Cavitation Model Research Articles

Effects of cavitation on the hydrodynamic loading and wake vortex evolution of a pre-swirl pump-jet propulsor

The purpose of this study is to investigate the effects of cavitation on the hydrodynamic loading and wake vortex evolution in a pre-swirl pump-jet propulsor, and also the cavitation-vortex interaction mechanism. The cavitating flow is simulated by delayed detached eddy simulation coupled with a homogeneous cavitation model. Based on available experimental validation, the cavitation patterns, hydrodynamic loadings, the tip leakage vortex (TLV) evolutions and trailing edge vortex interactions are orderly investigated under two typical cavitation conditions. Results show that the blade sheet cavitation, TLV cavitation and tip clearance cavitation are regard as the main cavitation types of the rotor, where the sheet cavity on adjacent blades is non-uniformly distributed under the perturbations of the stator wakes and phase effects. The interaction between the thickening sheet cavity and stator wakes causes the shift of dominant frequencies of rotor loading from the rotor blade passing frequency fBPF and its harmonics to stator blade passing frequency fs and its harmonics. The relative vorticity transport equation is used to analyze cavitation-vortex interaction of TLV. The TLV cavitation promotes the vorticity production of TLV at the incipient stage and increases its intensity downstream. The instability of TLV is triggered earlier when cavitation is heavy due to the enhanced mutual interaction between consecutive spirals of the TLVs and their interaction with sheet cavity induced shedding vortices. The trailing edge vortices of stator and rotor mutually interacts with blade sheet cavity, which accelerates the breakdown of trailing vortex system downstream.

Assessment of unsteady cavitating flow around modified NACA4412 hydrofoil

Cavitation is a complex two-phase flow phenomenon that includes unsteady characteristics. This work performs an unsteady 2D numerical analysis of cavitating flow on (i) cambered NACA4412 hydrofoil and (ii) the same hydrofoil geometry modified with dimple. The analysis is done with the objective of estimating the effect of the dimple on the hydrodynamic performance of the cavitating hydrofoil. The numerical simulations are performed using a flow solver by employing Realizable κ-ε turbulence model and Zwart-Gerber-Belamri (ZGB) cavitation model. The hydrodynamic performance is quantified in terms of coefficient of lift, coefficient of drag, lift to drag ratio, static pressure distribution, and cavity length at various cavitation numbers and angles of attack. From the assessment, it is observed that for 8⁰ angle of attack, the coefficient of drag on NACA4412 hydrofoil with the dimple is less as compared to NACA4412 without dimple. For higher angles of attack (α = 12⁰&16⁰) NACA4412 hydrofoil with the dimple has higher coefficient of lift compared to NACA4412 without dimple.

Comparison of the performance of propane ([formula omitted]) and propene ([formula omitted]) as alternative refrigerants for cooling during expansion in a helical capillary tube: A CFD-based insight investigation

The current research compared the efficiency of the new generation refrigerants, propane (R290) and propene (R1270), for cooling applications. The refrigerants’ flow and phase change properties in a helical capillary tube are simulated using ANSYS Fluent 2021 R2 CFD software. For this virtual experiment, a helical capillary tube with an inner diameter of 1.2 mm and a total length of 2100 mm is used. The flashing phenomenon, in which the refrigerants undergo a phase change, is simulated using a finite volume-based mixture model. The Zwart–Gerber–Belamri model is utilized to estimate mass transfer during flashing, which adheres to a homogeneous equilibrium strategy. A set of user-defined functions (UDF) are created to access the refrigerant properties and implement the cavitation model. Bilinear interpolation is used to calculate the fluid’s characteristics at a particular cell pressure and temperature. Available numerical and experimental results are used to verify the constructed numerical model. The investigation shows that under the same operating conditions, R290 refrigerant maintains a higher mass flow through the helical capillary tube than R1270. R1270 produces a lower temperature vapour-liquid mixture at the exit of the capillary tube in comparison to R290. CFD simulations have generated information and data that are helpful in choosing proper refrigerants for different purposes.

