Spontaneous Break of Symmetry in Unconfined Laminar Annular Jets

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Christian Del Taglia ◽  
Alfred Moser ◽  
Lars Blum
Keyword(s):  
Reynolds Number ◽  
Preferential Flow ◽  
Flow Direction ◽  
Blockage Ratio ◽  
Steady Regime ◽  
Single Plane ◽  
Flow Asymmetry ◽  
Annular Jet ◽  
Annular Jets ◽  
Flow Symmetry

Numerical investigations show that the spontaneous break of symmetry in annular incompressible jets occurs in the laminar flow regime and is controlled by both the Reynolds number and the blockage ratio. In the blockage ratio range between 0.50 and 0.89 the transition critical Reynolds number decreases with increasing blockage ratio, according to a defined formula. Transition to asymmetry happens in the steady regime, before the transition to the unsteady flow. Asymmetry is characterized by a preferential flow direction from one side of the jet boundary layer to the diametrically opposite side. The plane of preferential direction passes through the geometry centerline and represents the single plane of flow symmetry. Experiments reported in literature have confirmed the existence of flow asymmetry in an annular jet flow.

Numerical and Experimental Investigation of an Annular Jet Flow With Large Blockage

2004 ◽  
Vol 126 (3) ◽  
pp. 375-384 ◽  
Author(s):  
Christian Del Taglia ◽  
Lars Blum ◽  
Ju¨rg Gass ◽  
Yiannis Ventikos ◽  
Dimos Poulikakos
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Large Scale ◽  
Recirculation Zone ◽  
Blockage Ratio ◽  
Flow Conditions ◽  
Preferential Direction ◽  
Vortical Structures ◽  
Annular Jet ◽  
Unsteady Simulation

Unsteady 3-D numerical simulations and 3-D LDA measurements of an annular jet with a blockage ratio of 0.89 and Reynolds number 4400 are presented. At these flow conditions, the flow inside of the recirculation zone is asymmetric, with a preferential direction. Very good predictions of the velocity fluctuation values are achieved with the unsteady simulation technique in the same region, as the fluctuations are mainly large scale, structure dominated. A frequency near to 10 Hz is identified in the simulations, which is attributed to the principal shedding behavior of the vortical structures.

scholarly journals Simulation of Flexible Fibre Particle Interaction with a Single Cylinder

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 191
Author(s):  
Naser Hamedi ◽  
Lars-Göran Westerberg
Keyword(s):  
Reynolds Number ◽  
Shear Flow ◽  
Fibre Orientation ◽  
Flow Direction ◽  
Particle Interaction ◽  
Orientation Angle ◽  
Factors Affecting ◽  
Single Cylinder ◽  
Flow Past ◽  
Fibre Suspension

In the present study, the flow of a fibre suspension in a channel containing a cylinder was numerically studied for a very low Reynolds number. Further, the model was validated against previous studies by observing the flexible fibres in the shear flow. The model was employed to simulate the rigid, semi-flexible, and fully flexible fibre particle in the flow past a single cylinder. Two different fibre lengths with various flexibilities were applied in the simulations, while the initial orientation angle to the flow direction was changed between 45° ≤ θ ≤ 75°. It was shown that the influence of the fibre orientation was more significant for the larger orientation angle. The results highlighted the influence of several factors affecting the fibre particle in the flow past the cylinder.

scholarly journals Movement of a finite body in channel flow

2016 ◽  
Vol 472 (2191) ◽  
pp. 20160164 ◽  
Author(s):  
Frank T. Smith ◽  
Edward R. Johnson
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Flow Instability ◽  
Flow Direction ◽  
Finite Size ◽  
The Body ◽  
Thin Body ◽  
Shear Stresses ◽  
Unsteady Interaction ◽  
High Reynolds

A body of finite size is moving freely inside, and interacting with, a channel flow. The description of this unsteady interaction for a comparatively dense thin body moving slowly relative to flow at medium-to-high Reynolds number shows that an inviscid core problem with vorticity determines much, but not all, of the dominant response. It is found that the lift induced on a body of length comparable to the channel width leads to differences in flow direction upstream and downstream on the body scale which are smoothed out axially over a longer viscous length scale; the latter directly affects the change in flow directions. The change is such that in any symmetric incident flow the ratio of slopes is found to be cos ⁡ ( π / 7 ) , i.e. approximately 0.900969, independently of Reynolds number, wall shear stresses and velocity profile. The two axial scales determine the evolution of the body and the flow, always yielding instability. This unusual evolution and linear or nonlinear instability mechanism arise outside the conventional range of flow instability and are influenced substantially by the lateral positioning, length and axial velocity of the body.

