Frontiers of Manufacturing Science and Measuring Technology IV (3) The pump which rotates a circle will have 2Z (z is the number of flow fluctuation plunger) flow fluctuations. 3-a the velocity distribution of plunger from high pressure cavity into the low pressure cavity 3-b the velocity distribution of plunger from low pressure cavity into the high pressure cavity 3-c the Pressure distribution of plunger from high pressure cavity into the low pressure cavity 3-d the Pressure distribution of plunger from low pressure cavity into the high pressure cavity Fig.3 The velocity distribution and the pressure distribution of closed plunger pump vessel as regardless of the cavitation 4-a the velocity distribution of the plunger from high pressure cavity into the low pressure cavity 4-b the velocity distribution of plunger from low pressure cavity into the high pressure cavity
Applied Mechanics and Materials Vols. 599-601 235 4-c the Pressure distribution of plunger from high pressure cavity into the low pressure cavity 4-d the Pressure distribution of plunger from low pressure cavity into the high pressure cavity 4-f the cavitation distribution of plunger from 4-e the cavitation distribution of plunger from low pressure cavity into the high pressure cavity high pressure cavity into the low pressure cavity Fig.4 The velocity distribution and the Pressure distribution and the cavitation distribution of closed Plunger pump vessel as Regardless of the cavitation Rotate Speed (rpm) 300 1000 Fig. 5 The flow curve in condition of 15 MPa pressure and rotating speed of 1000 r/min Load (MPa) Table 5 Flow pulsation rate Qaver (L/min) Qmax (L/min) Qmin (L/min) δ (%) A B A B A B A B 0.1 21.292158 21.34351 21.403731 21.45568 21.064803 21.02301 1.591797 2.027174 10 21.293482 21.33827 21.406498 21.45315 21.019933 20.97192 1.815415 2.255244 15 21.288128 21.33781 21.406438 21.45315 20.993468 20.96511 1.939908 2.287207 0.1 70.9728 71.14402 71.346382 71.61151 70.243873 70.41203 1.553425 1.685988 10 70.9724 71.14221 71.346382 71.61292 70.19724 70.3597 1.61914 1.761570
236 Frontiers of Manufacturing Science and Measuring Technology IV 1500 15 70.9721 71.14161 71.346382 71.61292 70.18696 70.33264 1.633631 1.799622 0.1 106.460 106.7182 107.0256 107.2752 105.37641 105.4621 1.549117 1.69896 10 106.45899 106.7180 107.0256 107.2776 105.3553 105.4024 1.568961 1.767795 15 106.45959 106.7176 107.0256 107.2782 105.3289 105.3056 1.59375 1.848805 Condition A: without consideration of cavitation Condition B: with consideration of cavitation It can be seen from Table 5 that not considering cavitation occurs, flow pulsation rate values are between 1.54% and 1.94%,and it is consistent with the theoretical calculation results. When considering cavitation occurs, flow pulsation rate values are between 1.52% and 2.29%, and it is widely different from the theoretical calculation results. It can be seen from figure 3 and figure 4: hydraulic pump flow form use opening "negative". When the plunger cavity closed volume are between high and low, pressure mutation will come up, causing flow fluctuation. With the impact on load pressure, rotating speed of cylinder block and cavitation, the actual conditions of hydraulic pump flow pulsation rate and the theoretical calculation results is different, that means the speed and the working pressure of the pump field have effect on the rate of flow pulsation. Summary For the same axial plunger pump, from the above results may safely draw the conclusion as follows: (1) When the speed is same, the greater is the load pressure, the greater is the flow pulsation. (2) When the load pressure is same, the higher is the speed, the smaller is the flow pulsation. This kind of phenomenon is more obvious in high pressure; (3) The pump which rotates a circle will have 2Z (z is the number of flow fluctuation plunger) flow fluctuations. (4) For the flow pulsation, when considering holes are much larger than when not considering. To sum up, it should be considered rotation speed, load and the influence of cavitation on the discharge pulse pressure when designing or improving water finale to the plunger pump. Especially when the load s pressure is high and has high speed, it should be improved through the structure and the installation position of the pump, improving water finale to the plunger pump flow and pressure characteristics, reduce or eliminate the resulting fluid noise. Acknowledgements The corresponding author of this paper is Zhang Huan. This paper is supported by Natural Science Foundation of the Education Department of Sichuan Province, China[14ZB0296]. References [1] Deng Bin, Wang Jinnuo AnWeiSheng, KeJian. Noise and influence factors analysis of hydraulic piston pump [J]. Journal of machine tools and hydraulic, 2002 (6) : 150-154 [2] Xu Shengwu, plunger pump [M]. Mechanical industry publishing house, 1985 [3] Liu Donghai Huang Xiaoyun, piston diaphragm pump and the hydraulic diaphragm pump flow pulsation analysis [J]. Journal of hydraulic and pneumatic, 2012 (1 l) : 71-73 [4] Xu Bing, Song Yuechao, Yang Huayong, complex export pipeline plunger pump flow pulsation test principle [J]. Journal of mechanical engineering, 2012 (22) : 13, 162-167 [5] Yu Lijuan, wang, Zhang Xuecheng to plunger pump flow pulsation active control method and simulation study [J]. Journal of xi 'an jiaotong university, 2013,47 (11) : 43-47 [6] Wang Xingkun, the east, hu ShangJianDong, double-acting vane pump flow field numerical simulation and characteristics analysis [J]. Journal of hydraulics and pneumatics, 2013 (5) : 23-26
Frontiers of Manufacturing Science and Measuring Technology IV 10.4028/www.scientific.net/AMM.599-601 Cavitation Effect to the Hydraulic Piston Pump Flow Pulsation 10.4028/www.scientific.net/AMM.599-601.230