Numerical Comparative Study of Fuel Cavitation in Microchannels under Different Turbulence Models

The fuel injector is a critical component of the internal combustion engine. The diameters of the injector nozzle and the control chamber’s oil inlet and outlet are generally between 0.2 and 0.5 mm, which are typical microchannel structures. During high-pressure injection, the cavitation phenomenon in the channel seriously affects the reliability of the internal combustion engine. The choice of turbulence and cavitation models is the key to investigate the cavitation in the microchannel by using numerical methods. Based on the Winklhofer microchannel fuel experiment, five representative turbulence models were used to construct a microchannel model, and the results were compared and analyzed with the experiment. The results show that the pressure gradient values obtained from the combination of RNG k-ε and ZGB models were similar to the experimental data, with an error of less than 6%. The cavitation distribution calculated from the combination of LES and ZGB models was most consistent with the experimental observation data. The outlet mass flow rate obtained from the LES and ZGB models matched the trend of the experimental data in the pressure difference range of 19 bar to 85 bar, with an error of less than 2%. For the cross-sectional flow rate calculation, the RNG k-ε and ZGB models had the smallest calculation errors, with errors below 11%.

Internal Cavitating Flow Distribution and Performance Comparison of a Disc Pump with Radial Straight Blade

Disc pumps with radial straight blade are unconventional designs that have been developed for hard-to-pump mixtures for many industrial applications. They are frequently used in chemical industries, sub-sea petroleum pumping systems with multi-phase media and so on. Due to the radial straight blade arrangement, they may suffer from cavitation onsets when being used under different pressure conditions. To study the influence of cavitation characteristic inside the present disc pump flow passages, experimental data analysis on a radial blade disc pump for a wide flow rate range (0 to 110 m3/h) is obtained. In addition, the Reynolds averaged (RANS) approach using the RNG k-ε turbulence model, is carried out under different working conditions with and without cavitation modelling. Two different pump meshing models are also implemented: the first one without hub and shroud side channels between the discs and the volute casing, the second one with both side channels corresponding to the complete real case geometry. The comparisons between experimental and numerical results reveal first that the complete geometry meshing must be used to recover the experimental performance curve especially at low flow rates whatever the rotational speed. Secondly, the cavitation effect is found to take place in precise locations (straight blade and connection column) inside the impeller at high rotational speed and high flow rates. Their effects correspond to the unexpected performance curve deterioration found for the highest rotational speed and high flow rates. Moreover, with the decrease of the inlet absolute pressure, the cavitation degree becomes serious, and the coupling phenomenon of straight blade cavitation and connection column cavitation is formed, which enlarges the scope and enhances the degree of cavitation. The present study proposes a data reduction procedure when open loop experimental testing procedure is used for specific disc pump design and the importance of the impeller-side channels interactions on head pump decrease at low flow coefficients.

The Hydrodynamic Challenge of Initial to Sheet/Cloud Cavitating Flow Around ClarkY11.7% Hydrofoil Using Recent Turbulence and Cavitation Models

The Hydrodynamic Challenge of Initial to Sheet/Cloud Cavitating Flow Around ClarkY11.7% Hydrofoil Using Recent Turbulence and Cavitation Models

Influence of Fluid Viscosity on Cavitation Characteristics of a Helico-Axial Multiphase Pump (HAMP)

Fluid viscosity is one of the key factors affecting the cavitation characteristics of the Helico-axial Multiphase Pump (HAMP). In this paper, fluids with viscosities of 24.46 mm2/s, 48.48 mm2/s, 60.70 mm2/s, and 120.0 mm2/s were investigated by numerical simulation. The Ansys Fluent software was employed to conduct the simulation. The mixture multiphase flow model and the RNG k-ε turbulence model were adopted. The Singhal cavitation model was employed to consider the effects of the non-condensable gas on cavitation. An experiment was carried out to validate the numerical method. The results showed that the Net Positive Suction Head-available (NPSHA) of the pump decreased as the fluid viscosity increased. Under the critical NPSHA condition, the NPSHA decreased from 5.11 m to 3.68 m as the fluid viscosity increased from 24.46 mm2/s to 120.0 mm2/s. This suggested that the cavitation performance of the pump was deteriorated under high fluid viscosity. The impeller passage area occupied by the vapor increased when the fluid viscosity increased. Nearly half of the flow passages were occupied by cavitation bubbles when the fluid viscosity increased to 120.0 mm2/s. The vapor volume fraction, both on the suction surface and pressure surface of the blade, increased with the fluid viscosity. The vapor on the suction surface was mainly distributed in the region with the streamwise between 0 and 0.36 when the fluid viscosity was 24.46 mm2/s; while the high vapor volume fraction range increased to the streamwise of 0.42 when the fluid viscosity increased to 120.0 mm2/s. The higher vapor volume fraction corresponded with the lower pressure. It was also found that the turbulent kinetic energy, both on the suction surface and pressure surface, increased with the fluid viscosity, which was the favorite for producing more cavitation bubbles. Furthermore, the maximum velocity area was mainly concentrated in the inlet area of the impeller. The velocity distribution in the impeller was basically the same with the viscosity of 24.46 mm2/s and 48.48 mm2/s. When the viscosity further increased to 60.70 mm2/s, the maximum velocity area in the impeller was relatively large. This study provides a reference for designing the HAMP.

