The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Matevž Dular - One of the best experts on this subject based on the ideXlab platform.
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image post processed approaches for cavitating flow in orifice plate
Journal of Mechanical Science and Technology, 2017Co-Authors: Yong Wang, Matevž Dular, Suguo Zhuang, Houlin Liu, Zhenjiang Zhao, Jian WangAbstract:A comprehensive investigation on cavitating flow and Cavitation-induced erosion was performed experimentally in an orifice plate system. Three image post-processed approaches were applied to analyze the test data, in order to obtain the Cavitation characteristics. The cavitating flow pattern was studied by high speed images. In one Cavitation developing period, there could be three distinct Cavitation clouds, whereas the second one is not fully developed. The first image post-processing approach was applied to obtain the mean value and standard deviation distribution, which indicate the erosion area may cover almost all the Cavitation developing route and the most vulnerable erosion area locates near the Cavitation collapse site. It is coincides with the erosion tests analyzed through the pit-count algorithm approach. The Cavitation circulation frequency was invested via PSD analysis approach. It shows that the frequency linearly decreasing with decreasing Cavitation number. Additionally, the Cavitation intensity effect on Cavitation erosion was quantitatively studied based. It is found that the damages are strongly enhanced when increasing the flow velocity. Moreover, the growth rate of eroded pits number is actually stepwise instead of linear (similar to our previous work in a venturi tube), which supports the idea that the cloud Cavitation collapse is the primary reason for erosion. The present approaches applied here shows good potential ability of investigating cavitating flows and can be utilized for other apparatus.
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on the mechanisms of Cavitation erosion coupling high speed videos to damage patterns
Experimental Thermal and Fluid Science, 2015Co-Authors: Matevž Dular, Martin PetkovsekAbstract:Abstract Recently van Rijsbergen et al. (2012), by simultaneous observation of Cavitation and acoustic emission measurements, and Petkovsek and Dular (2013), by simultaneous observation of both Cavitation structures and Cavitation damage, have pointed to the fact that the small scale structures and the topology of the Cavitation clouds play a significant role in Cavitation erosive potential. Despite the two, before mentioned, studies opened some new insights to the physics of Cavitation damage, many new questions appeared. In the present study we attached a thin aluminum foil to the surface of a transparent Venturi section using two sided transparent adhesive tape. The surface was very soft – prone to be severely damaged by Cavitation in a very short period of time. Using high speed cameras, which captured the images at 30,000 frames per second, we simultaneously recorded Cavitation structures (from several perspectives) and the surface of the foil. Analysis of the images revealed that five distinctive damage mechanisms exist – spherical Cavitation cloud collapse, horseshoe Cavitation cloud collapse, the “twister” Cavitation cloud collapse and in addition it was found that pits also appear at the moment of Cavitation cloud separation and near the stagnation point at the closure of the attached cavity.
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development of a Cavitation erosion model
Wear, 2006Co-Authors: Bernd Stoffel, Matevž Dular, Brane ŠirokAbstract:A study of visual and erosion effects of Cavitation on simple single hydrofoil configurations in a Cavitation tunnel was made. A thin copper foil, applied to the surface of the hydrofoils, was used as an erosion sensor. The Cavitation phenomenon on hydrofoils at different flow conditions (system pressure, water gas content, flow velocity) was observed. Results that showed a significant relationship between Cavitation erosion and the visual effects of Cavitation made it possible to use these information to develop a Cavitation erosion model. The model is based on the physical description of different phenomena (Cavitation cloud implosion, pressure wave emission and its attenuation, micro-jet formation and finally pit formation), which are involved in the process of pit formation. It is capable to predict the influence of significant parameters as flow velocity and gas content of water. The model that was developed on the basis of measurements of Cavitation on a single hydrofoil was later tested on an actual hydraulic machine in the form of a radial pump. The predicted magnitude and distribution of Cavitation damage relates well to the experimentally measured one.
B P M Van Esch - One of the best experts on this subject based on the ideXlab platform.
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numerical analysis of unsteady tip leakage vortex Cavitation cloud and unstable suction side perpendicular cavitating vortices in an axial flow pump
International Journal of Multiphase Flow, 2015Co-Authors: Desheng Zhang, Lei Shi, Weidong Shi, Ruijie Zhao, Haiyu Wang, B P M Van EschAbstract:The objective of this work is to simulate and analyze the formations of three-dimensional tip leakage vortex (TLV) Cavitation cloud and the periodic collapse of TLV-induced suction-side-perpendicular cavitating vortice (SSPCV). Firstly, the improved SST k–ω turbulence model and the homogeneous Cavitation model were validated by comparing the simulation result with the experiment of unsteady Cavitation shedding flow around the NACA66-mod hydrofoil, and then the unsteady TLV cloud Cavitation and unstable SSPCV in an axial flow pump were predicted using the improved numerical method. The predicted three-dimensional Cavitation structures of TLV and SSPCV as well as the collapsing features show a good qualitative agreement with the high speed photography results. Numerical results show that the TLV Cavitation cloud in the axial flow pump mainly includes tip clearance Cavitation, shear layer Cavitation, and TLV Cavitation. The unsteady TLV Cavitation cloud occurs near the blade trailing edge (TE) where the shapes of sheet Cavitation and TLV Cavitation fluctuate. The inception of SSPCV is attributed to the tail of the shedding Cavitation cloud originally attached on the suction side (SS) surface of blade, and the entrainment affect of the TLV and the influence of the tip leakage flow at the tailing edge contribute to the orientation and development of the SSPCV. The existence of SSPCV was evidently approved to be a universal phenomenon in axial flow pumps. At the part-load flow rate condition, the SSPCV may trigger Cavitation instability and suppress the tip Cavitation in the neighboring blade. The Cavitation cloud on the SS surface of the neighboring blade grows massively, accompanying with a new SSPCV in the neighboring flow passage, and this SSPCV collapses in a relatively short time.
