Full Cavitation Model Research Articles

Numerical Study on Characteristics of Lead-Bismuth Lubricated Hydrodynamic Bearing Considering Non-Condensable Gas

Lead-Bismuth Eutectic (LBE) is an interesting candidate as a coolant for Generation IV nuclear power plants. Lead-bismuth lubricated radial guide bearing is the key component of the mechanical pump in a lead-bismuth coolant system. In this paper, the transient calculation model of multiphase lubrication flow field of journal bearing is established by using Singhal full cavitation model and structured dynamic grid technique. Due to the saturated vapors of LBE being very low, the effects of different Non-Condensable Gas (NCG) contents on the characteristics of lead-bismuth lubricated journal bearing systems were analyzed. The results show that the NCG content has an obvious influence on the working state of the bearing. With the increase in NCG content, the bearing load capacity decreases. Under the same load, with the increase in NCG content, the eccentricity of the static equilibrium position will be larger, which will increase the risk of bearing contact with the bearing bush. Moreover, the increase of NCG content will lead to the increase of tangential oil film force work, which is helpful to improve rotor stability.

Numerical Study on Cavitating Flow-Induced Pressure Fluctuations in a Gerotor Pump

Using the RNG k-ε turbulence model and a full cavitation model, this study numerically simulated cavitating flow-induced pressure fluctuations in a gerotor pump and analyzed the relationship between cavitating flow and pressure fluctuations. The results demonstrate that, as the inlet pressure decreases, the cavitation phenomenon in the gerotor pump intensifies, and the cavitation range in the rotor increases. Some of the vapor even spreads into the oil inlet groove, leading to high vapor content in the chamber that is in contact with the oil inlet groove. The pressure fluctuation characteristics of the flow field in the pump exhibit evident periodic changes. Under different cavitation conditions, the pressure fluctuation amplitude at the monitoring point decreases with increasing inlet pressure, whereas the main frequency of pressure fluctuation remains unaffected by cavitation conditions. The pressure fluctuation amplitude is the strongest at point O1 of demarcation between the low-pressure and high-pressure zones in the chamber, and the volume between the oil inlet groove and the oil outlet groove serves as the main vibration source in the rotor pump. To ensure the stable and efficient operation of the gerotor pump, it is recommended to operate it at a larger NPSH.

Research on the High Speed of Piston Pumps Based on Rapid Erecting of Launch Vehicles

Rapid erection is a key technology for modern warfare in vehicle weapon launch systems. It is challenging to attain rapidity with the hydraulic erecting system because of the intensified cavitation in the piston chamber at high speeds, which reduces volumetric efficiency and increases flow pulsation in the typical high-pressure axial piston pump. In this paper, an improved scheme for the cylinder window area overflow surface was proposed to solve this problem. Based on the full cavitation model and the compressible model, a numerical model of the internal flow in the piston pump was developed, and the effect of rotational speeds on the flow and cavitation characteristics of the pump was analysed. The results show that after the improvement, the maximum flow of the pump is increased from 1.765 kg/s to 2.295 kg/s, an increase of 30.028%, and the maximum speed corresponding to the volumetric efficiency of more than 90% is increased from 1500 rpm to 2100 rpm. At high speeds, the improved block can effectively suppress the cavitation and backflow in the piston chamber, improve the volumetric efficiency of the piston pump and reduce the flow pulsation, which is conducive to reducing the vibration and noise of the pump body.

Numerical study on the heat transfer enhancement outside the pipe bundle under the effect of continuous pressure waves

This paper presents a numerical study of the heat transfer enhancement outside the pipe bundle under the effect of continuous pressure waves (PW) stimulated by a vibrating membrane as a PW generator. Model 1 and 2 made of one and two rows of pipe bundles were investigated, respectively. An oscillating wall boundary condition was applied to the vibrating membrane. Based on the RNG k-ε turbulent model and full cavitation model, the computational fluid dynamics (CFD) model was developed. The prediction results of the model were in good agreement with the experimental data of other researchers. The validity of PW was investigated from the viewpoint of the affected scale by comparing the flow and heat transfer with ultrasound and PW. The effect of the frequency and amplitude of the membrane on the heat transfer enhancement was analyzed. The result shows that the continuous PW had significantly larger affected scale than ultrasonic waves, which can cover the whole pipe bundle space and increase the velocity amplitude of the fluid around the bundle. While the affected scale of ultrasonic waves was limited to the center place of the pipe bundle because of the acoustic stream. In addition, the effect of continuous PW on the convective heat transfer increased with increasing the frequency and amplitude of the membrane. The heat transfer was enhanced by 7.01% to 156.22% at a frequency of 20–160 Hz and an amplitude of 2 mm. Considering the benefits and the energy consumed of PW, the optimal frequencies of models 1 and 2 were 110 and 120 Hz, and the heat transfer coefficient were increased by 119.19% and 150.36% compared to the steady-state flow. The results confirm continuous PW has the great potential in enhancing the heat transfer of large-space pipe bundles.