Modeling the mass transfer at acoustically generated bubble interface using Rayleigh–Plesset equation second-order derivatives

One of the many ways of cavitation utilized for process intensification is through acoustically inducing it. As acoustic cavitation gained traction in recent industrial works, numerical modeling became an important study tool to scrutinize and optimize acoustic cavitation applications. However, available hydrodynamic cavitation models are found incapable of accurately predicting acoustic cavitation structures and flow features. This could source from the oversimplification of the Rayleigh–Plesset equation or from obscure effects of empirical model constants. To address this issue, new mass transfer source terms for Zwart–Gerber–Belamri model were derived based on the consideration of Rayleigh–Plesset's second-order derivatives. In addition, a design of experiments statistical approach, coupled with Monte Carlo simulations, was implemented to assess the influence of empirical model constants on the model's performance by examining variations in amplitude and frequency responses. Moreover, a set of optimized model constants was obtained: evaporation constant = 17.359 88, condensation constant = 0.1, Bubble Radius = 25 × 10−6 m, and Nucleation Site Volume Fraction = 5 × 10−4, to obtain a maximum pressure and frequency of 3.62 bar and 4128.73 Hz, respectively. The new model, with the new constants, was configured into ANSYS Fluent 22.1 and validated against experimental values. The new model resulted with maximum pressure and frequency of 3.48 bar and 4894.56 Hz, respectively, validating the statistical model and showing drastic improvement in qualitatively and quantitatively capturing acoustic cavitation.

Evaluation of the effects of interfacial tension forces in homogenous equilibrium mixture modeling of a cavitation flow of liquefied natural gas inside a Laval nozzle

Achieving the robust performance in turbomachinery equipments including the modern liquefied natural gas (LNG) fuel pumps, is highly dependent on prediction of cavitating patterns and control of consequent cavitation damages. In most studies to date of cryogenic cavitation, effects of vapor-liquid interfacial tension on the onset and development of transient cryogenic cavitation have not been addressed sufficiently. This is of more interest when it comes to numerical homogenous equilibrium mixture (HEM) modeling of cavitation where vapor fraction field is calculated through appropriate weighting functions, as opposed to that in transport-equation –based modeling, known as TEM approach, where separate transport equation is introduced for calculation of vapor phase fraction. In the present work, a HEM-based cryogenic cavitation solver is employed to examine the interfacial tension effects on the phase-change behavior of LNG inside a Laval nozzle. Based on the theoretical considerations and comparison of the results with available literature data, it is concluded that the presence of interfacial tension forces in the in-nozzle cavitation LNG flow can potentially stabilize cavitating patterns through modifying the local phase-change incidents. The net LNG vapor production in the nozzle is however observed not to be largely affected by the interfacial tensions, suggesting the pre-dominance of temperature-dependent inertia and advective forces in modulating LNG phase-change processes. Counting the calculations of interfacial tension forces in the cavitation solver is also found to improve accuracy of the modeling against the experimental data.

