Suppression Of Cavitation Research Articles

Suppression of hydrofoil unsteady cavitation by periodic jets based on fish gill respiration

Cavitation is a phase change phenomenon that occurs between the liquid and vapour phases inside a homogeneous liquid or at the interface between a solid and a liquid, and the generation, collapse and shedding of cavitation are the sources of undesirable characteristics of fluid machinery. A periodic jet scheme based on the principle of bionics is designed and applied to a Clark-Y hydrofoil with a chord length of 70 mm to suppress the cavitation of fluid machinery under high-speed flow conditions. Different schemes are numerically simulated using large eddy simulation combined with the Zwart–Gerber–Belamri cavitation model to numerically simulate the different schemes. The results show that adding periodic jet to the hydrofoil can reduce the cavitation of the hydrofoil without losing the lift resistance of the hydrofoil, and the cavitation volume is 47%–52% of the original hydrofoil.

Suppression of unsteady partial cavitation by a bionic jet

Suppression of unsteady partial cavitation by a bionic jet

The Problem of Filling a Spherical Cavity in an Aqueous Solution of Polymers.

The problem of filling a spherical cavity in a liquid has attracted the attention of many authors. The study of bubble behavior in liquid allows to estimate the consequences of cavitation processes, which can lead to the intensive destruction of the material surface. Regarding this connection, it becomes necessary to study the influence of impurities, including polymeric additives on the strengthening or suppression of cavitation. In this paper, this problem is considered in three models of a relaxing fluid. It is shown that for all models, the cavity filling time is finite if the surface tension is not equal to zero. This result was previously established for the cases of ideal and viscous fluids. However, the relaxation factor can significantly change the flow pattern by slowing down the filling process and lowering the level of energy accumulation during the bubble collapse.

Parametric analysis of the effects of blade exit angle on the cavitation characteristics in a hydraulic torque converter

Hydraulic torque converters are prone to cavitation due to their high impeller rotational speeds and their complex three-dimensional flow characteristics. Since the blades are the core components of torque converters, the shapes of the blades are important to the hydraulic performance and cavitation characteristics. Different cavitation computational fluid dynamics (CFD) models for a torque converter were developed to simulate the internal cavitation flow for different pump and turbine blade exit angles, and the influence of the blade angles on the cavitation characteristics and cavitation flow field in the torque converter was investigated. Experimental prototypes were produced and tested for verification. The results indicate that the pump and turbine blade exit angles had significant effects on the cavitation number of the torque converter. Increasing the pump and turbine blade exit angles promotes the generation and intensification of cavitation, resulting in severe changes in the shapes and locations of the cavitation bubbles due to changes in the fluid impact angles. Additionally, cavitation is quickly suppressed and the performance is improved when the blade exit angles are reduced within an appropriate range, in particular, that of the turbine blade. These research results can provide guidance for the design of a high-performance hydraulic torque converter cascade system and the suppression of cavitation for practical engineering applications.

Influence of Geometric Parameters of Tiny Blades on the Shroud of a Centrifugal Pump on the Cavitation Suppression Effect

In this paper, the effect of adding non-connected forms of tiny blades with different parameters of radial position, width, and length to the shroud of the impeller on the cavitation performance of a centrifugal pump is researched. A modified SST k-ω turbulence model combined with the Zwart–Gerber–Belamri cavitation model is used for numerical simulation of the model pump. The results show that the numerical prediction of the original pump agrees well with the experimental results. Adding tiny blades with different radial positions, widths, and lengths has a small effect on the pump head and efficiency under each working condition. Adding tiny blades near the impeller inlet has better suppression of cavitation in the initial stage, and adding tiny blades in the middle and backward positions has a better suppression effect on all stages of cavitation. There is an optimal tiny blade width to make the cavitation suppression effect optimal, and the optimal width of the model in this study is 3/4 of that of the main blade. The effect of a tiny blade length on cavitation performance is small. The existence of tiny blades slightly increases the turbulent kinetic energy in the low-turbulent kinetic energy region near the impeller inlet, significantly reduces the turbulent kinetic energy in the high-turbulent kinetic energy region near the outlet, and reduces the overall pressure pulsation main frequency amplitude during pump operation, making its operation more stable.

