Evolution and Turbulence Properties of Self-Sustained Transversely Oscillating Flow Induced by Fluidic Oscillator

2007 ◽  
Vol 129 (8) ◽  
pp. 1038-1047 ◽  
Author(s):  
Rong Fung Huang ◽  
Kuo Tong Chang
Keyword(s):  
Stagnation Point ◽  
Vortex Pair ◽  
Transverse Oscillation ◽  
Oscillating Flow ◽  
Near Wake ◽  
Fluidic Oscillator ◽  
Planar Jet ◽  
Oscillation Process ◽  
Gravity Driven ◽  
Flow Evolution

The evolution process and turbulence properties of a transversely oscillating flow induced by a fluidic oscillator are studied in a gravity-driven water tunnel. A planar jet is guided to impinge a specially designed crescent surface of a target blockage that is enclosed in a cavity of a fluidic oscillator. The geometric configuration of the cavity transforms the inherent stability characteristics of the jet from convective instability to absolute instability, so that the jet precedes the persistent back and forth swinging in the cavity. The swinging jet is subsequently directed through two passages and issued alternatively out of the fluidic oscillator. Two short plates are installed near the exits of the alternatively issuing pulsatile jets to deflect the jets toward the central axis. The deflected jets impinge with each other and form a pair of counter-rotating vortices in the near wake of the oscillator with a stagnation point at the impingement point. The stagnation point of the counter-rotating vortex pair moves back and forth transversely because of the phase difference existing between the two issued jets. The merged flow evolving from the counter-rotating vortices formed by the impingement of the two pulsatile jets therefore presents complex behavior of transverse oscillation. The topological models corresponding to the flow evolution are constructed to illustrate the oscillation process of the oscillating flow. Significant momentum dispersion and large turbulence intensity are induced by the transverse oscillation of the merged flow. The statistical turbulence properties show that the Lagrangian integral time and length scales of the turbulence eddies (the fine-scale structure) produced in the oscillating flow are drastically reduced.

scholarly journals NUMERICAL MODELLING OF OSCILLATING FLOW FOR ENERGY HARVESTING

2021 ◽  
Vol 2021 (6) ◽  
pp. 5360-5365
Author(s):  
TOMAS BLEJCHAR ◽  
◽  
SYLVA DRABKOVA ◽  
VACLAV JANUS ◽  
◽  
...  
Keyword(s):  
Flow Rate ◽  
Volume Flow Rate ◽  
Electrical Energy ◽  
Maximum Energy ◽  
Oscillating Flow ◽  
Cfd Simulations ◽  
Fluidic Oscillator ◽  
Microelectronic Devices ◽  
Piezoelectric Elements ◽  
New Generation

The energy efficiency of systems, equipment, and sensors is nowadays intensively studied. The new generation of microelectronic sensors is very sophisticated and the energy consumption is in the microwatts range. The energy to power the microelectronic devices can be harvested from oscillating flow in small size channels and so replaceable batteries could be eliminated. Piezoelectric elements can convert energy from oscillation to electrical energy. This paper focuses on the simulation of periodic flow in the fluidic oscillator. CFD simulations were performed for several values of the flow rate. Experimental measurement was carried out under the same conditions as the CFD experiment. The main monitored and evaluated parameters were volume flow rate and pressure loss. Fluid oscillations were analysed based on CFD simulations and the theoretical maximum energy available for the deformation of piezoelectric elements and transformable into electrical energy was evaluated.

Cavitation in Co-Rotating Tip Vortices

2019 ◽  
Author(s):  
J. J. Koncoski ◽  
M. H. Krane ◽  
J. P. Welz ◽  
D. R. Hanson ◽  
S. M. Willits ◽  
...  
Keyword(s):  
Rapid Prototype ◽  
Vortex Pair ◽  
Near Wake ◽  
Vortex System ◽  
Trailing Edge ◽  
Tip Vortices ◽  
Cavitation Inception ◽  
Flow Characterization ◽  
Strong Vortex ◽  
Surface Discontinuities

Abstract This work documents flow characterization and cavitation inception of a co-rotating vortex pair shed from a single fin with a rounded tip at zero angle of attack. The fin was outfitted with a removable tip fabricated using a rapid prototype method. The co-rotating vortices result from surface discontinuities on the removable tip, near a hard wax fairing used to cover the tip attachment bolt. The vortices are shed at different locations along the chord. Flow visualization by oil paint and developed cavitation, and SPIV of the near-wake, indicate that a strong vortex is shed at the trailing edge, while a weaker vortex is shed at 82% chord. Horizontal wandering of the vortices is uncorrelated. Vertical wandering of the vortices is characterized by opposing oscillations about their mutual center. Acoustic cavitation inception in the water tunnel environment is discerned at an index 13% greater than visual detection of cavitation, and occurs within one chord of the trailing edge. The influence of the co-rotating vortex system on cavitation inception must be determined from comparison with measurements of a solitary vortex generated by analogous geometry.

