Experimental Study on the Mechanism of the Combined Action of Cavitation Erosion and Abrasion at High Speed Flow

AbstractA new experimental method on simulating the combined action of cavitation erosion and abrasion was proposed to investigate the erosion mechanism of overflow structure induced by the said processes. An automatic sand mixing device was invented for high-pressure and high-speed flow based on the characteristics of Venturi cavitation generator and hydraulic Bernoulli principle. The experimental system for the combined action of cavitation erosion and abrasion was designed and constructed, and high-speed sand mixing flow only appeared in the test section. A series of tests on the combined and single action of cavitation erosion and abrasion on hydraulic concrete and cement was carried out by using the invented experimental device. Results show that the wear of concrete surface exhibited the combined characteristics of cavitation erosion and abrasion under their joint action. The damage degree of concrete surface under the combined action was more severe than that under a single action. The mass loss of concrete under the combined action was higher than sum of mass losses of concrete under two single actions. The promotion and enhancement between cavitation erosion and abrasion existed in high-speed sand mixing flow. A power exponential relationship was observed between erosion mass loss and flow speed, and the velocity indexes approximated 4.5. Small and light sand particles easily follow water flow. Thus, the strong coupling effect of cavitation erosion and abrasion resulted from the presence of small sand particles. Given the different mechanisms of cavitation erosion and abrasion, presenting the skeleton structure formed by cavitation erosion was notably difficult under the action of abrasion. Meanwhile, abrasion wear easily occurred under the impact of cavitation erosion, and this result is due to the mechanism of the combined action of both processes.

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Cavitation erosion behavior of hydraulic concrete under high-speed flow

Anti-Corrosion Methods and Materials ◽

10.1108/acmm-03-2021-2459 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Xin Wang ◽

Ting-Qiang Xie

Keyword(s):

Cavitation Bubble ◽

High Speed ◽

Cavitation Erosion ◽

Concrete Strength ◽

Bubble Collapse ◽

High Speed Flow ◽

Content Type ◽

Erosion Behavior ◽

Hydraulic Concrete ◽

Speed Flow

Purpose 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. Design/methodology/approach 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. Findings 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. Originality/value 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.

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Research on Oscillating Characteristics of the Shear Layer on the Ship Bottom with a Moonpool under the Action of the Current and Wave

Mathematical Problems in Engineering ◽

10.1155/2021/6657628 ◽

2021 ◽

Vol 2021 ◽

pp. 1-14

Author(s):

X. H. Huang ◽

X. L. Yao ◽

Z. Y. Shi ◽

W. Xiao

Keyword(s):

Shear Layer ◽

High Speed ◽

Fluid Motion ◽

Acoustic Detection ◽

High Speed Flow ◽

Bubble Generation ◽

Speed Flow ◽

The Right ◽

The Impact ◽

Oscillating Characteristics

For some research vessels, a sonar is installed in the moonpool, and some acoustic detection equipment are installed on the ship bottom behind the moonpool, which helps to avoid the impact of the high-speed flow. The moonpool causes the ship bottom discontinued, forming a particular shear layer oscillation. The shear layer oscillation affects the bubble generation and motion in and behind the moonpool. The sonar and acoustic equipment will malfunction when surrounded by many bubbles. However, there is almost no research on the shear layer oscillation near the moonpool. So, in this paper, by measuring the pressure near the moonpool and monitoring the fluid motion in the moonpool and bubbles’ distribution along the ship bottom, the shear layer oscillation near the moonpool is studied experimentally under the action of the incident current and wave. Furthermore, the effects of the sonar and the moonpool shape are investigated. It can be seen that the shear layer oscillation excites the fluid motion in the moonpool. The sonar forms a complicated boundary in the moonpool, resulting in the increase in the frequency of the shear layer oscillation. The shear layer propagates along the ship bottom in the form of the ship bottom wave. Clarifying the oscillating characteristics of the shear layer along the ship bottom with a moonpool is conducive to the design of moonpools in the research ships, and the detection instruments are arranged in the right place along the ship bottom, so as to make sure the detection instruments work properly and detect the marine environment more accurately.

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Numerical Prediction and Risk Analysis of Hydraulic Cavitation Damage in a High-Speed-Flow Spillway

Shock and Vibration ◽

10.1155/2018/1817307 ◽

2018 ◽

Vol 2018 ◽

pp. 1-11

Author(s):

Wuyi Wan ◽

Bin Liu ◽

Awais Raza

Keyword(s):

Numerical Simulation ◽

High Speed ◽

Concrete Surface ◽

Numerical Approach ◽

High Speed Flow ◽

Local Pressure ◽

Numerical Result ◽

Speed Flow ◽

Cavitation Region ◽

Computational Fluid Dynamics Cfd

Hydraulic cavitation is usually an undesirable phenomenon since it can damage the concrete surface of a chute spillway. In order to numerically predict the potential cavitation of a high-speed flow in a chute spillway, a compound risk assessment is proposed by combining probabilistic analysis with a computational fluid dynamics (CFD) technique. Based on the local pressure and flow velocity of the nodes, the traditional cavitation number is introduced to characterize the possibility of cavitation. The distribution of cavitation numbers was obtained according to the numerical simulation of the flow field in an open spillway. A hydraulic experiment was conducted to validate the numerical result. As a result, the potential cavitation region could be shown by visualizing the numerical result. Comparing the numerical results with the experimental results, hydraulic model validates the numerical simulation. The proposed numerical approach is economical and saves time; moreover, it can provide greater information about the potential cavitation region. This approach is more convenient for designers in their efforts to optimize the spillway shape and protect the concrete structure from cavitation erosion while maintaining lower costs and achieving higher visualization.

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Impact of High Inertia Particles on the Shock Layer and Heat Transfer in a Heterogeneous Supersonic Flow around a Blunt Body

Fluids ◽

10.3390/fluids6110406 ◽

2021 ◽

Vol 6 (11) ◽

pp. 406

Author(s):

Andrey Sposobin ◽

Dmitry Reviznikov

Keyword(s):

Heat Transfer ◽

Shock Layer ◽

High Speed ◽

Dynamic Structure ◽

Heat Fluxes ◽

Gas Dynamic ◽

Speed Flow ◽

Combined Action ◽

The Impact ◽

Impact Jet

One of the most important and complex effects associated with the presence of particles in the flow is the gas-dynamic interaction of particles with the shock layer. Of particular interest is the intensification of heat transfer by high inertia particles rebounding from the surface or by the products of erosion destruction, which reach the front of the bow shock wave and violate the gas-dynamic structure of the flow. In this case, according to experimental data, the increase in heat fluxes is much greater than it could be predicted based on the combined action of the kinetic energy of particles and a high-speed flow. The problem is related to the destruction of the flow structure. In this paper, the problem is studied with numerical simulation. We show that the key role in the intensification of heat transfer is played by the formation of an impact jet flowing onto the surface. An area of increased pressure and heat flux is formed in the zone of action of the impact jet. This effect is maintained over time by the successive action of particles.

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