CFD analysis on hydrodynamic characteristics of ultra-high-pressure water jets: stationary vs. translating nozzle conditions

Effect of technological parameters on hydrodynamic performance of ultra-high-pressure water-jet nozzle

When rocks are cut in coal mines by steel picks, frictional heating sometimes causes ignition of methane; high speed water jets may provide a method of cutting which is free from this hazard. A high speed water jet emerging from a nozzle slows down with increasing distance from the nozzle and breaks up into water drops. Studies were made of the behaviour of water jets: in most of the experiments the jets were produced by pressures of 600 atm., but some results are given of experiments at pressures up to 5000 atm. The jets were examined by short exposure optical photography with several different methods of illumination (parallel transmitted, diffuse, and schlieren) and by X-ray photography. In order to find out how the jet velocity decays with distance from a nozzle, and to compare nozzle designs, a target plate containing a hole smaller than the jet diameter was placed so that the jet impinged at right angles on to it, and the target plate was moved until the maximum pressure at the hole was found: this was measured for different distances from the nozzle. Nozzle shapes suggested in literature for minimizing jet dispersion were studied and an empirical investigation of a variety of nozzle shapes was carried out. Several nozzle shapes were found which gave good results, i.e. the maximum pressure on the target plate was half the pump pressure at a distance of about 350 nozzle diameters. In many cutting applications the first stage in the process would be the impingement of a water jet on a surface at right angles. The initial cutting would depend upon the stress distribution within the target, which in turn would depend upon the pressure distribution produced by the water jet on the surface. A theory is given of the pressure distribution on the target plate, which predicts that the pressure will fall to zero at about 2.6 jet radii: this was found to be in good agreement with experiments. Preliminary studies were made of the penetration of several types of rock by water jets of velocities up to about 1000 m/s (pressures about 5000 atm). It was found that a 1 mm diameter jet drills a cylindrical hole about 5 mm in diameter. The pressure that the water jet produces at the bottom of such holes was measured and shown to fall off to about one-tenth of the nozzle pressure at a hole depth of about 4 cm.

Submerged cavitating waterjet micro-forming is a novel jetting technology. Existing detection devices cannot accurately detect bubble distribution in still water domains and target workpiece processing areas. To investigate bubble generation and distribution in still water domains and their influence on target micro-forming, a submerged cavitating waterjet micro-forming fluid–solid coupling numerical model was established in this paper. The distribution of submerged cavitating waterjet cavitation effects and the hammering of micro waterjets on metal plates under the action of cavitation bubbles, as well as the coupled forces, were analyzed. The results show that bubble distribution in still water domains is closely related to turbulence, vortices, and pressure distributions. The collapse of cavitation bubbles generates enormous pressure, and the pressure generated by the collapse of cavitation bubbles causes the micro waterjet hammers to produce annular deformation zones on the metal plates. The bubble distribution laws and theoretical basis of cavitation micro-forming technology in submerged waterjets are provided in this study, which has very important engineering application significance.

This paper conducted a computational study on the KCS benchmark model at static drift conditions. At the first instance, the roles played by the grid size, turbulence model, and time step are qualitatively and quantitatively analyzed with the orthogonal experimental method (OEM). After the verification of simulated results compared with experimental data in a Static Oblique Towing Test (OTT), hydrodynamic performance is obtained with the employment of the SST κ-ω turbulence model. The grid size is set as 0.07 m while the time step as 0.01 s. The characteristics of the wake field are illustrated in different forms, such as contours of the free surface, distribution of pressure and hydrodynamic forces, variation of turbulent kinetic energy (TKE), and so on. For a deep insight into the physical mechanisms of the asymmetrical flow field, the Detached Eddy Simulation (DES) method is also utilized to capture vortical structures occurring around the hull, in comparison with results obtained through the Reynolds Averaged Navier Stokes (RANS) model. With the aim of a hydrodynamic derivative estimation or detailed flow characteristics analysis, corresponding selections of the computational method are disparate.

