Decrease Of Cavitation Number Research Articles

PIV measurement of cavitating flow around a pitching hydrofoil

Particle Image Velocimetry (PIV) and hydrodynamic measurements were applied to investigate the cavitating flow of a pitching hydrofoil in the form of triangular wave motion (mean incidence α 0=10°, amplitude Δα=5° and pitching frequency f*=2Hz). The Reynolds number is Re=4.5×105. The cavitation number is set to σ=2.3, 1.36. Different typical cavity patterns are observed by PIV images in the whole pitching period, including sub cavitation, inception cavitation, sheet cavitation and cloud cavitation. As the σ decreases, the cavity area increases. And the the corresponding time and position of cavitation patterns also changed significantly. In the instantaneous velocity field of an oscillating hydrofoil, the low velocity zone (LVZ) and the mainstream zone (MZ) are observed. The LVZ corresponds to the cavitation region and changes with the change of cavitation morphology. Meanwhile, the LVZ has a large velocity gradient. The velocity gradient in the MZ is larger along the direction parallel to the incoming flow, and the velocity tends to increase first and then decrease gradually downstream. With the decrease of cavitation number, the area of LVZ increases. And the distribution of LVZ is more uneven, which is mainly caused by oscillation motion and uneven water vapor mixing.

New type of cavitation instability with peculiar frequency characteristic in liquid rocket inducer

In a liquid rocket turbopump with low pressure and thin wall tanks, cavitation inevitably occurs at the inducer which is installed at the inlet of the turbopump. The cavities at each blade oscillate periodically, and the turbopump sometimes becomes unstable, called cavitation instability. Rotating cavitation is one of the common types of cavitation instability, in which the cavities at each inducer blade oscillate respectively and appear to propagate from blade to blade. However, the new type of cavitation instability which does not follow the conventional principle has been observed in our experiment with an inducer. Converting the frequency in the inertial frame to that in the rotational frame and organizing it in the cavitation number, it was found that the frequency of unsteady cavitation increases as the cavitation number decreases, and this is the peculiar point of this instability. Additionally, during the cavitation instability, a few numbers of backflow vortex cavities were observed and moved sub-synchronously from blade to blade. In addition, the tip leakage vortex cavitation on each blade also propagates like sub-synchronous rotating cavitation but in different propagation speed from that of the backflow vortex cavities. As a result, it was supposed that the new instability is one of the types of sub-synchronous rotating cavitation related to backflow vortex cavitation, tip leakage vortex cavitation, and interaction between cavity propagation and inducer blade.

A comprehensive investigation on the internal flow and outflow characteristics of GDI elliptical divergent nozzles

The substantial demand for enhanced combustion efficiency and achieving near-zero emissions in GDI engines has spurred the introduction of a novel approach employing elliptical divergent nozzle spray technology. This innovative method, which marries the elliptical shape with a divergent nozzle, not only elevates downstream atomization quality but also mitigates nozzle tip wetting. Nevertheless, there exists a dearth of documented research regarding the internal flow and outflow characteristics related to the atomization potential of elliptical divergent nozzles. Numerical investigations have been carried out to scrutinize alterations in the three-dimensional cavitation morphology, the dispersion of turbulent vortex structures, and the nozzle exit flow parameters across a range of cavitation number conditions for both circular and elliptical divergent nozzles. The research findings demonstrate that the cavitation intensity of the elliptical divergent nozzle consistently surpasses that of the circular divergent nozzle. Also, the elliptical divergent nozzle consistently exhibits a greater number of turbulent vortex structures compared to the circular divergent nozzle across all cavitation number conditions. Additionally, as the cavitation number decreases, the difference in turbulence vorticity magnitude between the exits of the circular and elliptical divergent nozzles gradually increases. Furthermore, the elliptical diverging orifices are more susceptible to cavitation compared to their circular counterparts. The elliptical divergent nozzle outperforms the circular nozzle with a substantial 24.6% increase in exit velocity, especially at a cavitation number of 1.016.