Computational model for predicting the dynamic dissolution and evolution behaviors of gases in liquids

Dynamic gas–liquid mass transfer behaviors are widely encountered in the chemical, environmental, and engineering fields. Referring to the Singhal full cavitation model, Henry's law, and Zhou's experiments, we innovatively developed a computational model for dissolved and released mass-transfer to revolutionize the independent unidirectional gas-to-liquid or liquid-to-gas theory. From a new perspective, coupled dissolution and evolution mechanisms were defined similar to how condensation and evaporation were redefined, where dissolution and release mass-transfer prediction methods that can be applied to three-dimensional calculations were integrated for the first time. The dissolved gas saturation concentration was the criterion for determining the direction of mass transfer. According to the theoretical derivation, the driving forces behind the dissolution and evolution are the remaining undissolved gas and real-time solution concentration, respectively. We confirmed the validity of the proposed dynamic model using an unsteady simulation after a grid independence study and an experimental verification of dissolved oxygen concentration in plug-discharge flow. The difference in dissolved oxygen concentration between simulations of this computational model and experiments could be low as 2.0%. A higher dissolved oxygen concentration was distributed in the flow separation and throat gas–liquid blocking zones, indicating that a surge in the flow velocity led to an increased mass transfer rate. In addition, a parametric study was conducted to consider the impact of the oxygen volume fraction and initial dissolved oxygen concentration on the real-time concentration.

Numerical Simulation of Unsteady Cavitation Flow in a Low-Specific-Speed Centrifugal Pump with an Inducer

Cavitation is an undesirable phenomenon in the pumps. In this paper, unsteady cavitation flow in a low-specific-speed centrifugal pump with an inducer is investigated based on the full cavitation model and standard k-ε turbulence model using the commercial software PumpLinx. The numerical results of external performance curve and cavitation performance curve of design condition agree well with that of the experiment. The bubbles in the inducer mainly appear on the outer blade leading edge. The regions of larger vapor volume fraction in the inducer and impeller increase with the decreasing of NPSHa. The regions of larger vapor volume fraction in the inducer expand from the outer edge of the blade inlet to the hub on suction surface. Under very low NPSHa, the impeller may be filled with bubbles in the passage and the pump head drops drastically, and there exist distinct back flows near the suction surface of the blade and impeller outlet. Affected by pre-swirl of inducer outlet and the circle flow of impeller blade inlet, the amplitude of pressure fluctuation near the impeller inlet is obviously larger than that at the inlet in the inducer. The dominant frequency of pressure fluctuation for four monitoring points is shaft frequency. Compared with the non-cavitation flows, the maximum amplitudes of pressure pulsation increase for cavitating flow.

Raising the Speed Limit of Axial Piston Pumps by Optimizing the Suction Duct

The maximum delivery pressure and the maximum rotational speed determine the power density of axial piston pumps. However, increasing the speed beyond the limit always accompanies cavitation, leading to the decrease of the volumetric efficiency. The pressure loss in the suction duct is considered a significant reason for the cavitation. Therefore, this paper proposes a methodology to optimize the shape of the suction duct aiming at reducing the intensity of cavitation and increasing the speed limit. At first, a computational fluid dynamics (CFD) model based on the full cavitation model (FCM) is developed to simulate the fluid field of the axial piston pump and a test rig is set to validate the model. Then the topology optimization is conducted for obtaining the minimum pressure loss in the suction duct. Comparing the original suction duct with the optimized one in the simulation model, the pressure loss in the suction duct gets considerable reduction, which eases the cavitation intensity a lot. The simulation results prove that the speed limit can increase under several different inlet pressures.

