High-speed Submerged Water Jet Research Articles

On unsteady cavitation flow of a high-speed submerged water jet based on data-driven modal decomposition

Harnessing the destructive effect of cavitation, high-speed submerged cavitating water jets have a wide range of engineering applications. However, the characteristics of complex unsteady flow patterns due to turbulence and super-cavitation are still unclear. This paper employs the data-driven modal decomposition to study the mechanism of the unsteady turbulent cavitation flow. The simulation is based on the stress-blended eddy simulation (SBES) turbulence model coupled with the Schnerr-Sauer cavitation model. The internal evolution and frequency characteristics of cavitation flow are analyzed. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) are utilized to identify the flow pattern of turbulent cavitation flow, including the vapor and the velocity fields. In results, the upstream part of the cavitating jet is characterized by growth and shedding behaviors, while the downstream part by decay and collapse behaviors. POD modes extract the most energetic structures within the flow field, with low-order modes capturing the majority of the energy. The vapor-based POD Mode 2 and Mode 3 reveal the behavior pattern of cavitation cloud shedding. While DMD identifies the shedding behavior and collapse behavior of cavitation through the decoupling of frequency domain.

Numerical simulations of cavitating water jet by an improved cavitation model of compressible mixture flow with an emphasis on phase change effects

Focusing on cavitation phenomena caused by high-speed submerged water jets, this paper presents an improved cavitation model for a compressible fluid mixture based on a concise estimation of fluid compressibility that considers phase change effects. The homogeneous two-phase flow assumption is adopted, and the gas phase is assumed to consist of vapor and non-condensable components. Equations of state for a pure liquid and an ideal gas are employed to evaluate the compressibility of the liquid and non-condensable components, and the compressibility of the vapor is treated semi-empirically as a constant. The model is embedded in an unsteady Reynolds-averaged Navier–Stokes solver, with the realizable k-ε model employed to evaluate the eddy viscosity. The turbulent cavitating flow caused by an impulsively started submerged water jet is treated. The pattern of periodic cavitation cloud shedding is acceptably captured, and the mass flow rate coefficient and its fluctuation frequency evaluated by simulations agree with the experimental results well. The validity of the proposed method is confirmed. The results reveal that cavitation occurs when pin/Pin reaches 0.65 and fluid flow begins to pulsate. In the well-developed stage, the leading cavitation cloud and a subsequent cloud are successively shed downstream, and this process is repeated. The subsequent cloud catches the leading cloud, and they coalesce in the range x/d≈ 2–3. The pressure fluctuations concentrate in the range of x/d≈2–5 corresponding to the periodic shedding of cavitation clouds. The mass flow rate coefficient pulsates from 0.59–0.66 under the effect of cavitation.

Experimental investigation of two-phase flow evolution in a high-speed submerged water jet with air ventilation

In order to improve the submerged cutting performance of water abrasive suspension jet an experimental investigation on the two-phase flow structure of submerged water jet with semi-coaxial air ventilation is conducted by the method of high-speed camera observation under the condition of flow dynamic similarity, and its unsteady behavior under different conditions is evaluated by analyzing of sequence images. Experiment results show that the flow pattern of air-ventilated jet depends upon the ventilation flow rate. It may be classified into bubbly flow surrounded jet, continuous air-layer covered jet and cavity-bubble flow surrounded jet. In the case of non-ventilation, high-speed water jet into water is accompanied by intensive cavitation and the flow field appears to be a narrow jet surrounded by cavitation bubble clouds. By ventilating to the cavitating jet, air-bubbles become bigger gradually and a cavity area is formed at the exit of nozzle head. When the ventilation flow ratio reaches to the level of 5 a large cavity covering the jet is formed and a continuous air-layer covered jet is then generated. Image analysis demonstrates that the continuous air-layer covering the liquid jet pulsates and sheds downstream periodically. The Strouhal number defined by the dominant frequency of jet pulsation decreases quickly with the increase of ventilation flow rate in the range of Cq ≤ 5. At a suitable ventilation flow ratio (Cq ≈ 6 ~ 8) a relative long stable continuous air-layer covering the jet is generated at high time ratio, which will dramatically enhance the processing ability of submerged water jets. Cutting tests demonstrates that the cutting ability of air ventilated jet depends on the ventilation flow ratio. The relation of processing ability with the flow structure of air ventilated jet is clarified.

