Flow and cavitation characteristics of a dampingorifice in water hydraulicsLiu Yinshui�, Zhu Bihai, Zhu Yuquan, and Li Zhuangyun

School of Mechanical Science and Engineering, Department of Mechatronic Engineering, Huazhong University of

Science and Technology, Wuhan, Hubei, People’s Republic of China

The manuscript was received on 5 May 2006 and was accepted after revision for publication on 31 July 2006.

DOI: 10.1243/09576509JPE323

Abstract: The flow in damping orifices when using water as the working media is of highReynolds number and cavitation is inevitable. In this article, experimental studies are madeon the flow and cavitation characteristics of water hydraulic orifices and the coefficient formulaein previous documents are testified with the Reynolds number ranging from 104 to 105. All theorifices are made of transparent materials, so the flow and the occurrence process of the cavita-tion can be observed with the naked eye. The experiments for each orifice are carried out underthe two cases with and without backpressure, respectively. Experimental results show that theflow coefficient with backpressure is larger than the case without it. The larger the aspectratio, the less the flow characteristics are influenced by backpressure. The cavitation firstoccurs at the inlet of orifices and then shifts to the outlet gradually. When there is cavitationhappening at the outlet, flow saturation emerges simultaneously.

Keywords: water hydraulics, flow characteristics, damping orifice, cavitation

1 INTRODUCTION

The damping orifice is often used in water hydrauliccomponents. For example, a damping orifice isplaced in the main valve in a piloted relief valve,and the main valve is opened once the force due tothe pressure drop across the orifice is larger thanthat exerted by the spring and friction. In a waterhydraulic pump, a damping orifice is also used inthe design of static and dynamic hydraulic bearings.Therefore, the flow coefficient and cavitation charac-teristics of orifices are the important parameters forthe design of water hydraulic components.

Many researchers carried out theoretical andexperimental investigations into the characteristicsof flow passing through damping orifices. Lichtaro-wicz et al. [1] reported experimental investigationsof the discharge coefficients for non-cavitating

incompressible flow through orifices, and an empiri-cal formula for the discharge coefficient of orificeswith a chosen value of l/d in the range 2–10 was pro-posed. Pearce and Lichtarowicz [2] found that thevalues of the discharge coefficient were defined interms of the cavitation number, k, and contractioncoefficient, Cc, for cavitating flow through sharp-edged orifices. Koivula and Ellman [3] conducteda study on the cavitation behaviour of hydraulic ori-fices and valves. They pointed out that cavitation canbe reduced by altering the operating conditions, suchas downstream pressure, flowrate, or temperature. Intheir researches, kerosene was used as the workingfluids. Yamaguchi et al. [4, 5] carried out experimentson cavitation in long orifices and derived formulaefor the cavitation limits in critical cavitating andchoking flows. They made a series of studies usingmineral oil, water–glycol fluid, spindle oil, highwater-based fluid (HWBF), and tap water as theworking media and orifices made of brass, acrylicresin, and stainless steel. In their report, the effectsof fluid properties and orifice material on cavitationwere discussed. They suggested that the growthrate of cavitation nuclei increased with a decreasein the viscosity of working media because the

�Corresponding author: School of Mechanical Science and

Engineering, Department of Mechatronic Engineering, Huazhong

University of Science and Technology, No. 1037, Luoyu Road,

Hongshan District, Wuhan, Hubei 430074, People’s Republic of

China. email: liuwater@tom.com

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JPE323 # IMechE 2006 Proc. IMechE Vol. 220 Part A: J. Power and Energy