Turbulent drag reduction and multistage transitions in viscoelastic minimal flow units

2010 ◽  
Vol 647 ◽  
pp. 421-452 ◽  
Author(s):  
LI XI ◽  
MICHAEL D. GRAHAM
Keyword(s):  
Drag Reduction ◽  
The Self ◽  
Sudden Increase ◽  
Minimal Flow ◽  
Mean Flow ◽  
Turbulent Friction ◽  
Minute Amount ◽  
Spatio Temporal ◽  
Open Question ◽  
High Degree

The observation that addition of a minute amount of flexible polymers to fluid reduces turbulent friction drag is well known. However, many aspects of this drag reduction phenomenon are not well understood; in particular, the origin of the maximum drag reduction (MDR) asymptote, a universal upper limit on drag reduction by polymers, remains an open question. This study focuses on the drag reduction phenomenon in the plane Poiseuille geometry in a parameter regime close to the laminar–turbulent transition. By minimizing the size of the periodic simulation box to the lower limit for which turbulence persists, the essential self-sustaining turbulent motions are isolated. In these ‘minimal flow unit’ (MFU) solutions, a series of qualitatively different stages consistent with previous experiments is observed, including an MDR stage where the mean flow rate is found to be invariant with respect to changing polymer-related parameters. Before the MDR stage, an additional transition exists between a relatively low degree (LDR) and a high degree (HDR) of drag reduction. This transition occurs at about 13%–15% of drag reduction and is characterized by a sudden increase in the minimal box size, as well as many qualitative changes in flow statistics. The observation of LDR–HDR transition at less than 15% drag reduction shows for the first time that it is a qualitative transition instead of a quantitative effect of the amount of drag reduction. Spatio-temporal flow structures change substantially upon this transition, suggesting that two distinct types of self-sustaining turbulent dynamics are observed. In LDR, as in Newtonian turbulence, the self-sustaining process involves one low-speed streak and its surrounding streamwise vortices; after the LDR–HDR transition, multiple streaks are present in the self-sustaining structure and complex intermittent behaviour of the streaks is observed. This multistage scenario of LDR–HDR–MDR recovers all key transitions commonly observed and studied at much higher Reynolds numbers.

scholarly journals Nucleation of Ga droplets self-assembly on GaAs(111)A substrates

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Artur Tuktamyshev ◽  
Alexey Fedorov ◽  
Sergio Bietti ◽  
Stefano Vichi ◽  
Riccardo Tambone ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Size Distribution ◽  
Self Assembly ◽  
Cluster Size ◽  
Droplet Size Distribution ◽  
Local Environment ◽  
The Self ◽  
Critical Cluster ◽  
Droplet Nucleation ◽  
High Degree

AbstractWe investigated the nucleation of Ga droplets on singular GaAs(111)A substrates in the view of their use as the seeds for the self-assembled droplet epitaxial quantum dots. A small critical cluster size of 1–2 atoms characterizes the droplet nucleation. Low values of the Hopkins-Skellam index (as low as 0.35) demonstrate a high degree of a spatial order of the droplet ensemble. Around $$350\,^{\circ }\hbox {C}$$ 350 ∘ C the droplet size distribution becomes bimodal. We attribute this observation to the interplay between the local environment and the limitation to the adatom surface diffusion introduced by the Ehrlich–Schwöbel barrier at the terrace edges.

Self-Formation, Development and Reproduction of the Artificial System

2004 ◽  
Vol 97-98 ◽  
pp. 77-84
Author(s):  
Juras Ulbikas ◽  
Liudas Leonas ◽  
Daiva Ulbikienė ◽  
Stepas Janušonis
Keyword(s):  
The Self ◽  
Artificial System ◽  
Technological Processes ◽  
Microelectronic Devices ◽  
Biological World ◽  
Microelectronics Technology ◽  
Open Question ◽  
Self Formation ◽  
Irreversible Evolution ◽  
Complexity Increase

Self-formation as a concept for irreversible evolution of the artificial object with complexity increase was introduced for understanding of the processes existing in microelectronics technology [1]. The concept of self-formation by itself was to some extend influenced by principles existing in biological world therefore from the very beginning there was an open question about limits of self-formation application: are we limited to the understanding of some technological processes or we can think about predicting new technological applications by applying selfformation concept. Recently developed tools for simulation of technological processes for Solar Cells manufacturing [2] clearly indicates that self-formation is becoming interesting tool for technologists trying to create and optimize microelectronic devices. The next step exploring selfformation application boundaries can be analysis of possibilities of the self-formation to demonstrate usual in biological life development and reproduction of the object. This presentation will be dedicated to the analysis of the conditions and possibilities by applying self-formation present self-formation, development and reproduction of artificial object.

