Cavitation refers to the formation of vapor cavities in a liquid when the local pressure becomes lower than the saturation pressure. In many hydraulic applications, cavitation is considered as a ...non-desirable phenomenon, as far as it may cause performance degradation, vibration problems, enhance broad-band noise-emission, and eventually trigger erosion. In this Special Issue, recent findings about cavitation instabilities are reported. More precisely, the dynamics of cavitation sheets are explored at very low Reynolds numbers in laminar flows, and in microscale applications. Both experimental and numerical approach are used. For the latter, original methods are assessed, such as smooth particles hydrodynamics or detached eddy simulations coupled to a compressible approach.
Synthesis-Analysis of the Use of Cavitation Technologies Radzyuk, Aleksandr Yu; Istyagina, Elena B; Kulagina, Lyudmila V ...
Journal of Siberian Federal University. Engineering & Technologies,
10/2022, Letnik:
15, Številka:
7
Journal Article
Recenzirano
Odprti dostop
An analysis of literature sources in the field of the use of cavitation technologies has shown that the effects of cavitation are used in a wide range of industrial technologies. This paper presents ...the main results of work on the cavitation treatment of various liquid compositions, multicomponent media in recent decades. The presented review allows us to conclude that the use of cavitation technologies in various fields of engineering and technology is relevant for solving important practical problems and, as a result, the need for their comprehensive study.
To mitigate the adverse effects of cavitation on the performance degradation and chemical corrosion of hydraulic machines, a jet hydrofoil physical model based on the structure of a guide vane model ...of a high-pressure mixed-flow hydraulic turbine was established. A density correction turbulence model based on filters was adopted to numerically simulate the cavitation characteristics on the surface of the jet hydrofoil. The results demonstrate that when the jet speed is 12 m/s and the jet angle is −15°, the scheme exhibits the best cavitation suppression effect among all combinations of jet angles and speeds. Cavities near the jet structure are prematurely collapsed after being pressurized, and the cavitation suppression effect in the low-pressure area at the trailing edge is also satisfactory. The time-averaged bubble volume fraction reaches its minimum at 2.17%, with the time-averaged bubble volume fraction being 27.3% of the prototype hydrofoil. At flow speeds of 2.4 m/s and 7.2 m/s, small-angle jet fluid accumulated will stick to the closed cavities on the surface of the hydrofoil and cause them to rupture, while the jet fluid at the jet angle of 60° and speeds of 7.2 m/s and 12 m/s will directly cut off the bubbles.
•DCMFBM model is used to simulate cavitation characteristics on hydrofoil.•Analysis of jet angle and velocity impact on cavitation characteristics.•High-speed jet at small angles most effectively suppresses cavities.
•Cavitation dynamic behaviors of the hydrofoil with whalelike leading-edge protuberances are simulated.•The k-ω SST model with local compressibility correction for turbulent viscosity is implemented ...in OpenFOAM.•Interactions between cavitation and streamwise vortex pairs are discussed.•Influence factors of monopole and dipole noise in cavitating flow are obtained from Lighthill's acoustic analogy theory.•Time domain characteristics of monopole and dipole noise in cavitating flow are discussed.
In this paper, the open source software OpenFOAM is used to perform a numerical investigation of the cavitating flow around a modified NACA634-021 hydrofoil with bioinspired, wavy leading edge, with particular emphasis on study of the interactions between the cavitation and the streamwise vortices and the far-field radiation noise. A modified k-ω shear-stress transport (SST) model coupled with the Schnerr-Sauer cavitation model and the Ffowcs Williams-Hawkings (FW-H) acoustic analogy approach are introduced to the simulation. The transient cavitation structure and the streamwise vortices are captured well and the results show significant interactions between the cavitation and the streamwise vortices. Cavitation can promote fragmentation of the streamwise vortices, while the streamwise vortices cause cavitation inception to occur earlier and bind the cavitation within the trough region by changing the pressure distribution on the hydrofoil. The transformation of the FW-H equation's solution indicates that the monopole noise is directly related to the cavitation volume acceleration and the dipole noise is related to the mechanical force of the hydrofoil on fluids and the rate at which this force changes. The collapse of cavitation cloud and the collision of the re-entrant jet and main flow will cause violent fluctuation of the mechanical force thus produce instantaneous extreme dipole noise values, while the monopole noise is relatively strong in the cavitation collapse stage due to significant cavitation volume acceleration. The time domain hydroacoustic characteristics are similar for the modified hydrofoil and the baseline hydrofoil.