Influences of eccentricity ratio on the internal flow and cavitation characteristics of progressing cavity pump

A Progressing Cavity Pump (PCP) works by forming a progressive seal cavity through the eccentric rotation of rotor. PCP parameters, such as eccentricity ratio [Formula: see text], can influence its performance and cavitation characteristics. The internal correlation among clearance fluid, cavitation characteristics, and pump performance should be explored to reveal the variation laws of internal flow and cavitation characteristics in PCP under different [Formula: see text]. In this study, a contrast analysis on external characteristics (e.g. volume efficiency) of pump with different eccentricity ratios was carried out by combining an RNG [Formula: see text] turbulence model based on Singhal full-cavitation model and the model pump test method. Moreover, gas volume distribution of PCP was analyzed and the optimal value range of eccentricity ratio was proposed. Results demonstrate that the axial force and axial power of PCP basically remain the same, volume efficiency increases, and cavitation performance decreases with the increase of [Formula: see text], and the optimal value for [Formula: see text] ranges from 0.17 to 0.24. In addition, a revised NPSHQ is proposed to quantify the cavitation characteristics of PCP.

Evaluations of the outcome variability of RANS simulations for marine propellers due to tunable parameters of cavitation models

There are two issues with cavitation modeling that need to be resolved: (1) the lack of sound physical meaning for the Vapor Volume Fraction (VVF) to set a threshold a priori for determining the range of cavitation extension; (2) the outcome variability (uncertainty) on the model's predictability resulting from the uncertainties of the model's tunable parameters, whose exact values are usually hard to obtain. This paper uses as a tool the methodology of the Cavitation Occurrence Probability (COP), which can be regarded as the resolution of the first issue, to resolve the second issue and evaluate the outcome variability due to the tunable parameters of three popular cavitation models, i.e. the Full Cavitation Model (FCM), Zwart-Gerber-Belamri (Z-G-B) and Schnerr-Sauer (S–S) models. RANS simulations were performed for a cavitating propeller flow with these three cavitation models, whose tunable parameters were varied to generate the VVF distributions and thrust data for comparisons with the experimental data. The results show that the FCM model is capable of yielding the most accurate predictions of cavitation at its default setting and thrust at some other setting, while the S–S model is capable of yielding the most precise (certain) predictions of cavitation and thrust.

Hydraulic axial plunger pump: gaseous and vaporous cavitation characteristics and optimization method

Gaseous and vaporous cavitation have extremely harmful effects on hydraulic axial plunger pumps, reducing flowrate and increasing flow pulsation. The collapse of vapor bubbles strongly impacts the inner wall and produces many pits. Therefore, it is very important to reduce gaseous and vaporous cavitation to improve the performance of hydraulic axial plunger pumps. In this work, a full cavitation model and a compressible model are used to simulate the two kinds of cavitation, which are validated by a series of experiments. It is found that the vapor and gaseous bubbles in the plunger chamber collapse owing to pressurization caused by the water hammer effect. The results show that a better combination of plunger chamber radius and swash plate angle can reduce the two kinds of cavitation when the theoretical flowrate is unchanged; increasing the angle of the inlet of valve plate can effectively reduce its cavitation and increase the filling mass of plunger chambers; increasing the angle of the relief groove can significantly reduce its vapor and gaseous volume fraction. The results can provide a useful reference for reducing gaseous and vaporous cavitation in the optimization and design of hydraulic axial plunger pumps.

Computational modeling on supercavitating flow over axisymmetric cavitators

Numerical simulations are carried out to analyse the cavitating effects over the circular disk cavitator and cone cavitator. The commercial software tool ANSYS Fluent 16 was used to simplify two dimensional Reynolds averaged Navier Stokes equation with the compressible fluid flow by considering the pressure-based solver with standard K- ω turbulence model. The Schnerr and Sauer cavitation model is employed to study the cavitation phenomena. The simulations are done by varying the diameter of circular disk and cone cavitator, by varying fixed cavitation numbers and by varying flow pressures. Initially flow past circular cavitator will be analysed by varying the cavity length and validated with other existing models [i.e., Kunz cavitation and full cavitation model]. Simultaneously, to analyse the capability and robustness of the computational analysis cone cavitator are adopted. The obtained results from the simulation are then validated with the experimental and theoretical correlations.

Numerical study of the impact of water injection holes arrangement on cavitation flow control.

A method of water injection to flow field using distributed holes on the suction surface of hydrofoil is presented in this article to control cavitation flow. Modified renormalization group k-ε turbulence model is coupled with full-cavitation model to calculate periodical cavitation patterns and the dynamic characteristics of the NACA66(MOD) hydrofoil. Water injection is found to be highly effective for cavitation suppression. The cavitation suppression effect of distributed regulation of jet holes and porosities along three-dimensional spanwise hydrofoil is also investigated. The appropriate porosities of single row spanwise jet holes and optimal jet position of double row jet holes are revealed for both cavitation suppression and good hydrodynamic performance. Double row jet holes setting in forward trapezoidal arrangement shows great potential for cavitation suppression and hydrodynamic performance. This research provides a method of water injection to flow field to actively control cavitation, which will facilitate development of engineering designs.