The Negative Effects of Using Smart Devices on the Physical and Psychological Health of Palestinian Children aged (13-16) years from their Perspective

2020 ◽  
Vol 8 (3) ◽  
pp. 01-19
Author(s):  
Nuha Iter
Keyword(s):  
Psychological Health ◽  
Smart Devices ◽  
Smart Device ◽  
Negative Effects ◽  
Physical And Psychological Health ◽  
Palestinian Children ◽  
Open Question ◽  
High Degree ◽  
The Relationship ◽  
Descriptive Method

The study aimed to explore the negative effects of using smart devices on the physical and psychological health of children aged (13-16) years from their perspective. The study was applied to a random sample of children aged (13-16), consisting of (102) male and female students. The descriptive method was used to answer the study questions, and a questionnaire was developed to collect data, which contains (3) sections, first section asked about the most used and preferred devices by children aged (13-16) years, and the number of hours the child used the smart device, the second one asked about the negative effects of using the smart devices on the physical and psychological health of children aged (13-16) years from their perspective, and the third section is an open question to know other negative effects of using the smart devices on the physical and psychological health of children aged (13-16) years. The study achieved a set of results, such as the smartphones are the most used and preferred devices by children aged (13-16) years, where (57%) of the study sample preferred to use, and there is  (86.3%) of children aged (13-16) use these devices at average from 4 up to 6 hours daily.  The responders highly agreed upon the negative effects of the use of smart devices on the physical health with average (4.2); which is a high degree, also the responders highly agreed upon the negative effects of  the use of smart devices on the physiological health with average  is  (3.73) which is also high,  added there are other effects caused by the use of smart devices for long hours on  children aged (13-16); the low rate of family discussions, and causes the low writing skills for child.   Depending on the results of the study, the researcher recommends that:  researchers should conduct a correlative study to know the relationship between the effects and the number of hours of daily use of devices; families should rationalize the use of smart devices.

Psychological Space-time Reinforcement Sensitivity Hypothesis & Mental Disorders: From Special to General Relativity Interpretation

2021 ◽  
Vol 19 (4) ◽  
pp. 01-14
Author(s):  
Meriama Hansali Mebarki
Keyword(s):  
General Relativity ◽  
Mental Disorders ◽  
Special Relativity ◽  
Conscious Experience ◽  
Space Time ◽  
The Self ◽  
Psychological Space ◽  
The Past ◽  
Reinforcement Sensitivity ◽  
Spatio Temporal

The reinforcement sensitivity theory lacks basic sources of any human experience :time, place, and learning contexts that have shaped the reinforcement; therefore I have assumed a missing link in Gray's framework based on special relativity relying on the «what, where, and when of happenning»? as major resources of human conscious experience, which under punishment or reward exceed the sensitivity to pleasant or unpleasant stimuli transcending therefore the Weber law, that's why I called it: Psychological Space-Time Reinforcement Sensitivity “PSTRS” axis. The lasts explains BAS and BIS systems sensitivity to reinforcement across the cognitive space-time continuum of episodic memory, and not only across the two great dimensions of fear/anxiety and defensive distance of the McNaughton & Corr model of 2004. So, based on the disruption of the high-sensitivity information processing system in the brain, the four-dimensional conscious experience is distorted by its underlying sources and context. Thus, one of the timedominating records prevents the individual from overcoming the present., such in depression, obsessive compulsive disorder and post-traumatic stress disorder (psychological sensitivity to the past). These temporal records clearly lose their sequence and associative nature in dissociative symptoms due to the disruption of the most important milestone on which Einstein's physics was based. Consequently, psychological space-time reinforcement sensitivity supposes that psychological disorders can be interpreted according to the laws of special relativity (acceleration / deceleration), but this seems more complicated when it comes to mental disorders where the self is disturbed on its spatio-temporal axis as observed in schizophrenia. Schizophrenia looks like a three-componements disorder characterized by a disruption of the experience of time, place and self, which could be asummed up as a “self space-time disturbance". Notably schizophrenic patients appear losing the ability to gather in a dynamic way these componements, as if the world seemed missig the gestalt characteristic or fragmented. The past felt like an inevitable destiny inhibits the direction towards the future; sometimes disorient the self to the point of feeling lost, as if the psychological time slows down to the point of feeling separated from the « now » the physical time. So are we dealing with an Euclidian space? The article attempts to provide a non-traditional interpretation of mental disorders by including general relativity in psychological studies, based on the neurobiological bases involved in the spatio-temporal processing of the conscious experience in the quantum brain.

