Water Jet Flow Research Articles

Numerical investigation on influence of focusing gas type on liquid micro-jet characteristics

Liquid micro-jets, produced from gas dynamic virtual nozzles (GDVNs), are used as sample carriers for interaction with X-ray beam in serial femtosecond crystallography (SFX). A numerical investigation of the effect of the focusing gas type on the liquid micro-jet properties (its length and thickness) is presented. The study complements our previous research on the influence of operating conditions and the nozzle geometry on GDVN performance. The influence of helium, argon, carbon dioxide and nitrogen gases (at a fixed mass flow rate of 1.6 × 104 mg/min) on focusing pure water jet (flow rate of 33 µl/min) is analysed. An experimentally validated numerical model, based on laminar two-phase Newtonian compressible flow with ideal gas assumption, finite volume method and volume of fluid interface tracking, is used. Helium is found to be the most suitable gas among the tested ones for producing thin, long and fast jets. The study provides a basis for the focusing gas selection in SFX experiments.

Study on Flow Field Characteristics of Nozzle Water Jet in Hydraulic cutting

Based on the theory of hydrodynamics, a mathematical model of nozzle water jet flow field in hydraulic cutting is established. By numerical simulation, the effects of nozzle convergence angle, nozzle outlet diameter and cylindrical section length on water jet flow impact is obtained, and the influence of three factors on the nozzle water jet flow field is analyzed. The optimal nozzle parameters are obtained by simulation as follows: convergence angle is 13 °, cylindrical section length is 8 mm and nozzle outlet diameter is 2 mm. Under this optimal nozzle parameters, hydraulic cutting has the best comprehensive effect.

Flow structures and cavitation in submerged waterjet at high jet pressure

Complexity of the submerged waterjet driven by high pressure resides in the jet itself and ambient water as well. To explore the traits of the high-pressure submerged waterjet, an experimental study is carried out at jet pressures of 13, 16 and 18MPa. The submerged waterjet flow is measured using particle image velocimetry in conjunction with seeded Rhodamine 6B fluorescence particles. Vorticity is calculated from velocity distribution. High-speed photography is utilized to capture the evolution of cavitation phenomenon near the nozzle. Pressure fluctuations excited in the water tank are acquired with miniature pressure transducers. At the three high jet pressures, submerged waterjet velocity attenuates remarkably along the streamwise direction, demonstrating substantial difference in comparison with low-pressure submerged waterjet. The semi-width of the waterjet stream increases downstream in a nearly linear manner. Pressure fluctuations in the water tank are featured by a wide frequency band within which low frequencies are most predominant. Meanwhile, relatively high frequencies are associated with cavitation evolution. Cavitation cloud development encompasses three distinct stages, namely cavitation cloud extending, cavitation cloud preserving and cavitation cloud shrinking. Of significance is the cavitation cloud profile, it is represented by disperse cavity elements at 13MPa. And the coherence of the cavitation cloud, as well as cavitation area fraction, is enhanced as jet pressure increases.

Study on failure of an ecological tunnel gate caused by jet-flow from air vents

Abstract This paper presents analysis of water jet flow state in an ecological tunnel in an abnormal condition and failure analysis of a temporary blocking gate of the ecological tunnel. Analysis consists of the determination of the hydrodynamic pressure on the gate by using experimental test and computational fluid dynamics, the calculation of stress distribution under different operating conditions using finite element method, and a simplified fatigue analysis. Results show that the water jet flow induces a vortex downstream the blocking gate, and under the large displacement and large dynamic stress the damage of gate begins with the local material failure and spreads to total damage with sandwich panel.

