Experimental Study of Mechanism of Silt Abrasion Influenced by Cavitation in Hydraulic Machinery

2011 ◽  
Author(s):  
Tao Zhang ◽  
CiChang Chen ◽  
Dan Li ◽  
DongLi Lv
Keyword(s):  
Abrasive Wear ◽  
Large Scale ◽  
Cavitation Erosion ◽  
Large Angle ◽  
Solid Particles ◽  
Bubble Collapse ◽  
Small Scale ◽  
Front Part ◽  
Trailing Edge ◽  
Experimental Conditions

Experiments of cavitation erosion, silt abrasion and their synergetic erosion on Al hydrofoils were made in a testing-section. The erosion depth on hydrofoils was measured, and results showed that the depth value increased gradually with the condition changed from silt abrasion to synergetic erosion (lie due to contemporary action of silt abrasion and cavitation bubble collapse) and meanwhile with the position changed form the front part to the trailing edge of hydrofoil. The microtopography on hydrofoils was observed under the three experimental conditions. The cavitation erosion results appeared as regular-shape pits which differed only in the number per unit area at different position. The silt abrasion patterns was uniform in characteristics around one fixed point on hydrofoil. From the front part to the trailing edge of hydrofoil, the main abrasive wear patterns changed from ploughing type to wedge type. Small scale ploughing or cutting type and large scale wedge type were the main erosion patterns of the synergetic erosion directly caused by solid particles. From the front part to the trailing edge of hydrofoil, the size of small and large scale abrasive wear patterns increased gradually. Combining the analysis and processing of cavitation structure with the silt abrasion and synergetic erosion patterns, a viewpoint about silt abrasion influenced by cavitation was put forward. During the stage of growth of attached cavity, the hydrofoil was eroded by solid particles at small angle as a result of solid particles subjected to cavitation nucleation being accelerated along the surface of hydrofoil, and the erosion patterns were dominated by ploughing or cutting type. During the stage of cavitation cloud collapse in main flow, the hydrofoil was eroded by impact abrasion of solid particles at large angle resulted from solid particles being accelerated to high velocity by micro-jet or pressure wave, and the dominating erosion pattern was wedge type.

On turbulent separation in the flow past a bluff body

1992 ◽  
Vol 241 ◽  
pp. 443-467 ◽  
Author(s):  
A. Neish ◽  
F. T. Smith
Keyword(s):  
Large Scale ◽  
Bluff Body ◽  
Separated Flow ◽  
Small Scale ◽  
Supporting Evidence ◽  
Turbulent Regime ◽  
Trailing Edge ◽  
Flow Past ◽  
Starting Point ◽  
Turbulence Factor

The basic model problem of separation as predicted by the time-mean boundary-layer equations is studied, with the Cebeci-Smith model for turbulent stresses. The changes between laminar and turbulent flow are investigated by means of a turbulence ‘factor’ which increases from zero for laminar flow to unity for the fully turbulent regime. With an attached-flow starting point, a small increase in the turbulence factor above zero is found to drive the separation singularity towards the trailing edge or rear stagnation point for flow past a circular cylinder, according to both computations and analysis. A separated-flow starting point is found to produce analogous behaviour for the separation point. These findings lead to the suggestion that large-scale separation need not occur at all in the fully turbulent regime at sufficiently high Reynolds number; instead, separation is of small scale, confined near the trailing edge. Comments on the generality of this suggestion are presented, along with some supporting evidence from other computations. Further, the small scale involved theoretically has values which seem reasonable in practical terms.

