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The purpose of this paper is to study the variation of cavitation scale with pressure and flow in poppet throttle valve, to obtain the cavitation scale under pressure and flow conditions and to provide experimental support for the research of suppressing throttle valve cavitation and cavitation theory.

A hydraulic cavitation platform was set up, a valve was manufactured with highly transparent PMMA material and a high-speed camera was used to observe the change in cavitation scale.

Through experiments, it is found that the pressure difference between inlet and outlet of throttle valve affects the cavitation scale, and the more the pressure difference is, the easier the cavitation will be formed. Under the condition of small pressure difference, the cavitation is not obvious and reducing the pressure difference can effectively suppress the cavitation; the flow rate also affects the cavitation scale, the smaller the flow rate, the more difficult the cavitation will be formed and the lower the flow rate, the more the cavitation will be suppressed.

Because of the magnification factor of the high-speed camera lens, the morphology of smaller bubbles cannot be observed in this study, and the experimental conditions need to be improved in the follow-up study.

This study can provide experimental support for the study of throttle valve cavitation suppression methods and cavitation theory.

The study aims to display the bubbles' evolution in the shear layer and their relationship with the pressure fluctuations. Furthermore, the coherent structures of the first six modes are extracted, in order to provide insight into their temporal and spatial evolution and determine the relationship between cavitating bubbles and coherent structures.

In the present study, numerical simulations of submerged jet cavitating flow were carried out at a cavitation inception condition inside an axisymmetric cavity using the large eddy simulation (LES) turbulence model and the Schnerr–Sauer (S–S) cavitation model. Based on snapshots produced by the numerical simulation, dynamic mode decomposition (DMD) was performed to extract the three-dimensional coherent structures of the first six modes in the shear layer.

The cavitating bubbles in the shear layer are deformed to elongated ellipsoid shapes by shear forces. The significant pressure fluctuations are induced by the collapse of the biggest bubble in the group. The first mode illustrates the mean characteristics of the flow field. The flow in the peripheral region of the shear layer is mainly dominated by large-scale coherent structures revealed by the second and third modes, while different small-scale coherent structures are contained in the central region. The cavitating bubbles are associated with small size coherent structures as the sixth or higher modes.

This work demonstrates the feasibility of LES for high Reynolds number shear layer flow. The dynamic mode decomposition method is a novel method to extract coherent structures and obtain their dynamic information that will help us to optimize and control the flow.

(1) This paper first displays the three-dimensional coherent structures and their characteristics in the shear layer of confined jet flow. (2) The relationship of bubbles shape and pressure fluctuations is illustrated. (3) The visualization of coherent structures benefits the understanding of the mixing process and cavitation inception in jet shear layers.

The purpose of this paper is to use the NACA 0015 symmetric hydrofoil as the research subject and control cloud cavitation on hydrofoils.

Based on observed distribution of caudal fin spines on fish, a bionic structure of fin-like spines is arranged on the hydrofoil suction surface, which maintains the cavitation in a quasi-steady state stage by eliminating the cyclic shedding process of cloud cavitation. Based on the modified shear stress transport k-ω turbulence model and the Zwart–Gerber–Belamri cavitation model, this paper compares and analyzes the NACA 0015 hydrofoil and the bionic NACA 0015 hydrofoil under condition of an angle of attack of 8° and a cavitation number of 0.8.

The results show that the average drag of the hydrofoil is reduced but the lift is decreased, and the lift-drag ratio is increased after arranging the bionic structure. The bionic structure can effectively reduce the turbulent kinetic energy and make the flow more stable; it also can effectively control the hydrofoil surface side-entrant jet and the vortex shedding process of the near wall region.

Based on the above conclusions, the bionic structure of fin-like spines can achieve a significant passive control in the hydrofoil cloud cavitation process.

Cavitation erosion has always been a common technical problem in a hydraulic discharging structure. This paper aims to investigate the cavitation erosion behavior of hydraulic concrete under high-speed flow.

A high-speed and high-pressure venturi cavitation erosion generator was used to simulate the strong cavitation. The characteristics of hydrodynamic loads of cavitation bubble collapse zone, the failure characteristics and the erosion development process of concrete were investigated. The main influencing factors of cavitation erosion were discussed.

The collapse of the cavitation bubble group produced a high frequency, continuous and unsteady pulse load on the wall of concrete, which was more likely to cause fatigue failure of concrete materials. The cavitation action position and the main frequency of impact load were greatly affected by the downstream pressure. A power exponential relationship between cavitation load, cavitation erosion and flow speed was observed. With the increase of concrete strength, the degree of damage of cavitation erosion was approximately linearly reduced.

After cavitation erosion, a skeleton structure was formed by the accumulation of granular particles, and the relatively independent bulk structure of the surface differed from the flake structure formed after abrasion.

The purpose of this paper is to study the cavitation erosion stages of AA5083 by electrochemical noise (EN).

EN technology including noise resistance and fast Fourier transform were used to characterize the electrochemical process during the cavitation erosion process.

AA5083 suffers from uniform corrosion during the cavitation erosion process. The whole cavitation erosion process can be divided into three stages: incubation stage, acceleration stage and steady-state stage. EN signals showed obvious differences in different stages of cavitation erosion.

EN technique is a suitable method that can be used to study cavitation erosion mechanism and identify cavitation erosion stages.

Ultrahigh-speed projectile running in water with the velocity close to the speed of sound usually causes large supercavity. The computation of such transonic cavitating flows is usually difficult, thus high-speed model reflecting the compressibility of both the liquid and the vapor phases should be introduced to model such flow. The purpose of this paper is to achieve a model within an in-house developed solver to simulate the ultrahigh-speed subsonic supercavitating flows.