Decomposition Characteristics of Tetrafluoromethane Using a Waterjet Plasma Scrubber

It is recognized that tetrafluoromethane (CF₄) has a great influence on global warming. The CF₄ is known to have a large impact on climate change due to its large global warming index. In this study, a waterjet plasma scrubber(WPS) was designed and manufactured for the CF₄ decomposition. The WPS is a novel technology which is combined a gliding arc plasma and water injection at the center of the plasma discharge. This can give an innovative way for CF₄ decomposition by achieving larger plasma columnand generating OH radicals. A performance analysis was achieved for the design factors such as waterjet flow rate, total gas flow rate, consumption electric power, and electrode gap. The highest CF4 decomposition and energy efficiencies were 64.8% and 6.43 g/kWh, respectively; Optimal operating conditions were 20 mL/min of waterjet flow rate, 200 L/min total gas flow rate, 5.3 kW consumption electric power, and 4.4 mm electrode gap. As for the 2 stage reactor of the WPS, the CF₄ decomposition efficiency improved as the 85.3% while the energy efficiency decreased as the 5.57 g/kWh.

Thrust Characteristics and Nozzle Role of Water Jet Propulsion

Surface pressure integration and momentum method were respectively performed to evaluate the impeller thrust and the system thrust of a contra-rotating axial flow water jet propulsion, and an interesting phenomenon so-called thrust paradox was revealed. To explain the paradox, the impeller thrust and the system thrust were physically and theoretically analyzed, the results show that the impeller thrust is head involved and is determined by the hydraulic parameters upstream and downstream the impeller, while the momentum method depicted by a classic equation is valid simply under the best efficiency point. Consequently, the role of a water jet propulsion nozzle was deduced that the nozzle is mainly to limit the flow rate that crosses the impeller and to assure the system working under the best efficiency condition apart from its ability to produce momentum difference. Related mathematical formula expressed the nozzle diameter is the dominant variable used to calculate the working condition of the water jet propulsion. Therefore the nozzle diameter can be steadily estimated by the former expression. The system thrust scaling characteristics under various speeds were displayed lastly.

Investigation on a Rock-breaking Drilling Mechanism by Using a High Pressure Jet Bit

How to effectively transfer and exert a pressure on drills in lateral drilling, and to raise the efficiency of rock-breaking and rate of penetration in a bid, is the key technology to improve the quality, speed and economic benefits of lateral drilling. Therefore, based on high pressure jet of 16-hole and 7-hole nozzles, which are suitable for lateral drilling in oilfield at the present stage, we carry out a research on the hydraulic calculation of high pressure water jet flow and the mechanism of rock-breaking. We use three-dimensional modeling software to establish models, and analyze the high pressure water jet velocity field combined with numerical simulation software. According to different injection, we calculate the local head of the two nozzles when the working fluid is pure water and the liquid-solid two phases of 4% solid content respectively, through the simulated relational expression between the local head and the injection rate to calculate the maximum speed of each hole and to ensure rock-breaking critical injection of 16-hole and 7-hole nozzles, then compare and analyze the rock-breaking effect of these two kinds of drill bits, at the same time to analyze the influence of nozzles angle on the effect of rock-breaking, so as to optimize the perfect angle of the nozzle and to provide theoretical basis for the popularization and application of lateral drilling high pressure jet rock-breaking.

Fuzzy prediction of AWJ turbulence characteristics by using typical multi-phase flow models

ABSTRACTFor the purpose of improving the working performance of AWJ (Abrasive waterjet) grinding in actual machining, and revealing the unknown influence mechanism of waterjet machining prediction, this research conducted a theoretical and experimental investigation concerning with the influences caused by multi- phase flow models, on the fuzzy prediction of turbulence characteristics. First, typical flow models describing the abrasive waterjet were presented and enunciated; Second, a series of turbulence characteristics were defined to quantitatively demonstrate the waterjet flow, which are responsible for the actual performances of AWJ grinding in the contact zone; Then a new fuzzy prediction system equipped with logic protocols was established and introduced to predict turbulence characteristics based upon the machining parameters by employing different flow models, therefore a set of quantified prediction results generated from the CFD (Computational Fluid Dynamics) simulation, orthogonal experiments and actual measurements can be obtained and distinguished systematically. Through a detailed performance analysis with benchmark indexes and prediction comparisons, the theoretical superiorities and specific applications of these flow models were fully discussed and then an integrated conclusion assessing their inherent influence mechanism was acquired. Based on these innovative achievements, the instantaneous machining inspection or parameter optimization in AWJ grinding process can be facilitated, simultaneously the new research ideas aimed at waterjet monitoring or grinding improvements can be presented as well.