THE INFLUENCE OF THE DIRECTION OF OVERHANGING GROOVES ON THE SUPPRESSION OF TLV CAVITATION AND ITS MECHANISMS

In this paper, the influence of the direction of overhanging grooves on the suppression of tip-leakage vortex (TLV) cavitation is investigated experimentally and numerically, and the mechanisms behind are discussed in detail. The results indicate that both the overhanging grooves (OHGs) with the overhanging at the suction and pressure sides show a significant suppression on TLV cavitation for a large range of gap sizes. Compared with the OHGs with overhanging at the suction side, a better suppression effect can be obtained by the OHGs with overhanging at the pressure side. Moreover, the OHGs with overhanging at the pressure side can provide a more satisfying suppression on the fluctuation of the cavity volume of TLV cavity. The experimental measurements indicate that the influence of the direction of overhanging grooves on the lift and drag coefficients of the hydrofoil is quite slight. The numerical results further indicate that the OHGs with overhanging at the pressure side can impede the flow from the pressure side to the suction side more effectively and disturb the development of TLV, which is helpful for the suppression of TLV cavitation.

Effects of polymers on the cavitating flow around a cylinder: A large-scale molecular dynamics analysis.

The cavitation flow of linear-polymer solutions around a cylinder is studied by performing a large-scale molecular dynamics simulation. The addition of polymer chains remarkably suppresses cavitation. The polymers are stretched into a linear shape near the cylinder and entrained in the vortex behind the cylinder. As the polymers stretch, the elongational viscosity increases, which suppresses the vortex formation. Furthermore, the polymers exhibit an entropic elasticity owing to stretching. This elastic energy increases the local temperature, which inhibits the cavitation inception. These effects of polymers result in the dramatic suppression of cavitation.

Thermodynamic effects on Venturi cavitation characteristics

In this paper, the thermodynamic effect is systematically studied by Venturi cavitation in a blow-down type tunnel for the first time, using water at temperatures up to relatively high levels and at controlled dissolved gas contents in the supply reservoir (measured by dissolved oxygen, DO). The mean attached cavity length Lcav is chosen to reveal the thermodynamic effect, and the cavitation characteristics are analyzed from the experiments. With an increase in the thermodynamic parameter Σ*, a decrease in Lcav vs the pressure recovery number κ is observed, which is consistent with suppression of cavitation by the thermodynamic effect, but the decrease is related not only to this effect. Based on the experimental results, a model is presented of the attached cavity cloud that develops from the Venturi throat. It is found that either the length of this cloud oscillates stably around a mean value or the cloud breaks regularly at some upstream position, allowing that a detached cavity cloud is shed, flows downstream, and collapses while the remaining attached cloud regenerates. Applying this model to experimental results obtained first with cold water, then with hot water, we find that when the mean length of the attached cavity cloud oscillates stably, temperature increase causes reduction of the mean cavitation length. This is interpreted to be a consequence of the thermodynamic effect. When detachment of large cavity clouds occurs, the mean length is increased at temperature increase. This is a consequence of cloud configuration changes being superposed on changes due to the thermodynamic effect. These observations explain conflicting results reported for attached cavity clouds in relation to the thermodynamic effect. The gas content in the water is found to be without significance within the range of DO tested.

Three-Dimensional Inverse Design Method for Hydraulic Machinery

Hydraulic machinery with high performance is of great significance for energy saving. Its design is a very challenging job for designers, and the inverse design method is a competitive way to do the job. The three-dimensional inverse design method and its applications to hydraulic machinery are herein reviewed. The flow is calculated based on potential flow theory, and the blade shape is calculated based on flow-tangency condition according to the calculated flow velocity. We also explain flow control theory by suppression of secondary flow and cavitation based on careful tailoring of the blade loading distribution and stacking condition in the inverse design of hydraulic machinery. Suggestions about the main challenge and future prospective of the inverse design method are given.

Suppression of cavitation in the draft tube of Francis turbine model by J-Groove

Cavitation is recognized as a phenomenon that can cause serious damage to a hydro turbine and can reduce its performance when operating at off-design point. This is an undesired phenomenon, which needs to be improved. In order to suppress the cavitation in the Francis turbine draft tube, a technology with grooved draft tube named J-Groove is introduced in the Francis turbine. The Francis turbine performance and the internal flow characteristic are investigated both with and without J-Groove installation by the experimental method and numerical simulation. Visualization was used to capture the cavitation rope in the Francis turbine draft tube to compare with the computational fluid dynamics analysis result. The results show that the turbine performance both with and without J-Groove installation is quite similar. Regardless of impact on performance of Francis turbine by J-Groove, it suppresses the cavitation vortex rope and pressure fluctuation in the Francis turbine draft tube efficiently.

