scholarly journals An experimental study of the motion of a light sphere in a rotating viscous fluid

2018 ◽  
Vol 847 ◽  
pp. 119-133 ◽  
Author(s):  
T. Sauma-Pérez ◽  
C. G. Johnson ◽  
L. Yang ◽  
T. Mullin
Keyword(s):  
Experimental Study ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Viscous Fluid ◽  
Fixed Points ◽  
Critical Reynolds Number ◽  
Solid Sphere ◽  
Rotating Cylinder ◽  
Quantitative Agreement ◽  
Rotation Rates

We present the results of an experimental investigation of the motion of a light, solid sphere in a horizontal rotating cylinder filled with viscous fluid. At high rotation rates, the sphere sits near the axis of the cylinder. At lower rotation rates, a set of off-axis fixed points are observed for a range of sphere radii. The locations of these fixed points are in quantitative agreement with the predictions of a model based on available theory. The fixed points are observed to become unstable to periodic orbits below a critical Reynolds number $Re_{c}$. The radius of the observed orbits increases with Reynolds number more slowly than a typical Hopf bifurcation, in this case, growing as $1/Re^{2}$.

Experimental Study of Vortex Shedding From a Solid Sphere in Turbulent Freestream

2005 ◽  
Author(s):  
Himanshu Tyagi ◽  
Rui Liu ◽  
David S.-K. Ting ◽  
Clifton R. Johnston
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Isotropic Turbulence ◽  
Vortex Formation ◽  
Perforated Plate ◽  
Solid Sphere ◽  
Mean Flow ◽  
Static Pressure Distribution

The study of vortex shedding from a sphere assumes an important role because of its relevance to numerous aerodynamic and hydrodynamic applications. Parameters such as coefficient of drag and static pressure distribution are largely influenced by vortex shedding, and it is found by past studies that the freestream turbulence can interact and alter the vortex formation and shedding drastically. Most of these studies, however, were conducted in the low Reynolds number regime and the vortex shedding results had been described only qualitatively. To better understand the aerodynamics of a sphere in turbulent flow, an experimental study was initiated in a low speed wind tunnel to quantify the vortex shedding characteristics. The Reynolds number of the flow, based on the diameter of the sphere (d), was set at 3.3 × 104, 5 × 104 and 6.6 × 104 by varying the mean flow velocity. The sphere was placed at 20D (= 7.5d) downstream from a perforated plate, where D = 37.5 mm is the size of the holes in the perforated plate, uniquely designed for generating near-isotropic turbulence. Hot-wire measurements were taken at 10D (= 3.75d), 20D (= 7.5d) and 30D (= 11.25d) downstream of the sphere in absence and presence of the perforated plate. The vortex shedding frequency was deduced from the instantaneous flow velocity data.

scholarly journals Experimental investigation of flow-induced vibration of a rotating circular cylinder

2017 ◽  
Vol 829 ◽  
pp. 486-511 ◽  
Author(s):  
K. W. L. Wong ◽  
J. Zhao ◽  
D. Lo Jacono ◽  
M. C. Thompson ◽  
J. Sheridan
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Circular Cylinder ◽  
Rotation Rate ◽  
Rotating Cylinder ◽  
Flow Induced Vibration ◽  
Amplitude Response ◽  
Number Range ◽  
Rotating Circular Cylinder ◽  
Numerical Predictions