High speed imaging of a supersonic waterjet flow

This work studies a jet formation process and a flow developing from a waterjet cutting head. In experiments, the high speed imaging of a supersonic jet (a Photron FASTCAM SA5 camera with a frame rate of 100 kHz) is complemented with the thermographic measurements conducted using an infrared camera FLIR Systems SC7700 with a frame rate of up to 415 Hz. This study aims to provide new knowledge about two-phase flows under extreme conditions, and is of particular importance for waterjet design optimisation.

Influence of process parameters on abrasive particle motion characteristics in abrasive water jet descaling

The motion characteristics of particles play important roles on the quality and efficiency in abrasive water jet machining. In this paper, the abrasive water jet flow field is simulated by computational fluid dynamics (CFD). It is found that when the jet is continuous, there will form a static pressure zone on the surface of the workpiece, where pressure is high and fluid velocity is low. As the existence of static pressure zone, the velocity and motion direction of particles will be changed. Particles with different diameters and densities are compared when they are piercing through the static pressure zone. It can be found that in particles with greater diameter, the motion direction will be hard to be changed and the impact velocity will be higher. Particles with higher density, the motion direction will be also hard to be changed and the impact velocity will be higher. The influence of the radial position has also been considered. Closer to the jet axis, the impact velocity will be higher and the change quantity of motion direction will be smaller. It also can be seen that with the increasing of diameter or density, the influence of radial position on motion direction and impact velocity decreases.

An optical study of high-pressure water-jet dynamics

This paper considers the results of an optical study of high-speed fluid jets ejected from a nozzle at 400 MPa. The objective was to study two-phase flows under extreme conditions and to analyze the possibility of the optimization of the device design. The process of a high-speed water jet as it exits the focusing tube of the Flow WaterJet Mach3 abrasive cutting machine, along with its development, and the state of the stationary flow are considered. The shadow method was used to investigate the initial stage of high-speed water-jet formation, as well as the jet-head dynamics during the first 200–400 µs after ejection at 400 MPa. A Photron FASTCAM SA5 high-speed camera with a frame rate of one million shots per second and an exposure time of 1 [mu]s and a FLIR SC7000 infrared thermal camera with a frame rate of 400 shot/s and an exposure time of 1 ms were employed in order to study the jet-formation process. The spatiotemporal characteristics of the jet-development process were analyzed. The jet velocity and the starting jet head acceleration were measured by post-processing of digital images.

Numerical modeling of the penetration area of reversed submerged jet by the methods of finite elements and finite volumes

Water jet flow has many usages in the field of management and water resource operation that can be applied in mixing, dilution and aerification. The current study has calculated the flow velocity, length and height of jet penetration area (jet and main flow are of opposite directions) by the use of methods of finite element (FEM) and finite volume (FVM) and k–e model. In order to evaluate and verify this turbulent model, the results of the numerical model have been compared with the experimental results. This model has been studied for consideration of various jet flow velocities and thicknesses. The conclusions have indicated that the length and the height of the penetration area have linear relationship with jet flow velocity; therefore, as the jet flow velocity increases, the length of jet penetration increases as well. The comparison of the results of numerical method with the experimental data have demonstrated that the FVM holds less convergence time and better results compared with FEM.

