Fluctuating Temperature Measurements on a Heated Cylinder Placed in a Cylinder Near-Wake

2004 ◽  
Vol 126 (1) ◽  
pp. 62-69 ◽  
Author(s):  
Z. J. Wang ◽  
Y. Zhou ◽  
X. W. Wang ◽  
W. Jin
Keyword(s):  
Hot Wire ◽  
Heat Transfer Characteristics ◽  
Near Wake ◽  
Heated Cylinder ◽  
Fbg Sensor ◽  
Vortex Shedding Frequency ◽  
Sensor Measurement ◽  
Shedding Frequency ◽  
Good Agreement ◽  
Pronounced Peak

The local time-averaged temperature θs¯ and its fluctuating component θs on the surface of a heated circular cylinder immersed in a cylinder near-wake were measured using a fiber-optic Bragg grating (FBG) sensor. Three cylinder center-to-center spacing, i.e., L/d=5.20, 2.50, and 1.18, were investigated. In order to validate the FBG sensor measurement, a thermocouple and a single hot-wire were employed to measure θs¯ on the heated cylinder and streamwise fluctuating velocity u in the near-wake of the downstream cylinder, respectively. The FBG sensor measurement of θs¯ is in good agreement with that simultaneously obtained by the thermocouple. The measured θs is closely correlated to the hot-wire measurement; the θs-spectrum exhibits a pronounced peak at the vortex shedding frequency, as identified in Eu, for each L/d. The results suggest that the FBG sensor can be used to measure reliably both time-averaged and fluctuating temperatures. The heat transfer characteristics of the heated cylinder are examined for different L/d and further compared with the case of an isolated cylinder.

Wind Tunnel Study of Vortex Shedding behind Cooling Tower Models

2014 ◽  
Vol 617 ◽  
pp. 280-284
Author(s):  
Petr Michálek ◽  
David Zacho
Keyword(s):  
Wind Tunnel ◽  
Vortex Shedding ◽  
Cooling Tower ◽  
Time Signal ◽  
Hot Wire ◽  
Model Surface ◽  
Surface Measurements ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Wind Tunnel Study

Wind tunnel measurements of vortex shedding behind cooling tower models were performed in VZLU. Two variants of cooling tower models were used, i.e. model with smooth wall outer surface and model with rough wall surface. Measurements were conducted using hot-wire anemometer. Time signal from the anemometer was transformed using Fast-Fourier routine into frequency spectrum. Measurements have shown significant differences between smooth and rough variant of model surface and dependency of vortex shedding frequency on Reynolds number.

Stability properties of forced wakes

2007 ◽  
Vol 579 ◽  
pp. 137-161 ◽  
Author(s):  
B. THIRIA ◽  
J. E. WESFREID
Keyword(s):  
Vortex Shedding ◽  
Mean Flow ◽  
Near Wake ◽  
Global Mode ◽  
Spatial Properties ◽  
Moderate Reynolds Number ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
The Stability ◽  
Selection Of

Thiria, Goujon-Durand & Wesfreid (J. Fluid Mech. vol. 560, 2006, p. 123), it was shown that vortex shedding from a rotationally oscillating cylinder at moderate Reynolds number can be characterized by the spatial coexistence of two distinct patterns, one of which is related to the forcing frequency in the near wake and the other to a frequency close to the natural one for the unforced case downstream of this locked region. The existence and the modification of these wake characteristics were found to be strongly affected by the frequency and the amplitude of the cylinder oscillation. In this paper, a linear stability analysis of these forced regimes is performed, and shows that the stability characteristics of such flows are governed by a strong mean flow correction which is a function of the oscillation parameters. We also present experiments on the spatial properties of the global mode and on the selection of the vortex shedding frequency as a function of the forcing conditions for Re = 150. Finally, we elucidate a diagram of locked and non-locked states, for a large range of frequencies and amplitudes of the oscillation.

Transport in the near aerodynamic wakes of flat plates

1982 ◽  
Vol 120 ◽  
pp. 185-197 ◽  
Author(s):  
A. S. M. Maclennan ◽  
J. H. Vincent
Keyword(s):  
Free Stream ◽  
Bluff Bodies ◽  
Wake Region ◽  
Small Particles ◽  
Flat Plates ◽  
Main Attention ◽  
Near Wake ◽  
Free Stream Turbulence ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

An experimental investigation has been carried out into the nature of the transport of airborne material in the near aerodynamic wakes of bluff bodies with simple shapes. The main attention was focused on the essential differences existing between axi- symmetric flows (as about disks) and two-dimensional flows (as about rectangular long thin flat plates). Measurements were made for such bodies of the near-wake residence time of injected small particles, along with other and more familiar near- wake properties such as the vortex-shedding frequency and base pressure. It was concluded for disks that the transport of material into and out of the near-wake region is dominated by turbulent diffusion, and is strongly influenced by free-stream turbulence, especially for free-stream turbulence whose length scale is substantially smaller than the disk diameter. For rectangular flat plates, transport is dominated by the periodic shedding of vortices, and to only a secondary extent by turbulent motions, and is not strongly influenced by free-stream turbulence.