Experiments and numerical analysis of rebounding behaviors of a laser-induced cloud cavitation

It is well known that a high-speed submerged water jet generates a cloud of cavitation bubbles experiencing a collective unsteady behavior that repeats growth and collapse. In particular, it is considered that a high-pressure shock wave may be emitted associated with the collapse of the cloud. However, its mechanism has not been enough clarified and hence it is required to be explored both from the experimental and numerical analyses. In this study, we fist make an observation of such a unsteady behavior of the cloud cavitation that is generated by a pulsed Ho:YAG laser-induced liquid jet using a high-speed video camera. Then, a two-dimensional numerical analysis based on the SPH method is examined to simulate the unsteady behavior of the cloud, in which the mixture model of liquids and gas bubbles is employed. Finally, the validity of our numerical analysis is illustrated by showing that the unsteady behavior of the cloud from its inception, growth, shrink, collapse to rebound is realized in qualitative agreement with the experimental data.

Numerical simulation of unsteady cavitating jet by a compressible bubbly mixture flow method

Focused on the unsteady behaviour of high-speed water jets with intensive cavitation a numerical analysis is performed by applying a compressible mixture flow method combined with a simplified bubble cavitation model. The mean flow of two-phase mixture is calculated by URANS for compressible flow and the intensity of cavitation in a local field is evaluated by the volume fraction of gas phase varying with the expansion and contraction of bubbles the mean flow field. High-speed submerged water jet issuing from a sheathed nozzle is treated when σ = 0.1 and Re = 4.5x105 . The distribution of cavitation clouds predicted approximately agrees with experiment data of visualization observation and the unsteady behaviour of cavitation cloud shedding is captured acceptably. Computational results reveal that cavitation occurs at the entrance of nozzle throat and bubble clouds expand and develop while flowing downstream along the boundary layer. Developed bubble clouds split into small blocks and sheds downstream periodically near the exit of sheath.

Numerical analysis of cavitation cloud shedding in a submerged water jet

Focused on the unsteady behavior of high-speed water jets with intensive cavitation a numerical analysis is performed by applying a practical compressible mixture flow bubble cavitation model with a simplified estimation of bubble radius. The mean flow of two-phase mixture is calculated by unsteady Reynolds averaged Navier-Stokes (URANS) for compressible flow and the intensity of cavitation in a local field is evaluated by the volume fraction of gas bubbles whose radius is estimated with a simplified Rayleigh-Plesset equation according to pressure variation of the mean flow field. High-speed submerged water jet issuing from a sheathed sharp-edge orifice nozzle is treated. The periodically shedding of cavitation clouds is captured in a certain reliability compared to experiment data of visualization observation and the capability to capture the unsteadily shedding of cavitation clouds is demonstrated. The results demonstrate that cavitation takes place near the entrance of nozzle throat and cavitation cloud expands consequentially while flowing downstream. Developed bubble clouds break up near the nozzle exit and shed downstream periodically along the shear layer. Under the effect of cavitation bubbles the decay of core velocity is delayed compared to the case of no-cavitation jet.

Effect of aeration on superficial residual stress level of carburised and quenched gears treated by water cavitation peening

Cavitation impacts, which are generally considered as the dominant factor affecting cavitation erosion of hydraulic machinery, can also be applied to introduce compressive residual stress in the surface layer of mechanical components in a similar way to traditional shot peening. By using a high speed submerged water jet instrument, in which high pressure water is passed through a jet nozzle to the specimen, a uniform cloud of large bubbles can be generated. Bubble collapse on the surface of the specimen will produce an impact effect very similar to shot peening. Therefore, the design of the jet nozzle is very important to obtain the optimum pressure of bubble collapse. In the present study, a new nozzle design with air addition was used, the effect of the air addition flux on the impulse pressure of bubble collapse was investigated, and a comparative study of the residual stress in a carburising quenched gear treated by water cavitation peening with and without air addition was carried out. The results show that after the new nozzle with air addition is adopted, the saturation time of peening is reduced from 30 to 10 min and a superficial compressive residual stress increase of about 30–40% is obtained. The increase in pressure of bubble collapse caused by air addition is responsible for such improvement.

