Models for the prediction of cavitation aggressiveness

Amila Džomba

Master's thesis

Abstract:

The introduction to cavitation and its effects is described at the beginning of this study, as well as properties of fluid that affects cavitation and mechanisms of cavitation bubble collapse. Research on models which are used for cavitation aggressiveness and cavitation erosion description are studied. Further, description of material response to cavitating flow impacts with description of cavitation erosion is presented. Main stages, incubation, acceleration and steady state period, of cavitation are briefly described and focus is set on steady state period of cavitation. Existing pitting tests and impact forces measurements are taken into consideration and are utilized in this study. Experiment on vibratory apparatus is conducted in order to obtain mass loss data and erosion rate curve, as well as cumulative mass loss curve. Mass loss is measured until the steady state period of cavitation is reached since steady state period is the one of interest in this study. Results of the experiment are presented in the form of erosion rate graph and cumulative mass loss curve, since these are characteristic curves which describe cavitation erosion stages. Experimentally obtained erosion rate curve is compared to theoretical erosion rate curve and it is proven to be similar. Phenomenological model for cavitation erosion rate computation is studied and erosion tests are used in validation of the model. Applicability of the model on available experimental data is studied and results are presented. Results of experimental and analytical methods are compared and proven to be similar, of the same order. Conclusion is made that the experiments conducted in a couple of minutes are sufficient and there is a possibility to predict erosion rate based on these relatively simple experiments.

Abstract:

The introduction to cavitation and its effects is described at the beginning of this study, as well as properties of fluid that affects cavitation and mechanisms of cavitation bubble collapse. Research on models which are used for cavitation aggressiveness and cavitation erosion description are studied. Further, description of material response to cavitating flow impacts with description of cavitation erosion is presented. Main stages, incubation, acceleration and steady state period, of cavitation are briefly described and focus is set on steady state period of cavitation. Existing pitting tests and impact forces measurements are taken into consideration and are utilized in this study. Experiment on vibratory apparatus is conducted in order to obtain mass loss data and erosion rate curve, as well as cumulative mass loss curve. Mass loss is measured until the steady state period of cavitation is reached since steady state period is the one of interest in this study. Results of the experiment are presented in the form of erosion rate graph and cumulative mass loss curve, since these are characteristic curves which describe cavitation erosion stages. Experimentally obtained erosion rate curve is compared to theoretical erosion rate curve and it is proven to be similar. Phenomenological model for cavitation erosion rate computation is studied and erosion tests are used in validation of the model. Applicability of the model on available experimental data is studied and results are presented. Results of experimental and analytical methods are compared and proven to be similar, of the same order. Conclusion is made that the experiments conducted in a couple of minutes are sufficient and there is a possibility to predict erosion rate based on these relatively simple experiments.

Keywords

cavitation aggressiveness, cavitation erosion, phenomenological model, erosion rate, steady state period of cavitation

Language used: English

Date on which the thesis was submitted / produced: 7. 6. 2021

Thesis defence

• Supervisor: Ing. Miloš Müller, Ph.D.

Technical University of Liberec

Faculty of Mechanical Engineering

Master programme / field:
Mechanical Engineering / Machines and Equipment Design