Special Issue "New Advances of Cavitation Instabilities"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Mechanical Engineering".

Deadline for manuscript submissions: 31 January 2021.

Special Issue Editor

Dr. Florent Ravelet
Website SciProfiles
Guest Editor
Arts et Metiers Institute of Technology, LIFSE, CNAM, HESAM University, 75013 Paris, France
Interests: Turbomachinery; Instabilities; Experiments; Cavitation

Special Issue Information

Dear Colleagues,

We are inviting submissions to the Special Issue regarding recent scientific advances in cavitation instabilities.

In many applications, cavitating flows are encountered at flow rates with very high Reynolds numbers. This formally unsteady flow type is very sensitive to disturbances. In the ordinary case of a 2D profile, it is rightly recognized that for sufficiently low cavitation numbers, periodic or quasi-periodic cavity shedding arises.

This phenomenon is similar to the classical concept of instability in dynamical systems. On more complex problems, like cavitation in inducers, several periodical behaviors can emerge. Firstly, the local intrinsic flow instabilities will depend on the region that presents hydrodynamic cavitation: tip-leakage vortices, backflow vortices, or blades suction surface. Secondly, interaction between adjacent blades can lead to rotating instability, with cells of various sizes that propagate from blade to blade. Finally, system instabilities are also observed, because of the blockage linked to the volume variation of the pockets, or to a possible positive slope of the inducer characteristics linked to a change in the angle of attack on the blades.

A more proper understanding of these instabilities is of crucial interest, especially in the field of turbomachinery, still motivating applied and fundamental research on cavitation instabilities. Recently, the use of modal analysis tools like POD and DMD on high-speed videos taken on 2D wedges or 2D profiles has shown that several mechanisms with various frequencies can be mixed: the so-called re-entrant-jet and a condensation shock wave. X-ray imaging was successfully used to measure the volume fraction, which highlighted this mechanism for the first time in the last five years. New numerical works with a compressible approach, a use of liquid and vapor state-laws, and LES are under development, and it may be useful to study in more details the physics of these instabilities. Finally, there are, nevertheless, advances to perform concerning the stability analysis of such complex multiphase flows.

This Special Issue, thus, serves to promote exploratory research and development on Hydrodynamic Cavitation Instabilities, both on academic geometries and on industrial cases, with experimental, numerical or analytical tools.

Dr. Florent Ravelet
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Hydrodynamic cavitation
  • New numerical methods for cavitating flows
  • System instabilities
  • Cavitation surge
  • Rotating cavitation
  • Experimental techniques for cavitating flow
  • Stability analysis of multiphase flows
  • Tip-vortex cavitation
  • Surface treatment and cavitation control

Published Papers (4 papers)

