scholarly journals The interaction between rotationally oscillating spheres and solid boundaries in a Stokes flow

2018 ◽  
Vol 849 ◽  
pp. 834-859 ◽  
Author(s):  
F. Box ◽  
K. Singh ◽  
T. Mullin
Keyword(s):  
Viscous Fluid ◽  
Standing Wave ◽  
Radial Distance ◽  
Separation Distance ◽  
Viscous Resistance ◽  
Rotational Axis ◽  
Phase Lag ◽  
Angular Oscillations ◽  
Oscillating Plate ◽  
Oscillating Sphere

We present the results of an experimental and theoretical investigation into the influence of proximate boundaries on the motion of an rotationally oscillating sphere in a viscous fluid. The angular oscillations of the sphere are controlled using the magnetic torque generated by a spatially uniform, oscillatory magnetic field which interacts with a small magnet embedded within the sphere. We study the motion of the sphere in the vicinity of stationary walls that are parallel and perpendicular to the rotational axis of the sphere, and near a second passive sphere that is non-magnetic and free to move. We find that rigid boundaries introduce viscous resistance to motion that acts to suppress the oscillations of the driven sphere. The amount of viscous resistance depends on the orientation of the wall with respect to the axis of rotation of the oscillating sphere. A passive sphere also introduces viscous resistance to motion, but for this case the rotational oscillations of the active sphere establish a standing wave that imparts vorticity to the fluid and induces oscillations of the passive sphere. The standing wave is analogous to the case of an oscillating plate in a viscous fluid; the amplitude of the wave decays exponentially with radial distance from the surface of the oscillating sphere. The standing wave introduces a phase lag between the motion of the active sphere and the response of the passive sphere which increases linearly with separation distance.

Effect of the Separation Distance on the Aeroacoustic Source of Multiple Shallow Cavities

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Ayman A. Shaaban ◽  
Samir Ziada
Keyword(s):  
Standing Wave ◽  
Separation Distance ◽  
Destructive Interference ◽  
Acoustic Standing Wave ◽  
Separation Ratio ◽  
Sound Levels ◽  
Standing Wave Method ◽  
Image Velocimetry ◽  
Strong Source ◽  
Shallow Cavities

Flow over ducted shallow cavities can excite fluid resonant oscillations. A common industrial application is the flow in corrugated pipes that can be modeled as a series of consecutive shallow cavities. In the current study, the effect of the separation distance on the aeroacoustic source of multiple shallow cavities is investigated. The standing wave method (SWM) is used to measure the source, where multiple microphones reconstruct the acoustic standing wave upstream and downstream of the cavities. The effect of the ratio between the separation distance to cavity length is investigated for a practical range from 0.5 to 1.375 for two- and three-cavity configurations. At low and intermediate sound levels, constructive hydrodynamic interference, resulting in a strong source, is observed for the extremum spacing ratios of 0.5 and 1.375. However, at high excitation levels, 10% and higher, the source, slightly but consistently, decreases upon increasing the separation ratio. These trends persist for both the double- and triple-cavity configurations. On the other hand, the separation distance of destructive interference is found to depend on the number of cavities of the tested configuration. Particle image velocimetry (PIV) measurements of the constructive interference cases show strong synchronized vorticity shedding in all cavities. Each cavity contribution to the total aeroacoustic source is then examined by means of Howe's analogy, and the percentage contribution of each cavity is found to depend on the excitation level.

scholarly journals Multipoint investigation of the source region of storm-time chorus

2004 ◽  
Vol 22 (7) ◽  
pp. 2555-2563 ◽  
Author(s):  
O. Santolík ◽  
D. A. Gurnett ◽  
J. S. Pickett
Keyword(s):  
Source Region ◽  
Rank Correlation ◽  
Radial Distance ◽  
Correlation Coefficients ◽  
Separation Distance ◽  
Characteristic Scale ◽  
Whistler Mode ◽  
Power Spectral ◽  
Distribution Of Power ◽  
The Individual

Abstract. In this case study we investigate the source region of whistler-mode chorus located close to the geomagnetic equator at a radial distance of 4.4 Earth radii. We use measurements from the four Cluster spacecraft at separations of less than a few hundreds of km, recorded during the geomagnetic storm of 18 April 2002. The waveforms of the electric field fluctuations were obtained by the WBD instruments in the frequency range 50Hz-9.5kHz. Using these data, we calculate linear and rank correlation coefficients of the frequency averaged power-spectral density measured by the different spacecraft. Those coefficients have been recently shown to decrease with spacecraft separation distance perpendicular to the static magnetic field cchor03 with a characteristic scale length of 100km. We find this characteristic scale varying between 60 and 200km for different data intervals inside the source region. We examine possible explanations for the observed large scatter of the correlation coefficients, and we suggest a simultaneously acting effect of random positions of locations at which the individual chorus wave packets are generated. The statistical properties of the observations are approximately reproduced by a simple 2-D model of the source region, assuming a perpendicular half-width of 35km (approximately one wavelength of the whistler-mode waves) for the distribution of power radiated from individual active areas.

