scholarly journals Plasma Flows in Solar Filaments as Electromagnetically Driven Vortical Flows

Physics ◽  
2021 ◽  
Vol 3 (4) ◽  
pp. 1046-1050
Author(s):  
Yuri E. Litvinenko
Keyword(s):  
Reynolds Numbers ◽  
Flow Speed ◽  
The Body ◽  
Exact Analytical Solutions ◽  
Electric And Magnetic Fields ◽  
Solar Filaments ◽  
Archimedean Force ◽  
Streaming Flows ◽  
Plasma Flow Speed ◽  
Scaling Arguments

Electromagnetic expulsion acts on a body suspended in a conducting fluid or plasma, which is subject to the influence of electric and magnetic fields. Physically, the effect is a magnetohydrodynamic analogue of the buoyancy (Archimedean) force, which is caused by the nonequal electric conductivities inside and outside the body. It is suggested that electromagnetic expulsion can drive the observed plasma counter-streaming flows in solar filaments. Exact analytical solutions and scaling arguments for a characteristic plasma flow speed are reviewed, and their applicability in the limit of large magnetic Reynolds numbers, relevant in the solar corona, is discussed.

scholarly journals Fish larvae exploit edge vortices along their dorsal and ventral fin folds to propel themselves

2016 ◽  
Vol 13 (116) ◽  
pp. 20160068 ◽  
Author(s):  
Gen Li ◽  
Ulrike K. Müller ◽  
Johan L. van Leeuwen ◽  
Hao Liu
Keyword(s):  
Larval Fish ◽  
Fish Larvae ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Bony Fish ◽  
The Body ◽  
Functional Explanation ◽  
Image Velocimetry ◽  
Median Fins

Larvae of bony fish swim in the intermediate Reynolds number ( Re ) regime, using body- and caudal-fin undulation to propel themselves. They share a median fin fold that transforms into separate median fins as they grow into juveniles. The fin fold was suggested to be an adaption for locomotion in the intermediate Reynolds regime, but its fluid-dynamic role is still enigmatic. Using three-dimensional fluid-dynamic computations, we quantified the swimming trajectory from body-shape changes during cyclic swimming of larval fish. We predicted unsteady vortices around the upper and lower edges of the fin fold, and identified similar vortices around real larvae with particle image velocimetry. We show that thrust contributions on the body peak adjacent to the upper and lower edges of the fin fold where large left–right pressure differences occur in concert with the periodical generation and shedding of edge vortices. The fin fold enhances effective flow separation and drag-based thrust. Along the body, net thrust is generated in multiple zones posterior to the centre of mass. Counterfactual simulations exploring the effect of having a fin fold across a range of Reynolds numbers show that the fin fold helps larvae achieve high swimming speeds, yet requires high power. We conclude that propulsion in larval fish partly relies on unsteady high-intensity vortices along the upper and lower edges of the fin fold, providing a functional explanation for the omnipresence of the fin fold in bony-fish larvae.

Application of PLC in the Expressway Intelligent Traffic Control System

2013 ◽  
Vol 361-363 ◽  
pp. 2219-2223
Author(s):  
Xin Hua Wei ◽  
Xian Xing Duan ◽  
Xiao Kan Wang
Keyword(s):  
Control System ◽  
Traffic Control ◽  
Flow Speed ◽  
The Body ◽  
Host Computer ◽  
Scientific Management ◽  
Traffic Lights ◽  
Traffic Control System ◽  
Vehicle Size ◽  
Sense Coil

The expressway intelligent traffic control system based on S7-200 series Programmable Logic Controller (PLC) was introduced in this paper.PLC has strong adaptability in the complex environment and rich internal timer resources, it is easily to realize accuracy controlling the traffic lights, specially for multi-crossroads.PLC analyzed and processed the signals of the body flow, speed, vehicle size and other data by the sense coil, then transmitting the information to the host computer. The host computer might automatically adjust the length of time from the final signal to achieve intelligent scientific management of traffic lights.

