By providing direct experimental evidence illustrating the cause of the shortcoming of the status-quo, the expected impact of this work is to challenge and augment existing concepts that will ultimately lead to the correct prediction of the onset of elastic turbulence.
Turbulence II movie download in mp4
Due to its relevance, many attempts have been made to parameterize the in situ effective rheology and predict the effective pressure drop of a viscoelastic fluid flowing in channels with constrictions or porous materials. Several scaling and dimensionless groups such as shear or extensional rate, Weissenberg number (Wi), and Deborah number (De) have been employed to understand the onset of this elastic turbulence (van Buel and Stark 2020; Walkama et al. 2019). Most of these parameters have identified transitions in flow regimes from steady to unsteady behaviour and even time-dependent flow behaviour (Zilz et al. 2012). However, when probing in detail the flow behaviour in more complex geometries having varying lengths between constrictions and varying aspect ratios, capturing the onset of turbulence is not as simple as the use of the dimensionless parameters mentioned above and attempts to predict the onset have been largely unsuccessful.
However, that systematics leaves a gap as to how the effective in situ behaviour becomes more than the sum of its individual parts. By addressing the problem with a sequence of constrictions at varying separation distances, it becomes evident why De, Wi and M do not provide an entirely sufficient description of the instability, including its onset. The cause is a more complex interaction between adjacent constrictions which couple via the flow field resulting from a combination of respective local geometry at the constriction and fluid rheology. Depending on the distance between adjacent throats in the flow geometry, the flow field turbulence, which is elastic in nature, moves upstream (Qin et al. 2019) and may interact with the preceding throat, depending on different conditions that relate to the interaction between the fluid velocity and the porous media geometry. By using a flow geometry consisting of a single channel, with a sequence of constrictions with varying distance between adjacent constrictions and varying aspect ratio, which is the elementary geometry typically considered for arterial stenosis (Khodaparast et al. 2014; Mustapha et al. 2008; Qin et al. 2019; Rabby et al. 2014; Zografos et al. 2020), we can show in an elementary way the varying interaction between subsequent throats via the (unstable) flow field, where the magnitude of the interaction depends on the degree of flow field instability, i.e. has an onset which coincides when the unstable flow field reaches the adjacent upstream pore throat. This means that for a given bulk fluid rheology, in a porous medium, the effective pressure drop is also influenced by the specifics of the porous medium in terms of distance between constrictions and size of the constrictions which introduces another length scale into the problem.
In our geometry, we observe that the systematically increasing separation distances has an influence on the onset of elastic turbulence which can be intuitively related to the coincidence with the overlap of the flow field between constrictions. However, the changing lengths between constrictions is not considered in De or Wi and consequently also not in M.
In summary, we have provided intuitive insight into the onset and evolution of elastic turbulence in complex geometries and geometries with multiple constrictions. By imaging the flow field of a non-Newtonian viscoelastic solution in a microfluidic complex geometry consisting of multiple constrictions with varying lengths between constrictions and varying the aspect ratio, we can relate the onset of elastic turbulence and subsequent evolution with the fact that flow fields between adjacent constrictions overlap.
We show that perturbations to the fluid behaviour which transform towards fully developed turbulence begins from a localized phenomenon, that is characterized by flow disturbances around the constriction of the microchannel and later transforms to a non-localized phenomenon, where the flow turbulence is infinite and fully developed reaching the total length of the pore body repeat unit distance. We further argue that these dimensionless parameters that have been used for over decades may not be the appropriate parameters to define the onset of the elastic turbulence in these geometries because of the unique and dynamic length scale formed by the flow fields as the velocity increases.
Our findings suggest that a criteria describing the onset of elastic turbulence would benefit from consideration of streamwise length scales of the confining geometry such as distances between adjacent pore throats. This length scale in relation to the dynamic length scale of the flow field could be a parameter describing how the pores are interacting with each other and potentially parameterize the transition of the flow regime from a local instability to a collective phenomenon with global flow field.
