The Near Wake Characteristics of Cavitating Bluff Sources

1990 ◽  
Vol 112 (4) ◽  
pp. 492-495 ◽  
Author(s):  
A. S. Ramamurthy ◽  
R. Balachandar
Keyword(s):  
Vortex Shedding ◽  
Vortex Formation ◽  
Cavitation Number ◽  
Test Results ◽  
Near Wake ◽  
Formation Region ◽  
Separation Velocity ◽  
Flow Test ◽  
Velocity Scale ◽  
Wake Characteristics

The influence of cavitation on vortex shedding behind constrained sharp-edged bluff prisms is studied experimentally. At a given blockage, the length of the vortex formation region is found to increase as the cavitation number of the flow is reduced. The vortex appears to be stabilized from breaking up in the partially cavitating regime of flow. Test results indicate that the separation velocity is the proper velocity scale to reduce or eliminate blockage effects.

Vortex Formation in the Wake of a Vibrating, Flexible Cable

1974 ◽  
Vol 96 (4) ◽  
pp. 317-322 ◽  
Author(s):  
S. E. Ramberg ◽  
O. M. Griffin
Keyword(s):  
Vortex Shedding ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Hot Wire ◽  
Near Wake ◽  
Formation Region ◽  
Vortex Streets ◽  
Region Length ◽  
Karman Vortex ◽  
Flexible Cables

The von Karman vortex streets formed in the wakes of vibrating, flexible cables were studied using a hot-wire anemometer. All the experiments took place in the flow regime where the vibration and vortex-shedding frequencies lock together, or synchronize, to control the wake formation. Detailed measurements were made of the vortex formation flow for Reynolds numbers between 230 and 650. As in the case of vibrating cylinders, the formation-region length is dependent on a shedding parameter St* related to the natural Strouhal number and the vibrational conditions. Furthermore, the near wake configuration is found to be dependent on the local amplitude of vibration suggesting that the vibrating cylinder rseults are directly applicable in that region.

On vortex formation from a cylinder. Part 1. The initial instability

1988 ◽  
Vol 190 ◽  
pp. 491-512 ◽  
Author(s):  
M. F. Unal ◽  
D. Rockwell
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Circular Cylinder ◽  
Shear Layer ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Absolute Instability ◽  
Near Wake ◽  
Lower Range ◽  
Fluctuation Amplitude

Vortex shedding from a circular cylinder is examined over a tenfold range of Reynolds number, 440 ≤ Re ≤ 5040. The shear layer separating from the cylinder shows, to varying degrees, an exponential variation of fluctuating kinetic energy with distance downstream of the cylinder. The characteristics of this unsteady shear layer are interpreted within the context of an absolute instability of the near wake. At the trailing-end of the cylinder, the fluctuation amplitude of the instability correlates well with previously measured values of mean base pressure. Moreover, this amplitude follows the visualized vortex formation length as Reynolds number varies. There is a drastic decrease in this near-wake fluctuation amplitude in the lower range of Reynolds number and a rapid increase at higher Reynolds number. These trends are addressed relative to the present, as well as previous, observations.

The effect of a bevelled trailing edge on vortex shedding and vibration

1973 ◽  
Vol 61 (2) ◽  
pp. 323-335 ◽  
Author(s):  
M. E. Greenway ◽  
C. J. Wood
Keyword(s):  
Vortex Shedding ◽  
Vortex Formation ◽  
Steady Motion ◽  
Visualization Technique ◽  
Rapid Decay ◽  
Formation Region ◽  
Towing Tank ◽  
Excited Vibration ◽  
Trailing Edges ◽  
Circulation Distribution

Experiments using a wind tunnel and a flow visualization technique in a towing tank were conducted to investigate the mechanism of vortex shedding from bevelled trailing edges. These reveal an important difference between the wake structures generated by heaving and steady motion. The suppression of vortex-excited vibration by means of bevelled trailing edges is attributed to the intermittency and rapid decay of the vortex trail resulting from an asymmetric circulation distribution in the vortex formation region.

