Growth Process to Cloud-Like Cavitation on Separated Shear Layer

2003 ◽  
Author(s):  
Yasuhiro Saito ◽  
Keiichi Sato
Keyword(s):  
Shear Layer ◽  
Liquid Flow ◽  
High Speed ◽  
Separation Bubble ◽  
Laser Sheet ◽  
Video Camera ◽  
Cloud Cavitation ◽  
Separated Shear Layer ◽  
High Speed Video Camera ◽  
Divergent Channel

It is important to explain a high-speed liquid flow phenomenon because of the developments of various fluid machines. Cavitation is one of the most important phenomena in high-speed liquid flow. When cavitation appears in a liquid flow, it causes some problems such as performance deterioration, vibrations, noise, and cavitation damage. So, it is important to observe the cavity behavior to solve such problems. Especially, it is well known that a cloud cavitation has heavy unsteadiness and high impulse. In this study, a fundamental experimental research on the process of growing to the cloud-like cavitation was performed. The aspect of the cavitation in a circular cylindrical orifice and in a convergent-divergent channel was observed by the high-speed video camera. As a result, the unsteady shedding behavior of the vortex cavity was characteristically observed in a region of the separation bubble at an inlet of a circular cylindrical orifice. There are several vortex cavities on the separated shear layer. These cavities behave pairing and coalescence with each other repeatedly and grow up into a cloud-like cavity. The cloud-like cavity is shed downstream and then generates high impulses at the collapse. In the case of a circular cylindrical orifice, the cavities can be observed clearly by using a laser sheet method. Similar behaviors of the cavity are observed on the separated shear layer in a two dimensional convergent-divergent channel. This paper discusses how the behaviors of vortex cavity relate closely to the flow pattern at non-cavitating condition on the separated shear layer and that the process of the vortex cavities develop to the cloud-like cavity.

Observations of Chain-Reaction Behavior at Bubble Collapse Using Ultra High Speed Video Camera

2003 ◽  
Author(s):  
Keiichi Sato ◽  
Shigemasa Shimojo ◽  
Jun Watanabe
Keyword(s):  
Circular Cylinder ◽  
High Speed ◽  
Video Camera ◽  
Wake Flow ◽  
Bubble Collapse ◽  
Chain Reaction ◽  
High Speed Video ◽  
Ultra High Speed ◽  
High Speed Video Camera ◽  
Divergent Channel

Collapsing behavior of cavitation bubbles is a very short phenomenon. In this study a new ultra-high-speed video camera with the maximum frame speed of 106 fps is used to observe the detailed aspects of three cavitation patterns such as separated vortex cavitation in a convergent-divergent channel, Karman-vortex-like cavitation in the wake flow of a circular cylinder and vibratory cavitation in an ultrasonic vibratory apparatus. For a convergent-divergent channel, the re-entrant motion within the separation zone was observed together with bubble collapse in the divergent part. It was found that minute bubbles collapsed in a chain-reaction manner inside the separated zone with the re-entrant motion after the shedding of cavitation cloud. For the wake flow of a circular cylinder, a collapsing motion of cavitation was observed as an axial-collapse type. The successive bubble collapses after the collapse of main bubble were caused due to pressure wave near the flow field. For cavitation in a vibratory apparatus, cavitation bubbles on the vibratory disk surface were examined in detail, especially from the viewpoint of a non-cavitation ring. The disappearance of bubbles spread radially toward the outer region through the motion of vibratory horn.