Unsteady characteristics of tip leakage vortex structure and dynamics in an axial flow pump

The aim of this work is to investigate the unsteady characteristics of tip leakage vortex (TLV) structure in an axial flow pump experimentally and numerically. Experiments were carried out to study the performance of an axial flow pump under cavitating cavitation. The numerical simulation was conducted by employing the Large Eddy Simulation turbulence and Zwart cavitation models, and the results show a good agreement with the experimental ones. The evolution mechanisms and influencing factors of the transient TLV morphology was revealed, and the correlation between pressure difference and leakage velocity were investigated in a systematic way. The TLV evolution appears periodic development, coinciding with the variation of leakage velocity driven by the pressure difference. The cylindrical coordinate system is more suitable for analyzing the TLV dynamics, due to the impeller rotation. The vorticity in the tip region is dominated by tangential vorticity ωθ and axial vorticity ωz. The transport terms of ωθ and ωz present a great relationship with TLV and TLV-induced cavitation. Relative vortex stretching dominants the vorticity generation in the tip region, and relative vortex dilation and Coriolis force are also important sources. In contrast, baroclinic torque has the least influence on the vorticity in the flow passage.

Cavitation effect on flow resistance of sleeve regulating valve

Sleeve regulating valve is the key component of the industrial system. As the main cause of vibration and noise inside the sleeve regulating valve, cavitation also increases the energy loss when fluid flows through the valve. In this paper, in order to quantitatively analyze the influence of cavitation in the sleeve regulating valve, the effects of throttling windows number, pressure difference, valve opening and flow direction on the resistance coefficient are investigated with the application of cavitation model. By defining the cavitation influencing factor of the resistance coefficient, the calculation formula of the resistance coefficient when cavitation occurs in the sleeve regulating valve is proposed. The results show that when the fluid flows forward and the aggravation degree of cavitation increases, the energy loss also increases. And in the backward flow, the effect of cavitation on the resistance coefficient is related to the valve opening and the throttling windows number. This work is of significance for the optimization and design of sleeve regulating valve and pipeline system.

Numerical investigation on the cloud cavitating flow over a Clark Y foil under free surface effect

For a high-speed vehicle in the presence of cavitating flow while operating near the free surface, the interaction between the cavitating flow and the free surface can be very critical. In this paper, the cloud cavitating flow over a Clark Y foil near the free surface was investigated via numerical approaches. The large eddy simulation (LES) turbulence model, the volume of fluid (VOF) method, as well as the Schnerr Sauer cavitation model were used in the simulation to solve for the cloud cavitation flow region and capture the interphase between the multiphase (air, water and vapour). The analysis centred on the results of the two- (2D) and three-dimensional (3D) cases for the Clark Y foil at various submerged depths for several evolution cycles. The free surface affects the cavity profile, evolution period, re-entrant jet inside/beneath the cavity and hydrodynamic coefficients. The cavity has become shorter and thicker under the free surface effect. Induced by the re-entrant jet thickness, the cavity becomes more stable as the submerged depth decreases. The cavity evolution, the cavity length and thickness of different cycles are similar, while the shedding cavity can delay the evolution. A similar phenomenon can be observed in 3D, but the flow structure is more complex than in 2D. The 3D effect likewise manifests as shortening the cavity length while changing the direction of the re-entrant jet inside/beneath the cavity.

Experiments and Computational Fluid Dynamics on Vapor and Gas Cavitation for Oil Hydraulics

AbstractA compressible Euler‐Euler computational fluid dynamics (CFD) model for vapor, gas, and pseudo‐cavitation in oil‐hydraulic flows is presented. For vapor, the Zwart‐Gerber‐Belamri (ZGB) model is used and for gas cavitation, the Lifante model. The aim is to determine the empirical parameters within the cavitation models for hydraulic oil by comparing CFD results to experiments in a realistic valve. The cavitating flow is visualized and measured for numerous operating points. By degassing, states of pure vapor cavitation are generated. The major findings are: (1) large eddy simulation turbulence modeling is essential, (2) vapor cavitation in mineral oil can be simulated very well with the ZGB model using the determined parameter, and (3) gas cavitation model provides useful results although not all details can be reflected and its scope is limited.

