Submerged Water Jet Research Articles

Interaction of a two-phase turbulent/bubbly submerged water jet with a single-phase jet: Measurements of the enhanced hydrodynamic near-field spectrum, part II

The interaction of mutually perpendicular submerged turbulent water jets is studied from measurements of the hydrodynamic near-field pressure spectrum. One jet is a conventional single-phase, free turbulent shear flow circular jet, while the other jet is a two-phase bubbly jet of similar construction. The overlap region is located at four nozzle diameters (4D) away from each orifice. A small hydrophone located outside the overlap region on the symmetry line 45° from each jet axis (and in the far quadrant from each nozzle exit) measures the near-field pressure signature. Spectra are measured at different radial positions from the overlap region (typically 4D–10D). Very small gas bubbles are generated in the two−phase turbulent jet by pressurized N2 gas passing through a fritted disk housed in a Buchner funnel located near the nozzle entrance. Spectra are compared for different void fractions and different Reynolds numbers (based on jet diameter). Typically, volume void fractions ∼0.001 significantly amplify the flow noise coming from jet nozzles (D=0.635 cm) with nozzle exit velocities of 10 m/s. [See earlier work, J. Acoust. Soc. Am. 102, 3184(A) (1997).] [Work supported by the Naval Acad. Res. Council.]

Experimental comparison of two laser-based velocimeters for flows with alluvial sand

Nonintrusive measurements in a sediment-laden flow using two laser-based techniques, Discriminator Laser-Doppler Velocimetry (DLDV) and Particle Tracking Velocimetry (PTV), are compared. DLDV was previously developed at the Iowa Institute of Hydraulic Research, while PTV was specially configured for this application. Mean and fluctuating velocity components for both flow fractions were simultaneously measured in a laboratory-scale, submerged water jet loaded with alluvial sand. This information cannot be obtained using existing measurement techniques. The jet Reynolds number was 6120, and the sediment sieve diameter ranged from 0.5 to 0.6 mm. Small mass loadings of sand with inertial time constant τ p of 0.6 ms were examined. The configuration, operation, and results obtained using the DLDV and PTV are presented. For each technique, means to precisely distinguish between the light scattered by suspended sand and that originating from seed-particles following the water were implemented. The agreement in measurement for the two methods validates one another since they are based on completely different principles of operation. The capabilities of DLDV and PTV to reliably measure sand and water velocities in sediment-laden flows are further indicated by the agreement of the present findings with those obtained previously in similar studies. The comparison suggests that PTV, due to its whole field nature, could become a powerful tool for flow and particle-related diagnostics, yielding fundamental information in an area with a long history of conflicting experimental evidence.

Cavitation and Erosion in Submerged Water Jet.

This paper is concerned with cavitation and erosion in submerged water jet. Impulse force generated by cavitation bubbles in the jet is measured by an impulse force gauge. The accumulated count of impulse force per unit time is shown against the impulse force and the standoff distance from the nozzle exit. It is found that there are maxima in impulse force at two different standoff distances of 30 and 80, which are the values normalized by the nozzle diameter (=1. 5 mm), and that the impulse force mainly appears in frequencies of a few Hz. Laser-microscopic observations show that erosion patterns on aluminum surfaces are classified into two ones.

Studies on Cavitation Impulse Force in Submerged Water Jet.

Studies on Cavitation Impulse Force in Submerged Water Jet.

Reattachment Phenomena and Diffusion of Plane Submerged Water Jets.

Plane submerged water jets which issue from nozzle into quiescent water in channel have been known to attach to the adjacent solid or free surface owing to the Coanda effect. This paper is concerned with an experimental investigation on the plane submerged jets. Flows are visualized by using hydrogen bubbles and tracer particles. The photographs show that the jets attaching to the free surface are classified into six types according to their behavior after issuing from the nozzle. Under some limited conditions, the free surface is found to make self-induced vibration. The velocity distributions are given in the form of the vector diagram and the flow patterns made in the channel for each type of the jets are indicated. The flow visualization by tracer particle method provides that the jets attaching to the free surface diffuse faster than those attaching to the solid boundary.

Useful Correlations for Cavitating Water Jet.

In order to use a submerged water jet accompanied with cavitation for practical applications, a cavitating jet was investigated experimentally. The static pressure on the impinging surface was measured to make clear the structure of the cavitating jet. The erosion tests were also carried out to measure the cavitation intensity. The optimum standoff distance at different cavitation condition was correlated by the cavitation number at the nozzle and the local cavitation number on the target. The relation between the cavitation intensity and the hydraulic parameters was also revealed.

Mutual interaction of a two-phase turbulent/bubbly submerged water jet with a single-phase jet for the measurement of the enhanced hydrodynamic near-field pressure spectrum

The interaction of mutually perpendicular submerged turbulent water jets is studied from the measurement of the enhanced hydrodynamic near-field pressure spectrum. One jet is a conventional single-phase, free turbulent shear flow circular jet, while the other jet is a two-phase bubbly jet of similar construction. The overlap region is located at four-nozzle diameters (4D) away from each orifice. A small hydrophone located outside the overlap region (4D away from the interaction region and 45 deg from the jet axis) measures the near-field pressure spectrum. Very small gas bubbles are required for this two-phase turbulent jet. They are generated by pressurized carbonated water flowing through a thin circular nozzle plate having an array of small holes. These CO2 gas bubbles are mixed within the entrance to the tapered jet nozzle. Alternatively, bubbles are generated by pressurized N2 gas passing through a fritted disk housed in a Buchner funnel located near the nozzle entrance. Spectra are measured and compared for different void fractions and different Reynolds numbers that are based on the jet diameter.