Experimental and numerical study on unsteady entrainment behaviour of ventilated air mass in underwater vehicles

The hydrodynamic characteristics of underwater vehicles are significantly affected by the ventilated cavity covered by the vehicle surface. In this paper, the unsteady flow characteristics of this ventilated cavity are studied using experimental and numerical methods, and the unsteady entrainment behaviour of the ventilated air mass is emphasised. The flow pattern of the ventilated air mass is recorded using a high-speed camera. The large eddy simulation turbulence model is employed for the numerical simulations, and a good agreement is observed between the experimental and numerical results. In the early stage of the formation of the ventilated air mass, the internal structure exhibits a symmetric kidney vortex system, while the ventilated cavity below the vent hole has a continuous hairpin vortex structure. The ventilated air mass experiences a growth stage, an entrainment stage, and a shedding stage. The entrainment behaviour enables the ventilated air mass to quickly fill the ventilated cavity and modifies the surface pressure distribution of the vehicle. As the cavitation number decreases, the radial size of the ventilated cavity increases, and the contact area between the cavity and the water body increases, thus enhancing the vertical drag coefficient of the vehicle.

Visualization of R134a cavitation flow in a rectangle Venturi tube and determination of thermal effects with cavity length and thickness

In order to study R134a cavitation behavior in a rectangle Venturi tube, high-speed photography combined with pressure, flow rate, and temperature measurements are performed to visualize the cavitation process and determine the cavity thickness and length through the tube in a closed-loop test system. The experimental results indicated that incipient cavitation of R134a is observed at the entrance of the tube throat when the cavitation number is below 2.50, regardless of the inlet temperature and pressure. The normalized cavity length is correlated with the cavitation number, and a critical cavitation number of 1.766 is defined to connect two linear functions. The throat and tail cavity thickness can be fitted as a cubic polynomial function with the cavitation number, and a transition cavitation number of 2.00 divides the growth rate of the thickness with the decrease of the cavitation number into fast and slow-growing parts. The temperature drop measured at the throat of the Venturi tube can be fitted to a cubic polynomial function about the cavitation number. Under the same cavitation number, the temperature drop decreases with the increase of the flow temperature. The B-factor can be fitted as a cavitation number quadratic polynomial function and a linear function of the tail cavity thickness. The transition cavitation number is defined by the transition point of the growth rate of the above function. The empirical correlation of B-factor is modified based on the throat and tail cavity thickness, and the cavitation thermal effect of R134a is accurately predicted. Combined with the inception cavitation number, the transition cavitation number, and the critical cavitation number, the shape of the cavity is divided into four regions: inception cavitation, attached cavitation, supercavitation, and fusion cavitation. The fast Fourier transformation analysis shows that the cavitation flow of R134a gradually changes from periodic flow to fully developed unsteady flow with the decrease of cavitation number.

Comparison of Cavitation in Two Axial-Flow Water Jet Propulsion Pumps

To investigate the appropriate design method of the water jet pump, numerical simulations are carried out to compare the cavitation in two pumps designed by the streamline method and the blade load method. Based on a brief description of the design methods, the internal flow fields and cavitation in the two axial flow water jet propulsion pumps are studied by using the SST k−ω turbulence model and barotropic law cavitation model. The cavitation location, disturbance velocity field, blade load, and their variations with the cavitation number are analyzed. The results show that the pump designed by the blade load method has a smaller cavitation bubble than the pump designed by the streamline method. With the decrease of cavitation number, the vapor bubbles first appear at the blade tip of the leading edge and then extend from the leading edge to the trailing edge. The bubble thickness and the area of the low pressure on the suction surface also increases. A whirl in the disturbance velocity is observed, which turns the direction of incoming flow to the cavitation area. Furthermore, the head drop of water jet pump is related to the decrease of blade load. The results also show that at the point of cavitation number equal to 0.319, an unexpected peak of head in the pump designed by the streamline method is observed, which indicates an unstable working point for the pump. If the priorities are anti-cavitation performance and high efficiency at the design condition, the blade load method is the first choice to design pumps. While the streamline method should be adopted if high efficiency at large flow rates is preferred.

Spatial and temporal features of cavitation in micropump by dynamic mode decomposing

This study investigates the spatial and temporal features of micropump cavitation. The numerical model is based on the k-Epsilon turbulence model and the Zwart cavitation model. Cases with different rotation speeds and flow volumes are carried out experimentally to validate the numerical model by changing rotation speed and flow rate separately. The periodic to chaos cavitation is observed by varying the cavitation number. Spatial modes of cavitation on the blade are identified by the dynamic mode decomposing. The frequencies of those modes are also obtained. The most energetic modes are presented and discussed. Cavitation of micropump on the suction side of the blade experiences growing, breaking, and shedding. With the decrease of cavitation number, the cavitation occurs at the leading-edge part, the middle part, and the entire blades. The leakage of cavitation can result in the interaction between cavitation between neighboring gaps of blades and the symmetrical distribution. The results also show that with the increase of cavitation number, there exists a downshift of frequency, and the bump point of the blade can influence the cavitation significantly.

