The self-excited oscillating cavitation jet nozzle (SEOCJN) serves as a crucial component for converting hydrostatic energy into dynamic pressure energy and ensuring optimal hydraulic and cavitation performance of cavitating jets. Thus, it is of crucial significance to understand the cavitation characteristics and the influence law of SEOCJN for its extensive industrial applications. This paper utilizes numerical simulation methods to analyze the dynamic process of cavitation initiation, development, and outlet cavitation performance of SEOCJN. It explores the effects of inlet pressure and flow rate on the frequency characteristics of SEOCJN, and establishes a mathematical relationship between self-excited oscillation frequency and outlet flow frequency. The results indicate that the self-excited oscillation nozzle has an inlet diameter (D1) of 4. 7 mm, an outlet diameter (D2) of 12. 2 mm, a length (L) of 52 mm, a chamber diameter (D) of 83 mm, an oscillation angle of 120°, and an inlet pressure (Pin) of 4. 8 MPa. At these parameters, the frequency of the pulse jet reaches 830. 01 Hz, with an internal flow period of approximately 0. 0024 s. The maximum vapor volume fraction is found to be located 0. 28 m from the outlet of the SEOCJN. Furthermore, the frequency of self-excited oscillation pulse increases with an increase in inlet pressure. These findings provide a theoretical basis for the industrial application of self-excited oscillation cavitation jet nozzles

Cavitation phenomenon can cause deterioration of the hydraulic performance, damage by pitting, material erosion, structure vibration and noise in fluid machinery, turbo-machinery, ship propellers and in many other applications. Therefore, it is important to detect inception of cavitation phenomenon. An experimental study has been carried out in order to investigate the noise radiated by various cavitating sources to determine the validity of noise measurements for detecting the onset of cavitation. Measurements have been made measuring the noise radiated by a number of configurations in a water tunnel at various operating condition to determine the onset of cavitation. The measurements have been conducted over a frequency range of 31. 5 Hz to 31. 5 kHz in one-third octave bands. The onset of cavitation was measured visually through a Perspex side of the working section of the water tunnel. Moreover, a theoretical estimate of the pressure radiated from the cavitation nuclei at their critical radii and their frequency was presented. Tests indicated that, generally, at the point of visual inception there was a marked rise of the sound pressure level in the high-frequency noise, whilst the low-frequency noise increased as the cavitation developed. This finding was supported by the theoretical estimate of the pulsating frequency of cavitation nuclei. The results illustrated that the visual observations of inception confirm the noise measurements.

In this paper, cavitation and non-cavitation flows around a marine propeller, DTMB 4119, with the RANS method, the K-03b5 turbulence model, the Singhal transfer model and the mixed model, were solved. The velocity and pressure fields around the propeller surfaces were obtained using the equations of continuity, momentum and the K-03b5 model of turbulence. The pressure coefficient for two sections of the propeller with experimental data (Jessup 1989) in non-cavitation flow, and three sections in cavitation flow with numerical data (Sun 2008), was validated. Thrust, torque and efficiency coefficients were extracted for this propeller in eight simulations and compared with experimental data. The cavitation pattern was specified and also the position and the cavity development area were obtained. Furthermore, numerical investigations for the three important parameters, such as: advance coefficient, propeller working depth and surface roughness of propeller in cavitation flow, were undertaken. An advanced coefficient effect study on the propeller surfaces showed that with less advance coefficient, more vapor phase value is observed. Also, cavity boundaries are extended. Between advance coefficient values of 0.833 and 0.7, cavity volume results are less than the advance coefficient values of 0.7 and 0.6.So, the cavity boundaries are significantly extended. By downing the propeller working depth under open water conditions (increasing hydrostatic pressure), cavity boundary movement, cavity volume variation and curve peak reduction of the vapor phase volume fraction were investigated. The cavity center was away from the leading edge and the probability of tip vortex cavitation was reduced. The sustainability of tip vortex cavitation is more than sheet cavitation, the casue of which is, first, tip vortex cavitation, and then, sheet cavitation of the leading edge. Investigation on propeller surface roughness showed that optimal roughness height could be found. A and B models showed less cavity volume than the smooth model, while the C model showed more cavity volume. When roughness height was increased, the vapor phase volume fraction was firstly reduced, the results of A and B models being nearly the same. As a result, increasing the roughness height to a specific value caused a decrease in the vapor phase volume fraction value, which afterwards grew.