Wake Topology of a Cylinder Undergoing Vortex-Induced Vibrations With Elliptic Trajectories

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Sina Kheirkhah ◽  
Serhiy Yarusevych ◽  
Sriram Narasimhan
Keyword(s):  
Vortex Shedding ◽  
Vortex Dynamics ◽  
Vortex Formation ◽  
Wake Vortex ◽  
Incoming Flow ◽  
Mass Ratio ◽  
Formation Region ◽  
Vortex Pairs ◽  
Vortex Induced Vibrations ◽  
Spanwise Vortex

Wake vortex shedding topology of a cylinder undergoing vortex-induced vibrations (VIV) is investigated experimentally. Vibration measurements and flow visualization are utilized to study the connection between the cylinder response and the wake topology. The experiments were performed for two different orientations of the elliptic trajectories relative to the incoming flow at a fixed Reynolds number, moment of inertia ratio, mass ratio, and reduced velocity. Similar to the classical 2P regime, two counter-rotating vortex pairs are produced per oscillating cycle for both cases of elliptic trajectories examined here. However, significant changes in wake vortex dynamics are observed along the cylinder span. These changes include merging of vortices, which leads to shedding patterns similar to 2S and P + S modes downstream of the vortex formation region. The observed changes in vortex dynamics are accompanied by splitting of spanwise vortex filament and are attributed primarily to the changes in the local amplitude of vibrations along the span of the pivoted cylinder. It is shown that, being dependent on both the local amplitude of vibrations and vortex dynamics, the observed wake topology cannot be captured by the classical map of shedding regimes developed for VIV of one degree-of-freedom (DOF) cylinders.

High Frequency Characteristics of the Near Wake and Vortex Past a Triangular Cylinder

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Lei Sun ◽  
Yong Huang ◽  
Xiwei Wang ◽  
Xiang Feng ◽  
Wei Xiao
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Core ◽  
High Frequency ◽  
Vortex Formation ◽  
Flame Stabilization ◽  
Near Wake ◽  
Freestream Velocity ◽  
Formation Region ◽  
Flow Past

Abstract The flow past a triangular cylinder is one of the fundamental flows and widely utilized in flame stabilization and heat transfer. In this study, the near wake and vortex characteristics of the flow past an equilateral triangular cylinder are experimentally measured by a high frequency particle image velocimetry (PIV) system at 3 kHz. The triangular cylinder is installed in a wind tunnel with Reynolds numbers ranging from 10,700 to 17,700. The Reynolds-averaged and phase-averaged methods are utilized to analyze the flow field. Based on the flow fields, the length of the vortex formation region is about 1.5 times of the length of the equilateral triangle side. The residence time of a vortex in the vortex formation region is equal to a vortex shedding period. The stream wise velocity of the vortex core center downstream the vortex formation is about 0.8 times of the freestream velocity, which is slightly larger than the value about 0.7 for the flow past a circular cylinder at the same Reynolds number. The maximum tangential velocity at the periphery of the vortex core maybe occurs slightly in advance of the vortex reaching the boundary of the vortex formation region. The normalized lengths of the recirculation zone of the triangular cylinder keep nearly unchanged and are about 1.55 to 1.9 times of those of the circular cylinder at the same Reynolds number. The normalized normal wise instead of stream wise turbulence intensity has stronger effects on the distribution of the normalized turbulent kinetic energy.

Symmetric Vortex Shedding From a Circular Cylinder Under Periodic Flow Forcing

2006 ◽  
Author(s):  
E. Konstantinidis ◽  
S. Balabani
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Excitation Frequency ◽  
Symmetric Mode ◽  
Near Wake ◽  
Wake Field ◽  
Vortex Pairs ◽  
Probabilistic Function ◽  
Number Of Cycles

This paper describes an experimental study of the near wake of a circular cylinder subjected to streamwise flow forcing. The wake field is examined by PIV and LDV for excitation frequencies in which symmetric shedding is likely. The results show that symmetric formation of vortex pairs occurs close to the cylinder synchronized with the oscillatory component of the flow. The symmetric mode rapidly breaks down and gives rise to an antisymmetric arrangement of single vortices further downstream. The number of cycles for which the symmetrical vortices persist in the near wake is a probabilistic function of the excitation frequency and forcing amplitude. Details of the related wake kinematics and frequencies are shown and the findings are discussed in relation to symmetric vortex formation occurring in self-excited streamwise oscillations.

A note on bluff body vortex formation

1995 ◽  
Vol 284 ◽  
pp. 217-224 ◽  
Author(s):  
Owen M. Griffin
Keyword(s):  
Bluff Body ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Initial Position ◽  
Bluff Bodies ◽  
Near Wake ◽  
Formation Region ◽  
Low Reynolds Numbers ◽  
Region Length ◽  
Low Reynolds

Green & Gerrard (1993) have presented in a recent paper the results of experiments to measure the distribution of vorticity in the near wake of a circular cylinder at low Reynolds numbers (up to Re = 220). They also compared the various definitions of the vortex formation region length which have been proposed by Gerrard (1966), Griffin (1974), and others for both high and low Reynolds numbers. The purpose of this note is to expand the work of Green & Gerrard, and to further their proposition that the end of the vortex formation region at all Reynolds numbers mark both the initial position of the fully shed vortex and the location at which its strength is a maximum. The agreement discussed here between several definitions for the formation region length will allow further understanding to be gained from investigations of the vortex wakes of stationary bluff bodies, and the wakes of oscillating bodies as well.