Laser Based Measurements of Instantaneous Characteristics in High Pressure Fuel Injection and Swirl Spray

2001 ◽  
Author(s):  
Murad M. Ismailov
Keyword(s):  
High Pressure ◽  
High Speed ◽  
Fuel Injection ◽  
Laser Sheet ◽  
Video Camera ◽  
Fuel Injectors ◽  
High Speed Video Camera ◽  
Swirl Injector ◽  
Phase Doppler Anemometer ◽  
Injection Effect

Abstract Transient dynamics of two injection flows, upstream and downstream from a swirl injector, are investigated. Capillary n-heptane pipe flow is measured using laser Doppler anemometer to obtain the instantaneous time series of centerline velocity and to reconstruct a series of instantaneous and integrated flow rates and pressure gradients. A collimated laser sheet and a high-speed video camera visualize injected spray flow. Finally, the phase Doppler anemometer measurements are introduced to analyze instantaneous patterns of droplets, velocity-size and number density in the fuel spray. All measurements are employed at similar temporal resolution close to 30 μs. Results indicate that both flows are strongly time-dependent and well correlated in time-phases. Initial transitions are completed by 100 μs. Opening or closing of the injector valve affects both flows as strong delta oscillation causes spray penetration dynamics and a post injection effect. A combination of non-intrusive laser-based techniques allows indication of the basic injection and spraying characteristics needed to optimize high-pressure fuel injectors and the late injection combustion mode.

scholarly journals Detonation effects of shallow buried explosive in sandy soil on target plate acceleration in a small-scale blast test

2018 ◽  
Vol 192 ◽  
pp. 02028
Author(s):  
Hassan Zulkifli Abu ◽  
Ibrahim Aniza ◽  
Mohamad Nor Norazman
Keyword(s):  
Sandy Soil ◽  
High Speed ◽  
Early Stage ◽  
Time History ◽  
Video Camera ◽  
Small Scale ◽  
Target Plate ◽  
Air Blast ◽  
High Speed Video Camera ◽  
The Impact

Small-scale blast tests were carried out to observe and measure the influence of sandy soil towards explosive blast intensity. The tests were to simulate blast impact imparted by anti-vehicular landmine to a lightweight armoured vehicle (LAV). Time of occurrence of the three phases of detonation phase in soil with respect to upward translation time of the test apparatus were recorded using high-speed video camera. At the same time the target plate acceleration was measured using shock accelerometer. It was observed that target plate deformation took place at early stage of the detonation phase before the apparatus moved vertically upwards. Previous data of acceleration-time history and velocity-time history from air blast detonation were compared. It was observed that effects of soil funnelling on blast wave together with the impact from soil ejecta may have contributed to higher blast intensity that characterized detonation in soil, where detonation in soil demonstrated higher plate velocity compared to what occurred in air blast detonation.

In Situ Observation Method for Quantitative Evaluation of Solidification Phenomena and Solidification Cracks during Welding

2014 ◽  
Vol 782 ◽  
pp. 3-7
Author(s):  
Kenji Shinozaki ◽  
Motomichi Yamamoto ◽  
Kohta Kadoi ◽  
Peng Wen
Keyword(s):  
High Speed ◽  
Video Camera ◽  
Solidification Cracking ◽  
In Situ Observation ◽  
High Speed Video Camera ◽  
Varestraint Test ◽  
Solidification Cracks ◽  
Observation Method ◽  
Solidification Crack

Solidification cracking during welding is very serious problem for practical use. Therefore, there are so many reports concerning solidification cracking. Normally, solidification cracking susceptibility of material is quantitatively evaluated using Trans-Varestraint test. On the other hand, local solidification cracking strain was tried to measure precisely using in-situ observation method, called MISO method about 30 years ago. Recently, digital high-speed video camera develops very fast and its image quality is very high. Therefore, we have started to observe solidification crack using in site observation method. In this paper, the local critical strain of a solidification crack was measured and the high temperature ductility curves of weld metals having different dilution ratios and different grain sizes to evaluate quantitatively the effects of dilution ratio and grain size on solidification cracking susceptibility by using an improved in situ observation method.