Locomotion in scombrid fishes: visualization of flow around the caudal peduncle and finlets of the chub mackerel Scomber japonicus

2001 ◽  
Vol 204 (13) ◽  
pp. 2251-2263 ◽  
Author(s):  
Jennifer C. Nauen ◽  
George V. Lauder
Keyword(s):  
Laser Light ◽  
Light Sheet ◽  
Flow Speed ◽  
The Body ◽  
Scomber Japonicus ◽  
Laser Light Sheet ◽  
Chub Mackerel ◽  
Caudal Peduncle ◽  
Local Flow ◽  
Scombrid Fishes

SUMMARY Scombrid fishes are known for high-performance locomotion; however, few data are available on scombrid locomotor hydrodynamics. In this paper, we present flow visualization data on patterns of water movement over the caudal peduncle and finlets (small fins on the dorsal and ventral body margin anterior to the caudal fin). Chub mackerel, Scomber japonicus, ranging in fork length from 20 to 26 cm, swam steadily at 1.2forklengthss−1 in a recirculating flow tank. Small, reflective particles in the flow tank were illuminated by a vertical (xy) or horizontal (xz) laser light sheet. Patterns of flow in the region near the caudal peduncle were measured using digital particle image velocimetry. Patterns of flow along the peduncle and finlets were quantified using manual particle tracking; more than 800 particles were tracked for at least 12ms over a series of tailbeats from each of four fish. In the vertical plane, flow trajectory and flow speed were independent of the position of the finlets, indicating that the finlets did not redirect flow or affect flow speed. Along, above and below the trailing surface of the peduncle, where the finlets were oriented along the peduncular surface, flow was convergent. Along, above and below the leading surface of the peduncle, where the finlets were absent, the flow trajectory was effectively horizontal. The lack of divergent flow on the leading surface of the peduncle is consistent with cross-peduncular flow formed by the lateral motion of the peduncle interacting with convergent flow resulting from forward movement of the body. In the horizontal plane, particles illuminated by the xz light sheet situated approximately 3 mm below the ventral body surface were tracked within the laser light sheet for up to 40ms, indicating strong planar flow. As the peduncle decelerates, the most posterior finlet is frequently at an angle of attack of at least 20° to the incident flow, but this orientation does not result in thrust production from lift generation. Finlet 5 does redirect cross-peduncular flow and probably generates small vortices undetectable in this study. These data are the first direct demonstration that the finlets have a hydrodynamic effect on local flow during steady swimming.

Empirical Estimates of Body Drag of Large Waterfowl and Raptors

1988 ◽  
Vol 135 (1) ◽  
pp. 253-264 ◽  
Author(s):  
C. J. PENNYCUICK ◽  
HOLLIDAY H. OBRECHT ◽  
MARK R. FULLER
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
The Body ◽  
Number Range ◽  
Empirical Estimates ◽  
A Value ◽  
Body Drag ◽  
Wind Tunnel Measurements ◽  
Large Living ◽  
Performance Estimates

To whom reprint requests should be addressed. Measurements of the body frontal area of some large living waterfowl (Anatidae) and raptors (Falconiformes) were found to vary with the two-thirds power of the body mass, with no distinction between the two groups. Wind tunnel measurements on frozen bodies gave drag coefficients ranging from 0.25 to 0.39, in the Reynolds number range 145 000 to 462 000. Combining these observations with those of Prior (1984), which extended to lower Reynolds numbers, a practical rule is proposed for choosing a value of the body drag coefficient for use in performance estimates.

scholarly journals Stabilisation and drag reduction of pipe flows by flattening the base profile

2019 ◽  
Vol 863 ◽  
pp. 850-875 ◽  
Author(s):  
Elena Marensi ◽  
Ashley P. Willis ◽  
Rich R. Kerswell
Keyword(s):  
Drag Reduction ◽  
Nonlinear Stability ◽  
Pipe Flow ◽  
Body Force ◽  
Initial Conditions ◽  
Reynolds Numbers ◽  
Streamwise Velocity ◽  
The Body ◽  
Random Disturbance ◽  
Good Proxy

Recent experimental observations (Kühnen et al., Nat. Phys., vol. 14, 2018b, pp. 386–390) have shown that flattening a turbulent streamwise velocity profile in pipe flow destabilises the turbulence so that the flow relaminarises. We show that a similar phenomenon exists for laminar pipe flow profiles in the sense that the nonlinear stability of the laminar state is enhanced as the profile becomes more flattened. The flattening of the laminar base profile is produced by an artificial localised body force designed to mimic an obstacle used in the experiments of Kühnen et al. (Flow Turbul. Combust., vol. 100, 2018a, pp. 919–943) and the nonlinear stability measured by the size of the energy of the initial perturbations needed to trigger transition. Significant drag reduction is also observed for the turbulent flow when triggered by sufficiently large disturbances. In order to make the nonlinear stability computations more efficient, we examine how indicative the minimal seed – the disturbance of smallest energy for transition – is in measuring transition thresholds. We first show that the minimal seed is relatively robust to base profile changes and spectral filtering. We then compare the (unforced) transition behaviour of the minimal seed with several forms of randomised initial conditions in the range of Reynolds numbers $Re=2400$–$10\,000$ and find that the energy of the minimal seed after the Orr and oblique phases of its evolution is close to that of a critical localised random disturbance. In this sense, the minimal seed at the end of the oblique phase can be regarded as a good proxy for typical disturbances (here taken to be the localised random ones) and is thus used as initial condition in the simulations with the body force. The enhanced nonlinear stability and drag reduction predicted in the present study are an encouraging first step in modelling the experiments of Kühnen et al. and should motivate future developments to fully exploit the benefits of this promising direction for flow control.

