Investigation of a submerged cavitating jet behavior, Part two: Influences of operating conditions, geometrical parameters and arrangements of detection system (original) (raw)
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Appearance of high submerged cavitating jet: The cavitation phenomenon and sono luminescence
Thermal Science, 2013
In order to study jet structure and behaviour of cloud cavitation within time and space, visualization of highly submerged cavitating water jet has been done using Stanford Optics 4 Quick 05 equipment, through endoscopes and other lenses with Drello3244 and Strobex Flash Chadwick as flashlight stroboscope. This included obligatory synchronization with several types of techniques and lenses. Images of the flow regime have been taken, allowing calculation of the non-dimensional cavitation cloud length under working conditions. Consequently a certain correlation has been proposed. The influencing parameters, such as; injection pressure, downstream pressure and cavitation number were experimentally proved to be very significant. The recordings of sono-luminescence phenomenon proved the collapsing of bubbles everywhere along the jet trajectory. In addition, the effect of temperature on sonoluminescence recordings was also a point of investigation.
High-Speed Observations of the Cavitation Cloud around a High-Speed Submerged Water Jet
JSME International Journal Series B, 1995
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 iniection pressure and the nozzle geometry on cavitation are also investigated. The experiments are perforrned with both a free jet and an irnpinging 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.
Thermal Science, 2013
Based on visualization results of highly-submerged cavitating water jet obtained with digital camera, the influences of related parameters such as: injection pressure, nozzle diameter and geometry, nozzle mounting (for convergent / divergent flow), cavitation number and exit jet velocity, were investigated. In addition, the influence of visualization system position was also studied. All the parameters have been found to be of strong influence on the jet appearance and performance. Both hydro-dynamical and geometrical parameters are playing the main role in behavior and intensity of cavitation phenomenon produced by cavitating jet generator. Based on our considerable previous experience in working with cavitating jet generator, the working conditions were chosen in order to obtain measurable phenomenon.
Observations of Cavitation Bubbles in a Starting Submerged Water Jet
Transactions of the Japan Society of Mechanical Engineers Series B, 2003
The behavior of cavitation bubbles in a starting submerged water jet discharging from a circular nozzle is studied by a simple photography technique in a moderately low range of jet exit velocity. A number of small spherical bubbles are initially generated in a starting vortex formed at the jet tip and often connected circumferentially with each other in the form similar to a vortex ring. Nearly axisymmetric lumps of disconnected bubbles are also observed frequently. By analyzing photographic data acquired from the side and end view pictures of the ring-like bubbles, their average properties, such as trajectory, geometry and size, are evaluated.
Dynamic behaviour of cavitation clouds: visualization and statistical analysis
Journal of the Brazilian Society of Mechanical Sciences and Engineering
High-speed visualization and subsequent statistical analysis of a high-speed cavitating water jet were performed with a custom image acquisition and processing system. In a cavitating water jet, cavity clouds form and collapse with an unsteady, periodic tendency where the frequency depends on the flow conditions. The aim of the presented investigations was to examine and analyse the dynamic behaviour of these cavity clouds to understand the effect of the influencing experimental working conditions, such as injection pressure, nozzle geometry and shape (convergent or divergent) on the size, integrity and life cycle of the clouds. The results show oscillation patterns in the geometry of the clouds (thickness, length, area, etc.), through shedding, growing, shrinking, which are related to upstream pressure fluctuations caused by the plunger pump and the interaction between the jet and the surroundings. The corresponding characteristic oscillation frequencies of the cavitating jets were also determined through cloud shape analysis.
Vizualization of the cavitating jet using flashlamp for illumination
EPJ Web of Conferences, 2012
The contribution deals with the ways of the illumination of the cavitating jet for the purposes of the visualization. The cavitation is induced by the fluid flow through the orifice with the diameter of 0,3mm. Region of the cavitating jet is illuminated by a different light sources. Goal of this paper is to compare the quality and the informative value of the obtained visual data. In addition, complicated structure of the cavitating jet is also shown and described
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright a b s t r a c t In this paper, the influence of nozzle geometry on cavitation and near-nozzle spray behavior under liquid pressurized ambient is studied. For this purpose, eight steel drilled plates, with different diameters and degrees of conicity of their holes, are analyzed. A special near-nozzle field visualization technique, using a test rig pressurized with fuel, is used. Due to the difference in refractive index between liquid and vapor phase, bubbles present at the outlet of the orifice are visualized. The pressure conditions at which bubbles start appearing at the orifice outlet are compared with those at which choked flow appears. The results showed that pressure conditions for inception of cavitation obtained in the visualization tests differs from those seen for choked flow (5–8% in terms of cavitation number). In addition to this, the images taken are analyzed to get the angle of the jet formed by fuel bubbles, showing that it increases significantly for those conditions more prone to cavitate. Furthermore, comparison of bubbles generation when increasing or decreasing backpressure indicates the presence of hysteresis in cavitation inception phenomena.
In present paper application of computer vision techniques to propeller cavitation experiments is presented. These techniques are widely adopted in many different environments and therefore they are well documented. They are also attractive from an economic point of view, due to relative low cost of the hardware involved. Nevertheless their application to study propeller behavior in cavitation tunnel is not straightforward, because of the nonstandard environment. However the adoption of these techniques may open a wide field of investigation and can result in a deepening of knowledge in propeller cavitation phenomena. In particular, obtained data can be linked to connected topics, such as propeller radiated noise or pressure signature, providing a better understanding on the sources of these effects, and invaluable information for validation of computer simulations. Present paper traces a possible path to develop an experimental technique, covering theoretical points as well as data analysis strategies and other practical aspects. All techniques are presented through practical application, thus making clearer their points of strength and their shortcomings. Besides achieved results, possible improvements and future developments are outlined.
Visualization of cavitating micro jets
EPJ Web of Conferences, 2012
The paper deals with one experimental set up integrated for research of the cavitating micro flows, which is incipient behind the micro channel or micro discharge nozzle outlet port. Experimental system is integrated from three major systems: hydraulic circuit with installed discharge nozzle (or micro channel), subsystem for data acquisition and data processing (DAQ system) and vision system compound of high speed video camera and pulse light source with highfrequency repetition. First few results of experiments (parameters such as inlet pressure, downstream pressure were changed) is also discussed.;