Incoherent turbulence structure in the near wake of a normal plate

1988 ◽  
Vol 190 ◽  
pp. 343-356 ◽  
Author(s):  
M. Kiya ◽  
M. Matsumura
Keyword(s):  
Vortex Shedding ◽  
Frequency Component ◽  
Turbulence Structure ◽  
Near Wake ◽  
Velocity Fluctuations ◽  
Coherent Vortices ◽  
Frequency Components ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Small Dispersion

In this paper experimentally studied characteristics of various frequency components of incoherent velocity fluctuations in the near wake behind a thin normal plate immersed in a uniform flow are described. Measurements were made at a position 8 plate heights downstream of the plate where the wake had a marked periodicity, so that coherent vortices shed from the plate are expected to have a small dispersion in streamwise spacing, transverse location, strength and shape. Shearing stress associated with the incoherent fluctuations is mainly contributed by components with frequencies around half of the vortex-shedding frequency fs on one side of the wake. The ½fs frequency component appears to be caused by the spanwise locations of ribs, which are connected to the coherent vortices, being different from vortex to vortex. A probable spanwise arrangement of the ribs is suggested.

Proximity-induced galloping of two interfering circular cylinders

1984 ◽  
Vol 146 ◽  
pp. 417-449 ◽  
Author(s):  
A. Bokaian ◽  
F. Geoola
Keyword(s):  
Circular Cylinders ◽  
Appreciable Effect ◽  
Dynamic Tests ◽  
Near Wake ◽  
Drag Coefficients ◽  
Free Stream Turbulence ◽  
Plane Normal ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Lift And Drag

Experiments were conducted to investigate the response of a rigid two-dimensional elastically mounted smooth circular cylinder, with oscillations restricted to a plane normal to the incident flow, as influenced by the vicinity of an identical fixed body placed inside the wake. The static lift and drag coefficients, as well as the vibration amplitude and frequency of the upstream cylinder as functions of relative position of the pair of cylinders are given. Most measurements were carried out under two conditions of free-stream turbulence. Whilst turbulence decreased the magnitude of drag coefficients, it had no appreciable effect on lift coefficients. The forces on the upstream body were found to be influenced by the proximity to the downstream one in a significant way only when the streamwise spacing is less than two diameters.In the dynamic tests, two kinds of instability, namely a vortex-resonance and galloping, were observed, with the latter only occurring when the downstream cylinder was well submerged in the near wake of the upstream one. The vortex-shedding frequency was always found to lock to oscillation frequency. Whereas the vibration characteristics remained essentially unaffected with changing turbulence intensity, the galloping amplitudes were observed to be sensitive to cylinders’ aspect ratio. A quasi-steady theory was developed to predict the galloping behaviour.

DEVELOPMENT OF ROBUST VELOCIMETER FOR NATURAL WATER FLOW MONITORING

2016 ◽  
Vol 78 (7) ◽  
Author(s):  
Masataka Shirakashi ◽  
Kye Wei Yeo ◽  
Mizuyasu Koide ◽  
Tsutomu Takahashi ◽  
Sheikh Ahmad Zaki Shaikh Salim
Keyword(s):  
Flow Velocity ◽  
Water Flow ◽  
Vortex Shedding ◽  
Natural Water ◽  
Dominant Frequency ◽  
Hot Wire ◽  
Flow Monitoring ◽  
University Of Technology ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The ring-velocimeter coupled with a hot wire/film probe was developed and has been applied to wind and water tunnel experiments in Fluids Engineering Laboratory of Nagaoka University of Technology.  In this study, the hot-wire/film probe is replaced by a cantilever attached by a strain gauge to detect the drag acting on the ring.  The vortex shedding frequency from the ring is determined from the drag fluctuation by applying the spectrum analysis, and the flow velocity in turn since it is proportional with the vortex shedding frequency.  This technique for flow velocity measurement is robust in the sense that it is strong against the noise or decay of the detected signal since the dominant frequency is insensitive to such disturbances, and that the detecting probe is strong against the contaminants or particles/objects carried by the fluid.  These advantages, together with its simple and cheap characteristics, make it possible to apply to natural water flow with severe conditions.