Rift and thrust tectonics associated with a translational block slide, Abbotsford, New Zealand

1986 ◽  
Vol 123 (1) ◽  
pp. 13-25 ◽  
Author(s):  
D. G. Bishop ◽  
R. J. Norris
Keyword(s):  
Large Scale ◽  
Ground Surface ◽  
Failure Surface ◽  
Bedding Plane ◽  
Small Scale ◽  
Trailing Edge ◽  
Cross Sectional ◽  
Thrust Tectonics ◽  
Sudden Decrease ◽  
Translational Block

AbstractThe East Abbotsford translational block landslide failed suddenly on 8 August, 1979, after months and probably years of slowly accelerating movement. A displacement of about 50 m occurred on a bedding plane dipping 7°, about 30 m below ground surface, at or very near the contact between two formations.The complex graben formed around the head of the landslide is a small scale example of extensional (rift) tectonics. A wedge and prism model is developed to fit the geometry, and meet the constraints of preserving the cross-sectional area and stratal length of the beds involved and also to account for the sequential retrogressive failures of the trailing edge of the sliding block.Reconstruction of the failure sequence at the toe shows the compressional zone to be dominated by overthrusting on upward sloping surfaces or ramps, with subsidiary backthrusting and buckling.The energy expended in overthrusting, coupled with the decrease in mass (and hence driving force) resulting from the retrogressive spalling of the trailing edge of the slide block, indicates that the phase of rapid movement was accompanied by a sudden decrease in resistance on the failure surface for a movement of 50 m to have occurred.Both the rift and thrust structures associated with the landslide have large scale tectonic analogues.

Crystallization

2015 ◽  
Author(s):  
Roger G. Harrison ◽  
Paul W. Todd ◽  
Scott R. Rudge ◽  
Demetri P. Petrides
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Crystal Form ◽  
Solid Particles ◽  
Dimensional Structure ◽  
Internal Quality ◽  
Small Scale ◽  
X Ray Diffraction ◽  
Production Scale ◽  
Homogeneous Phase

Crystallization is the process of producing crystals from a homogeneous phase. For biochemicals, the homogeneous phase from which crystals are obtained is always a solution. Crystallization is similar to precipitation in that solid particles are obtained from a solution. However, precipitates have poorly defined morphology, while in crystals the constituent molecules are arranged in three-dimensional arrays called space lattices. In comparison to crystallization, precipitation occurs at much higher levels of supersaturation and rates of nucleation but lower solubilities. These and other differences between crystallization and precipitation are highlighted in Table 9.1. Because of these differences and because the theory of crystallization that has been developed is different from that for precipitation, crystallization is considered separately from precipitation. Crystallization is capable of producing bioproducts at very high purity (say, 99.9%) and is considered to be both a polishing step and a purification step. Polishing refers to a process needed to put the bioproduct in its final form for use. For some bioproducts, such as antibiotics, this final form must be crystalline, and sometimes it is even necessary that a specific crystal form be obtained. In some instances, the purification that can be achieved by crystallization is so significant that other more expensive purification steps such as chromatography can be avoided. There are actually two very different applications of crystallization in biotechnology and bioproduct engineering: crystallization for polishing and purification, and crystallization for crystallography. In the latter case, the goal is a small number of crystals with good size (0.2–0.9 mm) and internal quality. Although it has become common to crystallize proteins for characterization of their three-dimensional structure by x-ray diffraction, this is performed only at small scale in the laboratory, and the knowledge about how to crystallize proteins at large scale in a production process is less developed. However, many antibiotics and other small biomolecules are routinely crystallized in production scale processes. This chapter is oriented toward the use of crystallization in processes that can be scaled up.

scholarly journals Altimetric observations of surface characteristics of the Antarctic ice sheet

1997 ◽  
Vol 43 (144) ◽  
pp. 265-275 ◽  
Author(s):  
Benoît Legrésy ◽  
Frédérique Rémy
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Leading Edge ◽  
Small Scale ◽  
Height Measurement ◽  
Trailing Edge ◽  
Antarctic Ice Sheet ◽  
Linear Effect ◽  
Continental Scale ◽  
The Antarctic

