Effects of Diffuser Length on Cloud Cavitation in an Axisymmetrical Convergent-Divergent Nozzle

2015 ◽  
Author(s):  
Keiichi Sato ◽  
Naoya Takahashi ◽  
Yasuhiro Sugimoto
Keyword(s):  
High Speed ◽  
Pressure Effect ◽  
Water Jet ◽  
Video Observation ◽  
Fluid Machinery ◽  
Cloud Cavitation ◽  
Frame Difference ◽  
Upstream Pressure ◽  
Cavitating Hydrofoil ◽  
Unsteady Behavior

Unsteady behavior of periodic cloud cavitation is typically observed in the field of fluid machinery under a high speed liquid flow such as a cavitating hydrofoil as well as cavitating water jet. The instability of cloud cavitation remains to be completely solved though it has been confirmed that there are two instabilities which is an intrinsic instability of cavitation and a system instability. Sato, et al. have found through previous investigations that the pressure wave at the collapse of shedding clouds can make a trigger to cause a reentrant motion. In the present study, the authors focus on a cavitating water jet to investigate the cavitation aspects in an axisymmetrical convergent-divergent nozzle and examine an unsteady behavior of cloud cavitation through high speed video observation and image analysis based on the frame difference method. Especially, the authors study the effect of nozzle divergent part (diffuser) as well as the upstream pressure effect on cloud cavitation in the nozzle. As a result the authors have found that there are two kinds in the shedding pattern and the reentrant motion pattern for cloud cavitation depending on the nozzle diffuser length.

Reentrant Motion in Cloud Cavitation due to Cloud Collapse and Pressure Wave Propagation

2010 ◽  
Author(s):  
Keiichi Sato ◽  
Youhei Wada ◽  
Yoshitaka Noto ◽  
Yasuhiro Sugimoto
Keyword(s):  
Image Analysis ◽  
Wave Propagation ◽  
Difference Method ◽  
Pressure Wave ◽  
High Speed ◽  
Video Observation ◽  
Cloud Cavitation ◽  
High Speed Video ◽  
Frame Difference ◽  
Cavity Closure

It is well known that reentrant jet motion in periodic cloud cavitation means upward flow from the cavity closure area of cloud cavitation. However the mechanism of reentrant motion seems to remain unsolved clearly. In the present study some experiments were conducted about the mechanism of reentrant motion in a fixed type cavity for a convergent-divergent nozzle. High speed video observation and image analysis based on the frame difference method were made about unsteady cloud cavitation with a periodic structure of cavitation cloud shedding. As a result, the main points are experimentally found as follows; 1) a typical pattern of reentrant motions can be caused by the pressure wave propagation from the collapse of cavitation cloud shed downstream and 2) the frame difference method is very useful in an image analysis for high speed video observation of cavitating flow because the trajectory of pressure waves can be clearly visualized by the method.

Structure of Emulsion Cavitation Jet and Jet Peening Impact on the Fatigue of Plan Carbon Steel Q235A

2011 ◽  
Vol 189-193 ◽  
pp. 476-483
Author(s):  
Zhi Sun ◽  
Yan Wei Sui ◽  
Jun Li ◽  
Yan Ni Zhou
Keyword(s):  
Carbon Steel ◽  
High Speed ◽  
Test System ◽  
Water Jet ◽  
High Speed Photography ◽  
Strengthening Effect ◽  
Initial Stage ◽  
Jet Impact ◽  
Upstream Pressure ◽  
Crack Initiation Life

Due to developing the strengthening effect of liquid jet peening on the surface modification for metallic materials, in this study, an emulsion jet peening is produced by injecting a high-speed emulsion jet into an emulsion filled tank. The test system and fixed emulsion of cavitation jet was developed. High speed photography technique was used to observe and analysis the structure of emulsion cavitation jet at various upstream pressures . The results indicate that the structure of emulsion cavitation jet in terms of jet impact pressure, intensive degree and uniformity is better than that water jet. The jet structure depends on the jet pressure. The cavitation jet length increases rapidly at the initial stage and then it stabilizes after few milliseconds. The stabilized length of jet increases and the diverges angle decreases with increasing pressures. Specimens made of plan carbon steel (Q235A, China standard) were exposed to emulsion jet peening at the stand-off distances of 20 mm with a constant upstream pressure, 20 MPa for 60 s. The fatigue test shows that the crack initiation life by treatment of emulsion jet peening increases about 12.5% and 20.2% compared to water jet and unpeened specimen respectively.

