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Research Papers: Multiphase Flows

Dissipation and Cavitation Characteristics of Single-Hole Orifices

[+] Author and Article Information
Stefano Malavasi

Dipartmento Ingegneria Idraulica, Infrastrutture Viarie, Ambientale, Rilevamento Politecnico di Milano Piazza Leonardo Da Vinci, 32 20133 Milano, Italystefano.malavasi@polimi.it

Gianandrea Vittorio Messa

Dipartmento Ingegneria Idraulica, Infrastrutture Viarie, Ambientale, Rilevamento Politecnico di Milano Piazza Leonardo Da Vinci, 32 20133 Milano, Italygianandrea.messa@mail.polimi.it

J. Fluids Eng 133(5), 051302 (Jun 07, 2011) (8 pages) doi:10.1115/1.4004038 History: Received October 27, 2010; Revised April 19, 2011; Published June 07, 2011; Online June 07, 2011

Abstract

The purpose of this work is to study the dependence of the pressure losses through sharp-edged orifices with respect to the most significant parameters and to find an efficient way to check whether cavitation is likely to occur. Computational fluid dynamics was used to simulate the flow through orifices with different geometrical characteristics for various incoming flow velocities. In particular, the diameter ratio was varied between 0.39 and 0.70, the relative thickness between 0.30 and 1.40, and the pipe Reynolds number between 3.85 $×$ 104 and 1.54 $×$ 105 . The computed pressure drop coefficient in the region of self-similarity with respect to the pipe Reynolds number was first compared to that obtained from some literature models. Afterwards, the comparison with experimental data revealed that an extended pressure criterion is suitable to predict the presence of cavitating conditions. A dimensionless minimum pressure coefficient was then defined, and its dependence upon the above mentioned geometrical and flow parameters was investigated. Finally, a practical formula for the prediction of cavitation was provided.

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Figures

Figure 4

Configuration of the computational domain

Figure 5

Comparison between experimental data and numerical predictions in the region of self-similarity with respect to Rp

Figure 7

Pressure distribution around the orifice before (a) and after (b) the interpolation of the solution on a grid of square cells of 1.00 mm side. The plot of the streamlines curves is reported too.

Figure 8

Minimum pressure obtained from a linear interpolation of the initial computed pressure P* on a grid of square cells of side s for the points A*, B*, C*, D*, and E* in Fig. 6. The values at s = 0 are those of the initial field P* without interpolation. The vertical line identifies the value of s chosen in the present work.

Figure 9

Grid-independence study for the case of β = 0.39, t/dh  = 1.00, and Rp  = 1.10 × 105 . The vertical dotted line identifies the discretization considered in the present work.

Figure 6

Trend of the flow rate as a function of the square root of the pressure drop for the orifice plate with β = 0.39 and t/dh  = 1.40. Comparison between experimental data and numerical predictions (marked with *).

Figure 1

Geometrical sketch of the system and position of the reference sections according to the ISA-RP75.23-1995 normative [2]

Figure 2

Qualitative trend of ΠΔ p as a function of Rp

Figure 3

Trend of ΠΔ p versus t/dh according to the models developed by Chisholm [3], Miller [5], and Idelcick [4]. The curves are drawn for β = 0.40.

Figure 12

Trend of Π*M,1.0 as a function Rp for different values of β, t/dh being equal to 1.00

Figure 10

Identification of the regions in which the interpolated pressure P*1.0 is lower than the vapor pressure PV for the points C*, D*, and E* in Fig. 6

Figure 11

Trend of ΠΔ p as a function of β, t/dh in the range of self-similarity with respect to Rp : comparison between the numerical predictions and some literature models

Figure 13

Trend of Π*M,1.0 as a function t/dh for different values of β, Rp being in the self-similarity range

Figure 14

Dependence of ΠM ,1.0 upon β. Numerical predictions and fitting curve in a linear plot (a) and a semi-log one (b).

Figure 15

Experimental data about the flow through an orifice plate with β = 0.50 and t/dh  = 0.33, with the points a, b, c, d, and e considered for the comparison. The trendline was calculated using the least square method applied to all the data not subjected to cavitation.

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