Stability and dynamics of the laminar wake past a slender blunt-based axisymmetric body

2011 ◽  
Vol 676 ◽  
pp. 110-144 ◽  
Author(s):  
P. BOHORQUEZ ◽  
E. SANMIGUEL-ROJAS ◽  
A. SEVILLA ◽  
J. I. JIMÉNEZ-GONZÁLEZ ◽  
C. MARTÍNEZ-BAZÁN
Keyword(s):  
Stability Analysis ◽  
Numerical Simulations ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Velocity Ratio ◽  
Reynolds Numbers ◽  
Base Flow ◽  
Direct Numerical Simulations ◽  
The Body ◽  
Stream Velocity

We investigate the stability properties and flow regimes of laminar wakes behind slender cylindrical bodies, of diameter D and length L, with a blunt trailing edge at zero angle of attack, combining experiments, direct numerical simulations and local/global linear stability analyses. It has been found that the flow field is steady and axisymmetric for Reynolds numbers below a critical value, Recs (L/D), which depends on the length-to-diameter ratio of the body, L/D. However, in the range of Reynolds numbers Recs(L/D) < Re < Reco(L/D), although the flow is still steady, it is no longer axisymmetric but exhibits planar symmetry. Finally, for Re > Reco, the flow becomes unsteady due to a second oscillatory bifurcation which preserves the reflectional symmetry. In addition, as the Reynolds number increases, we report a new flow regime, characterized by the presence of a secondary, low frequency oscillation while keeping the reflectional symmetry. The results reported indicate that a global linear stability analysis is adequate to predict the first bifurcation, thereby providing values of Recs nearly identical to those given by the corresponding numerical simulations. On the other hand, experiments and direct numerical simulations give similar values of Reco for the second, oscillatory bifurcation, which are however overestimated by the linear stability analysis due to the use of an axisymmetric base flow. It is also shown that both bifurcations can be stabilized by injecting a certain amount of fluid through the base of the body, quantified here as the bleed-to-free-stream velocity ratio, Cb = Wb/W∞.

Distributed Flow Sensing Using Bayesian Estimation for a Flexible Fish Robot

2015 ◽  
Author(s):  
Feitian Zhang ◽  
Francis D. Lagor ◽  
Derrick Yeo ◽  
Patrick Washington ◽  
Derek A. Paley
Keyword(s):  
Flow Model ◽  
Pressure Sensors ◽  
Estimation Algorithm ◽  
Flow Speed ◽  
The Body ◽  
Fish Robot ◽  
Flow Estimation ◽  
Flow Sensing ◽  
Time Flow ◽  
Recursive Bayesian Filter

Flexibility plays an important role in fish behaviors by enabling high maneuverability for predator avoidance and swimming in turbulence. In this paper, we present a novel, flexible fish robot equipped with distributed pressure sensors for flow sensing. The body of the robot is made of a soft, hyperelastic material that provides flexibility. The fish robot features a Joukowski-foil shape conducive to modeling the fluid analytically. A quasisteady potential-flow model is adopted for real-time flow estimation, whereas a discrete-time vortex-shedding flow model is used for higher-fidelity simulation. The dynamics for the flexible fish robot are presented, and a reduced model for one-dimensional swimming is derived. A recursive Bayesian filter assimilates pressure measurements for estimating the flow speed, angle of attack, and foil camber. Simulation and experimental results are presented to show the effectiveness of the flow estimation algorithm.