Influence of cavitation state and launch angle on water-exit process of vehicle based on moving domain method

This paper, aiming at the water-exit process of the vehicle with cavitation, based on the moving domain method coupled with the SDOF (six degrees of freedom) solver, using VOF (volume of fluid) multiphase model and the Schnerr-Sauer cavitation model, carrying out numerical simulation research on multi-conditions. Comparing vertical launch vehicles with different water-exit Ca (cavitation number) cases, the sudden decrease in cavitation number is closely related to the cavitation state, and there is a maximum influent cavitation state of the cavitation collapse on the process of the water-exit. Comparing different initial launch angle cases, it is found that there is a most unstable launch angle, which makes the angular deflection of the vehicle the most severe during the water-exit process.

Assessment of cavitation noise in a centrifugal pump using acoustic finite element method and spherical cavity radiation theory

To examine the cavitation noise characteristics of centrifugal pumps, the combination of test and simulation was applied in this study. The numerical method is based on spherical cavity radiation theory and the acoustic finite element method. A multi-field synchronized test-rig was built to study and validate the numerical results under cavitating flow and cavitation noise conditions. The three-dimensional unsteady flow-field simulation was carried out inside the centrifugal pump based on DES and the improved-RZGB cavitation model. The constructed numerical method for cavitation noise was used to solve the acoustic-field based on the flow-field solutions. The test–simulation comparison reveal that the numerical simulation results are consistent and reliable. The development of cavitation has a stronger influence on the strong vorticity regions in the impeller flow channel, and the vortex has a promotional-effect on the formation of cavitation. With the same cavitation number, the acoustic-power on the blade suction-side is greater than the pressure-side of the blade. As the cavitation number decreases, the pulsating radiated noise of cavitation volume is the primary noise-source for the increased acoustic-power value. At this stage, the SPL and total SPL at the model pump inlet show a decreasing trend during the severe cavitation-stage.

Numerical Investigation of Cavitation Flow Characteristics in a Hydrodynamic Levitated Micropump with Eccentric Rotation

In this study, the anti-cavitation performance and cavitation flow characteristics in a hydrodynamic levitated micropump were investigated based on numerical simulation and experiment. The cavitation characteristic curves and the development process of cavitation in the levitated micropump was firstly analyzed. Special emphasis was put on the effects of eccentricity on the anti-cavitation performance. The results show that as the eccentricity increases, the critical cavitation number gradually decreases, indicating that the eccentric rotation is beneficial to improve the anti-cavitation ability of the levitated micropump. The coupling effects between the radial force on the impeller and cavitation were also numerically studied. With the decrease of cavitation number, the radial force on the impeller gradually declines at first, then has a sudden increase and finally reduces with fluctuation. The drop of the radial force will lead to the decrease of eccentricity, resulting in the deterioration of cavitation further. In addition, the unsteady pressure pulsation was analyzed. The predominant frequencies of pressure pulsation are the blade passing frequency (BPF) and the harmonic frequency of BPF under both noncavitation and critical cavitation. Under critical cavitation, the amplitude of BPF has a drop, while the amplitude of low frequency less than BPF becomes larger.

Multiscale modeling of different cavitating flow patterns around NACA66 hydrofoil