Effect of the Molten Metal Stream’s Shape on Particle Size Distribution of Water Atomized Metal Powder

The current knowledge indicated that water pressure, molten metal temperature, water flow rate and water jet configuration are very important factors which affect on the particle size distribution and shapes of atomized powder. This study aimed to investigate whether the shape of molten affects the particle size of atomized powder. The experiments were the production of copper powder with the fixed atomization process conditions, but varied the shape of molten metal by using two different shapes of tundish nozzle’s orifice to make the round and rectangular cross section of molten metal stream. There were three sizes for each orifice shape to determine the rate of production (metal flow rate) at 13 kg/min, 19 kg/min and 26 kg/min. The results showed that at the same flow rate of molten metal the production of flat metal stream from rectangular orifice made higher yield of finer particle, smaller median size (D50) and narrower range of size distribution than the production with the round cross section orifice for every production rates.

A technology to extract coal mine gas using thin sub-layer mining with hydraulic jet

A high-pressure water jet can cut a slit in the coal seam to relieve the stress and improve the permeability, which makes coal mine gas be extracted more easily. Currently, the inner diameter of the nozzle and the flow of present high-pressure water jet for the cutting technology are small, which causes small cutting depth and width and a low efficiency of permeability improvement. To solve this problem, a new water jet technology with large flow was studied. By this technology a thin sub-layer of a coal seam can be mined effectively to relieve the stress and improve the permeability. This technology was tested in the Zhao Zhuang coal mine, the test parameters were determined, the test results were analysed, and it was found that after mining the thin sub-layer, the pressure of the coal seam reduced sufficiently and its permeability was significantly improved. [Received: February 4, 2015; Accepted: September 20, 2015]

ホウ素中性子捕捉療法の液体ターゲットを模擬した高液膜噴流の流動特性に関する研究

The stability of high speed thin water jet was studied by means of surface observation and droplet generation characteristics experimentally as the fundamental study of the liquid lithium target jet for the boron neutron capture therapy (BNCT). The characteristics of disturbances and the droplet formation of a water jet flow at high velocity. The cross section of nozzles used were rectangular with a gap of 0.5 mm, a width of 60 mm and lengths of 10 mm and 70 mm. The water outlet velocity was in the range of 5 - 15 m/s. The surface disturbance was observed using a high speed video camera, and the droplet generation characteristics from the surface was measured using Phase Doppler Anemometry (PDA). In case of the 10mm-long nozzle, a lot of droplets were generated from the jet surface, i. e. the jet was unstable. In case of 70mm-long nozzle, few droplets were generated from the surface of the jet, i. e. the jet was stable and the surface was very smooth. The stability of the jet with the 70 mm-long nozzle was caused by the dump of turbulence inside the nozzle by making a fully developed flow.

Experimental Investigation of Pile Installation by Vertical Jet Fluidization in Sand

The paper examines the mechanism of pile installation by vertical jet fluidization in saturated sand in order to define the constitutive parameters that control installation geometry and pile depth of embedment. A series of laboratory model tests representative of offshore torpedo piles was carried out using downwardly directed vertical water jets in both medium and dense sands. Measurements from model tests at three different scales indicate that the geometry of fluidized cavities is not influenced by the initial density of the sand and that the perturbed zone is constrained to a distance of about two pile diameters from the pile centerline during pile installation. Following the laws of dimensional analysis, an expression for the embedment of fluidized piles is derived and shows that penetration depth is a function of pile weight and geometry, fluidized water jet flow rate and velocity, as well as the soil and fluid properties. Penetration is shown to increase with increasing flow rate and pile weight and decreasing soil relative density. Although the results have to be validated by tests at larger scales to prove compatibility with the full-scale behavior, model tests indicate maximum embedment depth of the order of 50 times the pile diameter.