Desheng Zhang - One of the best experts on this subject based on the ideXlab platform.
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numerical analysis of unsteady tip leakage vortex Cavitation cloud and unstable suction side perpendicular cavitating vortices in an axial flow pump
International Journal of Multiphase Flow, 2015Co-Authors: Desheng Zhang, Lei Shi, Weidong Shi, Ruijie Zhao, Haiyu Wang, B P M Van EschAbstract:The objective of this work is to simulate and analyze the formations of three-dimensional tip leakage vortex (TLV) Cavitation cloud and the periodic collapse of TLV-induced suction-side-perpendicular cavitating vortice (SSPCV). Firstly, the improved SST k–ω turbulence model and the homogeneous Cavitation model were validated by comparing the simulation result with the experiment of unsteady Cavitation shedding flow around the NACA66-mod hydrofoil, and then the unsteady TLV cloud Cavitation and unstable SSPCV in an axial flow pump were predicted using the improved numerical method. The predicted three-dimensional Cavitation structures of TLV and SSPCV as well as the collapsing features show a good qualitative agreement with the high speed photography results. Numerical results show that the TLV Cavitation cloud in the axial flow pump mainly includes tip clearance Cavitation, shear layer Cavitation, and TLV Cavitation. The unsteady TLV Cavitation cloud occurs near the blade trailing edge (TE) where the shapes of sheet Cavitation and TLV Cavitation fluctuate. The inception of SSPCV is attributed to the tail of the shedding Cavitation cloud originally attached on the suction side (SS) surface of blade, and the entrainment affect of the TLV and the influence of the tip leakage flow at the tailing edge contribute to the orientation and development of the SSPCV. The existence of SSPCV was evidently approved to be a universal phenomenon in axial flow pumps. At the part-load flow rate condition, the SSPCV may trigger Cavitation instability and suppress the tip Cavitation in the neighboring blade. The Cavitation cloud on the SS surface of the neighboring blade grows massively, accompanying with a new SSPCV in the neighboring flow passage, and this SSPCV collapses in a relatively short time.
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numerical and experimental investigation of tip leakage vortex Cavitation patterns and mechanisms in an axial flow pump
Journal of Fluids Engineering-transactions of The Asme, 2015Co-Authors: Desheng Zhang, Weidong Shi, Dazhi Pan, Michel DubuissonAbstract:The tip leakage vortex (TLV) cavitating flow in an axial flow pump was simulated based on an improved shear stress transport (SST) k-ω turbulence model and the homogeneous Cavitation model. The generation and dynamics of the TLV Cavitation throughout the blade cascades at different Cavitation numbers were investigated by the numerical and experimental visualizations. The investigation results show that the corner vortex Cavitation in the tip clearance is correlated with the reversed flow at the pressure side (PS) corner of blade, and TLV shear layer Cavitation is caused by the interaction between the wall jet flow in the tip and the main flow in the impeller. The TLV Cavitation patterns including TLV Cavitation, tip corner vortex Cavitation, shear layer Cavitation, and blowing Cavitation are merged into the unstable large-scale TLV cloud Cavitation at critical Cavitation conditions, which grows and collapses periodically near trailing edge (TE).
Akio Tomiyama - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of incipient Cavitation flow in a nozzle of fuel injector
Computers & Fluids, 2014Co-Authors: Akira Sou, Baris Bicer, Akio TomiyamaAbstract:Abstract Cavitation clouds shedding in a nozzle of fuel injector for Diesel Engines play a dominant role in the fuel spray atomization process and the subsequent spray combustion. Since a high speed Cavitation flow in a tiny nozzle with a complicated geometry is not easy to be visualized and measured, large efforts have been paid to carry out numerical simulations of the transient cavitating flow in the nozzle. Most of the previous simulations are based on the Homogeneous Equilibrium Model (HEM), a simplified bubble dynamics model or a barotropic equation, and the Reynolds-Averaged Navier–Stokes (RANS) turbulence model, which do not predict the Cavitation cloud shedding. Cavitation in the nozzle takes various forms, such as a transparent Cavitation sheet and clouds of Cavitation bubbles, which makes its prediction difficult. As a first step to develop a Cavitation model which can accurately treat both the sheet and cloud Cavitations, in this study we propose a new combination of Large Eddy Simulation (LES), Eulerian–Lagrangian Bubble Tracking Method (BTM), and the Rayleigh–Plesset (RP) equation to simulate an incipient Cavitation, in which only Cavitation bubble clouds appear. A precursor simulation of a fully developed turbulent flow in a channel, in which periodic boundary condition is adopted for the inlet and exit, is carried out to generate inlet boundary condition for a nozzle simulation. To verify the validity of the model, transient Cavitation motion and turbulent velocity in a rectangular nozzle are acquired by using a high speed camera and Laser Doppler Velocimetry (LDV). As a result, a recirculation flow and a Cavitation cloud shedding are accurately predicted by LES using a fine grid, and the RP equation for all nuclei tracked in a Lagrangian manner.
