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Review
. 2017 Mar;473(2199):20160345.
doi: 10.1098/rspa.2016.0345. Epub 2017 Mar 15.

Fluid dynamics of acoustic and hydrodynamic cavitation in hydraulic power systems

A Ferrari  1
Affiliations
Review

Fluid dynamics of acoustic and hydrodynamic cavitation in hydraulic power systems

A Ferrari. Proc Math Phys Eng Sci. 2017 Mar.

Abstract

Cavitation is the transition from a liquid to a vapour phase, due to a drop in pressure to the level of the vapour tension of the fluid. Two kinds of cavitation have been reviewed here: acoustic cavitation and hydrodynamic cavitation. As acoustic cavitation in engineering systems is related to the propagation of waves through a region subjected to liquid vaporization, the available expressions of the sound speed are discussed. One of the main effects of hydrodynamic cavitation in the nozzles and orifices of hydraulic power systems is a reduction in flow permeability. Different discharge coefficient formulae are analysed in this paper: the Reynolds number and the cavitation number result to be the key fluid dynamical parameters for liquid and cavitating flows, respectively. The latest advances in the characterization of different cavitation regimes in a nozzle, as the cavitation number reduces, are presented. The physical cause of choked flows is explained, and an analogy between cavitation and supersonic aerodynamic flows is proposed. The main approaches to cavitation modelling in hydraulic power systems are also reviewed: these are divided into homogeneous-mixture and two-phase models. The homogeneous-mixture models are further subdivided into barotropic and baroclinic models. The advantages and disadvantages of an implementation of the complete Rayleigh-Plesset equation are examined.

Keywords: Rayleigh–Plesset equation; acoustic cavitation; barotropic and baroclinic models; hydrodynamic cavitation; nozzle discharge coefficient; sound speed.

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Figures

Figure 1.
Figure 1.
Straight nozzle layout and pressure evolution. (Online version in colour.)
Figure 2.
Figure 2.
Cavitation evolution with respect to p2.
Figure 3.
Figure 3.
Different cavitation regimes. (Online version in colour.)
Figure 4.
Figure 4.
Dependence of Cd on CN. (a) Rectangular cross-section nozzle [43]. (b) Circular cross-section nozzle [43]. (c) Cavitation inception and development.
Figure 5.
Figure 5.
Mass flow rate, cavitation and choking conditions for diesel oil (p1 is constant and p2 changes) [24]. (Online version in colour.)
Figure 6.
Figure 6.
Cd versus Re [71]. (Online version in colour.)
Figure 7.
Figure 7.
Influence of L/d on the Cd versus Re curve for oil [68].
Figure 8.
Figure 8.
Square root of (1 + χ)1/2 as a function of Cc for different A2/A1 ratios. (Online version in colour.)
Figure 9.
Figure 9.
CNcrit and CNstart versus Re [24]. (Online version in colour.)
Figure 10.
Figure 10.
Cc versus Re for an orifice and Viersma asymptotic approximation. (Online version in colour.)
Figure 11.
Figure 11.
Contraction coefficient as a function of d/d1.
Figure 12.
Figure 12.
Blake's radius and critical liquid pressure.
Figure 13.
Figure 13.
Measurement of N(R) in water with different purities (T = 293 K) [110]. (Online version in colour.)
Figure 14.
Figure 14.
Activated nuclei as a function of water tensile strength for a ship propeller [21]; curve σ1 refers to a high content of large nuclei, curve σ2 refers to a high content of medium-sized nuclei; curve σ3 refers to a low content of medium-sized nuclei and curve σ4 refers to heavily degassed water.
Figure 15.
Figure 15.
Effect of water tensile strength on the number of activated nuclei for different dissolved gas fractions and different pressure conditions [21].
Figure 16.
Figure 16.
Cavitation inception and development.
Figue 17.
Figue 17.
Cavitation desinence.
Figure 18.
Figure 18.
Analysis of cavitation inception. (a) Pressure and void fraction distribution. (b) Characteristic lines related to the (u + a) eigenvalue.
Figure 19.
Figure 19.
Analysis of cavitation desinence. (a) Pressure and void fraction distribution. (b) Characteristic lines related to the (u − a) eigenvalue.
Figure 20.
Figure 20.
Choking-flow conditions (Mach number field, CN ≈ 1.29).
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