Radial Deformation Frequency Effect on the Three-Dimensional Flow in the Cylinder Wake

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Mohamed Aissa ◽  
Ahcène Bouabdallah ◽  
Hamid Oualli
Keyword(s):  
Circular Cylinder ◽  
Three Dimensional ◽  
Frequency Effect ◽  
Radial Deformation ◽  
Cylinder Wake ◽  
Near Wake ◽  
Flow Evolution ◽  
Computational Fluid Dynamics Cfd ◽  
Vortex Shedding Frequency ◽  
Forces Behavior

In the current paper, the three-dimensional air flow evolution around a circular cylinder is studied. The main aim is to control the flow field upstream and downstream of a circular cylinder by means of radial deformation. Within a particular step, one focuses on the response of the topological structures, which is developing in the cylinder near wake to applied pulsatile motion. Furthermore, a special care is considered to the aerodynamics forces behavior in adjusting the applied controlling strategy. The used controlling frequency range extends from f = 1fn = 17 Hz to f = 6fn = 102.21 Hz, which corresponds to a series of multiharmonic frequency varying from one to six times the natural vortex shedding frequency (VSF) in none forced wake. Throughout this work, the forcing amplitude is fixed at 16% of cylinder diameter and the Reynolds number as Re = 550. Through Fluent computational fluid dynamics (CFD) code and Matlab simulations, the obtained results showed a good accordance with the calculated ones.

A Quantitative Comparison of Delta Wing Vortices in the Near-Wake For Incompressible and Supersonic Free Streams

2005 ◽  
Vol 127 (6) ◽  
pp. 1071-1084 ◽  
Author(s):  
Frank Y. Wang ◽  
Ivana M. Milanovic ◽  
Khairul B. M. Q. Zaman ◽  
Louis A. Povinelli
Keyword(s):  
Incompressible Flow ◽  
Axial Velocity ◽  
High Speed ◽  
Delta Wing ◽  
Vortex Pair ◽  
Pressure Probe ◽  
Spanwise Direction ◽  
Near Wake ◽  
Low Speed ◽  
Axis Switching

When requiring quantitative data on delta wing vortices for design purposes, low-speed results have often been extrapolated to configurations intended for supersonic operation. This practice stems from a lack of database in high-speed flows due to measurement difficulties. In the present paper an attempt is made to examine this practice by comparing data from an incompressible flow experiment designed specifically to correspond to an earlier experiment in supersonic flows. The comparison is made for a 75° sweptback delta wing at angles of attack of 7° and 12°. For the incompressible flow, detailed flow-field properties including vorticity and turbulence characteristics are obtained by hot-wire and pressure probe surveys. The results are compared, wherever possible, with available data from the earlier Mach 2.49 experiment. The results indicate that quantitative similarities exist in the distributions of total pressure and swirl velocities. Qualitative similarities also exist in other properties, however, many differences are observed. The vortex core is smaller and rounded at low speed. At high speed, it is elongated in the spanwise direction near the trailing edge but goes through “axis switching” within a short distance downstream. The vortex is located farther outboard, i.e., the spacing between the two legs of the vortex pair is larger, at low speed. The axial velocity distribution within the core is significantly different in the two flow regimes. A “jet-like” profile, observed at low speed, either disappears or becomes “wake-like” at high speed. The axial velocity characteristics are examined in the light of an analytical model.