The multiscale effect of cavitation is a complicated multiphase phenomenon involving macroscale cavities and microscale bubbles. The cavitating flows at four different patterns around a (National Advisory Committee for Aeronautics) NACA66 hydrofoil are simulated based on the multiscale model under the Eulerian–Lagrangian framework. The volume-of-fluid method is used to capture the transportation of large-scale cavities in the Eulerian framework, while small-scale bubbles smaller than the threshold value of computational cells are solved using the Lagrangian method and the simplified Rayleigh–Plesset equation. The turbulent flow is solved using the large-eddy simulation approach, and the two-way coupling source for momentum is calculated by integrating interacting forces of discrete bubbles. This work proposes a multiscale model to better investigate the vapor structure with an extensive range of length scales, and analyzes the evolution mechanism of vapor morphology and scale in different cavitation patterns first. The simulation results are compared with the experimental observations to verify the accuracy of the numerical method. Meanwhile, the results illustrate that the turbulence has a significant influence on the bubble behavior. With a decrease in cavitation number, the number and size of discrete bubbles increase significantly, and the probability density function of discrete bubble diameter similarly conforms to Gamma distribution at all cavitation patterns. For inception cavitation, sheet cavitation, and supercavitation, the shape of large-scale cavity is relatively stable, and the standard deviation of the number and Sauter mean diameter of microscale bubbles are much smaller than cloud cavitating flow. In contrast, the large-scale cavity sheds periodically in the cloud cavitating flow leading to the periodical variation of the number and the Sauter mean diameter of microscale bubbles as well. Additionally, the discrete bubbles are mainly distributed in the region with strong turbulence intensity and high vorticity.

Experiment and numerical simulation investigation on cavitation evolution and damage in the throttling section of pressure reducing valve

AbstractFor the phenomenon of widespread and serious cavitation damage in the throttling section of pressure reducing valve under high temperature and high pressure in the chemical technology process of petroleum and coal, according to actual coordination structure widely applied between the valve core and valve seat, the cavitation throttling section with symmetrical contraction and expansion was made, and the visualized cavitation water tunnel experimental apparatus was designed and constructed. The cavitation evolution process with time under different cavitation numbers σ was recorded by the high‐speed photography, the variation law of cavitation damage length and area with time was investigated by using aluminum film as cavitation damage carrier. Based on the experimental cavitation characteristic length L*, the evaporation coefficient Fv, and condensation coefficient Fc in the Zwart–Gerber–Belamri cavitation numerical model were modified, and the cavitation damage region was predicted by the gas phase condensation rate of numerical simulation. The results show that with the decrease of cavitation number, the characteristic length of cavitation strip increases; the cavitation characteristic length fluctuates greatly at σ = 1.22, and there are cavitation cloud periodic formation, shedding, collapse, and disappearance at the tail of the cavitation strip on the upper valve seat; the cavitation damage length of the upper and lower valve seat remains unchanged with time, and the cavitation damage area increases approximately linearly with time; the initial position and length of cavitation damage predicted by the gas phase condensation rate are basically consistent with the experimental results, which verifies the accuracy of the modified numerical simulation.

Experimental Study on the Relationship Between Cavitation and Lift Fluctuations of S-Shaped Hydrofoil

In order to study the energy loss of bi-directional hydraulic machinery under cavitation conditions, this paper uses high-speed photography combined with six-axis force and torque sensors to collect cavitating flow images and lift signals of S-shaped hydrofoils simultaneously in a cavitation tunnel. The experimental results show that the stall angle of attack of the S-shaped hydrofoil is at ±12° and that the lift characteristics are almost symmetrical about +1°. Choosingα= +6° andα= −4° with almost equal average lift for comparison, it was found that both cavitation inception and cloud cavitation inception were earlier atα= −4° than atα= +6°, and that the cavitation length atα= −4° grew significantly faster than atα= +6°. Whenα= +6°, the cavity around the S-shaped hydrofoil undergoes a typical cavitation stage as the cavitation number decreases: from incipient cavitation to sheet cavitation to cloud cavitation. However, whenα= −4°, as the cavitation number decreases, the cavitation phase goes through a developmental process from incipient cavitation to sheet cavitation to cloud cavitation to sheet cavitation to cloud cavitation, mainly because the shape of the S-shaped hydrofoil at the negative angle of attack affects the flow of the cavity tails, which is not sufficient to form re-entrant jets that cuts off the sheet cavitation. The formation mechanism of cloud cavitation at the two different angles of attack (α = +6°、−4°) is the same, both being due to the movement of the re-entrant jet leading to the unstable shedding of sheet cavity. The fast Fourier analysis reveals that the fluctuations of the lift signals under cloud cavitation are significantly higher than those under non-cavitation, and the main frequencies of the lift signals under cloud cavitation were all twice the frequency of the cloud cavitation shedding.