Pressure Drop Measurements for Air Flow Through Open-Cell Aluminum Foam

2004 ◽  
Author(s):  
Nihad Dukhan ◽  
Angel Alvarez
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Flow Rate ◽  
Aluminum Foam ◽  
Flow Direction ◽  
The Other ◽  
Turbulent Regime ◽  
Thick Sample ◽  
Open Cell ◽  
Two Samples

Wind-tunnel pressure drop measurements for airflow through two samples of forty-pore-per-inch commercially available open-cell aluminum foam were undertaken. Each sample’s cross-sectional area perpendicular to the flow direction measured 10.16 cm by 24.13 cm. The thickness in the flow direction was 10.16 cm for one sample and 5.08 cm for the other. The flow rate ranged from 0.016 to 0.101 m3/s for the thick sample and from 0.025 to 0.134 m3/s for the other. The data were all in the fully turbulent regime. The pressure drop for both samples increased with increasing flow rate and followed a quadratic behavior. The permeability and the inertia coefficient showed some scatter with average values of 4.6 × 10−8 m2 and 2.9 × 10−8 m2, and 0.086 and 0.066 for the thick and the thin samples, respectively. The friction factor decayed with the Reynolds number and was weakly dependent on the Reynolds number for Reynolds number greater than 35.

Integrated reservoir characterization: Beyond tomography

Geophysics ◽  
1995 ◽  
Vol 60 (2) ◽  
pp. 354-364 ◽  
Author(s):  
Larry Lines ◽  
Henry Tan ◽  
Sven Treitel ◽  
John Beck ◽  
Richard Chambers ◽  
...  
Keyword(s):  
History Matching ◽  
Preferential Flow ◽  
Reservoir Characterization ◽  
Seismic Anisotropy ◽  
Flow Direction ◽  
Geophysical Methods ◽  
Reservoir Properties ◽  
Traveltime Tomography ◽  
Sonic Log ◽  
Primary Water

In 1992, there was a collaborative effort in reservoir geophysics involving Amoco, Conoco, Schlumberger, and Stanford University in an attempt to delineate variations in reservoir properties of the Grayburg unit in a West Texas [Formula: see text] pilot at North Cowden Field. Our objective was to go beyond traveltime tomography in characterizing reservoir heterogeneity and flow anisotropy. This effort involved a comprehensive set of measurements to do traveltime tomography, to image reflectors, to analyze channel waves for reservoir continuity, to study shear‐wave splitting for borehole stress‐pattern estimation, and to do seismic anisotropy analysis. All these studies were combined with 3-D surface seismic data and with sonic log interpretation. The results are to be validated in the future with cores and engineering data by history matching of primary, water, and [Formula: see text] injection performance. The implementation of these procedures should provide critical information on reservoir heterogeneities and preferential flow direction. Geophysical methods generally indicated a continuous reservoir zone between wells.

Wall Normal Jet Produced by DBD Plasma Actuator With Doughnut-Shaped Electrode

2008 ◽  
Author(s):  
Takehiko Segawa ◽  
Hiro Yoshida ◽  
Shinya Takekawa ◽  
Timothy Jukes ◽  
Kwing-So Choi
Keyword(s):  
Atmospheric Pressure ◽  
Room Temperature ◽  
Particle Image ◽  
Barrier Discharge ◽  
Plasma Actuator ◽  
Dbd Plasma ◽  
Annular Jet ◽  
Image Velocimetry ◽  
Inner Diameter ◽  
Annular Jets