Turbulent Friction Drag Reduction on Clark-Y Airfoil by Passive Uniform Blowing

AIAA Journal ◽  
2020 ◽  
Vol 58 (9) ◽  
pp. 4178-4180
Author(s):  
Shiho Hirokawa ◽  
Masahiro Ohashi ◽  
Kaoruko Eto ◽  
Koji Fukagata ◽  
Naoko Tokugawa
Keyword(s):  
Drag Reduction ◽  
Friction Drag ◽  
Turbulent Friction ◽  
Friction Drag Reduction

A Mean Flow Model for Polymer and Fiber Turbulent Drag Reduction

2005 ◽  
Vol 15 (6) ◽  
pp. 370-389 ◽  
Author(s):  
Anshuman Roy ◽  
Ronald G. Larson
Keyword(s):  
Drag Reduction ◽  
Weissenberg Number ◽  
Extensional Viscosity ◽  
Mean Flow ◽  
Dimensionless Numbers ◽  
Zero Shear Viscosity ◽  
Mean Velocity ◽  
Fiber Concentration ◽  
Turbulent Drag ◽  
The Mean

Abstract We present a one-parameter model that fits quantitatively the mean velocity profiles from experiments and numerical simulations of drag-reduced wall-bounded flows of dilute solutions of polymers and non-Brownian fibers in the low and modest drag reduction regime. The model is based on a viscous mechanism of drag reduction, in which either extended polymers or non-Brownian fibers increase the extensional viscosity of the fluid and thereby suppress both small and large turbulent eddies and reduce momentum transfer to the wall, resulting in drag reduction. Our model provides a rheological interpretation of the upward parallel shift S+ in the mean velocity profile upon addition of polymer, observed by Virk. We show that Virk’s correlations for the dependence on polymer molecular weight and concentration of the onset wall shear stress and slope increment on the Prandtl-Karman plot can be translated to two dimensionless numbers, namely an onset Weissenberg number and an asymptotic Trouton ratio of maximum extensional viscosity to zero-shear viscosity. We believe that our model, while simple, captures the essential features of drag reduction that are universal to flexible polymers and fibers, and, unlike the Virk phenomenology, can easily be extended to flows with inhomogeneous polymer or fiber concentration fields.

Effect of small flow reversals on aerosol mixing in the alveolar region of the human lung

2004 ◽  
Vol 97 (6) ◽  
pp. 2083-2089 ◽  
Author(s):  
Chantal Darquenne ◽  
G. Kim Prisk
Keyword(s):  
Human Lung ◽  
Sudden Increase ◽  
Residual Volume ◽  
Research Aircraft ◽  
Residual Capacity ◽  
Small Flow ◽  
The One ◽  
High Degree ◽  
Flow Reversals

It has been suggested that irreversibility of alveolar flow combined with a stretched and folded pattern of streamlines can lead to a sudden increase in mixing in the lung. To determine whether this phenomenon is operative in the human lung in vivo, we performed a series of bolus studies with a protocol designed to induce complex folding patterns. Boli of 0.5- and 1-μm-diameter particles were inhaled at penetration volumes (Vp) of 300 and 1,200 ml in eight subjects during short periods of microgravity aboard the National Aeronautics and Space Administration Microgravity Research Aircraft. Inspiration was from residual volume to 1 liter above 1 G functional residual capacity. This was followed by a 10-s breathhold, during which up to seven 100-ml flow reversals (FR) were imposed at Vp = 300 ml and up to four 500-ml FR at Vp = 1,200 ml, and by an expiration to residual volume. Bolus dispersion and deposition were calculated from aerosol concentration and flow rate continuously monitored at the mouth. There was no significant increase in dispersion and deposition with increasing FR except for dispersion between 0 and 7 FR at Vp = 300 ml with 0.5-μm-diameter particles, and this increase was small. This suggested that either the phenomenon of stretch and fold did not occur within the number of FR we performed or that it had already occurred during the one breathing cycle included in the basic maneuver. We speculate that the phenomenon occurred during the basic maneuver, which is consistent with the high degree of dispersion and deposition observed previously in microgravity.