The modelling of internal and external flow phenomena of high pressure injection systems has developed significantly in the last few decades. The challenge currently however, is to model these areas ...of flow together accounting for different multi-phase phenomena that require a wide range of resolutions. More specifically, the highly turbulent nature of internal nozzle cavitation requires a high grid and temporal resolution, whereas the external nozzle atomisation processes exists over a comparatively much larger space with lower time and space resolution needed. The research described in this thesis is focused on coupling the internal nozzle and external processes using a single Eulerian Volume Of Fluid (VOF) multiphase model. First, investigations into the dynamics of internal nozzle cavitation is presented, through simulation of two phase nozzle flows without spray formation demonstrating sensitivities to discretization techniques and boundary conditions. Then, the simulation of internal nozzle cavitation with spray formation using a single model was achieved by the construction of a three phase VOF model with cavitation which is described. A non-condensable gaseous phase is considered alongside the liquid and vapours phases, the liquid interface is sharp with a diffusive interface between gaseous phases. Comparisons were made with both experimental data and previous numerical investigations. Finally, a new solver with the introduction of the Eulerian-Lagrangian Spray Atomization (ELSA) framework with the Interface Capturing Method (ICM) for surface density to the system to describe the liquid structures below the Sub-Grid Scale (SGS) is presented. Thus quantities such as droplet Sauter Mean Diameter (SMD) and droplet spray angle at these scales can be extracted, with comparisons made with experimental data. The coupling of the ELSA-ICM model with the three phase cavitating model allows for processes of the entire spray formation to be resolved. More specifically, for the first time, the evolving surfaces of the entire injection process, from internal nozzle cavitation to spray atomisation, can thus be tracked throughout even at the SGS. This allows for a direct insight into the interaction between the cavitation and atomisation processes.
The combined application of electric fields and ultrasonic waves has shown promise in controlling cell membrane permeability, potentially resulting in synergistic effects that can be explored in the ...biotechnology industry. However, further clarification on how these processes interact is still needed. The objective of the present study was to investigate the atomic-scale effects of these processes on a DPPC lipid bilayer using molecular dynamics simulations. For higher electric fields, capable of independently forming pores, the application of an ultrasonic wave in the absence of cavitation yielded no additional effects on pore formation. However, for lower electric fields, the reduction in bilayer thickness induced by the shock wave catalyzed the electroporation process, effectively shortening the mean path that water molecules must traverse to form pores. When cavitation was considered, synergistic effects were evident only if the wave alone was able to generate pores through the formation of a water nanojet. In these cases, sonoporation acted as a mean to focus the electroporation effects on the initial pore formed by the nanojet. This study contributes to a better understanding of the synergy between electric fields and ultrasonic waves and to an optimal selection of processing parameters in practical applications of these processes.
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•Computational analysis of electric fields and ultrasound sinergy in lipid membranes.•Ultrasonic waves had no effect on pore formation under high electric fields.•The waves thinned the bilayer, catalyzing electroporation in lower electric fields.•Cavitation enhances electroporation by directing its effects with a water nanojet.
•The re-entrant jet induced cloud shedding is confirmed in hot water.•Whole stages of the cavity clouds developing and collapsing are presented.•Shedding dynamics of cavitation over a wide ...tempetature range are identified.•The thermal transition and increase-decrease trend of cavity length are analyzed.
The effects of temperature on hydraulic cavitation dynamics are investigated under various operating conditions, in a close loop cavitation tunnel with a small-scale venturi type section. A systematic study is performed with temperatures varying between 24°C and 85°C, using a high-speed visualization system to observe the cavitating flow. The image processing methods provided in the paper present a quantitative comparison of the cavitation dynamics and structure development. The results show that the increase of the fluid temperature induces the growth of the cavitation volume up to about 55°C, thereafter an additional increase in temperature has the opposite effect. This evolution is interpreted as a competition between a Reynolds effect and the well-known thermal effect. Cavitation is more closely investigated within the temperature range 50°C - 65°C, to analyze the changes in the structure and the cavitation dynamics. For the prediction of thermal suppression head, the thermal effect parameter Σ which can be used empirically, is derived at the maximum cavitation length. This fluid thermodynamic parameter Σ(Ttrans) at the transition peak can be referred to to avoid the maximum cavitation aggressiveness induced vibration or erosion for thermos-fluids around the thermal transition temperature. Finally, the factors influencing cavitation length and shedding frequency are presented and analyzed.
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