Linking cavitation collapse energy with the erosion incubation period (original) (raw)
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Prediction of Cavitation Erosion: An Energy Approach
Journal of Fluids Engineering-transactions of The Asme, 1998
The objective is to define a prediction and transposition model for cavitation erosion. Experiments were conducted to determine the energy spectrum associated with a leading edge cavitation. Two fundamental parameters have been measured on a F. Avellan symmetrical hydrofoil for a wide range of flow conditions: the volume of every Professor. transient vapor cavity and its respective rate of production. The generation process of transient vapor cavities is ruled by a Strouhal-like law related to the cavity size. The analysis of the vapor volume data demonstrated that vapor vortices can be Ph. Dupont assimilated to spherical cavities. Results are valid for both the steady and unsteady Research Associate. cavitation behaviors, this latter being peculiar besides due to the existence of distinct volumes produced at specific shedding rates. The fluid energy spectrum is formulated IMHEF-EPFL, and related to the flow parameters. Comparison with the material deformation energy Institut de Machines Hydrauliques spectrum shows a remarkable proportionality relationship defined upon the collapse et de Mé canique des Fluides, efficiency coefficient. The erosive power term, formerly suggested as the ground Swiss Federal Institute of Technology, Av. de Cour 33, 1007 Lausanne, component of the prediction model, is derived taking into account the damaging Switzerland threshold energy of the material. An erosive efficiency coefficient is introduced on this basis that allows to quantify the erosive potential of a cavitation situation for a given material. A formula for localization of erosion is proposed that completes the prediction model. Finally, a procedure is described for geometrical scale and flow velocity transpositions.
Development of a cavitation erosion model
Wear, 2006
A study of visual and erosion effects of cavitation on simple single hydrofoil configurations in a cavitation tunnel was made. A thin copper foil, applied to the surface of the hydrofoils, was used as an erosion sensor. The cavitation phenomenon on hydrofoils at different flow conditions (system pressure, water gas content, flow velocity) was observed. Results that showed a significant relationship between cavitation erosion and the visual effects of cavitation made it possible to use these information to develop a cavitation erosion model. The model is based on the physical description of different phenomena (cavitation cloud implosion, pressure wave emission and its attenuation, micro-jet formation and finally pit formation), which are involved in the process of pit formation. It is capable to predict the influence of significant parameters as flow velocity and gas content of water.
Towards quantitative assessment of material resistance to cavitation erosion
Wear, 2005
The progress in developing a new method of assessing material resistance to cavitation erosion is reported. The method proposed incorporates procedures for determining cavitation impingement structure, superposing erosive effects of various cavitation impingement fractions and determining the set of parameters needed to describe material performance under cavitation load of given amplitude distribution. The experimental techniques applied and results obtained in the process of validating and developing the method are presented. At the moment, the Sitnik model of erosion progress under uniform cavitation impingement seems especially well suited for further work on erosion modeling. No evidence of cavitation macropulses due to collective phenomena acting simultaneously on a major part of a specimen has been identified in the IMP PAN cavitation tunnel. It is shown that cavitation pulses distribution can be approximated by means of a power-exponential distribution. The mean erosion rates of PA2 aluminium alloy and E04 Armco iron have been found almost proportional to the ME cavitation intensity index even after a test of 10 h duration.
Scaling of cavitation erosion progression with cavitation intensity and cavitation source
Wear, 2012
A simple mathematical expression is presented to describe cavitation mean depth of erosion versus time for cavitating jets and ultrasonic cavitation. Following normalization with a characteristic time, t*, which occurs at 75% of the time of maximum rate of erosion, and a corresponding material characteristic mean erosion depth, h*, the normalized erosion depth is related to the normalized time byh = 1 − e −t 2 + e −1t1.2 . This was obtained by conducting systematic erosion progression tests on several materials and varying erosion field intensities. Both a modified ASTM-G32 method and Dynaflow's cavitating jets techniques were used and the jet pressures were varied between 1000 and 7000 psi. The characteristic parameters were obtained for the different configurations and the correlation was found to be very good, exceeding an R 2 of 0.988 for all cases. Relationships between these parameters and the jet pressure were obtained and resemble familiar trends presented in the literature for mass loss. The study allowed a comparative evaluation and ranking of the various materials with the two accelerated erosion testing methods used. While several materials ranked the same way with the different erosion intensities and testing method, the relative ranking of erosion resistance of some materials was seen to be dependent on the cavitation intensity.