Investigation on multiscale features of cavitating flow in convergent-divergent test section using Eulerian–Lagrangian method

Cavitating flows in fluid machineries always present complicated phase morphologies including a wide range of interface length scales. In the present work, an Eulerian–Lagrangian cavitation model is proposed for simulating the unsteady cavitating flow and investigating the multiscale cavitating flow features in a convergent-divergent test section. Most importantly, a two-way transition algorithm is newly developed mainly based on the shape of resolved cavities and the relative size of microscale bubbles compared to the cells, for taking the transition between microscale discrete bubbles and macroscale vapor cavities into consideration. The transient flow field of the two-phase system is described by the filtered Navier–Stokes equation and the sub-grid scale model. The volume of fluid (VOF) method and a discrete bubble model (DBM) are combined for simulating resolvable water-vapor interfaces and unresolvable discrete bubbles, respectively. Applying the proposed multiscale modeling framework, the dissipated bubbles caused by the collapse of shedding cavities that are unable to be represented by the VOF method are well predicted. The results show that the VOF-DBM model is less sensitive to the mesh resolution compared to the VOF method and it is found the dissipated bubbles are transporting around the vortex core region. Detailed bubble dynamics including DBM to VOF and VOF to DBM transitions and the interaction between macroscale cavities and microscale bubbles are well presented, indicating that the proposed VOF-DBM model is a promising approach to reveal the multiscale cavitation characteristics within limited computing resources.

Numerical investigation of ventilated cavitating flow from high to low cavitation numbers

Cavitation occurs when an underwater vehicle moves at a high speed, causing the water to change from the liquid phase into the vapour phase in the low-pressure region. As one of the most efficient drag reduction technologies for high-speed underwater vehicles, the artificially ventilated cavitation flow needs to be studied. In this paper, the ventilated cavitating flow over a high-speed underwater vehicle is analysed with a multi-phase solver from high to low natural cavitation numbers. The large eddy simulation turbulence model, volume of fluid method and Kunz cavitation model are used in the numerical calculation to simulate and capture the three-phase (air, liquid water, and vapour) cavitation flow. The miscibility of the air and vapour phases inside the cavity is also considered in the simulation. To validate the solver, two benchmark cases with air ventilated into a cavitating flow are simulated. Then the characteristics of the ventilated cavitating flows from a high to low natural cavitation number are analysed to study the development of the ventilated cavity with miscible air and vapour inside it. The results show that air ventilation can prevent pressure fluctuations at the surface of an underwater vehicle caused by cloud cavitating flow at a moderate natural cavitation number. Compared to no ventilation, drag reduction of ventilated cavitating flow can reach up to about 85% at a low cavitation number.

Mitigation of Hub Vortex Cavitation with Application of Roughness

This study investigates the influence of roughness on hydrodynamic performance, especially for the hub vortex—and, hence, hub vortex cavitation—of a benchmark propeller operating under uniform flow conditions using the RANS method. The Schnerr–Sauer cavitation model is also used for modelling the cavitation on and off the propeller blades. In order to include the effects of roughness in the numerical calculations, the experimentally obtained roughness functions were incorporated with the wall function of the CFD solver. The applicability and effectiveness of the roughness application applied on the propeller hub as a novel concept were explored to mitigate hub vortex cavitation. The results are first validated with experimental data on smooth conditions through the propeller hydrodynamic performance characteristics and cavitation extension. Then, the propeller hub is covered with four different sizes of roughness. The results show that the degradation effects of roughness applied to the hub on propeller performance are negligible, and the maximum efficiency loss is around 0.25% with respect to the smooth condition when the propeller hub was roughened. Favourable impacts of roughness are found for the hub vortex, and hence, hub vortex mitigation. Applying the roughness on the propeller changed the flow properties (e.g., pressure, velocity and turbulent kinetic energy) inside the vortex, enabling the early breakdown of the extension of hub vortices. These flow changes in the presence of roughness result in a mitigation of hub vortex cavitation up to 50% depending on the roughness size with respect to the smooth condition. Thus, this proposed novel concept, application of roughness to the propeller hub, can be used to mitigate hub vortex cavitation, rudder erosion and propeller URN for both newly designed and retrofitted projects by keeping the efficiency loss as minimum as possible.