Non-Contact Guideway for Substrate Transportation by Ultrasonic Oscillation

2008 ◽  
Vol 2 (3) ◽  
pp. 199-204
Author(s):  
Hiromi Isobe ◽  
◽  
Akira Kyusojin ◽  
Keyword(s):  
Standing Wave ◽  
Relative Position ◽  
Silicon Substrate ◽  
Traveling Wave ◽  
Polycrystalline Silicon ◽  
Transportation System ◽  
Experimental Results ◽  
Rectangular Plates ◽  
Ultrasonic Oscillation ◽  
Oscillating Plate

In recent years, the enlargement of plane substrates and semiconductor wafers has advanced. To carry the longer and wider substrate with conventional thickness requires more fragility. The development of non-contact transportation system is desired to prevent the fracture of the substrate. In this study, a new non-contact transportation system to provide damage-free transportation is proposed. The substrate is supported by aerostatic force and transported by acoustic viscous streaming, which is induced by traveling wave deformation of disk-type stators. The desktop size non-contact transportation apparatus for polycrystalline silicon substrate (150(W)×150(L)×0.3(t)) is constructed to clarify the basic carrying performance. In order to realize non-contact transportation, a unique guide technique is proposed. The standing wave deformations of rectangular plates guide the substrate without contacting to avoid dropping off from the carrier way. Experimental results demonstrate that holding force varies with relative position between oscillating plate and substrate. The maximum holding force is obtained when the center of oscillating plate is on the edge of substrate.

Energy dissipation in an oscillating sphere filled with a viscous fluid.

AIAA Journal ◽  
1969 ◽  
Vol 7 (9) ◽  
pp. 1793-1796 ◽  
Author(s):  
R. APRAHAMIAN ◽  
R. L. JOHNSON ◽  
L. R. KOVAL
Keyword(s):  
Energy Dissipation ◽  
Viscous Fluid ◽  
Oscillating Sphere

Heat Pipe Array for Planar Cooling of Rotating Radar Systems

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Wessel W. Wits ◽  
Gert Jan te Riele
Keyword(s):  
Heat Pipe ◽  
Elevation Angle ◽  
Radial Distance ◽  
Ambient Air ◽  
Planar Structure ◽  
Working Fluid ◽  
Rotational Axis ◽  
Centrifugal Forces ◽  
Rotating Platform ◽  
Radar Systems

This paper presents a planar cooling strategy for rotating radar systems using heat pipe technology. The proposed design uses six 1 m long heat pipes in parallel oriented in an evaporator-down modus at an elevation angle of 85 deg. An analytical model based on conventional heat pipe limits is used to predict the performance taking into account both gravitational and centrifugal forces. The heat pipe array is mounted on a rotating platform of which both the mounting angle w.r.t. the rotational arm and rotational speed can be varied. The radial distance w.r.t. the rotational axis was set at 0.5 m. The setup was tested in an environmental chamber to simulate higher ambient temperatures as well. Moreover, measurements were conducted by varying the heat sink airflow rates. The performance was determined by the temperature gradient across the planar structure. Successful heat pipe operation and experimental performances were determined for a number of application parameters. At higher rotational speeds, the influence of centrifugal forces that may assist or hinder the working fluid circulation became discernible. For higher rotational frequencies, the mounting angle proved to be of (minor) influence on the performance in agreement with the developed model. The current design was validated for effective planar cooling of a rotating radar system for planar heat loads up to 1000 W. Temperature gradients across the planar structure remain below critical limits and overall thermal resistances from planar to ambient air conditions of 0.040 K/W and below were observed.

Buoyancy-Driven Flow Reversal Phenomena in Radially Rotating Serpentine Ducts

1999 ◽  
Vol 122 (1) ◽  
pp. 179-183 ◽  
Author(s):  
J. J. Hwang ◽  
W.-J. Wang ◽  
Cha’o Kuang Chen
Keyword(s):  
Flow Separation ◽  
Hot Spots ◽  
Richardson Number ◽  
Radial Flow ◽  
Radial Distance ◽  
Flow Reversal ◽  
Rotational Axis ◽  
Reversed Flow ◽  
Square Duct ◽  
Cooling Channels

Convective characteristics are analyzed numerically in a rotating multipass square duct connecting with 180-deg sharp returns. Isoflux is applied to each duct wall and periodic conditions are used between the entrance and exit of a typical two-pass module. Emphasis is placed on the phenomenon of buoyancy-driven reversed flow in the serpentine duct. Predictions reveal that the radial distance from the rotational axis to the location of flow separation in the radial-outward duct decreases with increasing the Richardson number. In addition, the local buoyancy that is required to yield the radial flow reversal increases with increasing the rotation number. This buoyancy-driven reversed flow in the radial-outward duct always results in local hot spots in the cooling channels. The critical buoyancy for the initiation of flow reversal is therefore concluded for the design purpose. [S0022-1481(00)01101-4]

Hydrodynamic Interaction Between Whistling Axisymmetric Cavities in the Presence of a Coupling Longitudinal Standing Wave

2011 ◽  
Author(s):  
Gu¨nes¸ Nakibog˘lu ◽  
Oleksii Rudenko ◽  
Joachim Golliard ◽  
Avraham Hirschberg
Keyword(s):  
Standing Wave ◽  
Hydrodynamic Interaction ◽  
Unit Element ◽  
Industrial Applications ◽  
Separation Distance ◽  
Critical Conditions ◽  
Sustained Oscillation ◽  
Axisymmetric Cavity ◽  
Acoustic Interaction ◽  
Axisymmetric Cavities

An axisymmetric cavity along a pipe is a commonly encountered construction in industrial applications, which can also be considered as a unit element of a corrugated pipe. At critical conditions such a configuration causes severe noise problems, called whistling. Whistling is a self-sustained oscillation, driven by a flow-acoustic interaction. In the current study, the hydrodynamic interaction between two such cavities is addressed in the presence of a coupling standing wave along the pipe. The phenomenon is investigated both experimentally and numerically. The hydrodynamic interaction has a strong effect both for the amplitude and for the Strouhal number of the whistling, which depends critically on the separation distance between two adjacent cavities.

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