While flow-induced vibration of bluff bodies has been extensively studied over the last half-century, only limited attention has been given to flow-induced vibration of elastically mounted rotating cylinders. Since recent low-Reynolds-number numerical work suggests that rotation can enhance or suppress the natural oscillatory response, the former could find applications in energy harvesting and the latter in vibration control. The present experimental investigation characterises the dynamic response and wake structure of a rotating circular cylinder undergoing vortex-induced vibration at a low mass ratio ($m^{\ast }=5.78$) over the reduced velocity range leading to strong oscillations. The experiments were conducted in a free-surface water channel with the cylinder vertically mounted and attached to a motor that provided constant rotation. Springs and an air-bearing system allow the cylinder to undertake low-damped transverse oscillations. Under cylinder rotation, the normalised frequency response was found to be comparable to that of a freely vibrating non-rotating cylinder. At reduced velocities consistent with the upper branch of a non-rotating transversely oscillating cylinder, the maximum oscillation amplitude increased with non-dimensional rotation rate up to $\unicode[STIX]{x1D6FC}\approx 2$. Beyond this, there was a sharp decrease in amplitude. Notably, this critical value corresponds approximately to the rotation rate at which vortex shedding ceases for a non-oscillating rotating cylinder. Remarkably, at $\unicode[STIX]{x1D6FC}=2$ there was approximately an 80 % increase in the peak amplitude response compared to that of a non-rotating cylinder. The observed amplitude response measured over the Reynolds-number range of ($1100\lesssim Re\lesssim 6300$) is significantly different from numerical predictions and other experimental results recorded at significantly lower Reynolds numbers.

Primary instability of a shear-thinning film flow down an incline: experimental study

2017 ◽  
Vol 821 ◽  
Author(s):  
M. H. Allouche ◽  
V. Botton ◽  
S. Millet ◽  
D. Henry ◽  
S. Dagois-Bohy ◽  
...  
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Primary Stability ◽  
Shear Thinning ◽  
Driving Frequency ◽  
Neutral Curves ◽  
Theoretical Predictions ◽  
Sommerfeld Equation ◽  
Primary Instability

The main objective of this work is to study experimentally the primary instability of non-Newtonian film flows down an inclined plane. We focus on low-concentration shear-thinning aqueous solutions obeying the Carreau law. The experimental study essentially consists of measuring wavelengths in marginal conditions, which yields the primary stability threshold for a given slope. The experimental results for neutral curves presented in the $(Re,f_{c})$ and $(Re,k)$ planes (where $f_{c}$ is the driving frequency, $k$ is the wavenumber and $Re$ is the Reynolds number) are in good agreement with the numerical results obtained by a resolution of the generalized Orr–Sommerfeld equation. The long-wave asymptotic extension of our results is consistent with former theoretical predictions of the critical Reynolds number. This is the first experimental evidence of the destabilizing effect of the shear-thinning behaviour in comparison with the Newtonian case: the critical Reynolds number is smaller, and the ratio between the critical wave celerity and the flow velocity at the free surface is larger.

Effect of Vibration on Heat Transfer for Flow Normal to a Cylinder

1969 ◽  
Vol 91 (1) ◽  
pp. 140-144 ◽  
Author(s):  
J. M. Faircloth ◽  
W. J. Schaetzle
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Horizontal Plane ◽  
Critical Reynolds Number ◽  
Wire Vibration ◽  
Surface Vibrations ◽  
Sinusoidal Current ◽  
The Wire ◽  
Forced Air

An experimental investigation of the effect that surface vibrations have on the heat transfer by forced convection was studied. A no. 40 gauge wire was vibrated in the horizontal plane by a sinusoidal current and simultaneously exposed to a forced air current in the same plane. The frequency and amplitude of the wire vibration were varied within the ranges of 20 to 40 Hz and 0.3 to 0.5 in., respectively. The Reynolds number experienced by the wire varied between 0 and 15. The results of the investigation revealed that above a critical Reynolds number the instantaneous convective coefficient was increased from 20 to 30 percent.

An experimental study of low-Reynolds-number exchange flow of two Newtonian fluids in a vertical pipe

2011 ◽  
Vol 682 ◽  
pp. 652-670 ◽  
Author(s):  
F. M. BECKETT ◽  
H. M. MADER ◽  
J. C. PHILLIPS ◽  
A. C. RUST ◽  
F. WITHAM
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Viscous Fluid ◽  
Flow Regime ◽  
Low Reynolds Number ◽  
Velocity Profiles ◽  
Newtonian Fluids ◽  
Exchange Flow ◽  
Volume Flux ◽  
Two Fluids

