Submerged Water Jet Research Articles

Characterization of Pulsating Submerged Jet—A Particle Image Velocimetry Study

An experimental investigation has been performed to determine the flow characteristics of an axisymmetric submerged water jet with superimposed periodically oscillating flow. The objective of the study is to quantify in detail the near field of a pulsating jet using the particle image velocimetry (PIV) technique. The amplitude and frequency of oscillations are varied separately and the effect of each parameter is determined for a range of Reynolds numbers (ReD = 1602, 2318, and 3600). The experimental results indicate that for a given Reynolds number and amplitude, with an increase in the frequency of pulsation, the vortex formation shifts toward the nozzle exit. The number of vortices also increases with an increase in the jet pulsation frequency. Broadening of the jet and shortening of the potential core length are also observed. This indicates that mixing with the surrounding fluid is higher with pulsating jet even at relatively low Reynolds numbers. It is observed that frequency up to a critical frequency helps increase entrainment of the surrounding fluid. An upper critical frequency beyond which pulsation does not affect the entrainment is also determined. These results should eventually lead to a better understanding of the physical phenomena responsible for enhanced heat transfer rates in the presence of pulsating jets.

Impingement capability of high-pressure submerged water jet: Numerical prediction and experimental verification

At jet pressures ranging from 80 to 120 MPa, submerged water jets are investigated by numerical simulation and experiment. Numerical simulation enables a systematic analysis of major flow parameters such as jet velocity, turbulent kinetic energy as well as void fraction of cavitation. Experiments facilitate an objective assessment of surface morphology, micro hardness and surface roughness of the impinged samples. A comparison is implemented between submerged and non-submerged water jets. The results show that submerged water jet is characterized by low velocity magnitudes relative to non-submerged water jet at the same jet pressure. Shear effect serves as a key factor underlying the inception of cavitation in submerged water jet stream. Predicted annular shape of cavity zone is substantiated by local height distributions associated with experimentally obtained footprints. As jet pressure increases, joint contribution of jet kinetic energy and cavitation is demonstrated. While for non-submerged water jet, impingement force stems exclusively from flow velocity.

Assessment of cavitation and impingement effects of submerged water jet on Ti alloy surface

An investigation is conducted to explore the effect of submerged water jet on solid material surface. With jet pressures ranging from 80 to 150 MPa, jet impingement on Ti-6Al-4 V samples is implemented experimentally. Experiments enable a quantitative evaluation of surface morphology features, residual stress and surface roughness associated with the impinged samples. A comparison is performed between submerged and non-submerged water jets. The results show that cavitation phenomenon manifests itself in submerged water jet as a ring-shape cavity zone, and the occurrence of cavitation is confirmed by the surface morphology features and local surface roughness on impinged surfaces. An almost linear relationship between residual stress and impingement time is corroborated. As for the resultant pits on impinged surfaces, smooth perimeters are caused by submerged water jets, while non-submerged water jets give rise to rather irregular pit perimeters along with comparatively powerful impingement force.

Simulation of the impinging liquid jet cooling process of a flat plate

Purpose – The purpose of this paper is to develop a numerical model to simulate the flow field as well as the conjugate heat transfer during unsteady cooling of a flat plate with a single submerged water jet. At wall temperatures above the liquid boiling point, the vapor formation process and the interaction of the vapor phase with the developing jet-flow field are included. Design/methodology/approach – The time-dependent flow and temperature distribution during all occurring boiling phases as well as the local and temporal distribution of the heat transfer coefficient on a flat plate can be simulated. Findings – The influence of the liquid jet flow rate (10,800=Re_d=32,400) and the nozzle distance to the plate (4=H/d=20) on the transient cooling process are analyzed. This includes the time-dependant positions of the transition regions between the boiling phases on the plate as well as the temperatures at these transition regions. Additionally, the local heat transfer rates are a direct result of the unsteady cooling simulation. Originality/value – A single model approach is developed and utilized to simulate the unsteady cooling process of a flat plate with an impinging water jet including all occurring boiling phases.

Flow Characteristics and Cavitation Effect of the Submerged Water Jet Discharged from a Central-Body Nozzle

To assess the impingement capability of water jet, submerged water jet discharged from a centralbody nozzle is investigated. Efforts are devoted to both the wavy jet edge and the cavitation phenomenon involved. Three configurations of the central body are examined and jet pressure is fixed at 15 MPa. Jet edge is visualized using high speed photography. Numerical simulation is performed to extract flow parameter distributions in the jet stream and to predict cavity profiles. Furthermore, an impingement experiment with target sandstone samples is conducted as well. The results indicate that both lateral fluctuation amplitude and frequency of the jet stream vary with axial position of the central body. Cavitation tongues of different stream wise dimensions are manifested in the wake flows downstream of the central body. In case of the downstream end of the central body parallel with nozzle outlet section, the largest stream wise dimension of cavitation zone is obtained. Relative to the round nozzle with the same equivalent outlet diameter, the central-body nozzle yields preferable impinging effect.