Investigation of the cavitation model in an inducer for water and liquid nitrogen

Cavitation commonly occurs in the hydraulic machineries like inducers. Cavitation happening in the cryogens is sophisticated due to their complicated thermodynamic properties. Computational fluid dynamics could provide relatively precise prediction for water. However, existing computational fluid dynamics methods may fail to simulate the cryogens cavitation precisely. This study presents a computational fluid dynamics simulation of four major cavitation models in both the liquid nitrogen and the water in an inducer. Four different cavitation models analyzed in this work are full cavitation model, Kunz model, Zwart–Gerber–Belamri, and Schnerr & Sauer. And the computational fluid dynamics simulation results are verified by the experiment to ensure the cavitation model's applicability in both liquid. Comparison of cavitation in water and liquid nitrogen is conducted and analyzed. The four cavitation models can predict cavitation in water, but the Zwart–Gerber–Belamri model and Schnerr & Sauer model also feature high capability to predict tip vortex cavitation. The results show that the full cavitation model is suitable for simulating the liquid nitrogen cavitation without changing of the model constants. The empirical constants of the other models should be adjusted in the liquid nitrogen cavitation simulation. Full cavitation model features high robustness in various liquids. The Schnerr & Sauer model can achieve the best results by adopting different empirical constants. In addition, the inducer performs better in the liquid nitrogen than water at low cavitation number regime as the head coefficient drops smoothly in liquid nitrogen with decreasing cavitation number.

Experimental and numerical study of a cryogenic valve using liquid nitrogen and water

In the present study, a cryogenic valve used in launch vehicle liquid propulsion systems is experimentally and numerically characterized. Two independent measurement campaigns are performed with liquid nitrogen and water as working fluids. Two equivalent facilities have been designed and manufactured to perform the cryogenic and the water tests. The characteristic relationship between the volumetric flow rate and pressure drop across the test valve is obtained for both the fluids. As far as cryogenic tests are concerned, temperature measurements at the test valve inlet and outlet are presented as well as visualizations of the flow upstream the test section. The experimental results show that the test valve flow coefficient is independent of the working fluid provided single phase flow conditions. To further validate this result a numerical study is conducted using the commercial code CFD-ACE+. A good agreement between numerical and experimental results is found. Furthermore, test cases in the semi-critical and critical flow conditions are simulated using the so-called full cavitation model. The computed liquid recovery factor is shown to be also independent from the working fluid nature.

Cavitation Evolution around a NACA0015 Hydrofoil with Different Cavitation Models Based on Level Set Method

Cavitation is a complex multiphase flow phenomenon that is usually involved in marine propulsion systems, and can be simulated with a couple of methods. In this study, three widespread cavitation models were compared using experimental data and a new modified simulation method. The accuracy of the three cavitation models was evaluated regarding their steady and unsteady characteristics, such as the flow field, re-entrant jet, vortex-shedding, and so on. Based on the experimental data and numerical results, the applicability of different cavitation models in different conditions was obtained. The Kunz model can accurately capture both the adverse pressure gradient and the action of the re-entrant jet in sheet cavitation, while the full cavitation model (FCM) has an accurate prediction for the flow field structure and the shedding characteristic of cloud cavitation. Through comparing the results, the optimal selection of cavitation models for further study at different conditions was obtained.

Analysis and Improvement of the Suction Performance of Axial Piston Pumps in Swash Plate Design

The article illustrates a systematic investigation of the suction performance of hydrostatic pumps on the example of an axial piston pump in swash plate design. The focus is on pressure losses in the suction duct as well as on losses due to the interaction between the suction flow and the rotating group. The investigations of the suction flow are performed by means of numerical and experimental methods. Also a full cavitation model and a two-way fluid-structure-interaction approach were introduced for the numerical works. The experimental works were used to validate the CFD model. For the improvement of the suction performance two approaches are pursued. The bionic design of the suction duct based on meandering rivers and the suction pressure pulsation reduction by the help of a Helmholtz resonator. As a result of the CFD analysis, regions with the largest total pressure losses were identified. Based on CFD simulation significant improvements of the suction performance were shown due to the two presented measures. By means of the meander shape design the pressure losses reduced by more than 50 % and the pressure ripple was dampened by about 9.5 dB using the integrated Helmholtz resonator.