We present an experimental study of a buoyancy-driven, low-Reynolds-number (Re < 1) exchange flow of two Newtonian fluids in a vertical cylindrical pipe (length 1 m and diameter 38.4 mm) connecting two fluid reservoirs. The denser, more viscous fluid was golden syrup and the less dense, less viscous fluid was a golden syrup–water solution; the ratio of the viscosities of the two fluids (β) ranged from 2 to 1180. Flows were initiated by removing a bung in the base of the upper reservoir or sliding out a gate positioned at the top, middle or bottom of the pipe. We observe the flows over long time durations (up to 356 h), and define the development of the flow with reference to a non-dimensional time (τ). The initial transient development of the flow was dependent on which of the two fluids initially filled the pipe, but this did not systematically affect the flow regime observed at τ ≫ 1. Two distinct flow regimes were observed: axisymmetric core-annular flow (CAF), in which the less viscous fluid occupies a cylindrical core and the denser fluid flows downwards in an annulus, and side-by-side (SBS) flow where both fluids are in contact with the pipe and there is a single interface between them. CAF formed at β ≥ 75 and SBS flow at β ≤ 117. In several experiments, for 5 ≤ β ≤ 59, a slowly developing transitional SBS (TSBS) flow was observed where SBS flow and CAF occurred simultaneously with SBS in the lower portion of the pipe; SBS existed throughout most of the pipe and in one case grew with time to entirely fill the pipe. Velocity profiles determined by tracking tracer particles show that the observed CAFs are adequately described by the formulation of Huppert & Hallworth (J. Fluid Mech., vol. 578, 2007, pp. 95–112). Experimental SBS velocity profiles are not well produced by the formulation of Kerswell (J. Fluid Mech., 10.1017/jfm.2011.190), possibly because the latter is restricted to flows whose cross-section has an interface of constant curvature. Despite the variations in flow regime, volume fluxes can be described by a power-law function of β, Q1 = 0.059 β−0.74. A comparison of experimental data with the theoretical approaches of Huppert Hallworth (2007) and Kerswell (2011) indicates that fluids are not arranged in the regime that maximises volume flux (e.g. SBS or CAF), nor do they adopt the geometry that maximises volume flux within that particular regime.

Flow around a Rotating Cylinder near the Critical Reynolds Number.

1999 ◽  
Vol 47 (540) ◽  
pp. 33-40
Author(s):  
Nobuyuki OHKURA ◽  
Hidetoshi HAYAFUJI ◽  
Muneshige OKUDE
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Rotating Cylinder

Experimental Study of Wake Shielding Effects of Three Cylinders in Currents

2004 ◽  
Author(s):  
Shan Huang ◽  
Jarle Bolstad ◽  
Adolfo Maro´n
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Drag Reduction ◽  
Experimental Work ◽  
Critical Reynolds Number ◽  
Flow Direction ◽  
Towing Tank ◽  
The Past ◽  
Number Of Publications ◽  
Shielding Effects

A large amount of experimental work has been carried out in the past to understand forces on a single cylinder in cross flows. In comparison substantially less work can be found on the interference between multiple cylinders and the number of publications available becomes drastically smaller as the number of cylinders involved increases. The current experimental work systematically examines the wake shielding effects of three cylinders by testing in a towing tank. Though staggered, the three cylinders are arranged mainly along the flow direction. The tests are carried out in the subcritical and critical Reynolds number regimes. Significant drag reduction on downstream cylinders is identified.

scholarly journals EXPERIMENTAL RESULTS OF A VISCOUS FLOW AROUND A “T” PROFILE

2017 ◽  
Vol 18 (2) ◽  
Author(s):  
MIHAI SCHIAUA ◽  
CARMEN-ANCA SAFTA ◽  
VALERIU PANAITESCU
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Viscous Fluid ◽  
Viscous Flow ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Flow Speed ◽  
Plane Flow ◽  
Vortex Flowmeter

<p>The purpose of the paper is to visualise the vortex shedding process behind a bluff body. It was considered a plane flow of a viscous fluid (water) around a ²T² profile having the geometric sizes modified. It was measured the fluid flow speed in the section of the measurements and the frequency of the vortex detachment from the profile. The vortex development phenomenon depends by the profile’s geometry and the Reynolds number of the flow. The relation between Reynolds number and Strouhal number was obtained for different sizes ²T² profiles. The experimental study is necessary to improve the vortex flowmeter performances.</p>

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