AbstractThe aim of this paper is to investigate the geophysical characteristics of the Antarctic ice sheet using radar altimetric observations. To do this, we use an altimetric waveform simulator, in situ observations, ERS-1 (European remote-sensing satellite) data and SPOT (Satellite pour l’observation de la terre) images. The small-scale study takes place at Dome C, Terre Adélie, which is a relatively flat region with gentle undulations and low wind speed. Despite this, the altimetric waveform parameters (height, energy, leading edge and trailing edge) are highly noisy. The effect of undulations on the waveform parameters is found to be dominant. The combination of a subsurface signal and a rough surface produces a linear effect on the altimetric backscattering or on the trailing edge of the waveform, but a strongly non-linear effect on the leading edge of the waveform or height estimation. As a consequence, the height measurement is very sensitive to the altimeter technical or orbital characteristics and is not reproducible from one mission to another. Observations show sastrugi fields that enhance the leading edge and affect the whole waveform. Observed local backscattering changes, probably due to local variations in surface microroughness, enhance the backscattered energy and may artificially create a topographic signal. The continental-scale study shows coherent patterns. Even if both surface and subsurface components affect the altimetric observation, the large-scale signal is mostly controlled by surface backscattering variations. The surface or near-subsurface characteristics of the snowpack may then be reached by altimetric observations.

scholarly journals Altimetric observations of surface characteristics of the Antarctic ice sheet

1997 ◽  
Vol 43 (144) ◽  
pp. 265-275 ◽  
Author(s):  
Benoît Legrésy ◽  
Frédérique Rémy
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Leading Edge ◽  
Small Scale ◽  
Height Measurement ◽  
Trailing Edge ◽  
Antarctic Ice Sheet ◽  
Linear Effect ◽  
Continental Scale ◽  
The Antarctic

AbstractThe aim of this paper is to investigate the geophysical characteristics of the Antarctic ice sheet using radar altimetric observations. To do this, we use an altimetric waveform simulator, in situ observations, ERS-1 (European remote-sensing satellite) data and SPOT (Satellite pour l’observation de la terre) images. The small-scale study takes place at Dome C, Terre Adélie, which is a relatively flat region with gentle undulations and low wind speed. Despite this, the altimetric waveform parameters (height, energy, leading edge and trailing edge) are highly noisy. The effect of undulations on the waveform parameters is found to be dominant. The combination of a subsurface signal and a rough surface produces a linear effect on the altimetric backscattering or on the trailing edge of the waveform, but a strongly non-linear effect on the leading edge of the waveform or height estimation. As a consequence, the height measurement is very sensitive to the altimeter technical or orbital characteristics and is not reproducible from one mission to another. Observations show sastrugi fields that enhance the leading edge and affect the whole waveform. Observed local backscattering changes, probably due to local variations in surface microroughness, enhance the backscattered energy and may artificially create a topographic signal. The continental-scale study shows coherent patterns. Even if both surface and subsurface components affect the altimetric observation, the large-scale signal is mostly controlled by surface backscattering variations. The surface or near-subsurface characteristics of the snowpack may then be reached by altimetric observations.

scholarly journals Laser generated Richtmyer–Meshkov and Rayleigh–Taylor instabilities and nonlinear wave-vortex paradigm in turbulent mixing. II. Near-central region of Gaussian spot

2017 ◽  
Vol 35 (2) ◽  
pp. 210-225 ◽  
Author(s):  
Stjepan Lugomer
Keyword(s):  
Central Region ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Three Dimensional ◽  
Target Surface ◽  
Bubble Collapse ◽  
Small Scale ◽  
New Paradigm ◽  
Vortex Filaments ◽  
Coherent Wave