0610 水中ウォータージェット洗浄装置の最新動向

0610 水中ウォータージェット洗浄装置の最新動向

Numerical simulation of high-speed cavitating flows in submerged water jet

Properties of existing cavitation models are discussed and a compressible mixture flow method based a simplified estimation of bubble cavitation is then presented for numerical simulation of high-speed water jets accompanied by intensive cavitation. Two-phase fluid media of cavitating flow are treated as a mixture of liquid and bubbles, and the mean flow is computed by solving RANS equations for compressible fluids considering the effect of bubble expansion a/o contraction. The intensity of cavitation is evaluated by the gas volume fraction, which is governed by the compressibility of bubble-liquid mixture corresponding to the status of mean flow field. Numerical results of cavitating water jet issuing from a submerged nozzle are presented and its applicability to intensively cavitating jets is demonstrated.

Scour under submerged circular vertical jets in cohesionless sediments

The results of an experimental study on scour under submerged circular vertical jets of water in cohesionless sediments are presented. The laboratory experiments were carried out to investigate the response of gravel beds to the action of vertical submerged water jets. Eight experimental runs were conducted to know the behavior of scour process under submerged vertical jet. The experiments involved various jet diameters and jet heights from the bed level. Measurements were made for both maximum dynamic and static scour depths of the scour hole. It was found that the dynamic scour depth is much larger than the static scour depth at the asymptotic state. The temporal variations of scour depth and maximum static scour depth have been quantified.

Numerical and Experimental Studies of Cavitation Behavior in Water-Jet Cavitation Peening Processing

Water-jet cavitation peening (WCP) is a new technology for the surface modification of metallic materials. The cavitation behavior in this process involves complex and changeable physics phenomena, such as high speed, high pressure, multiple phases, phase transition, turbulence, and unstable features. Thus, the cavitation behavior and impact-pressure distribution in WCP have always been key problems in this field. Numerous factors affect the occurrence of cavitation. These factors include flow-boundary conditions, absolute pressure, flow velocity, flow viscosity, surface tension, and so on. Among these factors, pressure and vapor fraction are the most significant. Numerical simulations are performed to determine the flow-field characteristics of both inside and outside the cavitating nozzle of a submerged water jet. The factors that influence the cavitation intensity of pressure are simulated. Fujifilm pressure-sensitive paper is used to measure the distribution of impact pressure along the jet direction during the WCP process. The results show that submerged cavitation jets can induce cavitation both inside and outside a conical nozzle and a convergent-divergent nozzle when the inlet pressure is 32 MPa. Moreover, the shock wave pressure induced by the collapse of the bubble group reaches up to 300 MPa.

Numerical and Experimental Studies of Cavitation Behavior in Water-Jet Cavitation Peening Processing

Water-jet cavitation peening (WCP) is a new technology for the surface modification of metallic materials. The cavitation behavior in this process involves complex and changeable physics phenomena, such as high speed, high pressure, multiple phases, phase transition, turbulence, and unstable features. Thus, the cavitation behavior and impact-pressure distribution in WCP have always been key problems in this field. Numerous factors affect the occurrence of cavitation. These factors include flow-boundary conditions, absolute pressure, flow velocity, flow viscosity, surface tension, and so on. Among these factors, pressure and vapor fraction are the most significant. Numerical simulations are performed to determine the flow-field characteristics of both inside and outside the cavitating nozzle of a submerged water jet. The factors that influence the cavitation intensity of pressure are simulated. Fujifilm pressure-sensitive paper is used to measure the distribution of impact pressure along the jet direction during the WCP process. The results show that submerged cavitation jets can induce cavitation both inside and outside a conical nozzle and a convergent-divergent nozzle when the inlet pressure is 32 MPa. Moreover, the shock wave pressure induced by the collapse of the bubble group reaches up to 300 MPa.