To investigate the limit behaviours of cavitation flow around a circular cylinder at a high speed cavitation tunnel, stainless steel models with different diameters, including 10 mm, 15 mm and 20 mm were made and tested in a supercavitation tunnel. Two holes designed in a way that the radial hole is connected to the axial one to measure the back pressure of models at various cavitation numbers. Before appearing clear silver regime at the back of model, pressure fluctuating is violent and after forming visible stable clear silver regime the fluctuating pressure will be reduced and the length of attached bubble will be increased strongly. In this case, the longitudinal oscillation occurs randomely. The measure of minimum back pressure for all models is the same and is equal to 13500 Pa. When the cavitation length is small, shedding vortices occur regularly, based on von-karmen pattern. In supercavitation regime, the collapse noise of bubble for the 20 mm model is very stronger than the 10 mm model. The ultimate cavitation number (chocking regime), will be reduced by decreasing the model diameter. The minimum cavitation number for 10 and 20 mm models are 0. 125 and 0. 49 respectively. The results show that the difference in ultimate cavitation number between experimental and theory methods are approximately 14%.

The flow field of a low specific speed centrifugal pump is investigated in the present work based on numerical simulation to establish the effect of circumferential positions of balance holes on cavitation behaviour and cavitation erosion of the centrifugal pump. The distribution of the pressure around balance holes is studied, the initiation and development of cavitation at different balance hole schemes are compared, and the distribution of cavitation erosion for the original pump and the ideal scheme is also predicted. The results show that when the NPSHa is high, there is low pressure zone in balance hole, which leads to cavitation in the pump. The cavitation performance of pump is improved by gradually moving balance holes away from blade suction surface, as this reduces low pressure zones around the balance hole and incipient cavitation. Under critical cavitation conditions, the cavitation shows a tendency to collapse as the angle (φ) of circumferential position of balance holes decreases, and the proportion of the higher vapor volume fraction in cavitation core zones also decreases. The cavitation erosion zones on blade surfaces are predicted by using the Erosive Power Method (EPM). The erosion impact of the original pump is more pronounced in the comparative results.

Cogitating flow is investigated around marine propellers, experimentally and numerically. Two different types of conventional model propellers are used for the study. The first one is a four bladed model propeller, so called model A, and the second one is a three bladed propeller, model B. Model A is tested in different cavitation regimes in a K23 cavitations tunnel. The results are presented in characteristic curves and related pictures. Finally, the results are discussed. Model B is investigated based on existing experimental results. In addition, model B is used for validation of the numerical solution prior to the testing of model A. The cavitations phenomenon is predicted numerically on a two dimensional hydrofoil, NACA0015, as well as propeller models A and B. The cavitation prediction on a hydrofoil is carried out in both steady and unsteady states. The results show good agreement in comparison with available experimental data. Propeller models are simulated according to cavitations tunnel conditions and comparisons are made with the experimental results, quantitatively and qualitatively. The results show good agreement with experimental data under both cogitating and noncavitating conditions. Furthermore, propeller cavitation breakdown is well reproduced in the proceeding. The overall results suggest that the present approach is a practicable tool for predicting probable cavitations on propellers during design processes.

Cavitation is a major problem in pump design and operation because this phenomenon may lead to various types of instabilities, including hydraulic performance loss and catastrophic damage to the pump material caused by bubble collapse. Therefore, it is critical to predict the cavitation performance of the pump in the design phase itself. The motivation of this study is to develop a systematic methodology to calculate the cavitation performance of radial flow pumps. In the first step of the present work, a cavitating nozzle flow case for which the bubble dynamic behavior is accurately resolved in literature is studied numerically. Subsequently, the capabilities of three cavitation models, implemented in the commercial code Fluent, are evaluated for three radial flow pumps designed at specific speeds ns = 10. 4, 22. 4, and 34. 4. The numerical results are validated with global quantities based on net positive suction head (NPSH) measurements. The results led to the determination of reasonably accurate NPSH values for the defined range of specific speeds.