AbstractLaser-induced three-dimensional (3D) Richtmyer–Meshkov and Rayleigh–Taylor instabilities (RMI and RTI) on metal target in the semi-confined configuration (SCC) show the new paradigm of wave-vortex mixing. The SCC enables extended lifetime of a hot vapor/plasma plume above the target surface and the formation of fast multiple reshocks. This causes – in the central region (CR) of Gaussian-like spot – the evolution of RMI with the spike breakup (Lugomer, 2016b), while in the near CR causes the RMI followed by the RTI. The density interface is transformed into the large-scale broken irregular, quasi-periodic web, which comprises the RTI mushroom-shape spikes and the coherent wave-vortex structures such as the line solitons and vortex filaments. The intensity and direction of reshocks change (due to irregularity of the interface) and cause the formation of domains with the weak and the strong reshocks effects. The weak reshocks affect mushroom-shape spikes only slightly, while the strong ones cause their deformation and symmetry break, bubble collapse, and separation of the horizontal flow into vortex ribbons. Interaction of ribbons with spikes and bubbles causes the ribbon pinning, looping, winding, and formation of knotted and tangled structures. The line solitons, vortex filaments, and ribbons tend to organize into complex large-scale structures with the low wave-vortex turbulent mixing. They represent the new paradigm of 3D RMI and RTI in which the transition to the small-scale turbulent mixing does not appear.

SAMPLE VARIANCE IN LARGE-SCALE COSMIC MICROWAVE BACKGROUND ANISOTROPY MEASUREMENTS

1998 ◽  
Vol 07 (01) ◽  
pp. 89-96 ◽  
Author(s):  
KIN-WANG NG
Keyword(s):  
Correlation Function ◽  
Cosmic Microwave Background ◽  
Large Scale ◽  
Large Angle ◽  
Density Fluctuations ◽  
Sample Variance ◽  
Small Scale ◽  
Microwave Background ◽  
Cosmic Microwave Background Anisotropy ◽  
Computationally Intensive

The effects of limited sky coverage in large-angle cosmic microwave background anisotropy experiments are investigated by computing the variance of the angular two-point correlation function with an incomplete sphere. We find that, assuming a power spectrum of density fluctuations with spectral index n = 1, the Galactic cut of half-width 20° (40°) about the Equator made by the COBE DMR experiment would induce a sample variance on the rms temperature fluctuation [(ΔT/T) rms ]2 (or equivalently, the correlation function at zero lag), which is 12% (38%) greater than the cosmic variance with a whole sky coverage. This result is about two times smaller than the naive expectation that the cosmic variance is enhanced by a factor of [Formula: see text], where A is the solid angle sampled by the experiment. We also find that the sample variance of the correlation function at nonzero lag can approach the cosmic variance limit. Our approach provides an analytic way of finding a theoretical error to the theoretical prediction for a particular experiment (either large- or small-scale), without having recourse to computationally intensive Monte Carlo or maximum likelihood methods.

Experimental and numerical study of mixing characteristics of a rectangular lobed mixer in supersonic flow

2015 ◽  
Vol 119 (1216) ◽  
pp. 701-725 ◽  
Author(s):  
J.-H. Feng ◽  
C.-B. Shen ◽  
Q.-C. Wang ◽  
J. Lei
Keyword(s):  
Total Pressure ◽  
Large Scale ◽  
Pressure Ratio ◽  
Velocity Ratio ◽  
Interfacial Area ◽  
Small Scale ◽  
Trailing Edge ◽  
Turbulence Structures ◽  
Scale Turbulence ◽  
Total Pressure Ratio

AbstractA combined experimental and computational study on a rectangular lobed mixer is performed. A series of simulations based on a steady Reynolds-averaged Navier-Stokes Simulation (RANS) are conducted to analyse the mixing mechanisms of large-scale streamwise structure shed by the trailing edge of lobed mixer, with emphasis being placed on the effect of turbulence modeling and inflow conditions. The simulations are validated in respect of velocity and scalar distribution against the data obtained through Particle Image Velocimetry (PIV) and Nanoparticle-based Planar Laser Scattering (NPLS) technique. The computational results predicted by the SSTk–ω turbulence model show better agreement with the experimental data. But the small-scale turbulence structures are not captured accurately by these turbulence models. The convoluted shear layer shed from trailing edge is stretched and rotated by the large-scale streamwise vortices, forming an unstable ‘pinching-off’ structure, which increases the interfacial area. And at the interface of two streams, a large number of small-scale turbulence structures are formed, which contribute a lot to the mixing enhancement along with the increased interfacial area. The streamwise vorticity decays more rapidly with the decrease of velocity ratio and total pressure ratio of two streams. The scalar thickness which reflects the mixing rate of two streams increases with the decreasing velocity ratio and total pressure ratio.