Strut Interference Effects on Pitot Tube Velocity Measurements

2007 ◽  
Author(s):  
Sandra K. S. Boetcher ◽  
Ephraim M. Sparrow
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
The Body ◽  
Pitot Tube ◽  
Velocity Measurements ◽  
Measuring Device ◽  
Number Range ◽  
Low Reynolds Numbers ◽  
Velocity Measuring ◽  
The Impact

The possible impact of the presence of the strut portion of a Pitot tube on the efficacy of the tube as a velocity-measuring device has been evaluated by numerical simulation. At sufficiently low Reynolds numbers, there is a possibility that the precursive effects of the strut could alter the flow field adjacent to the static taps on the body of the Pitot tube and might even affect the impact pressure measured at the nose. The simulations were performed in dimensionless form with the Reynolds number being the only prescribed parameter, but the dimensions were taken from a short-shanked Pitot tube. Over the Reynolds number range from 1500 to 4000, a slight effect of the strut was identified. However, the variation due to the presence of the shank of the velocity measured by the Pitot tube operating in that range of Reynolds numbers was only 1.5%.

scholarly journals Dynamics of Attached Cavities on Bodies of Revolution

1992 ◽  
Vol 114 (1) ◽  
pp. 93-99 ◽  
Author(s):  
S. L. Ceccio ◽  
C. E. Brennen
Keyword(s):  
Reynolds Numbers ◽  
Cavitation Number ◽  
The Body ◽  
Cavity Surface ◽  
Bodies Of Revolution ◽  
The Mean ◽  
Cavity Thickness ◽  
Cavity Closure ◽  
Axisymmetric Bodies ◽  
Single Cavity

Attached cavitation was generated on two axisymmetric bodies, a Schiebe body and a modified ellipsoidal body (the I. T. T. C. body), both with a 50.8 mm diameter. Tests were conducted for a range of cavitation numbers and for Reynolds numbers in the range of Re = 4.4 × 105 to 4.8 × 105. Partially stable cavities were observed. The steady and dynamic volume fluctuations of the cavities were recorded through measurements of the local fluid impedance near the cavitating surface suing a series of flush mounted electrodes. These data were combined with photographic observations. On the Schiebe body, the cavitation was observed to form a series of incipient spot cavities which developed into a single cavity as the cavitation number was lowered. The incipient cavities were observed to fluctuate at distinct frequencies. Cavities on the I. T. T. C. started as a single patch on the upper surface of the body which grew to envelope the entire circumference of the body as the cavitation number was lowered. These cavities also fluctuated at distinct frequencies associated with oscillations of the cavity closure region. The cavities fluctuated with Strouhal numbers (based on the mean cavity thickness) in the range of St = 0.002 to 0.02, which are approximately one tenth the value of Strouhal numbers associated with Ka´rma´n vortex shedding. The fluctuation of these stabilized partial cavities may be related to periodic break off and filling in the cavity closure region and to periodic entrainment of the cavity vapor. Cavities on both headforms exhibited surface striations in the streamwise direction near the point of cavity formation, and a frothy mixture of vapor and liquid was detected under the turbulent cavity surface. As the cavities became fully developed, the signal generated by the frothy mixture increased in magnitude with frequencies in the range of 0 to 50 Hz.

scholarly journals Feedback control of unstable flows: a direct modelling approach using the Eigensystem Realisation Algorithm

2016 ◽  
Vol 793 ◽  
pp. 41-78 ◽  
Author(s):  
Thibault L. B. Flinois ◽  
Aimee S. Morgans
Keyword(s):  
Robust Control ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Open Loop ◽  
The Body ◽  
Nonlinear Flow ◽  
Balanced Truncation ◽  
Unstable Flow ◽  
Feedback Controllers ◽  
Modelling Approach

Obtaining low-order models for unstable flows in a systematic and computationally tractable manner has been a long-standing challenge. In this study, we show that the Eigensystem Realisation Algorithm (ERA) can be applied directly to unstable flows, and that the resulting models can be used to design robust stabilising feedback controllers. We consider the unstable flow around a D-shaped body, equipped with body-mounted actuators, and sensors located either in the wake or on the base of the body. A linear model is first obtained using approximate balanced truncation. It is then shown that it is straightforward and justified to obtain models for unstable flows by directly applying the ERA to the open-loop impulse response. We show that such models can also be obtained from the response of the nonlinear flow to a small impulse. Using robust control tools, the models are used to design and implement both proportional and $\mathscr{H}_{\infty }$ loop-shaping controllers. The designed controllers were found to be robust enough to stabilise the wake, even from the nonlinear vortex shedding state and in some cases at off-design Reynolds numbers.

Sign in / Sign up

Export Citation Format

Share Document