Чисельне моделювання нестаціонарної течії в гідравлічній системі за каві-туючою шайбою

This paper addresses the construction of an efficient mathematical model to be used in the numerical simulation of unsteady liquid flows in hydraulic systems with cavitating restrictors. Existing approaches to cavitation simulation are based either on accounting for a two-phase flow structure or on representing a cavitating flow as a homogeneous medium of variable density. In the latter case, the pressure and the density are related via the barotropic equation of liquid–vapor mixture state. The goal of this work is to verify the applicability of a cavitation model based on the barotropic equation of liquid–vapor mixture state to the numerical simulation of an unsteady flow in a hydraulic system with a cavitating ring plate. The method employed is a numerical flow simulation in the axisymmetric approximation using the complete averaged Navier–Stokes equations. It is shown that the use of the barotropic equation of liquid–vapor mixture state provides a satisfactory agreement between the computed results and the experimental data available in the literature. In agreement are the peak-to-valley values of the oscillating pressure on the pipe wall immediately downstream of the cavitating ring plate and the presence of a pronounced periodic component in the pressure vs. time relationship. It is shown that the parameters of the unsteady flow downstream of the cavitating ring plate vary when going from the ring plate to the cavity collapse location: the peak-to-valley value of the oscillating pressure on the pipe wall increases and so does the contribution of high-frequency periodic components to the pressure vs. time relationship. It seems desirable that the turbulence model employed be refined further to correctly simulate cavitation oscillations generated by periodically detached cavitation in Venturi tubes, which are used in various cavitation pulse plants.

Cavitation in cryogenic fluids: A critical research review

Cavitation occurs as the fluid pressure is lower than the vapor pressure at a local thermodynamic state and may result in huge damage to the hydraulic machinery. Cavitation in cryogenic liquids is widely present in contemporary science, and the characteristics of cryogenic cavitation are quite different from those of water due to thermal effects and strong variations in fluid properties. The present paper reviews recent progress made toward performing experimental measurements and developing modeling strategies to thoroughly investigate cryogenic cavitation. The thermodynamic properties of cryogenic fluids are first analyzed, and different scaling laws for thermal effects estimation are then introduced. As far as cryogenic cavitation experimental research is concerned, the progress made in the cavitation visualization and cavity dynamics and the synchronous measurements of the multi-physical field are mainly introduced. As for the study on numerical simulation of cryogenic cavitation, the commonly used cavitation models and turbulence models are, respectively, classified and presented, and the modifications and improvements of the cavitation model and turbulence model for thermal effect modeling of cryogenic cavitation are examined. Then, several advances of critical issues in cryogenic fluid cavitation research are reviewed, including the influences of thermal effects, unsteady shedding mechanisms, cavitation–vortex interactions, and cavitation-induced vibration/noise. This review offers a clear vision of the state-of-the-art from both experimental and numerical modeling viewpoints, highlights the critical study developments and identifies the research gaps in the literature, and gives an outlook for further research on cryogenic cavitation.

Investigation of the cavitation processes behind a cylinder located in a microchannel in a wide range of Reynolds numbers

Numerical modeling and experimental investigation of hydrodynamic cavitation on a microcylinder located in a microchannel were carried out. The Zwart–Gerber–Belamri cavitation model was employed to simulate cavitation processes, and turbulence was simulated using the LES model. Experimental studies were performed by visualization with a shooting frequency of 960 Hz. Fluid pressure at the channel inlet ranged from 2 to 30 bar. Time dependences of pressure, velocity and vapor volume fraction, as well as their average values, were obtained at five points. Stable developed cavitation was found to exist for inlet pressures above 18 bar; no cavitation at all was observed for inlet pressures below 8 bar as confirmed by experimental studies. A fairly good agreement was revealed between the calculated and experimental data. The cavitation pulsation frequency (480–2200 Hz) and hydrodynamic pulsation frequency values (26–96 kHz) were obtained. The presence of cavitation was shown to shift the frequency of hydrodynamic pulsations towards larger values. Dependence of the relative drag coefficient on the inlet pressure, well approximated by a correlation ζ r = (2Δp) 0.5 , was obtained.

Dynamics of homogeneous cavitation with pressure feedback

Theoretical studies of homogeneous cavitation have largely been based on the classical nucleation theory. However, existing cavitation models cannot adequately describe its dynamics at nanosecond timescale, which has been called for in other fields. We develop a model coupling nucleation kinetics with cavity growth and pressure feedback as saturation mechanisms. Our numerical studies reveal the exponential dependence of cavitation characteristics such as saturation cavity density and most probable cavity radius on model parameters: Tolman length and initial pressure. This work also sheds light on the possibility of accurately determining Tolman length, whose value has a large spread in the literature.