scholarly journals A visual study of turbulent shear flow

1973 ◽  
Vol 61 (3) ◽  
pp. 513-540 ◽  
Author(s):  
Stavros G. Nychas ◽  
Harry C. Hershey ◽  
Robert S. Brodkey
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Outer Region ◽  
Solid Particles ◽  
Turbulent Shear ◽  
Small Scale ◽  
Wall Region ◽  
Wall Area ◽  
Sequence Of Events ◽  
Local Mean

The outer region of a turbulent boundary layer along a flat plate was photographed and analysed; in addition, limited observations of the wall area were also made. The technique involved suspending very small solid particles in water and photographing their motion with a high-speed camera moving with the flow.The single most important event observed in the outer region was fluid motion which in the convected view of the travelling camera appeared as a transverse vortex. This was a large-scale motion transported downstream almost parallel to the wall with an average velocity slightly smaller than the local mean. It appeared to be the result of an instability interaction between accelerated and decelerated fluid, and it is believed to be closely associated with the wall-region ejections. The transverse vortex was part of a deterministic sequence of events; although these events occurred randomly in space and time. The first of these events was a decelerated flow exhibiting velocities considerably smaller than the local mean. It was immediately followed by an accelerated flow. Both these events extended from near the wall to the far outer region. Their interaction resulted in the formation of one or more transverse vortices. While the transverse vortex was transported downstream, small-scale fluid elements, originating in the wall area of the decelerated flow, were ejected outwards (ejection event). After travelling some distance outwards the ejected elements interacted with the oncoming accelerated fluid in the wall region and were subsequently swept downstream (sweep event). The sequence of events closed with two large-scale motions.Estimated positive and negative contributions to the instantaneous Reynolds stress during the events were many times higher than the local mean values.

scholarly journals Regulatory mechanisms of group distributions in a gregarious arthropod

2015 ◽  
Vol 2 (11) ◽  
pp. 150428 ◽  
Author(s):  
Pierre Broly ◽  
Romain Mullier ◽  
Cédric Devigne ◽  
Jean-Louis Deneubourg
Keyword(s):  
Spatial Patterns ◽  
Large Scale ◽  
Common Species ◽  
Self Organization ◽  
Small Scale ◽  
Environmental Cues ◽  
Experimental Conditions ◽  
Social Species ◽  
Homogeneous Set ◽  
Set Up

In a patchy environment, how social animals manage conspecific and environmental cues in their choice of habitat is a leading issue for understanding their spatial distribution and their exploitation of resources. Here, we experimentally tested the effects of environmental heterogeneities (artificial shelters) and some of their characteristics (size and fragmentation) on the aggregation process of a common species of terrestrial isopod (Crustacea). One hundred individuals were introduced into three different heterogeneous set-ups and in a homogeneous set-up. In the four set-ups, the populations split into two aggregates: one large (approx. 70 individuals) and one smaller (approx. 20 individuals). These aggregates were not randomly distributed in the arena but were formed diametrically opposite from one another. The similarity of the results among the four set-ups shows that under experimental conditions, the environmental heterogeneities have a low impact on the aggregation dynamics and spatial patterns of the isopod, merely serving to increase the probability of nucleation of the larger aggregation at these points. By contrast, the regulation of aggregate sizes and the regular distribution of groups are signatures of local amplification processes, in agreement with the short-range activator and long-range inhibitor model (scale-dependent feedbacks). In other words, we show how small-scale interactions may govern large-scale spatial patterns. This experimental illustration of spatial self-organization is an important step towards comprehension of the complex game of competition among groups in social species.

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