An improved TAIT equation adjusted by local temperature is adopted as the equation of state (EOS) for the liquid phase, and the Peng-Robinson EOS is used for the vapor phase. An all-speed variable coupling algorithm is used to unify the computations and regulate the convergence at arbitrary Mach number. The ultrahigh-speed (Ma=0.7) supercavitating flows around circular disk are investigated in contrast with the case of low subsonic (Ma=0.007) flow.

The characteristic physical variables are reasonably predicted, and the cavity profiles are compared to be close to the experimental empirical formula. An important conclusion in the compressible cavitating flow theory is verified by the numerical result that, at any specific cavitation number the cavity’s size and the drag coefficient both increase along with the rise of Mach number. On the contrary, it is found as well that the cavity’s slenderness ratio decreases when Mach number goes up. It indicates that the compressibility has different influences on the length and the radius of the supercavity.

A high-speed model reflecting the compressibility of both the liquid and the vapor phases was suggested to model the ultrahigh-speed supercavitating flows around underwater projectiles.

The purpose of this paper is to quantify the relative importance of the multiphase model for the simulation of a gas bubble impacted by a normal shock wave in water. Both the free-field case and the collapse near a wall are investigated. Simulations are performed on both two- and three-dimensional configurations. The main phenomena involved in the bubble collapse are illustrated. A focus on the maximum pressure reached during the collapse is proposed.

Simulations are performed using an inviscid compressible homogeneous solver based on different systems of equations. It consists in solving different mixture or phasic conservation laws and a transport-equation for the gas volume fraction. Three-dimensional configurations are considered for which an efficient massively parallel strategy was developed. The code is based on a finite volume discretization for which numerical fluxes are computed with a Harten, Lax, Van Leer, Contact (HLLC) scheme.

The comparison of three multiphase models is proposed. It is shown that a simple four-equation model is well-suited to simulate such strong shock-bubble interaction. The three-dimensional collapse near a wall is investigated. It is shown that the intensity of pressure peaks on the wall is drastically increased (more than 200 per cent) in comparison with the cylindrical case.

The study of bubble collapse is a key point to understand the physical mechanism involved in cavitation erosion. The bubble collapse close to the wall has been addressed as the fundamental mechanism producing damage. Its general behavior is characterized by the formation of a water jet that penetrates through the bubble and the generation of a blast wave during the induced collapse. Both the jet and the blast wave are possible damaging mechanisms. However, the high-speed dynamics, the small spatio-temporal scales and the complicated physics involved in these processes make any theoretical and experimental approach a challenge.

Cavitation erosion is a major problem for hydraulic and marine applications. It is a limiting point for the conception and design of such components.

Such a comparison of multiphase models in the case of a strong shock-induced bubble collapse is clearly original. Usually models are tested separately leading to a large dispersion of results. Moreover, simulations of a three-dimensional bubble collapse are scarce in the literature using such fine grids.

The purpose of this paper is to provide a review of recent developments in electromagnetic radiation (EMR) sensing.

Following a short introduction, this paper discusses a selection of recent research and development activities concerning the sensing of gamma radiation, X‐rays and ultraviolet (UV) radiation.

This shows that novel sensors are being developed for all of these classes of EMR. Improved gamma sensors are attracting strong interest in the USA, reflecting concerns regarding nuclear security. Novel X‐ray and UV sensors are often being developed in response to new and emerging uses of these types of radiation.

This paper provides a technical review of recent research into sensors for detecting gamma radiation, X‐rays and UV radiation.

Seeks to examine the performance of conventional turbulence models modelling strongly swirling flows within a Symmetrical Turn up Vortex Amplifier, with adjustment of the turbulence model constants to improve agreement with experimental data.

First, the standard k‐ε model and the Reynolds Stress Model (RSM) were used with standard values of model constants, using both the first order upwind and the quadratic upstream interpolation for convective kinetics (QUICK) schemes. Then, the swirling effect was corrected by adjusting the model coefficients.

The standard RSM with the QUICK did produce better predictions but still significantly overestimated the experimental data. Much improved simulation was obtained with the systematic adjustment of the model constants in the standard k‐ε model using the QUICK. The physical significance of the model constants accounted for changes of the eddy viscosity, and the production and destruction of k and ε.

More industrial cases could benefit from this simple and useful approach.

The constant adjustment is regular and directed, based on the eddy viscosity and the production and destruction of k and ε. The regularity of the effect of the model constants on the solutions makes it easier to quickly adjust them for other industrial applications.

The present study aims to resolve the adjustment problem of cavitation bubble number density in simulations of the cavitating flows within the diesel injection nozzle holes using a two-fluid cavitation model.

The basic rule that determines the variations of cavitation bubble number density has been checked through the scaling analysis of a two-fluid model under the assumption of hydrodynamic similarity of the cavitating flows. Moreover, a phenomenological model for the number density of cavitation bubbles that takes the hydrodynamic effect into account has been developed through the combined analysis of cavitation bubble dynamics and internal flow characteristics of diesel injection nozzle holes. This new model has also been validated by the discharge coefficient measures in a wide range of injection conditions.

The values of cavitation bubble number density must rationally match changes both in liquid quality effect and in hydrodynamic effect corresponding to different cavitating flows. The validation results show that the two-fluid cavitation model together with this new cavitation bubble number density model predicts well both the cavitation content inside the diesel nozzle hole and the relationship between discharge coefficient and cavitation number, and the new cavitation bubble number density model has the potential to further expand the application range of the two-fluid cavitation model.

This study provides insight into hydrodynamic effect corresponding to cavitating flows inside diesel nozzle holes and presents an idea to model the cavitation bubble number density phenomenologically. The model idea and the developed model are useful to researchers and engineers in the area of nozzle internal flow and cavitating flow.