Numerical and experimental study in pressure pulsation and vibration of a two-stage centrifugal pump under cavitating condition

Instantaneous cavitating turbulent flow in a two-stage centrifugal pump with diffuser was simulated using a hybrid RANS/LES model and rotating corrected-based cavitation model in this paper. The predicted results of numerical simulation were in good agreement with the experimental results. The mechanism of pressure pulsation in the two-stage centrifugal pump was discussed. Some representative main frequencies of pressure pulsation such as main blade passing frequency, sub-blade passing frequency and intersection frequency of impeller blade and diffuser blade were analyzed systematically. Uncertainty estimation was used to ensure the accuracy of experimental results and it was also used to analyze the variation of pressure pulsation and vibration signals at different positions with the intensification of cavitation degree in the centrifugal pump. According to the results of uncertainty estimation, the center frequency of 1/3 octave band and the root mean square method were used to evaluate the energy change of the pressure pulsation signals and vibration signals at different frequency bands as the cavitation number decreases. The characteristics of pressure pulsation and vibration signals at different positions were analyzed in different frequency bands.

Experimental Research on Cavitation Evolution and Movement Characteristics of the Projectile during Vertical Launching

Aiming at the problem of unsteady cavitation during a projectile’s vertical water-exit process, scaled model experiments were carried out based on the self-designed underwater launch platform and high-speed cameras, which focus on changes in cavitation shape and projectile posture. In this paper, the general process of the cavitation evolution and projectile’s movement is described; the relationship between the re-entry jet, local cavitation number and cavitation stability is discussed. Meanwhile, the effect of head forms and launch speeds on the cavitation evolution and movement characteristics is analyzed, including 60° cone, 90° cone and hemispherical head with velocity of 16.8 m/s, 18.5 m/s and 20.0 m/s, whose launch cavitation number is 0.714, 0.589 and 0.504. The results show that the attached cavities fall off from the bottom up under the influence of the end-re-entry jet and the shedding frequency declines when the launch cavitation number decreases. The cavitation growth of 60° cone is easily disturbed by the air mass near the launcher, the cavitation development of 90° cone is characterized by small-scale and high-frequency growth and shedding, while the hemispherical head is not prone to cavitation. Moreover, increasing the speed can improve the stability of cavitation development and the projectile’s movement.

Numerical prediction of cavitation erosion to investigate the effect of wake on marine propellers

This paper presents validation studies to simulate performance, cavitation and cavitation erosion properties of the King's College (KCD) KCD-193 model propeller. The simulations are performed to investigate the effect of wake on the cavitation formation and the cavitation erosion intensity. The numerical (CFD) study is achieved by using unsteady Reynolds Averaged Navier-Stokes (RANS) and Detached Eddy Simulation (DES) techniques with SST (Menter) k-ω turbulence model. The Schnerr-Sauer cavitation model and Eulerian approach with the Volume of Fluid (VOF) multiphase model are used to model a two-phase cavitation flow. The sliding mesh technique is applied to simulate the rotation of the propeller, and particular mesh refinement is performed on the regions where cavitation development is observed. Erosion intensity values on the propeller surface are obtained by Erosive Power Method (EPM) approach, and erosion formation on the blades is illustrated by utilizing the erosion intensity dataset. Numerical comparison for the erosion intensity values using RANS and DES models is carried out to evaluate the effect of wake in behind condition. Numerical results are evaluated against cavitation tunnel measurements at the Emerson Cavitation Tunnel (ECT) of Newcastle University. The main objectives of the study are to obtain the cavitation and cavitation erosion formation on the propeller in good agreement with experimental data obtained in ECT and to investigate the characteristics of the erosion intensity subject to cavitation conditions. In view of the flow conditions investigated, the RANS model is also found appropriate and required less computing efforts to predict the erosion intensity than the DES model. The results confirm the EPM method is to be compatible in predicting the erosion intensity. The results of the simulations indicate that a decrease in cavitation number does not necessarily cause an increase in the erosion intensity, requiring further investigation.