Computational cavitating viscous liquid flows in a pump as turbine and Reynolds number effects

Cavitating flows of viscous oils in an experimental centrifugal pump with low specific speed are modeled and simulated by using the time-averaged Navier–Stokes equations and standard [Formula: see text] turbulence model as well as full cavitation model based on the computational fluid dynamics method, when the pump operates in the reverse direction as turbine to generate power. The cavitation characteristics are identified at part-load, best efficiency and over-load points and five viscosities. Effects of viscosity on net positive suction head required are clarified. Net positive suction head required correction factor and conversion factor curves are obtained and correlated to impeller Reynolds number. The flow and cavitation models are validated with the existing experimental results and empirical correlations. Pressure and helix angle profiles at the draft tube entrance, cavity shape, swirling flow pattern in the draft tube, and the pressure coefficient distribution over the blade surfaces are presented. The presented results can be useful for design, selection, performance prediction, and impeller redesign of a pump as turbine.

Numerical study of choked cavitation in high temperature hydrocarbon liquid jets

A numerical study was conducted on a practical plain orifice injector issuing pressurized high-temperature aviation fuel, in order to simulate injection of fuel after use as a coolant in the active cooling system of a hypersonic vehicle. A three-dimensional unstructured mesh inside the orifice was created using ICEMCFDTM S/W, and the CFD analysis was performed using FLUENTTM S/W. A multiphase mixture model was used to simulate cavitating two-phase flow, and the full cavitation model was activated to predict the mechanism and effects of cavitation induced by the high fuel vapor pressures at elevated temperature conditions. The simulation was performed for fuel heated up to 553 K (280 °C) at an upstream pressure (Pinj) of up to 1.0 MPa, and various ambient pressures (P∞). The results were compared with experimental data, and the simulation was found to predict the discharge coefficient (Cd) with respect to the fuel injection temperature (Tinj) quite well at the given conditions. The CFD analyses for high fuel temperature conditions revealed that the mainstream flow inside the injector separates from the orifice wall at the vena contracta due to the generated fuel vapor cavity, and the attached flow at the end of the cavity separates again to produce a very small recirculation zone. In addition, for a given pressure drop, the sharply decreasing trend of the mass flow rate (or Cd) with increasing Tinj varies depending on P∞, because the mass flow choking is determined by the relationship between P∞ and the vapor pressure (Psat) at Tinj. Finally, Cd with respect to cavitation number was found to follow an almost identical line, even at different P∞. This confirms that choked cavitation at high fuel temperature conditions depends on the downstream pressure of the orifice, and the effect of cavitation on Cd at high Tinj is well represented by the cavitation numbers, regardless of Pinj, P∞, and Tinj.

Water hydraulic axial piston motor cavitation characteristics based on CFD technology

PurposeThe purpose of this paper is to analyze the cavitation characteristics of a water hydraulic axial piston motor (WHAPM) to improve the water motor performance, to reduce the vibration and noise and to prolong the service life of the motor.Design/methodology/approachThe computational fluid dynamics (CFD) software PumpLinx is chosen to do cavitation analysis of the WHAPM. In this case, first, cavitation mechanism of the water piston motor is analyzed in depth. Then, considering the effects of bubble dynamics, the rate of phase transition, turbulence effects and non-condensable gas, the full cavitation model is selected, the dynamic CFD numerical model of internal flow field on the water hydraulic piston motor is established based on PumpLinx software and the fluid cavitation inside is numerically studied. Finally, the influence of the valve plate and pistons on motor cavitation is analyzed.FindingsResearch results show that there are two serious cavitation regions: one is the pressure transition region of the valve plate that is near the top dead center, and the other is the low-pressure region of the piston that is near the low-pressure transition area. Moreover, the more serious cavitation area is on the valve plate region.Originality/valueThe simulation results show that the proposed algorithm is able to detect the cavitation characteristics of the water piston motor. Besides, it is deduced that valve-plate structure optimization is more important than pistons to reduce cavitation influence.

Judgment Criteria for Cavitation Based on Jet Flow Field of V-type Valve Port

In high- and extra high- voltage systems, cavitation often occurs, which affects normal operation of the system and the service life of the hydraulic components. The paper introduces a criterion to judge cavitation through predicting the primary cavitation using the stress state rather than relying on average pressure. Based on this judgment criterion, we established a full cavitation model of incompressible gas that has cavitation characteristics to analyze the distribution of pressure, stress and the volume fracture of cavitation of V-type valve port. This full cavitation model can make reasonable prediction for the cavitation of V-type valve port.