Attitude control of a spacecraft using an extended self-organizing fuzzy logic controller

1987 ◽  
Vol 201 (2) ◽  
pp. 97-106 ◽  
Author(s):  
S Daley ◽  
K F Gill
Keyword(s):  
Fuzzy Logic ◽  
Attitude Control ◽  
Fuzzy Logic Controller ◽  
The Self ◽  
Extended Self ◽  
Simple Method ◽  
Excellent Control ◽  
High Degree ◽  
Self Organizing

A simple method for extending the range of sensitivity of the self-organizing fuzzy logic controller (SOC) is proposed. The performance of the resulting controller is studied through its application to the attitude control of a flexible satellite. It is found that the extended SOC can provide excellent control and also possesses a high degree of robustness.

scholarly journals Influence of the cis/trans configuration on the supramolecular aggregation of aryltriazoles

2019 ◽  
Vol 15 ◽  
pp. 2881-2888
Author(s):  
Sara Tejera ◽  
Giada Caniglia ◽  
Rosa L Dorta ◽  
Andrea Favero ◽  
Javier González-Platas ◽  
...  
Keyword(s):  
Self Assembly ◽  
Bromine Atom ◽  
The Self ◽  
Stacking Interactions ◽  
Aromatic Rings ◽  
X Ray ◽  
High Degree ◽  
Crystal Packings ◽  
Supramolecular Aggregation ◽  
Self Aggregation

The ability of trans- and cis-1,2-glucopyranosyl and cyclohexyl ditriazoles, synthesized by CuAAC "click" chemistry, to form gels was studied, their physical properties determined, and the self-aggregation behavior investigated by SEM, X-ray, and EDC studies. The results revealed that self-assembly was driven mainly by π–π stacking interactions, in addition to hydrogen bonding, with the aromatic rings adopting a high degree of parallelism, as seen in crystal packings and ECD data. Furthermore, π–bromine interactions between the bromine atom of the aryl substituents and the triazole units might also contribute to an overall stabilization of the supramolecular aggregation of bis(4-bromophenyl)triazoles. The trans or cis spatial disposition of the triazole rings is highly important for gelation, with the cis configuration having higher propensity.

An Experimental Investigation of Turbulent Drag Reduction in Concentric Annulus Using Particle Image Velocimetry Technique

2013 ◽  
Author(s):  
Fabio Ernesto Rodriguez Corredor ◽  
Majid Bizhani ◽  
Ergun Kuru
Keyword(s):  
Particle Image Velocimetry ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Particle Image ◽  
Reynolds Shear Stress ◽  
Polymer Concentration ◽  
Mean Flow ◽  
Flow Loop ◽  
Mean Velocity ◽  
Image Velocimetry

Polymer drag reduction is investigated using the Particle Image Velocimetry (PIV) technique in fully developed turbulent flow through a horizontal flow loop with concentric annular geometry (inner to outer pipe radius ratio = 0.4). The polymer used was a commercially available partially hydrolyzed polyacrylamide (PHPA). The polymer concentration was varied from 0.07 to 0.12% V/V. The drag reduction is enhanced by increasing polymer concentration until the concentration reaches an optimum value. After that, the drag reduction is decreased with the increasing polymer concentration. Optimum concentration value of PHPA was found to be around 0.1% V/V. Experiments were conducted at solvent Reynolds numbers of 38700, 46700 and 56400. The percent drag reduction was found to be increasing with the increasing Reynolds number. The study was also focused on analyzing the mean flow and turbulence statistics for fully-turbulent flow using the velocity measurements acquired by PIV. Axial mean velocity profile was found to be following the universal wall law close to the wall (i.e., y+ <10), but it deviated from log law results with an increased slope in the logarithmic zone (i.e., y+ >30). In all cases of polymer application, the viscous sublayer (i.e., y+ <10) thickness was found to be higher than that of the water flow. Reynolds shear stress in the core flow region was found to be decreasing with the increase in polymer concentration.

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