O-008. Influence of Hypertension in Pregnancy on Hematological Phenotypes of Preterm Infants with Gestational Age Inferior to 32 Weeks

This paper presents validation studies to simulate performance, cavitation and cavitation erosion properties of the King's College (KCD) KCD-193 model propeller. The simulations are performed to investigate the effect of wake on the cavitation formation and the cavitation erosion intensity. The numerical (CFD) study is achieved by using unsteady Reynolds Averaged Navier-Stokes (RANS) and Detached Eddy Simulation (DES) techniques with SST (Menter) k-ω turbulence model. The Schnerr-Sauer cavitation model and Eulerian approach with the Volume of Fluid (VOF) multiphase model are used to model a two-phase cavitation flow. The sliding mesh technique is applied to simulate the rotation of the propeller, and particular mesh refinement is performed on the regions where cavitation development is observed. Erosion intensity values on the propeller surface are obtained by Erosive Power Method (EPM) approach, and erosion formation on the blades is illustrated by utilizing the erosion intensity dataset. Numerical comparison for the erosion intensity values using RANS and DES models is carried out to evaluate the effect of wake in behind condition. Numerical results are evaluated against cavitation tunnel measurements at the Emerson Cavitation Tunnel (ECT) of Newcastle University. The main objectives of the study are to obtain the cavitation and cavitation erosion formation on the propeller in good agreement with experimental data obtained in ECT and to investigate the characteristics of the erosion intensity subject to cavitation conditions. In view of the flow conditions investigated, the RANS model is also found appropriate and required less computing efforts to predict the erosion intensity than the DES model. The results confirm the EPM method is to be compatible in predicting the erosion intensity. The results of the simulations indicate that a decrease in cavitation number does not necessarily cause an increase in the erosion intensity, requiring further investigation.

Experimental study on unsteady characteristics of the transient cavitation flow

The characteristics of unsteady cavitation flow under different cavitation numbers are investigated experimentally. An optical test rig is designed to visualize the cavitation flow and the cavity length is defined based on high-speed camera technology. The development of cavitation flow can be divided into inception and fusion region, expansion region and collapse region. Due to the interaction between the re-entrant jet and the cavity interface, the cavitation bubbles near the solid wall collapse earlier than them in the downstream. The cavitation number is also the important factor determining the cavity length pulsation. Further analysis shows that the smaller the cavitation number, the smaller the frequency of cavity length fluctuations and the larger the mean cavity length. The cavitation intensity is stronger at lower cavitation number. Meanwhile, the cycle collapsing frequency of cavitation is around 220–320 Hz. With the decrease of cavitation number, the amplitude of cavitation pulsation increases while the corresponding collapsing frequency decreases.

Cavitation and Induced Excitation Force of Ice-Class Propeller Blocked by Ice

The presence of broken ice in the flow field around a propeller causes severe blade erosion, shafting, and hull vibration. This study investigates the performance of the propeller of a ship sailing in the polar regions under the propeller–ice non-contact condition. To this end, we construct a test platform for the propeller-induced excitation force due to ice blockage in a large circulating water channel. The hydrodynamic load of the propeller, and the cavitation and propeller-induced fluctuating pressure, were measured and observed by varying the cavitation number and ice–propeller axial distance under atmospheric pressure and decompression conditions. The results show that the fluctuation range of the blade load increases with a decrease in cavitation number and ice–propeller axial distance. The decrease in the cavitation number leads to broadband characteristics in the frequency-domain curves of the propeller thrust coefficient and blade-bearing force. Under the combined effects of ice blockage and proximity, propeller suction, the circumfluence zone around the ice, and the Pirouette effect, propeller–hull vortex cavitation is generated between the ice and propeller. The decrease in cavitation number leads to a sharp increase in the amplitude of the high-order frequency of the propeller-induced fluctuating pressure.

Effect of cavitation on energy conversion characteristics of a multiphase pump

To reveal the effect of cavitation on the energy conversion characteristics of helical axial multiphase pump (Abbreviated to multiphase pump), the cavitation flow in multiphase pump is simulated. The results show that with the decrease of cavitation number σ, cavitation firstly extends along the streamwise of blade suction side, and then turns to the pressure side of blade. When cavitation develops to fracture stage, the suction side of the blade is completely covered by bubbles; The vapor volume fraction in the impeller is almost 0 at the inception and critical cavitation stages; When cavitation develops to fracture stage, cavitation extends to the whole impeller passage. The output power of impeller is mainly contributed to the power done by the pressure. The power done by the viscous force in the critical fracture cavitation stage is slightly reduced. While, the power done by the pressure in the fracture cavitation stage decreases greatly. With the evolution of cavitation, the turbulence dissipation loss in the impeller decreases gradually. Moreover, in the critical fracture and fracture cavitation stages, the friction loss increases greatly compared with the previous two cavitation stages, resulting in an increment of the total energy loss.