High-Speed Observation of a Cavitating Jet in Air

The use of cavitation impact is a practical method for improving the fatigue strength of metals in the same way as shot peening. In the case of peening using cavitation impact, cavitation is produced by a high-speed submerged water jet with cavitation, i.e., a cavitating jet. A cavitating jet in air was successfully generated by injecting a high-speed water jet into a low-speed water jet injected into air using a concentric nozzle. In order to investigate the various appearances of cavitating jets in air, an observation was carried out using high-speed photography and high-speed video recording. In this study, periodical shading of the cavitation cloud was observed and the frequency of the shading was found to be a function of the injection pressure of the low-speed water jet. Unsteadiness of the low-speed water jet, which is related to the periodical shading of the cloud, was also observed.

Gettering of Cu in Silicon Wafer by Using Cavitation Impacts

A novel gettering method using cavitation impacts is presented. Gettering is very important technique for IC manufacturing. Silicon wafers used as a substrate for semiconductors are often exposed to contamination during the device processes. If crystal defects are intentionally introduced into back-side of silicon wafer, metal impurities such as Cu and Fe in the wafer are trapped in the defects and gather into the region during heat cycles. As a result, the zone near the surface of the wafer that is used as active device region is kept off unwanted impurities. This technique is called gettering. In this paper, to introduce backside damage, which is one of the gettering techniques, cavitation impacts are utilized. Cavitation bubbles produce high-pressure impacts upon collapsing. The suitable damage can be introduced by controlling the intensity of cavitation impacts. The high speed submerged water jet with cavitation, i.e., a cavitating jet, was used to cause cavitation impacts. The cavitating jet can introduce backside damage without the use of particles, as in shot blasting that is popular technique. In order to confirm the gettering effectiveness of the damage introduced by a cavitating jet, an experimental study was carried out. The silicon wafer treated by the cavitating jet was intentionally contaminated with solution of Cu(NO3)2. The wafer was then thermally treated. The surface was observed after etching that makes defects on the surface observable. On the surface of the wafer having no gettering effectiveness, defects which were induced by contamination are observed. If the wafer has gettering effectiveness, defects are not observed on the surface. Gettering effectiveness of the damage introduced by the cavitating jet was shown.

Evaluation of the Damage for Gettering in Silicon Wafer Introduced by a Cavitating Jet

Damage for gettering can be introduced by a high speed submerged water jet with cavitation, i.e., a cavitating jet, into a silicon wafer. Gettering is an important technique for removing unwanted impurities from the surface of the silicon wafer that is active device region. Metal contaminations diffuse in bulk of the wafer and adhere to the defects through the thermal treatments in semiconductor processes. If the damage was intentionally introduced into the silicon wafer, these contaminations can be gathered within the intended region. Consequently, the surface of the wafer can be kept free from impurities. The method presented here utilizes cavitation impacts to introduce the damage for gettering. By using cavitation impacts, the damage can be introduced without the use of particles which form sources of contamination during farther wafer handling, as in shot blasting that is a popular technique. The cavitation impacts caused by a cavitating jet were used since the intensity of cavitation impacts can easily be controlled by controlling hydraulic parameters. The gettering effect of the damage introduced by the cavitating jet was already confirmed, but the detail information of the introduced damage has not been obtained. After applying thermal treatment to the wafer treated by the cavitating jet, there are Oxidation-induced stacking faults (OSF) which would be gettering sites. However, the source of OSF is not yet confirmed. In this paper, the damage on the silicon wafer surface introduced by the cavitating jet for gettering is observed to evaluate the source of OSF.

Numerical Simulation of High-Speed Submerged Water Jet with Cavitation.

A numerical analysis was carried out to clarify the unsteady behavior and the large-scale structure of high-speed submerged water jet with cavitation. A finite volume formulation with an upwind scheme was used to discretize the compressible Navier-Stokes equations with an assumption of locally homogeneous model of gas-liquid two-phase media. First, the validation of the present numerical method was discussed by comparing numerical results with experiments of jet flow. Further, the difference between the jet structures with and without cavitation was investigated. As a result, it is indicated that the cavitating jet flow corresponds basically to an unsteady transonic flow condition. Also, it is found that the present numerical method is available to predict the complex structure and the unsteady behavior of the cavitating jet flow.