Numerical Simulation of Cavitation Erosion Aggressiveness Induced by Unsteady Cloud Cavitation
Applied Sciences
A numerical investigation of the erosion aggressiveness of leading edge unsteady cloud cavitation based on the energy balance approach has been carried out to ascertain the main damaging mechanisms and the influence of the free stream flow velocity. A systematic approach has permitted the determination of the influence of several parameters on the spatial and temporal distribution of the erosion results comprising the selection of the cavitation model and the collapse driving pressure. In particular, the Zwart, Sauer and Kunz cavitation models have been compared as well as the use of instantaneous versus average pressure values. The numerical results have been compared against a series of experimental results obtained from pitting tests on copper and stainless steel specimens. Several cavitation erosion indicators have been defined and their accuracy to predict the experimental observations has been assessed and confirmed when using a material-dependent damaging threshold level. In ...
Cavitation erosion : the effect of fluid and flow parameters
2016
This thesis describes an investigation into the effect of fluid and flow parameters on cavitation dynamics and cavitation erosion. A rotating disc test apparatus was developed fo: dow-type cavitation studies. A vibratory test device was also developed to study the role of cathodic and anodic potentials applied to cavitating bodies. Some major results are given below. Erosion "peaksat about 50°C in water, but under certain conditions material degradation caused by increased corrosion rate cancels out thermodynamic effects at higher temperatures. An erosion peak is also observed as a function of static pressure. Damage increases with velocity until cavitation is fully developed, at which stage the influence of velocity becomes negligible. The changes in erosion zone geometry and mass loss caused by temperature, velocity and pressure variations may be correlated with the effect these parameters have on the cavitation pressure profile. Efforts are described to develop a system for ...
Wear, 1999
Ž. In September 1987, during the ELSI VII Conference, the start of the International Cavitation Erosion Test ICET project was Ž announced. The experimental programme consisted in testing 6 selected materials single-phase aluminium and brass alloys, Armco iron,. carbon and chromium-nickel steel, and a polyamide 6 plastics at various laboratory rigs. Tests were conducted at 4 cavitation tunnels, 4 rotating disks, 6 vibratory rigs, 1 liquid jet and 2 cavitating jet facilities. The results, now available in form of a MS Access database and the ICET Preliminary Report, convince that in addition to standardisation of selected experimental techniques, one should strive to develop methods allowing to predict material performance under variable cavitation loading conditions. In the present contribution, a method of quantitative material resistance assessment based on an idea of defining response to individual fractions of cavitation pulses histograms is proposed. Cavitation pulses are classified as micro-and macro pulses, depending on the affected area size, and divided into Ž. amplitude fractions. Erosion due to individual fractions is assumed to follow the same general law DV s A P ME P U k , E with A the i i eroded area, ME the power flux delivered to a unit area of impinged surface, E the cumulative energy delivered to this area, and k the i i material resistance vector consisting of parameters of the erosion progress function U. The erosion progress due to the polyfractional cavitation impingement is assumed to follow a superposition law described by a differential equation presented in the paper. Advantages and weakpoints of the approach are discussed.
Comparison of erosion mechanisms in different types of cavitation
Wear, 1986
A new cavitation erosion device producing vortex cavitation has been extensively used. A comparative study between various cavitation erosion situations was carried out to verify the ability of this vortex cavitation generator to produce realistic cavitation erosion with respect to that observed in hydraulic machinery.
Time accurate numerical cavitation erosion prediction of multiphase flow through a venturi
2017
Cavitation erosion affects the efficient operation of the vessel’s propeller, leading to increased costs of operation and maintenance. Traditionally, erosion is predicted using dedicated cavitation tests with utilization of soft paint application or materials as erosive sensors. However, even with materials that are most susceptible to erosion, such tests constitute significant amount of time. It is well-known that cavitation erosion occurs with the impact of high velocity liquid jets generated by the imploding bubbles, also called water hammer effect, and induced shock waves over time. However, it is both not a viable approach to simulate the complete duration of an experiment using numerical methods and extremely expensive in terms of computational time. Therefore, it is a common simplification to assume cavitation events to be repetitive for numerical simulations and based on this assumption there has been a plethora of studies utilizing the numerical simulations for cavitation e...