Near-Wake Characteristics and Acoustic Resonance Excitation of Crimped Spirally Finned Cylinders in Cross-Flow

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Mohammed Alziadeh ◽  
Atef Mohany
Keyword(s):  
Vortex Shedding ◽  
Sound Pressure ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Diameter Ratio ◽  
Wake Flow ◽  
Near Wake ◽  
Velocity Deficit

This paper presents an experimental investigation of the near-wake flow characteristics for isolated crimped spirally finned cylinders in cross-flow and its influence on the generated sound pressure during flow-excited acoustic resonance. Four crimped spirally finned cylinders are investigated, which have pitch-to-root diameter ratio (p/Dr) ranging between 0.384 ≤ p/Dr ≤ 1. A new equivalent diameter equation (Dc) has been developed to better capture the vortex shedding frequency emanating from the crimped spirally finned cylinders. The addition of crimped spiral fins reduces the coherence of the vortex shedding process as compared to that of a bare cylinder. Moreover, the addition of crimped spiral fins causes an elongation in the vortex formation region, as well as induces a larger velocity deficit in the near-wake. Reduction in the pitch-to-diameter ratio (p/Dr) leads to a progressive increase in the strength and coherence of the vortex shedding process. It also results in a gradual reduction in the vortex formation length and velocity deficit. The near-wake flow characteristics of the crimped spirally finned cylinders inherently affect the sound pressure during flow-excited acoustic resonance. Furthermore, the helical fins impose an asymmetrical inclination of the acoustic particle velocity. This hinders the flow-acoustic coupling, leading to a weakened energy transfer between the flow and sound fields. The findings of this investigation provide better understanding of the complex flow-sound interaction mechanism from crimped spirally finned cylinders in heat exchanger tube bundle.

Near Wake Properties of a Strumming Marine Cable: An Experimental Study

1985 ◽  
Vol 107 (1) ◽  
pp. 86-91 ◽  
Author(s):  
R. D. Peltzer ◽  
D. M. Rooney
Keyword(s):  
Cross Section ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Wind Tunnel Experiments ◽  
Near Wake ◽  
Cable System ◽  
Fluid Forces ◽  
Flow Speeds ◽  
Shedding Frequency ◽  
Marine Cable

Resonant flow-induced oscillations of a flexible cable can occur when the damping of the cable system is sufficiently small. The changes in the flow field that occur in the near wake of the cable during these resonant oscillations are closely related to the changes in the fluid forces that accompany these oscillations. The present wind tunnel experiments were undertaken to examine the effects that forced synchronized vibration and the helically-wound cross section of the cable have on near wake vortex shedding-related parameters; specifically the shedding frequency, vortex formation length Lf, reduced velocity Ur, vortex strength and the wake width Lw. The range of flow speeds over which the vortex shedding was locked on to the vibration frequency varied directly with the vibration amplitude. The helical cross section and the synchronized vibration caused significant changes in the near wake development that could be directly related to the increase in hydrodynamic forces associated with unforced synchronized vibration.

Airfoil Vibration Due to Upstream Alternating Vortices Generated by a Circular Cylinder

2002 ◽  
Author(s):  
K. F. Luk ◽  
R. M. C. So ◽  
S. C. Kot ◽  
Y. L. Lau ◽  
R. C. K. Leung
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Dynamic Responses ◽  
Laser Vibrometer ◽  
Flow Induced Vibration ◽  
Formation Region ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Rapid Drop

An experimental investigation of airfoil vibration due to upstream alternating vortices was carried out in a re-circulating wind tunnel. A circular cylinder with a diameter D = 102mm was positioned upstream of an airfoil (NACA0012), with a chord length c = 200mm and a zero angle of attack placed at a gap distance S, to generate the vortex street. The circular cylinder and airfoil were arranged in tandem and the spacing ratio S/D was varied from 0.5 to 6.5 to investigate the effect of the vortices generated upstream on the vibration of the airfoil. The experiment was carried out in a free stream Re range of 1.6×105 to 2.3×105. The vortex formation region behind a single circular cylinder was measured using a hot wire anemometer and the airfoil dynamic responses were examined using a laser vibrometer. It is found that when S/D is reduced beyond a critical value, there is a rapid drop in vortex shedding frequency and a suppression in airfoil vibration. This critical S/D is found to be the normalized length of the vortex formation region behind the single cylinder. It is hypothesized that the vortex could not be formed at this location within the gap distance in the presence of the airfoil, but instead is formed behind the airfoil. Consequently, as vortex shedding is switched from upstream to downstream of the airfoil, the flow-induced vibration of the airfoil is suppressed at the same time.

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