Multi-objective optimization of a mixed-flow pump impeller using modified NSGA-II algorithm

In order to maintain a uniform distribution of pareto-front solutions, a modified NSGA-II algorithm coupled with a dynamic crowding distance (DCD) method is proposed for the multi-objective optimization of a mixed-flow pump impeller. With the pump meridional section fixed, ten variables along the shroud and hub are selected to control the blade load by using a three-dimensional inverse design method. Hydraulic efficiency, along with impeller head, is applied as an optimization objective; and a radial basis neural network (RBNN) is adopted to approximate the objective function with 82 training samples. Local sensitivity analysis shows that decision variables have different impacts on the optimization objectives. Instead of randomly selecting one solution to implement, a technique for ordering preferences by similarity to ideal solution (TOPSIS) is introduced to select the best compromise solution (BCS) from pareto-front sets. The proposed method is applied to optimize the baseline model, i.e. a mixed- flow waterjet pump whose specific speed is 508 min-1·m3s-1·m. The performance of the waterjet pump was experimentally tested. Compared with the baseline model, the optimized impeller has a better hydraulic efficiency of 92% as well as a higher impeller head at the design operation point. Furthermore, the off-design performance is improved with a wider high- efficiency operation range. After optimization, velocity gradients on the suction surface are smoother and flow separations are eliminated at the blade inlet part. Thus, the authors believe the proposed method is helpful for optimizing the mixed-flow pumps.

Concentration degree prediction of AWJ grinding effectiveness based on turbulence characteristics and the improved ANFIS

In this paper, turbulence characteristics and an improved adaptive neural fuzzy inference system (ANFIS) have been presented, in order to predict and assess the concentration degrees of abrasive waterjet (AWJ) grinding effectiveness on given workpiece surface. Firstly, grinding effectiveness was defined to introduce the influence mechanism of waterjet flow that quantitatively describing the practical performances of AWJ grinding; then, an improved ANFIS was established to predict the concentration degrees of grinding effectiveness on targeted surface. Statistical analysis supports its accuracy and reliability in practical machining performances; therefore, a more stable prediction and clearer results can be ensured. It was concluded that this proposed ANFIS system can be used as a suitable and effective tool to investigate the complicated influential relationship between waterjet characteristics and grinding effectiveness in different conditions, which provides an applicable guidance to monitor AWJ machining operation in return.

PIV investigations on the turbulent mixing of two opposing flows inside a scaled chimney model of a research reactor

Experiments and numerical simulations were carried out to study the turbulent mixing behaviour of two opposing flows inside a 1/18th scaled down model of square chimney structure of a pool type research reactor. The chimney design facilitates drawing pool water in the downward direction, thereby suppressing the upward flow of radioactive water jet to limit the radiation field at the reactor pool top. Experiments were performed using the particle image velocimetry (PIV) technique, considering a mass flow rate of 0.5kg/s and 1.0kg/s for the upward flowing water from the core, which corresponds to Reynolds number of 20000 and 40000 respectively. Mass flow ratios of the downward flow and the upward flow were 0.00, 0.05, 0.1 and 0.15. PIV data shows the effect of mass flow ratio on the velocity distribution inside the chimney model. The experiments showed that the jet height decreased with increase in downward flow due to the opposing momentum of downward flow against the upward jet. The effects of Reynolds number on the jet height were found to be marginal. It was observed that both κ–ε and κ–ω turbulence models were able to simulate the experimental data of turbulent mixing.

Numerical analysis of head degrade law under cavitation condition of contra-rotating axial flow waterjet pump

In order to study the flow-head characteristic curve, the SST turbulence model, homogeneous multiphase model and Rayleigh-Plesset equation were applied to simulate the cavitation characteristics in contra-rotating axial flow waterjet pump under different conditions based on ANSYS CFX software. The distribution of cavity, pressure coefficient of the blade at the design point under different cavitation conditions were obtained. The analysis results of flow field show that the vapour volume distribution on the impeller indicates that the vapour first appears at the leading edge of blade and then extends to the outlet of impeller with the reduction of Net Positive Suction Head Allowance (NPSHA). The present study illustrates that the main reason for the decline of the pump performance is the development of cavitation, and the simulation can truly reflect the cavitation performance of the contra-rotating axial flow waterjet pump.