The Effect of Uniform Blowing on the Flow Past a Circular Cylinder

2002 ◽  
Vol 124 (2) ◽  
pp. 452-464 ◽  
Author(s):  
Lionel Mathelin ◽  
Franc¸oise Bataille ◽  
Andre´ Lallemand
Keyword(s):  
Circular Cylinder ◽  
Stream Flow ◽  
Boundary Layer Thickness ◽  
Free Stream ◽  
Thermal Protection ◽  
Viscous Drag ◽  
Near Wake ◽  
Flow Past ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

This work describes blowing through the whole surface of a porous circular cylinder for the control of the near wake dynamics and the thermal protection of the surface. The flow past the cylinder is numerically studied and the blowing is modeled. Comparisons with experimental data are used for validation. It is shown that the blowing tends to increase the boundary layer thickness, to promote its separation and to decrease the viscous drag induced. Similarly, the convective heat transfer is lowered, and in the case of a nonisothermal blowing, the surface is very effectively protected from the hot free stream flow. The near wake is also affected. The vortex shedding frequency is shown to decrease when blowing occurs and a qualitative model is presented to identify the different mechanisms.

The Influence of Boundary Layer Velocity Gradients and Bed Proximity on Vortex Shedding From Free Spanning Pipelines

1984 ◽  
Vol 106 (1) ◽  
pp. 70-78 ◽  
Author(s):  
A. J. Grass ◽  
P. W. J. Raven ◽  
R. J. Stuart ◽  
J. A. Bray
Keyword(s):  
Boundary Layer ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Combined Effects ◽  
Maximum Increase ◽  
Velocity Gradients ◽  
Large Velocity ◽  
Layer Velocity ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The paper summarizes the results of a laboratory study of the separate and combined effects of bed proximity and large velocity gradients on the frequency of vortex shedding from pipeline spans immersed in the thick boundary layers of tidal currents. This investigation forms part of a wider project concerned with the assessment of span stability. The measurements show that in the case of both sheared and uniform approach flows, with and without velocity gradients, respectively, the Strouhal number defining the vortex shedding frequency progressively increases as the gap between the pipe base and the bed is reduced below two pipe diameters. The maximum increase in vortex shedding Strouhal number, recorded close to the bed in an approach flow with large velocity gradients, was of the order of 25 percent.

An Experimental Study on the Vertical Flow Past a Finite-Length Horizontal Cylinder at Low Reynolds Numbers

2014 ◽  
Vol 493 ◽  
pp. 68-73 ◽  
Author(s):  
Willy Stevanus ◽  
Yi Jiun Peter Lin
Keyword(s):  
Finite Length ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Horizontal Cylinder ◽  
Vortex Street ◽  
Vertical Flow ◽  
Low Reynolds Numbers ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The research studies the characteristics of the vertical flow past a finite-length horizontal cylinder at low Reynolds numbers (ReD) from 250 to 1080. The experiments were performed in a vertical closed-loop water tunnel. Flow fields were observed by the particle tracer approach for flow visualization and measured by the Particle Image Velocimetry (P.I.V.) approach for velocity fields. The characteristics of vortex formation in the wake of the finite-length cylinder change at different regions from the tip to the base of it. Near the tip, a pair of vortices in the wake was observed and the size of the vortex increased as the observed section was away from the tip. Around a distance of 3 diameters of the cylinder from its tip, the vortex street in the wake was observed. The characteristics of vortex formation also change with increasing Reynolds numbers. At X/D = -3, a pair of vortices was observed in the wake for ReD = 250, but as the ReD increases the vortex street was observed at the same section. The vortex shedding frequency is analyzed by Fast Fourier Transform (FFT). Experimental results show that the downwash flow affects the vortex shedding frequency even to 5 diameters of the cylinder from its tip. The interaction between the downwash flow and the Von Kármán vortex street in the wake of the cylinder is presented in this paper.

Study of the Laminar Free-Convection Wake Above an Isothermal Vertical Plate

1973 ◽  
Vol 95 (3) ◽  
pp. 289-294 ◽  
Author(s):  
N. E. Hardwick ◽  
E. K. Levy
Keyword(s):  
Free Convection ◽  
Vertical Plate ◽  
Fluid Motion ◽  
Heated Plate ◽  
Two Dimensional ◽  
Wake Region ◽  
Hot Wire ◽  
Near Wake ◽  
Steady Laminar ◽  
Finite Difference Techniques

The steady, laminar, two-dimensional wake above a thin vertical isothermal heated plate cooled by free convection was investigated theoretically and experimentally. The system of partial differential equations governing the fluid motion and heat transfer in the vicinity of the plate and in the near wake region was formulated and solved using finite difference techniques. Using air, the temperature and velocity profiles in the wake region were measured experimentally using a laser holographic interferometer and a constant temperature hot wire anemometer.

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