The multi-physics analysis using both the CFD and thermo-mechanical analysis is carried out to estimate the life of the heat exchanger which is operated under the conditions of high temperature and high pressure. First CFD analysis is carried out to obtain the distribution of flow, pressure and temperature around heat exchanger. The distribution of pressure, temperature and heat transfer coefficient obtained from the CFD analysis is transferred to the thermo-mechanical analysis using finite element analysis technique and is used as data to calculate the mechanical and thermal stress distribution in the heat exchanger. For the CFD analysis, it is considered a segment of heat exchangers using the symmetric and periodic conditions. For the thermo-mechanical analysis, the present finite element model considered both a segment and a half of full geometry by using the symmetric and periodic conditions. Alloy 625 is used for the present heat exchanger design due to its high strength at the elevated temperatures. The temperature-dependent physical properties of Alloy 625 for the thermo-mechanical analysis are used in a temperature ranges of 300∼1100K. Fatigue analysis is performed using a Goodman-diagram to assess the life of the present heat exchanger.

The removal of rust from large equipment such as trains and ship hulls poses a significant challenge. Traditional methods, such as chemical cleaning, flame rust removal, and laser rust removal, suffer from drawbacks such as high energy consumption, operational complexity, and poor mobility. Sandblasting and high-pressure water jet rust removal face issues such as high consumable costs and environmental pollution. Existing robotic grinding systems often rely on precise measurement of the workpiece surface geometry to perform deburring and polishing tasks; however, they lack the sufficient adaptability and robustness required for rust removal operations. To address these limitations, this study proposes a floating grinding actuator scheme based on compound force-position fuzzy control. By implementing simplified path-point planning, continuous grinding and rust removal can be achieved without requiring the pre-measurement of workpiece geometry data. This solution integrates force and laser displacement sensors to provide real-time compensation for path deviations and ensures adaptability to complex surfaces. A fuzzy derivative-leading PID algorithm was employed to control the grinding force, enabling adaptive force regulation and enhancing the control precision. Rust removal test results demonstrate that under varying advancing speeds, fuzzy derivative-leading PID control can significantly reduce fluctuations in both the grinding force and average error compared to traditional PID control. At a speed of 40 mm/s, excellent control performance was maintained, achieving a rust removal rate of 99.73%. This solution provides an efficient, environmentally friendly, and high-precision automated approach to rust removal using large-scale equipment.

The internal geometry of water jet orifices is important to determine water velocity and structure of the jet: the geometrical features of orifices, such as diameter, rounding of the entrance edge, taper angle of internal walls and so on, play an important role under the fluid-dynamic point of view and, consequently, on water velocity and jet behaviour in air, which are responsible for the available value of specific power on the workpiece. The aim of this study is to experimentally evidence possible differences among performances of orifices coming from different manufacturers in order to point out the effects of orifices geometrical features on water velocity and cutting capability in case of abrasive water jet cutting of Aluminium.

Sand jets in water have extensive engineering applications. A detailed numerical modeling of sand jets in water was conducted at high initial sand concentration using a commercial computational fluid dynamics package (ANSYS CFX 11.0). The results of the numerical simulation were first compared with some recent laboratory experiments. Simulations were then conducted to investigate the effect of sand particle sizes on velocity distribution, concentration profile, and turbulent properties. Turbulent flow characteristics, such as turbulent kinetic energy, turbulence intensity, rate of energy dissipation, and turbulent eddy frequency, were evaluated and the trend compared with the previous studies in the literature. The location of maximum kinetic energy was found to be independent of particle size. The turbulent kinetic energy and rate of dissipation of the water phase decrease with increasing particle size.

Supersonic steam injector is a passive jet pump without rotating machine and high efficient heat exchanger because of the direct contact condensation between the supersonic steam and the subcooled water jet. It is considered that flow behavior in the steam injector is governed by the direct contact condensation and complicated turbulent flow with large shear stress induced by velocity difference between the steam and water. However, the studies about the turbulent flow under the large shear stress with direct contact condensation are not enough. Especially mechanisms of the momentum and the heat transfer are not clarified in detail. Objective of the present study is to investigate the turbulent behaviors of the water jet and the interface between the supersonic steam and the water jet. Radial distribution of total pressure is measured by a special pitot tube. In order to investigate the interfacial behavior, radial distribution of total pressure gradient and that of the fluctuation are applied. The surface of the turbulent water jet is observed by high speed camera in order to identify the position of unstable interface and its behavior.

The objective of this work is to investigate the cavitating flow mechanism of a specific hydrofoil, Tulin hydrofoil, and better understand the vortex-cavitation interactions in transient cavitating flows. The numerical investigations are performed using a large eddy simulation method and the Zwart cavitation model. The predicted cavity formation and evolution agree well with the experimental observation. An asymmetric vortex street has been formed, with the upper one (the trailing edge vortex street) has a regular vortex shape and a clear boundary between vortex structures, while the lower one (the leading edge vortex street) has a larger cavitation area due to the low pressure distribution on the suction side of the foil. The turbulent kinetic energy transport equation has been adopted to examine the balance and contribution of different mechanisms. The formation and evolution of the leading and trailing edge vortex structures are responsible for the generation and modification of the turbulent kinetic energy distributions. The convection term varies significantly in the cavity region during the phase change process, and the boundary of the vortex structures enhance the production term of the turbulent kinetic energy.