Destructive frequency of oblate spheroidal air-balloon for suppression of propeller cavitation induced hull excitation.

The air-balloon can effectively neutralize hull excitations induced by the propeller cavitation. For the design, it is essential to derive the destructive frequency of an oblate spheroidal air-bubble, which is elaborated on in this paper. Beginning with the exact modal-series solution proposed by Yeh [Ann. Phys. 468, 53-61 (1964)], an approximated form of the scattered pressure is set up by assuming that the acoustic wavelength is much larger than the size of the balloon in the low frequency ranges. An algebraic formula for the destructive frequency can then be written as a function of the resonance frequency and a spatial variable. It is well known that the resonance frequency of a deformed bubble is higher than that of an ideal spherical one with the same volume. In addition to this, the current investigation puts an emphasis on the fact that asphericity induces a more severe shift of the destructive frequency than the resonance frequency, and that its effect needs to be reflected in the balloon design.

Design of air-balloons for suppression of propeller cavitation induced hull-excitation at multi-frequencies

The main objective of the present study is to establish a practical design strategy of air-balloons for a suppression of the propeller cavitation induced hull pressures at multi frequencies. Theoretical foundation is initiated with the existing modal series solution of a multiple scattering problem. An approximated form is then derived by a monopole regime which is valid in a low frequency range. Subsequent parametric analysis with a variation of the separation distance between the balloons provides an analytical evidence that the mutual interaction can be neglected unless they are too close to each other. Hence it is addressed that the individual balloon can be designed separately without a consideration of their coupling characteristics. Finally, the water tunnel test with two balloons demonstrates noticeable vibration reductions at the first- and second- order of blade passing frequencies by 72% and 59%, respectively.

ケーシングトリートメントによるインデューサのキャビテーション不安定の抑制

In high speed turbopump inducers for rocket engines, cavitation occurs and often causes flow instabilities. In the present study, we tried to suppress all cavitation instabilities by adding swirl breakers to an original circumferential groove of a casing in wide ranges of flow rates in consideration of coming reusable rockets. The casing with swirl breakers succeeded in the suppression of almost all cavitation instabilities without degradations of pump and suction performances by suppressing backflow vortex cavitation. The swirl breaker drastically decreased circumferential velocities near the tip of the leading edge of the inducer and also created a circumferential strong vortex which suppressed a backflow. This is a mechanism of the suppression of backflow vortex cavitation.

Balanced electrical, thermal and mechanical properties of epoxy composites filled with chemically reduced graphene oxide and rubber nanoparticles

Epoxy composites filled with 2D chemically reduced graphene oxide (CRGO) sheets and preformed 3D powdered rubber (PR) nanoparticles were fabricated to investigate the effect of hybrid nanofillers on the electrical, thermal and mechanical properties as well as fracture toughness. As expected, the presence of CRGO sheets endows epoxy with electrical conductivity and enhances its thermal properties, stiffness and toughness; while the addition of PR results in significant reductions in thermal stability and stiffness, but produces dramatic improvements in fracture toughness. Compared with the binary composites, the ternary composites containing hybrid 2D CRGO and 3D PR fillers provide a good balance among electrical conductivity, thermal stability, glass transition temperature, stiffness, strength and fracture toughness, which cannot be achieved by independent single-phase fillers. Based on the morphologies of the fracture surfaces and damage zones around the crack tip, various toughening mechanisms such as crack-bridging by GO sheets, sheet/sheet delamination and sheet/matrix debonding, rubber cavitation and matrix shear banding, were identified and correlated with the fracture toughness of the hybrid composites studied. Results obtained disclosed suppression of deformation and/or cavitation of the PR nanoparticles after the incorporation of CRGO, which explained the moderate improvement in fracture toughness of the hybrid composites.

Numerical Analysis of Nozzle Hole Shape to the Spray Characteristics from Premix Injector in Burner System : A Review

Fuel injection system is widely used in the field of burner system nowadays. Spray nozzles having various operating conditions depends on the design of nozzle and it is precision components designed to perform very specific spray characteristics under specific conditions. This review paper focuses on spray characteristics, effects of geometry of injector, influence of fuel and hole shaped nozzle with cylindrical and conical holes on spray characteristics. The parameters were discussed based on an overview of the research in the field of simulations with nozzle shaped injectors. A massive majority researcher reported that conical nozzle hole is better due to it contributed suppression of cavitation in nozzle hole, slowed down primary breakup process and thus produced larger spray droplets, high spray penetration.