Flow meter based on the trapped vortex pair fluidic oscillator

1989 ◽  
Vol 60 (5) ◽  
pp. 935-938 ◽  
Author(s):  
Hussein Mansy ◽  
David R. Williams
Keyword(s):  
Vortex Pair ◽  
Flow Meter ◽  
Fluidic Oscillator ◽  
Trapped Vortex

Contrails and aircraft downwash

1970 ◽  
Vol 43 (3) ◽  
pp. 451-464 ◽  
Author(s):  
R. S. Scorer ◽  
L. J. Davenport
Keyword(s):  
Flow Pattern ◽  
Stagnation Point ◽  
Vortex Core ◽  
Vortex Pair ◽  
Tip Vortices ◽  
The Core ◽  
Wing Tip ◽  
Mixed Fluid

Aircraft downwash consists initially of a vortex pair descending with its accompanying fluid through the atmosphere. Condensation trails are formed in exhaust emitted into the accompanying fluid and the shapes of them and their evolution depend on the positions of the engines in relation to the wing tip vortices.The atmosphere is stably stratified and so the descending accompanying fluid acquires upward buoyancy. Consequently vorticity is generated at the outside of the accompanying fluid and the flow pattern in the vortex pair is altered so as to produce detrainment of its exterior part. So long as any air which is a mixture of accompanying fluid and exterior air is detrained, the vortices remain stable, but the width of the pair decreases and its downward velocity increases with time as a result of the buoyancy. Eventually the upper stagnation point in the motion relative to the vortices begins to move upwards relative to the vortices so that some mixed fluid is entrained into the circulation and the vortices immediately become unstable, mixing occurs, the pressure in the core rises, and any vortex core trails that may exist appear to burst.The motion produces downward-thrust blobs in trails from centrally placed engines, which correspond to the holes sometimes seen in cloud when distrails are formed.

Rear stagnation point location in a subsonic near-wake

1976 ◽  
Vol 13 (5) ◽  
pp. 319-320 ◽  
Author(s):  
R. A. Merz ◽  
R. H. Page ◽  
C. E. G. Przirembel
Keyword(s):  
Stagnation Point ◽  
Point Location ◽  
Near Wake ◽  
Rear Stagnation Point

scholarly journals Observation of the Development of Secondary Features in a Richtmyer–Meshkov Instability Driven Flow

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Tennille Bernard ◽  
C. Randall Truman ◽  
Peter Vorobieff ◽  
Clint Corbin ◽  
Patrick J. Wayne ◽  
...  
Keyword(s):  
Experimental Studies ◽  
Vortex Pair ◽  
Shock Acceleration ◽  
Shock Focusing ◽  
Planar Shock ◽  
Gravity Driven ◽  
The Subject ◽  
Counter Rotating Vortex Pair ◽  
Heavy Gas ◽  
Gaseous Tracer

Richtmyer–Meshkov instability (RMI) has long been the subject of interest for analytical, numerical, and experimental studies. In comparing results of experiment with numerics, it is important to understand the limitations of experimental techniques inherent in the chosen method(s) of data acquisition. We discuss results of an experiment where a laminar, gravity-driven column of heavy gas is injected into surrounding light gas and accelerated by a planar shock. A popular and well-studied method of flow visualization (using glycol droplet tracers) does not produce a flow pattern that matches the numerical model of the same conditions, while revealing the primary feature of the flow developing after shock acceleration: the pair of counter-rotating vortex columns. However, visualization using fluorescent gaseous tracer confirms the presence of features suggested by the numerics; in particular, a central spike formed due to shock focusing in the heavy-gas column. Moreover, the streamwise growth rate of the spike appears to exhibit the same scaling with Mach number as that of the counter-rotating vortex pair (CRVP).

On the singular points in the laminar two-dimensional near wake flow field

1968 ◽  
Vol 33 (1) ◽  
pp. 39-63 ◽  
Author(s):  
Sheldon Weinbaum
Keyword(s):  
Stagnation Point ◽  
Series Solution ◽  
Wake Flow ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Near Wake ◽  
Type Series ◽  
Stagnation Points ◽  
Insight Into ◽  
Rear Stagnation Point

It is shown that useful information concerning the flow in the neighbourhood of the various separation and stagnation points in the laminar near wake of a blunt-based two-dimensional wedge can be learned from the locally valid Stokes type series solutions to the incompressible Navier-Stokes vorticity equation derived previously by Dean & Montagnon (1949) and Moffatt (1964). This theory, which is in qualitative agreement with the experiments of Hama (1967) and Donaldson (1967), shows that the flow separates from the base of a blunt-based body and not from its trailing edge. The series solution for the two-dimensional stagnation point is treated in detail and compared with Howarth's (1934) numerical solution in order to study the convergence and conditions for completeness of the Stokes type series solution. Finally, the wake rear stagnation point is examined to provide insight into the problem of wake closure.

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