Scale Effects on the Cavitation Development in Fluid Machinery

2011 ◽  
Author(s):  
Weiping Yu ◽  
Xianwu Luo ◽  
Yao Zhang ◽  
Bin Ji ◽  
Hongyuan Xu
Keyword(s):  
Turbulence Model ◽  
High Speed ◽  
Scale Effects ◽  
Design Procedure ◽  
Leading Edge ◽  
Characteristic Size ◽  
Cavitation Model ◽  
Fluid Machinery ◽  
Cloud Cavitation ◽  
Sheet Cavitation

The prediction of cavitation in a design procedure is very important for fluid machinery. However, the behaviors of cavitation development in the flow passage are believed to be much different due to scale effects, when the characteristic size varies greatly for fluid machines such as pumps, turbines and propellers. In order to understand the differences in cavitation development, the evolution of cavity pattern in two hydro foils were recorded by high-speed video apparatus. Both foils have the same section profile, and their chord lengths are 70mm and 14mm respectively. For comparison, the cavitating flows around two foils were numerically simulated using a cavitation model based on Rayleigh-Plesset equation and SST k-ω turbulence model. The experiments depicted that for both hydro foils, there was attached sheet cavitation near the leading edge, which separated from the rear part of the cavity and collapsed near the foil trailing edge. There was clear cloud cavitation in the case of the mini foil. The results also indicated that the numerical simulation captured the cavitation evolution for the ordinary foil quite well compared with the experiments, but could hardly predict the cloud cavitation for the mini foil. Thus, it is believed that both the cavitation model and the turbulence model should be carefully treated for the scale effect on cavitation development in fluid machinery.

High-Speed Imaging to Study an Auto-Oscillating Vocal Fold Replica for Different Initial Conditions

2017 ◽  
Vol 09 (05) ◽  
pp. 1750064 ◽  
Author(s):  
A. Van Hirtum ◽  
X. Pelorson
Keyword(s):  
Vocal Fold ◽  
High Speed ◽  
Initial Conditions ◽  
Vocal Folds ◽  
High Speed Imaging ◽  
Human Voice ◽  
Manual Intervention ◽  
Geometrical Features ◽  
Upstream Pressure

Experiments on mechanical deformable vocal folds replicas are important in physical studies of human voice production to understand the underlying fluid–structure interaction. At current date, most experiments are performed for constant initial conditions with respect to structural as well as geometrical features. Varying those conditions requires manual intervention, which might affect reproducibility and hence the quality of experimental results. In this work, a setup is described which allows setting elastic and geometrical initial conditions in an automated way for a deformable vocal fold replica. High-speed imaging is integrated in the setup in order to decorrelate elastic and geometrical features. This way, reproducible, accurate and systematic measurements can be performed for prescribed initial conditions of glottal area, mean upstream pressure and vocal fold elasticity. Moreover, quantification of geometrical features during auto-oscillation is shown to contribute to the experimental characterization and understanding.

Numerical Analysis of Influence of Roughness of Material Surface on High-Speed Liquid Droplet Impingement

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Hirotoshi Sasaki ◽  
Yuka Iga
Keyword(s):  
Numerical Analysis ◽  
High Speed ◽  
Erosion Rate ◽  
Liquid Droplet ◽  
Material Surface ◽  
Liquid Droplets ◽  
Fluid Machinery ◽  
Droplet Impingement ◽  
Surface Liquid ◽  
Droplet Impingement Erosion

This study explains why the deep erosion pits are formed in liquid droplet impingement erosion even though the droplets uniformly impinge on the entire material surface. Liquid droplet impingement erosion occurs in fluid machinery on which droplets impinge at high speed. In the process of erosion, the material surface becomes completely roughened by erosion pits. In addition, most material surface is not completely smooth and has some degree of initial roughness from manufacturing and processing and so on. In this study, to consider the influence of the roughness on the material surface under droplet impingement, a numerical analysis of droplets impinging on the material surface with a single wedge and a single bump was conducted with changing offsets between the droplet impingement centers and the roughness centers on each a wedge bottom and a bump top. As results, two mechanisms are predicted from the present numerical results: the erosion rate accelerates and transitions from the incubation stage to the acceleration stage once roughness occurs on the material surface; the other is that deep erosion pits are formed even in the case of liquid droplets impinging uniformly on the entire material surface.

Radiated Sound of a High-Speed Water-Jet-Propelled Transportation Vessel

2016 ◽  
pp. 951-956
Author(s):  
Alexis B. Rudd ◽  
Michael F. Richlen ◽  
Alison K. Stimpert ◽  
Whitlow W. L. Au
Keyword(s):  
High Speed ◽  
Water Jet ◽  
Radiated Sound

High-speed singulation of electronic packages using a frequency-doubled Nd:YAG laser in a water jet and realization of a 200-W green laser

2003 ◽  
Author(s):  
Frank R. Wagner ◽  
Wentao Hu ◽  
Akos Spiegel ◽  
Nandor Vago ◽  
Bernold Richerzhagen
Keyword(s):  
Nd:Yag Laser ◽  
High Speed ◽  
Green Laser ◽  
Water Jet ◽  
Electronic Packages
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