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Research

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Open AccessFeature PaperArticle
Development of Attached Cavitation at Very Low Reynolds Numbers from Partial to Super-Cavitation
Appl. Sci. 2020, 10(20), 7350; https://doi.org/10.3390/app10207350 - 20 Oct 2020
Abstract
The present study focuses on the inception, the growth, and the potential unsteady dynamics of attached vapor cavities into laminar separation bubbles. A viscous silicon oil has been used in a Venturi geometry to explore the flow for Reynolds numbers ranging from R [...] Read more.
The present study focuses on the inception, the growth, and the potential unsteady dynamics of attached vapor cavities into laminar separation bubbles. A viscous silicon oil has been used in a Venturi geometry to explore the flow for Reynolds numbers ranging from Re=800 to Re=2000. Special care has been taken to extract the maximum amount of dissolved air. At the lowest Reynolds numbers the cavities are steady and grow regularly with decreasing ambient pressure. A transition takes place between Re=1200 and Re=1400 for which different dynamical regimes are identified: a steady regime for tiny cavities, a periodical regime of attached cavity shrinking characterized by a very small Strouhal number for cavities of intermediate sizes, the bursting of aperiodical cavitational vortices which further lower the pressure, and finally steady super-cavitating sheets observed at the lowest of pressures. The growth of the cavity with the decrease of the cavitation number also becomes steeper. This scenario is then well established and similar for Reynolds numbers between Re=1400 and Re=2000. Full article
(This article belongs to the Special Issue New Advances of Cavitation Instabilities)
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Open AccessArticle
Compressible Two-Phase Viscous Flow Investigations of Cavitation Dynamics for the ITTC Standard Cavitator
Appl. Sci. 2020, 10(19), 6985; https://doi.org/10.3390/app10196985 - 07 Oct 2020
Abstract
In this paper, the ITTC Standard Cavitator is numerically investigated in a cavitation tunnel. Simulations at different cavitation numbers are compared against experiments conducted in the cavitation tunnel of SVA Potsdam. The focus is placed on the numerical prediction of sheet-cavitation dynamics and [...] Read more.
In this paper, the ITTC Standard Cavitator is numerically investigated in a cavitation tunnel. Simulations at different cavitation numbers are compared against experiments conducted in the cavitation tunnel of SVA Potsdam. The focus is placed on the numerical prediction of sheet-cavitation dynamics and the analysis of transient phenomena. A compressible two-phase flow model is used for the flow solution, and two turbulence closures are employed: a two-equation unsteady RANS model, and a hybrid RANS/LES model. A homogeneous mixture model is used for the two phases. Detailed analysis of the cavitation shedding mechanism confirms that the dynamics of the sheet cavitation are dictated by the re-entrant jet. The break-off cycle is relatively periodic in both investigated cases with approximately constant shedding frequency. The CFD predicted sheet-cavitation shedding frequencies can be observed also in the acoustic measurements. The Strouhal numbers lie within the usual ranges reported in the literature for sheet-cavitation shedding. We furthermore demonstrate that the vortical flow structures can in certain cases develop striking cavitating toroidal vortices, as well as pressure wave fronts associated with a cavity cloud collapse event. To our knowledge, our numerical analyses are the first reported for the ITTC standard cavitator. Full article
(This article belongs to the Special Issue New Advances of Cavitation Instabilities)
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Open AccessArticle
Numerical Investigation of Methodologies for Cavitation Suppression Inside Globe Valves
Appl. Sci. 2020, 10(16), 5541; https://doi.org/10.3390/app10165541 - 11 Aug 2020
Abstract
Cavitation inside globe valves, which is a common phenomenon if there is a high-pressure drop, is numerically investigated in this study. Firstly, the cavitation phenomenon in globe valves with a different number of cages is compared. When there is no valve cage, cavitation [...] Read more.
Cavitation inside globe valves, which is a common phenomenon if there is a high-pressure drop, is numerically investigated in this study. Firstly, the cavitation phenomenon in globe valves with a different number of cages is compared. When there is no valve cage, cavitation mainly appears at the valve seat, the bottom of the valve core, and the downstream pipelines. By installing a valve cage, cavitation bubbles can be restricted around the valve cage protecting the valve body from being damaged. Secondly, the effects of the outlet pressure, the working temperature, and the installation angle of two valve cages in a two-cage globe valve are studied to find out the best method to suppress cavitation, and cavitation number is utilized to evaluate cavitation intensity. Results show that cavitation intensity inside globe valves can be reduced by increasing the valve outlet pressure, decreasing the working temperature, or increasing the installation angle. Results suggest that increasing the outlet pressure is the most efficient way to suppress cavitation intensity in a globe valve, and the working temperature has a minimal effect on cavitation intensity. Full article
(This article belongs to the Special Issue New Advances of Cavitation Instabilities)
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Review

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Open AccessFeature PaperReview
Cavitating Jet: A Review
Appl. Sci. 2020, 10(20), 7280; https://doi.org/10.3390/app10207280 - 17 Oct 2020
Abstract
When a high-speed water jet is injected into water through a nozzle, cavitation is generated in the nozzle and/or shear layer around the jet. A jet with cavitation is called a “cavitating jet”. When the cavitating jet is injected into a surface, cavitation [...] Read more.
When a high-speed water jet is injected into water through a nozzle, cavitation is generated in the nozzle and/or shear layer around the jet. A jet with cavitation is called a “cavitating jet”. When the cavitating jet is injected into a surface, cavitation is collapsed, producing impacts. Although cavitation impacts are harmful to hydraulic machinery, impacts produced by cavitating jets are utilized for cleaning, drilling and cavitation peening, which is a mechanical surface treatment to improve the fatigue strength of metallic materials in the same way as shot peening. When a cavitating jet is optimized, the peening intensity of the cavitating jet is larger than that of water jet peening, in which water column impacts are used. In order to optimize the cavitating jet, an understanding of the instabilities of the cavitating jet is required. In the present review, the unsteady behavior of vortex cavitation is visualized, and key parameters such as injection pressure, cavitation number and sound velocity in cavitating flow field are discussed, then the estimation methods of the aggressive intensity of the jet are summarized. Full article
(This article belongs to the Special Issue New Advances of Cavitation Instabilities)
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