Evaluation of the sensitivity and response of IR thermography from a transparent heater under liquid jet impingement

The feasibility of a visible/IR transparent heater and its suitability for IR thermography is experimentally examined. The most common transparent conductive coating, Indium Tin Oxide (ITO), is quite reflective and its optical properties depend on thickness and manufacturing process. Therefore, the optical properties of several thicknesses and types of ITO, coated on an IR window (BaF2), are examined. A highly transparent Cadmium Oxide (CdO) coating on a ZnS window, also examined, is found to be unusable. Transmissivity is found to increase with a decrease in coating thickness, and total emittance is relatively low. A thick ITO coating was examined for IR thermography in the challenging test case of submerged water jet impingement, where temperature differences were characteristically small and distributed. The measurements under steady state conditions were found to agree well with the literature, and the method was validated. Comparison of two IR cameras did not show the LWIR low-temperature advantage, up to the maximal acquisition rate examined, 1.3KHz. Rather the MWIR camera had a stronger signal to noise ratio, due to the higher emissivity of the heater in this range. The transient response of the transparent heater showed no time-delay, though the substrate dampens the thermal response significantly. Therefore, only qualitative transient measurements are shown for the case of pulsating free-surface jet impingement, showing that the motion of the hydraulic jump coincides with thermal measurements. From these results, recommendations are made for coating/window combination in IR thermography.

Nonlinear scattering of crossed ultrasonic beams in a constricted flow for the detection of a simulated deep vein thrombosis: Part II

Experiments show that the turbulence generated by a thrombosis (ping pong ball) lodged into a polyethylene cylindrical tube (leg vein) can be detected by the nonlinear scattering at the combination (3.8 MHz sum frequency) from two mutually perpendicular primary wave components (f1=1.8 MHz and f2 = 2.0 MHz). In study (1) the nonlinear scattering at the sum frequency is measured vs. angle from turbulence generated by a submerged water jet. In (2) the thrombosis model vein is submerged in the turbulent flow field, while in (3) the vein remains in place but the thrombosis is removed. Nonlinear scattering at the combination frequency in (1) shows significant Doppler shift and frequency broadening vs. angle. In (2) nonlinear scattering exists but is diminished in amplitude, Doppler shift and spectral broadening, as was expected. In case (3), there is virtually no scattering at the sum frequency, since the vein mitigates the turbulent flow. Results are presented at fine angular increments, and improved alignments to measure mean Doppler shift, standard deviation, skewness and kurtosis vs. scattering angle and thus characterize certain aspects of the turbulence behind the clot. Results extend the original work of Sean M. Mock [J. Acoust. Soc. Am., 129, 2410 (2011)].

Numerical modelling of supercritical submerged water jets in a subcritical co-flow

Among the different applications of supercritical fluids, the use of water submerged jets is common in different processes such as the production of nanoparticles or combustion applications. This paper presents a computational methodology for the modelling and simulation of subcritical and supercritical injection of water in a subcritical co-flow. In this work, we focus on numerical simulation of the process, emphasizing mixing modelling. Subcritical to supercritical submerged water jets in a subcritical co-flow are analysed and validated against experimental data with good accuracy (below 5% of absolute average deviation). The main results show that mixing zones are longer at subcritical temperatures than well above the critical point. Besides, due to the low dissipation rate found, the system is poorly micromixed and complete mixing at the molecular scale is never achieved. A methodology based on the evaluation of a macro-mixing length has been used. Using this method, the presence and location of mixing zones are better identified, showing that when pressure is well above the critical point, fluid-dynamic behaviour is more similar to subcritical conditions. Implications of these results are commented and analysed.

Submerged Jet Impingement Boiling of Water Under Subatmospheric Conditions

An experimental study of jet impingement boiling is presented for water under saturated and subcooled conditions. Unique to this study is the documentation of boiling curves of a submerged water jet under subatmospheric conditions. Data are reported at a fixed nondimensional nozzle-to-surface distance of H/dj = 6 and for a fixed surface-to-nozzle diameter ratio, dsurf/dj, of 23.8. Saturated jet impingement experiments are performed at three subatmospheric pool pressures of 0.176 bar, 0.276 bar, and 0.478 bar with corresponding saturation temperatures of 57.3 °C, 67.2 °C, and 80.2 °C. At each pressure, jet impingement boiling at varying Reynolds numbers are characterized and compared with pool boiling heat transfer. The effect of surface roughness and fluid subcooling is studied at the lowest pressure of 0.176 bar. Boiling curves indicate a strong dependence of heat flux on jet Reynolds number in the partially developed nucleate boiling region but only a weak dependence in the fully developed nucleate boiling region. At a fixed wall superheat, fluid subcooling is found to shift the boiling curve to the left thereby enhancing heat transfer performance. Critical heat flux is found to increase with increases in pressure, surface roughness, and Reynolds number.

Flow Structure in the Near-Wall Region of a Submerged Impinging Jet

An experimental investigation was performed to study the flow structure of a submerged water jet impinging normally on a smooth and flat surface using particle image velocimetry (PIV). The jet issued from a 112 diameter long pipe which ensured fully developed turbulent flow conditions at the outlet. A semiconfined setting provided properly characterized flow boundary conditions. The Reynolds number based on jet mean exit velocity was Re = 15,895. The pipe-to-plate separation was varied between 1 and 8 pipe diameters. The current study focused on characterizing the flow structure close to the pipe outlet, in the impingement and wall-jet regions. Statistically averaged mean and RMS velocities are reported for a 6D wide and 1D high, near-plate, rectangular region.