It is noteworthy that our geometry, which finds importance in a wide variety of applications in industrial and biological processes, will have significant impact in understanding the onset of fluid turbulence and threshold during polymer extrusion processes, moulding, fluid behaviour in porous media for remediations and local arterial opening during multiple stenosis formation in the prevention of cardiovascular diseases. We also find that our work opens a pathway towards a vast field of research correlating in detail the actual flow field behaviour towards predicting the onset of elastic turbulence.
This video shows a snapshot of ocean turbulence in the North Atlantic Ocean from January through March of 2012. The animation was created with a groundbreaking super-high-resolution global ocean simulation (approximately 1.2 miles, or 2 kilometers, horizontal resolution) developed at JPL. The colors represent the magnitude of surface relative vorticity, a measure of the spin of fluid parcels. The animation emphasizes fast-rotating, small-scale turbulence (6.2 to 31-mile, or 10 to 50 kilometer, range), during the winter. High levels of relative vorticity caused by small-scale turbulence are believed to strongly transport heat and carbon vertically in the ocean.
These data appear in a study (Su et al. 2018), entitled Ocean submesoscales as a key component of the global heat budget, published recently in Nature Communications. The study suggests that upper-ocean small-scale turbulence transports heat upward in the ocean at a level five times larger than larger-scale heat transport by ocean eddies, significantly affecting the exchange of heat between the ocean interior and atmosphere. Such interactions have a crucial impact on the Earth's climate.
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
The amount by which the speed of smaller noise features differsfrom the speed of larger noise features. A value of 0 makes themovement of the noise resemble the noise generated by the FractalNoise effect, in which smaller noise features move at the same speedas larger noise features. A larger value makes the multiple layersof noise appear to roil in a manner more like that of natural turbulencein a fluid.
A hypothetical small solid body with a radius \(\gtrsim\)1 km formed in a protoplanetary disk is called a planetesimal. Planetesimals grow by collisional coagulation owing to mutual gravity (Wetherill and Stewart 1989; Kokubo and Ida 1996, 1998). The formation processes of planetesimals from dust particles are not fully understood (Chiang and Youdin 2010). There are two major theories for the formation of planetesimals. One is the mutual sticking of dust aggregates (Weidenschilling and Cuzzi 1993), and another is the gravitational instability of the dust layer (Safronov 1969; Goldreich and Ward 1973). In this work, we restrict ourselves to considering the formation of planetesimals through the gravitational instability in a dead zone where the ionization fraction is not sufficient for the magneto-rotational instability to drive turbulence.
The dust layer fragments into a number of clumps. The dust densities in the clumps increase not only around \(x_+\), where the metallicity grows, but also around \(x_-\), where the metallicity decreases. Although particle-clumping occurs at both null points \(x_+\) and \(x_-\) of the pressure gradient, the maximum density is higher around \(x_+\) because of the high metallicity. As shown in the inlet of Fig. 4, the maximum dust density exceeds the Roche density after 100 orbits. These high-density clumps are not temporal, but continue to grow in density without migrating radially until the end of our simulation (see Additional files 1, 2 for movies that show the time evolutions; the last frames of these movies correspond to Figs. 4 and 5, respectively). We can expect further growth of the density for clumps that have a density exceeding the Roche density owing to gravitational instability. Hence, planetesimal formation due to gravitational instability would proceed around \(x_+\).
Low Density Turbidity Current(Relatively) Low Density Turbidity Current Movie from Gary Parker, St. Anthony Falls Hydraulic Laboratory, University of Minnesota.Slow moving, relatively low density turbidity current. Note the relatively minor turbulence seen in the flow head. Scale is marked off in centimeters. Close up of head from 1:12 to 1:23 shows nearly laminar movement of the turbid cloud through water. The turbidity flow lifts up at the end of the ramp it is moving along due to recirculation of water at the end of the tank.
Mp3 Juice is the most popular free mp3 search engine tool and music downloader, is very popular. MP3 Juice is a great tool to convert and download youtube videos and music. The Mp3 Juice website is the best way to quickly and easily download mp3 music. Its simplicity makes Mp3juice easy to use, so anyone can search for and download high-quality audio files 2ff7e9595c