Properties of coaxial annular jets produced by a dielectric barrier discharge (DBD) plasma actuator with a doughnut shaped electrodes were investigated under atmospheric pressure and room temperature. The actuator consists of two circular electrodes sandwiching a thin dielectric layer. By applying 0 – ±3.3 kV between the electrodes at radio frequencies, the plasma jet is formed near the inner edge of the top electrode. The radial jet runs toward the center of the electrode and then impinges at the center to generate a wall normal annular jet. The evolution of the wall normal jet was observed precisely using particle image velocimetry (PIV) system. It was found that characteristic velocities increase in proportion to the bursting frequency and inversely proportional to the inner diameter of the electrode at the surging time of the voltage at 5.0 × 10−6sec.

scholarly journals Cavitation Inception in Spool Valves

1981 ◽  
Vol 103 (4) ◽  
pp. 564-575 ◽  
Author(s):  
C. Samuel Martin ◽  
H. Medlarz ◽  
D. C. Wiggert ◽  
C. Brennen
Keyword(s):  
Reynolds Number ◽  
Hydraulic Systems ◽  
Cavitation Inception ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Annular Jet ◽  
Directional Control ◽  
Valve Opening ◽  
Response Pressure ◽  
Spool Valves

Cavitation has been investigated in directional control valves in order to identify damage mechanisms characteristic of components of aircraft hydraulic systems. Tests have been conducted in a representative metal spool valve and in a model three times larger. Data taken under noncavitating conditions with both valves showed that the position of the high-velocity annular jet shifts orientation, depending upon valve opening and Reynolds number. By means of high-frequency response pressure transducers strategically placed in the valve chamber cavitation could be sensed by the correlation of noise with a cavitation index. The onset of cavitation can be detected by comparing energy spectra for a fixed valve opening and a constant discharge. Another sensitive indicator of cavitation inception is the ratio of cavitating to noncavitating spectral densities. The incipient cavitation number as defined in this investigation is correlated with the Reynolds number for both valves.

Heat Transfer Enhancements in Rotating Two-Pass Coolant Channels With Profiled Ribs: Part 2—Detailed Measurements

2000 ◽  
Vol 123 (1) ◽  
pp. 107-114 ◽  
Author(s):  
D. E. Nikitopoulos ◽  
V. Eliades ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Mass Transfer ◽  
Blockage Ratio ◽  
Average Heat ◽  
Rotation Numbers ◽  
Naphthalene Sublimation ◽  
Side Walls ◽  
Made In

Detailed heat/mass transfer distributions are presented inside a two-pass rotating ribbed coolant channel for two profiled-rib configurations. Several profiled-rib configurations have been studied (Acharya et al., 2000), and it was found that the best performance was achieved by saw-tooth ribs, and a pyramid–valley rib combination. The profiled ribs were placed directly opposite to each other on the leading and trailing surfaces. Smooth side walls were used in all the experiments. Heat transfer measurements were compared with straight ribs of equal blockage ratio. The measurements were made in a two-pass rotating facility using the naphthalene sublimation mass transfer technique, which provides highly resolved surface distributions. The results presented are for a Reynolds number of 30,000, two rotation numbers (0 and 0.3), and include average heat/mass transfer over the entire inter-rib module as well as detailed heat/mass transfer contours for two profiled-rib cases. Significant enhancement of up to 25 percent in heat/mass transfer was obtained with the pyramid–valley and saw-tooth shaped ribs under rotating conditions.

VIV Response and Drag Measurements of Circular Cylinders Fitted With Permeable Meshes

2015 ◽  
Author(s):  
Murilo M. Cicolin ◽  
Gustavo R. S. Assi
Keyword(s):  
Reynolds Number ◽  
Long Range ◽  
Flow Direction ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Peak Response ◽  
Vortex Induced Vibrations ◽  
Different Types ◽  
Cylindrical Tubes ◽  
Low Mass

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of amplitude of vibration and drag force are presented for models with low mass and damping which are free to respond in the cross-flow direction. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the peak response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. All the three meshes have increased drag when compared with that of the bare cylinder. Reynolds number ranged from 5,000 to 25,000 and reduced velocity was varied between 2 and 15.

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