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

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

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

Turbulence statistics in the stagnation region of an axisymmetric impinging jet flow

Turbulence statistics in the stagnation region of an axisymmetric jet impinging vertically on a flat plate are reported. The measurements were made in a submerged water jet facility at a Reynolds number of approximately 13,000 based on the nozzle exit velocity and the nozzle diameter. Particle-tracking velocimetry was used for the measurement of highly turbulent flows near the stagnation point. The axial mean momentum balance was examined to clarify the effect of the turbulent normal stress on the axial mean momentum transport. It was found that the turbulent normal stress of the axial component made a substantial contribution to the increase in the static pressure near the impingement wall. Detailed distributions of the turbulent stresses and the triple correlations of velocity fluctuations are presented. The state of turbulence was studied by means of an invariant map of the turbulent stress anisotropy. It was revealed that the turbulence was close to an axisymmetric state in the stagnation region. The budget equation for the turbulent kinetic energy evaluated from the present data shows that the net negative production takes place in the vicinity of the wall. This negative production is compensated by the pressure diffusion. Other unique features of the budget for the turbulent kinetic energy are also discussed.

High-speed observation of ultrahigh-speed submerged water jets

Some peculiar phenomena occur around ultrahigh-speed submerged water jets accompanied by very severe cavitation erosion. Using the flow visualization technique with a xenon flash, the water jets were carefully observed, and the spatial distributions of highly erosive impulsive pressures around the jets were measured by means of a pressure-sensitive film technique. The effects of the injection pressure and the nozzle configuration are systematically clarified. Thus, the characteristics and structures of ultrahigh-speed submerged water jets are clearly shown.

B213 二次元水噴流の可視化と流動解析

Two-dimensional submerged water jets have been visualized by two kinds of methods, i.e. a method of using hydrogen bubbles and one of tracing small solid particles. The flow characteristics are investigated systematically. On the strength of the results of visualization experiments, the flow can be classified into some typical patterns, depending on the flow conditions.

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

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

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.

Effects of Polymer Addition on Structure of Submerged Water Jet and Damage of Material.

Experimental studies are carried out to clarify the effects of a polymer additive on the structure of a submerged water jet and the damage process of a metallic material. Tap water and an aqueous solution of polymer additive are pressurized up to 147 MPa and injected into still water at atmospheric pressure through a nozzle of 0.50 mm in diameter. Specimens of aluminum alloy are used for erosion tests. The structure of the submerged water jet is analyzed from instantaneous photographs. It is found that the structure of the submerged water jet is affected greatly by the addition of a polymer additive. Furthermore, the addition of a polymer additive improves the cutting and drilling capacity of the submerged water jet.

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.

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.

Marked Effects of Ambient Pressure on Impinging Erosion Induced by High-Speed Submerged Water Jets.

In order to extend the working range of high-speed submerged water jets and to improve its accuracy confidence, the jet working characteristics are studied under the condition of widely varying ambient pressures P2. The erosion tests were systematically carried out by using aluminum-alloy specimens, and the aspects of the cavitation clouds around the jets were simultaneously observed. Clearly, the pressure P2 drastically affects the aspects of cavitation and its occurrence region. With increasing P2, the length of the cavitating jet decreases, so that the standoff distance, where the most severe erosion appears, shifs upstream. In short, the intensity and the distribution of the impulsive pressures induced by the cavitating jets also drastically change with P2. The impinging erosion characteristics are also sensitive to the standoff distance and the injection time.

Instrumentation to generate a two-phase turbulent (bubble) submerged water jet for flow noise measurements

It has been demonstrated that the near-field pressure spectrum (generated by a turbulent submerged water jet) is enhanced when the turbulent flow is modified to become a two-phase flow containing air bubbles [‘‘Proceedings of the 14th ICA, Beijing, China,’’ Acoustica 76, supplement to No. 4, May (1992), paper B6-1, p. 70]. An amplification factor G =∫p2two-phasedf/∫p2single-phasedf is measured as a function of the gross void fraction β of the air bubbles. Results showed that G∼β2 and G∼20 at β=0.0065. The range of void fraction was limited due to the use of the bubble maker (located at the jet nozzle entrance) which consisted of a fritted ceramic disk that was housed in a glass Buchner funnel and fed compressed nitrogen gas. It is possible to improve this apparatus by using carbonated water at high pressure in a nozzle that consists of an array of small holes in a thin circular plate. This arrangement can be controlled to yield small bubbles with an average diameter of about 100 μm in water. Larger void fractions are possible and the necessary constraint of having the resonant bubble frequencies well above the region of the low-frequency flow noise spectrum (<500 Hz) is obtained. A brief videotape will be shown. [Work supported in part by ONR.]

Cavitation Noise Characteristics around High-Speed Submerged Water Jets.

In order to clarify structures of high-speed submerged water jets and to predict the jet working capacity, we systematically measured the cavitation noise around the jets using a hydrophone, for several nozzles. The power spectra and the rms values of the cavitation noise are carefully analyzed. Clearly, cavitation noise created by the jets is related to the behavior of cavitation bubble clouds, and the cavitation noise characteristics are markedly changed with the injection pressure and nozzle geometry.