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effects of Cavitation in a nozzle on liquid jet atomization
International Journal of Heat and Mass Transfer, 2007Co-Authors: Akira Sou, Shigeo Hosokawa, Akio TomiyamaAbstract:Abstract Cavitation in two-dimensional (2D) nozzles and liquid jet in the vicinity of the nozzle exit were visualized using high-speed cameras to investigate the effects of Cavitation on liquid jet under various conditions of Cavitation and Reynolds numbers σ and Re . Liquid velocity in the nozzle was measured using a laser Doppler velocimetry to examine the effects of Cavitation on the flow in the nozzle and liquid jet. As a result, the following conclusions were obtained: (1) Cavitation in the nozzles and liquid jet can be classified into the four regimes: (no Cavitation, wavy jet), (developing Cavitation, wavy jet), (super Cavitation, spray) and (hydraulic flip, flipping jet), (2) liquid jet near the nozzle exit depends on Cavitation regime, (3) Cavitation and liquid jet are not strongly affected by Re but by σ , and (4) strong turbulence induced by the collapse of Cavitation clouds near the exit plays an important role in ligament formation.
Weidong Shi - One of the best experts on this subject based on the ideXlab platform.
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numerical analysis of unsteady tip leakage vortex Cavitation cloud and unstable suction side perpendicular cavitating vortices in an axial flow pump
International Journal of Multiphase Flow, 2015Co-Authors: Desheng Zhang, Lei Shi, Weidong Shi, Ruijie Zhao, Haiyu Wang, B P M Van EschAbstract:The objective of this work is to simulate and analyze the formations of three-dimensional tip leakage vortex (TLV) Cavitation cloud and the periodic collapse of TLV-induced suction-side-perpendicular cavitating vortice (SSPCV). Firstly, the improved SST k–ω turbulence model and the homogeneous Cavitation model were validated by comparing the simulation result with the experiment of unsteady Cavitation shedding flow around the NACA66-mod hydrofoil, and then the unsteady TLV cloud Cavitation and unstable SSPCV in an axial flow pump were predicted using the improved numerical method. The predicted three-dimensional Cavitation structures of TLV and SSPCV as well as the collapsing features show a good qualitative agreement with the high speed photography results. Numerical results show that the TLV Cavitation cloud in the axial flow pump mainly includes tip clearance Cavitation, shear layer Cavitation, and TLV Cavitation. The unsteady TLV Cavitation cloud occurs near the blade trailing edge (TE) where the shapes of sheet Cavitation and TLV Cavitation fluctuate. The inception of SSPCV is attributed to the tail of the shedding Cavitation cloud originally attached on the suction side (SS) surface of blade, and the entrainment affect of the TLV and the influence of the tip leakage flow at the tailing edge contribute to the orientation and development of the SSPCV. The existence of SSPCV was evidently approved to be a universal phenomenon in axial flow pumps. At the part-load flow rate condition, the SSPCV may trigger Cavitation instability and suppress the tip Cavitation in the neighboring blade. The Cavitation cloud on the SS surface of the neighboring blade grows massively, accompanying with a new SSPCV in the neighboring flow passage, and this SSPCV collapses in a relatively short time.
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numerical and experimental investigation of tip leakage vortex Cavitation patterns and mechanisms in an axial flow pump
Journal of Fluids Engineering-transactions of The Asme, 2015Co-Authors: Desheng Zhang, Weidong Shi, Dazhi Pan, Michel DubuissonAbstract:The tip leakage vortex (TLV) cavitating flow in an axial flow pump was simulated based on an improved shear stress transport (SST) k-ω turbulence model and the homogeneous Cavitation model. The generation and dynamics of the TLV Cavitation throughout the blade cascades at different Cavitation numbers were investigated by the numerical and experimental visualizations. The investigation results show that the corner vortex Cavitation in the tip clearance is correlated with the reversed flow at the pressure side (PS) corner of blade, and TLV shear layer Cavitation is caused by the interaction between the wall jet flow in the tip and the main flow in the impeller. The TLV Cavitation patterns including TLV Cavitation, tip corner vortex Cavitation, shear layer Cavitation, and blowing Cavitation are merged into the unstable large-scale TLV cloud Cavitation at critical Cavitation conditions, which grows and collapses periodically near trailing edge (TE).