Suppression of cavitation in melted tungsten by doping with lanthanum oxide

Melting and boiling behaviour of pure tungsten and 1 wt% lanthanum-oxide-doped tungsten (WL10) are investigated, focusing on the material selection with respect to material loss induced by cavitation. Melting experiments under high heat loads are carried out in the high heat flux facility GLADIS. Pulsed hydrogen neutral beams with heat flux of 10 and 23 MW m−2 are applied onto the adiabatically loaded samples for intense surface melting. Melt layer of the two tungsten grades exhibit different microstructure characteristics. Substantive voids owning to cavitation in the liquid phase are observed in pure W and lead to porous resolidified material. However, little cavitation bubbles can be found in the dense resolidified layer of WL10. In order to find out the gaseous sources, vapour collection is performed and the components are subsequently detected. Based on the observations and analyses, the microstructure evolutions corresponding to melting and vapourization behaviour of the two tungsten grades are tentatively described, and furthermore, the underlying mechanisms of cavitation in pure W and its suppression in WL10 are discussed.

Enhancing the high temperature plasticity of a Cu-containing austenitic stainless steel through grain boundary strengthening

The addition of 3wt% Cu to heat-resistant SUS 304H austenitic steel enhances its high temperature mechanical properties. To further improve the properties, particularly the creep resistance and ductility at high temperatures, a post-solutionizing heat-treatment method that involves an intermediated annealing either at 700 or 800°C after solutionizing for durations up to 180min was employed. The purpose this heat-treatment is to precipitate planar Cr23C6 at the grain boundaries, which results in the boundaries getting serrated. Detailed microstructural analyses of these ‘grain boundary engineered’ alloys was conducted and their mechanical performance, both at room temperature and at 750°C, was evaluated. While the grain size and texture are unaffected due to the high temperature hold, the volume fraction of Ʃ3 twin boundaries was found to increase significantly. While the strength enhancement was only marginal, the ductility was found to increase significantly, especially at high temperature. A marked increase in the creep resistance was also noted, which is attributed to the reduction of the grain boundary sliding by the grain boundary serrations and the suppression of grain boundary cavitation through the optimization of the volume fraction and spacing of the Cr23C6 precipitates. The special heat-treatment performed with holding time of 3h at 700°C resulted in the optimum combination of strength, ductility and creep resistance at high temperature.

927 柔軟なひれによるバタフライ弁キャビテーションの抑制(GS-5 流体機械(3))

927 柔軟なひれによるバタフライ弁キャビテーションの抑制(GS-5 流体機械(3))

Megasonic Cleaning of Blanket and Patterned Samples in Carbonated Ammonia Solutions for Enhanced Particle Removal and Reduced Feature Damage

An investigation of particle removal efficiency and feature damage has been conducted in NH4OH/NH4HCO3 cleaning solutions irradiated with megasonic energy. By adjusting the pH of the solution in the range of 8.2 - 8.5, high particle removal efficiency (PRE) was achieved while feature damage was reduced significantly. The sonoluminescence data collected from NH4OH and NH4OH/NH4HCO3 solutions indicate significant suppression of transient cavitation in alkaline solutions containing aqueous CO2.

Effect of back pressure on emulsification of lipid nanodispersions in a high-pressure homogenizer

We examined the effect of 0–20% back pressure, which functions as a resistance to emulsification in a high-pressure homogenizer, on emulsification of lipid nanodispersions (emulsion and liposomes) less than 100 nm in diameter. Back pressure in the range of 0.9–3.8% of the emulsification pressure enhanced the emulsification, and the particle diameter of lipid nanodispersion was the smallest at 2% back pressure. The back pressure effect was independent of the actual pressure, which was regarded as the difference between the emulsification and the back pressures. The mechanism of the back pressure effect was considered to be enhancement of emulsification by suppression of collapse cavitation in the high-pressure emulsification module. This back pressure effect appeared in emulsification of emulsion and liposomes, and was seen predominantly in the early emulsification phase (within 10 passages). The particles of lipid nanodispersions prepared at 2% back pressure with adequate re-circulation achieved physicochemically optimal diameter with a narrow size distribution, and were more stable at 60 °C for 7 days than particles prepared with 20% back pressure. Our results indicate that emulsification with a low level of back pressure is effective for production of stable lipid nanodispersions with narrow size distribution.