Generation of Ultrasonic-Wave by a Submerged Water Jet

Submerged water jet accompanied by ultrasonic-waves is considered to be able to warm up bones under the skin effectively and it is utilized at the rehabilitation facilities. However, there exist few reports about the submerged water jet with ultrasonic-waves. In this paper, an experimental study of ultrasonic- wave generated by a submerged water jet has been carried out using various size of the nozzle and varying jet velocity. Sound pressure level (SPL) is measured by a hydrophone in a water tank. It is found that the water jet without air mixed and that water mixed show higher SPL in the range of ultrasonic-wave than the conventional jet with air mixed, whereas SPL of the former at low frequency is decreased remarkably. Furthermore, SPL for the jet without air mixed persists to the downstream section. In the case of the jet without air mixed, a cap installed at the outlet of the nozzle is found to enhance SPL of the ultrasonic-wave, and optimum sizes of the nozzle are clarified. In addition, an increase in SPL in the range of the ultrasonic-wave is confirmed to be related to the cavitation, but the generation of ultrasonic-wave doesn't depend only on the cavitation.

Heat Induced Separation in Upward Impinging Jet Flows Experimental Verification and Underlying Mechanism

A confined, round, laminar impinging jet, fed upward against the gravity, is studied, both experimentally and numerically, under the influence of an impingement-surface heating. It is a submerged water jet that steeply separates from the surface at a small distance from the stagnation point, due to a downward natural convection. The region after the separation point turns into a dead zone where the heat transfer deteriorates. It severely undermines the overall heat-transfer efficiency of the jet. Moreover, the separated jet is found to be highly transient, with the separation location oscillating in a cyclic fashion. Its mechanism is also discussed in detail.

0411 気中ウォータージェットの水面および没水物体衝突時におけるキャビティの挙動(OS4-3 キャビテーションおよびマイクロバブル効果とその応用技術,オーガナイズドセッション)

To clear the time-dependent feature of the cavity in a submerged water jet, we study the high-speed behavior of the cavity development process from the free surface to the surface of the test specimen, by means of a high-speed video camera and the VOF-simulation method. It is found that after the water jet impacts on the free surface, the submerged jet forms a cavity, whose configuration is similar to a line like a string of beads within a limited time, and the time series of the cavity aspect correspond to those simulated by VOF method.

0141 水中水噴流による共鳴音の発生に関する研究(OS1-8 噴流,後流および剥離流れの流動解析と応用,オーガナイズドセッション)

An experimental study of acoustic resonance generated by a submerged water jet has been carried out using various size of the nozzle and various jet velocities. Sound pressure level is measured by a hydrophone in a small water tank. It is found that the jet with water mixed and the jet without air mixed show higher SPL level than the conventional jet with air mixed. Furthermore, SPL level for the jet without air mixed persists in the downstream section. In addition, the optimum nozzle size and the optimum jet velocity are investigated.

Rock Damage Mechanisms under Ultra-high Pressure Water Jet Impact

Research on the damage mechanism of rock under the action of water jet has always been a difficult problem due to high turbulence of water jet and complicacy of rock material. According to fully-decoupled fluid-structure interaction (FSI) theory,the standard k-e two equations and control volume method for water jet,and the elastic orthotropic continuum and finite element method for rocks,are employed respectively to establish a numerical analyzing model of ultra-high pressure water jet impinging on rock. In terms of the stress distribution of rock interior,which is computed under submerged water jet with different velocities,and based on the theory that the rock micro-unit strength obeys Weibull probability distribution,a theoretical equation of damage variables evolution and a rock statistical constitutive model are developed,with Mohr-Coulomb damage criterion as distribution variable. A damage criterion,with non-dimensional coefficient to characterize rock damage,is also set up for analyzing rock failure mechanism with water jet. The process of jet impact on the rock is simulated,by using the FSI model,the statistical constitutive damage model and the damage criterion. Micro failure mechanism test and analysis with scanning electron microscope (SEM) for rock failure surface by jets cutting were performed,whose results show that the micro-mechanism of rock failure due to water jet impingement is a brittle fracture in the condition of tensile and shearing stress. The test results also agree well with the numerical simulation analysis,which constructs a bridge between the micro-failure mechanism and macro-breaking analysis of rock with water jets impact. The investigation affords a method for studying the mechanism of rock failure under ultra-high pressure water jet impingement.