701 高速水中水噴流の材料壊食特性 : ノズル出口形状の影響(流体工学1)

701 高速水中水噴流の材料壊食特性 : ノズル出口形状の影響(流体工学1)

K-1317 超高速水中水噴流用垂直型回流式試験水槽のキャビテーション核分布(S15-5 噴流計測)(S15 噴流・はく離流れの計測と制御)

K-1317 超高速水中水噴流用垂直型回流式試験水槽のキャビテーション核分布(S15-5 噴流計測)(S15 噴流・はく離流れの計測と制御)

Use of Cavitating Jet for Introducing Compressive Residual Stress

In an attempt to strengthen the surface of materials, the potential of using a cavitating jet to form compressive residual stress has been investigated. Introducing compressive residual stress to a material surface provides improvement of the fatigue strength and resistance to stress corrosion cracking. In general, cavitation causes damage to hydraulic machinery. However, cavitation impact can be used to form compressive residual stress in the same way as shot peening. In the initial stage, when cavitation erosion progresses, only plastic deformation, without mass loss, takes place on the material surface. Thus, it is possible to form compressive residual stress without any damage by considering the intensity and exposure time of the cavitation attack. Cavitation is also induced by ultrasonic, high-speed water tunnel and high-speed submerged water jet, i.e., a cavitating jet. The great advantage of a cavitating jet is that the jet causes the cavitation wherever the cavitation impact is required. To obtain the optimum condition for the formation of compressive residual stress by using a cavitating jet, the residual stresses on stainless steel (JIS SUS304 and SUS316) and also copper (JIS C1100) have been examined by changing the exposure time of the cavitating jet. The in-plane normal stresses were measured in three different directions on the surface plane using the X-ray diffraction method, allowing for the principal stresses to be calculated. Both of the principal stresses are found changing from tension to compression within a 10 s exposure to the cavitating jet. The compressive residual stress as a result of the cavitating jet was found to be saturated after a certain time, but it starts decreasing, and finally, it approaches zero asymptotically. It could be verified in the present study that it was possible to form compressive residual stress by using a cavitating jet, and the optimum processing time could also be realized. The great difference between the water jet in water and air has also been shown in this regard. [S1087-1357(00)00501-3]

High-speed observations of the cavitation cloud around a high-speed submerged water jet

High-speed observations of the cavitation cloud around a high-speed submerged water jet

Suitable region of high-speed submerged water jets for cutting and peening

Suitable region of high-speed submerged water jets for cutting and peening

Jet Structure Analyses on High-Speed Submerged Water Jets through Cavitation Noises.

In order to establish a useful monitoring method for material erosion caused by high-speed submerged water jets, we clarify the main source of cavitation noises around free jets by using two hydrophones, and also analyze the AE characteristics of the impulsive pressures induced by cavitation on the specimen for the impinging jets. Clearly, the energies of high-frequency components in the jets change markedly with injection pressure and standoff distance.

Formation Process of Vortex Ring Cavitation in High-Speed Submerged Water Jets.

Formation Process of Vortex Ring Cavitation in High-Speed Submerged Water Jets.

High-Speed Observations of the Cavitation Cloud around a High-Speed Submerged Water Jet.

In this paper, we attempt to clarify the jet structure and the behavior of severely erosive cavitation clouds around a high-speed submerged water jet, using a high-speed movie camera with a framing rate of ten thousand frames. The effects of the injection pressure and the nozzle geometry on cavitation are also investigated. The experiments are performed with both a free jet and an impinging jet. It is clearly found that the cavitation clouds are periodically discharged. The cavitation clouds are also closely related to downstream instability and to the impinging erosion.

Suitable Region of High-Speed Submerged Water Jets for Cutting and Peening.

In order to establish useful techniques of cutting, drilling, peening and flushing by high-speed submerged water jets, we systematically observe the eroded surface on aluminum-alloy specimens in relation to the characteristics of cavitating jets, especially for the impinging jet through lucite specimens, for several types of nozzles. The impulsive pressures induced by the cavitating jets are also measured by means of pressure-sensitive film. It is concluded that the erosion characteristics are quite different in two typical standoff distances, i. e., the 1st and the 2nd peak. Cylindrical, small and deep pits predominantly occur at the 1st peak, while small lots of plastic deformations predominantly occur in the 2nd peak. Therefore, the 1st peak is suitable for cutting, while the 2nd peak is suitable for peening.