Study on Magnetic Barrel Machine Equipped with Three-Dimensional Arrangement of Magnets

2007 ◽  
Vol 329 ◽  
pp. 761-766 ◽  
Author(s):  
Y. Zhang ◽  
Masato Yoshioka ◽  
Shin-Ichiro Hira
Keyword(s):  
High Speed ◽  
Permanent Magnets ◽  
Three Dimensional ◽  
Video Camera ◽  
High Speed Video ◽  
High Speed Video Camera ◽  
The Media ◽  
Set Up

At present, a commercially available magnetic barrel machine equipped with permanent magnets has some faults arising from constructional reason. That is, grinding or finishing ability is different from place to place in the machining region, resulting in the limitation on the region we can use in the container of workpieces. Therefore, in this research, authors made the new magnetic barrel machine equipped with three dimensional (3D) magnet arrangement to overcome these faults. The grinding ability of the new 3D magnetic barrel machine converted was experimentally examined, and compared with that of the traditional magnetic barrel machine. As a result, it was shown that we can use much broader region in the new 3D machine. It was also shown that the grinding ability became higher. The distribution of barrel media in action was recorded by means of a high speed video camera. It was clarified that the media rose up higher and were distributed more uniformly in the container by the effect of the magnet block newly set up. It was supposed that this must be the reason for the above-mentioned improvement of grinding ability.

Exploitation of Subharmonics for Separated Shear Layer Control on a High-Lift Low-Pressure Turbine Using Acoustic Forcing

2013 ◽  
Vol 136 (5) ◽  
Author(s):  
Chiara Bernardini ◽  
Stuart I. Benton ◽  
Jen-Ping Chen ◽  
Jeffrey P. Bons
Keyword(s):  
Shear Layer ◽  
Separation Bubble ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Linear Instability ◽  
Laminar Separation ◽  
Significant Control ◽  
Low Pressure Turbine ◽  
Separated Shear Layer ◽  
Sound Control

The mechanism of separation control by sound excitation is investigated on the aft-loaded low-pressure turbine (LPT) blade profile, the L1A, which experiences a large boundary layer separation at low Reynolds numbers. Previous work by the authors has shown that on a laminar separation bubble such as that experienced by the front-loaded L2F profile, sound excitation control has its best performance at the most unstable frequency of the shear layer due to the exploitation of the linear instability mechanism. The different loading distribution on the L1A increases the distance of the separated shear layer from the wall and the exploitation of the same linear mechanism is no longer effective in these conditions. However, significant control authority is found in the range of the first subharmonic of the natural unstable frequency. The amplitude of forced excitation required for significant wake loss reduction is higher than that needed when exploiting linear instability, but unlike the latter case, no threshold amplitude is found. The fluid-dynamics mechanisms under these conditions are investigated by particle image velocimetry (PIV) measurements. Phase-locked PIV data gives insight into the growth and development of structures as they are shed from the shear layer and merge to lock into the excited frequency. Unlike near-wall laminar separation sound control, it is found that when such large separated shear layers occur, sound excitation at subharmonics of the fundamental frequency is still effective with high-Tu levels.

Grease soap particles passing through an elastohydrodynamic contact under side slip conditions

2000 ◽  
Vol 214 (4) ◽  
pp. 317-325 ◽  
Author(s):  
P Eriksson ◽  
V Wikström ◽  
R Larsson
Keyword(s):  
Film Thickness ◽  
High Speed ◽  
Previous Investigation ◽  
Video Camera ◽  
Slip Conditions ◽  
High Speed Video ◽  
Elastohydrodynamic Contact ◽  
High Speed Video Camera ◽  
Pure Rolling ◽  
Minimum Film Thickness

In a previous investigation, grease thickener fibres were tracked as they passed through an elastohydrodynamic (EHD) contact in pure rolling using interferometry in a standard ball-and-disc apparatus. In order to capture single thickener fibres, a high-speed video camera was used. Here, the experiments have been repeated introducing different amounts of side slip for different rolling speeds and a faster video camera capable of capturing 4500 frames/s. The contact was lubricated with a continuous supply of grease. Two greases, based on the same synthetic poly(α-olefin) but thickened with Li-12-OH and lithium complex soap respectively, were studied. It was observed that the thickener fibres were stretched both before entering the contact and as they passed through it. Fibres seem to avoid the minimum film thickness regions and, if they enter, the film is restored immediately after passage.

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