Preface. Acknowledgments. 1. Preliminaries. 2. Overview of Turbulent Flow Physics and Equations. 3. Experimental and Numerical Methods. 4. Properties of Bounded Turbulent Flows. 5. Properties of Turbulent Free Shear Flows. 6. Turbulent Transport. 7. Theory of Idealized Turbulent Flows. 8. Turbulence Modeling. 9. Applications of Turbulence Modeling. 10. Large Eddy Simulations. 11. Analysis of Turbulent Scalar Fields. 12. Turbulence Theory. Author Index. Subject Index.

The numerical simulation and fluid dynamics simulation of the internal flow field and its influence mechanism of a commercial vehicle intake system were carried out aim at studying the flow field characteristics of the intake system. The internal and surface pressure, velocity, and turbulent kinetic energy distribution of intake systems under the rated operating conditions and three high torque conditions of the engine were analyzed. The simulation results showed that with the increase of the mass flow of the intake air, the pressure distribution on the surface of the intake system increased, and the pressure drop of the inlet and outlet increased rapidly. With the increase of the mass flow, the scale and number of vortexes in the intake system increased sharply. The distribution of turbulent kinetic energy is more related to the velocity field distribution. However the internal turbulent energy distribution of the intake system is concentrated under one condition. As the intake air mass flow rate drops from 1,500 kg/h to 764 kg/h, the pressure drop of the intake system drops from 2,858,566 Pa to 721,411 Pa; the average turbulent energy decreases from 5.41 m2/s2; to 0.896 m2/s2. In this paper, the research on the flow field of the engine intake system aims to provide research directions for the early stage of the structural design of the intake system of large agricultural vehicles.

Experimental analysis of high-speed air–water jet flow in an abrasive water jet mixing tube

High-pressure water jet technology is widely used in hot-rolling billet descaling process. Impact force and behavior of jets play a vital role on effect of water jet billet descaling. The parameters of nozzles and jet determine the characteristics of jetting. Some of these parameters, however, can only be obtained through experimentation. The mechanism of high-pressure water jet billet descaling was analyzed in this paper. The factors affecting billet descaling were also discussed. Furthermore, theoretical formula accounting for water jet impact force was derived from the discussion. An indoor test set-up investigating impact properties of water jet descaling nozzles was established. Virtual instrument Lab VIEW was combined with mathematics software MATLAB to develop a measuring system of the test set-up. The real-time test of descaling nozzles parameters can be achieved through the system. The measuring system included three modules: pressure-flow curve, three-dimensional platform movement track and jet impact force measurement. Various parameters of the nozzles and jet can be obtained by means of the modules. Experimental results were compared with theoretical ones and observations were made regarding the variation of parameters. Results showed that variation of the parameters yielded by experiments agreed well with theoretical prediction. Variation of each parameter was visually depicted. The impact force and behavior of the jet were accurately measured. It contributes to descaling nozzle design improvement and descaling system structure optimization.

A steam injector is a simple, compact and passive device and has a capability of passive water injection system for a next-generation reactor. Steam injector performance depends on the phenomena of steam condensation onto the water jet surface and heat transfer in the water jet due to turbulent heat exchanger. To develop high performance steam injector, it is necessary to quantify the relationships between physical properties of the flow field. We carried out experiments to observe the internal behavior of the water jet as well as measure the velocity and temperature. The water jet oscillation and surface wave grow larger along the flow due to large shear stress from high speed steam jet, acoording to the photographs of a flashlight. It was confirmed that the steam was supersonic, 400-490 m/s at the outlet of the steam and the dependence of radial velocity distributions on steam nozzle throat area and steam inlet pressure was cleared by using LDV. The steam and water jet temperature distributions were obtained by tensioned-wire thermocople, it was confirmed that the steam and water jet temperature increase because the latent heat was transferred gradually into the center of the water jet mainly as the result of turbulent eddy diffusivity. Furthermore, it is conducted that conceming turbulence heat transfer, the similarity rule is applicable to the water jet in a steam injector as well as the turbulence flow in a circular pipe.