VIV Strouhal Number for Long Slender Structures

This paper deals with the topic of upper surface blowing noise. Using a model-scale rectangular nozzle of an aspect ratio of 10 and a sharp trailing edge, detailed noise contours were acquired with and without a subsonic jet blowing over a flat surface to determine the noise source location as a function of frequency. Additionally, velocity scaling of the upper surface blowing noise was carried out. It was found that the upper surface blowing increases the noise significantly. This is a result of both the trailing edge noise and turbulence downstream of the trailing edge, referred to as wake noise in the paper. It was found that low-frequency noise with a peak Strouhal number of 0.02 originates from the trailing edge whereas the high-frequency noise with the peak in the vicinity of Strouhal number of 0.2 originates near the nozzle exit. Low frequency (low Strouhal number) follows a velocity scaling corresponding to a dipole source where as the high Strouhal numbers as quadrupole sources. The culmination of these two effects is a cardioid-shaped directivity pattern. On the shielded side, the most dominant noise sources were at the trailing edge and in the near wake. The trailing edge mounting geometry also created anomalous acoustic diffraction indicating that not only is the geometry of the edge itself important, but also all geometry near the trailing edge.

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Nonlinear dynamics of flexible slender structures moving in a limited space with application in nuclear reactors

Nonlinear Dynamics ◽

10.1007/s11071-021-06582-1 ◽

2021 ◽

Author(s):

R. Bulín ◽

Š. Dyk ◽

M. Hajžman

Keyword(s):

Nonlinear Dynamics ◽

Nuclear Reactors ◽

Limited Space ◽

Slender Structures

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Aerodynamic Instability of Circular Slender Structures Due to Bistable Flow Activity

Structural Engineering International ◽

10.1080/10168664.2021.1929670 ◽

2021 ◽

pp. 1-7

Author(s):

Adel Benidir ◽

Olivier Flamand ◽

Grigorios Dimitriadis ◽

Philippe Delpech

Keyword(s):

Aerodynamic Instability ◽

Flow Activity ◽

Bistable Flow ◽

Slender Structures

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Effect of an Oscillating Flow Direction on Leading Edge Heat Transfer

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3239538 ◽

1984 ◽

Vol 106 (1) ◽

pp. 222-228 ◽

Cited By ~ 2

Author(s):

M. L. Marziale ◽

R. E. Mayle

Keyword(s):

Heat Transfer ◽

Strouhal Number ◽

Large Scale ◽

Flow Direction ◽

Leading Edge ◽

Periodic Variation ◽

Scale Model ◽

Transfer Rates ◽

Large Scale Model ◽

Turbulence Length

An experimental investigation was conducted to examine the effect of a periodic variation in the angle of attack on heat transfer at the leading edge of a gas turbine blade. A circular cylinder was used as a large-scale model of the leading edge region. The cylinder was placed in a wind tunnel and was oscillated rotationally about its axis. The incident flow Reynolds number and the Strouhal number of oscillation were chosen to model an actual turbine condition. Incident turbulence levels up to 4.9 percent were produced by grids placed upstream of the cylinder. The transfer rate was measured using a mass transfer technique and heat transfer rates inferred from the results. A direct comparison of the unsteady and steady results indicate that the effect is dependent on the Strouhal number, turbulence level, and the turbulence length scale, but that the largest observed effect was only a 10 percent augmentation at the nominal stagnation position.

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

Journal of Energy Resources Technology ◽

10.1115/1.3231028 ◽

1984 ◽

Vol 106 (1) ◽

pp. 70-78 ◽

Cited By ~ 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.

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Mixing of an Acoustically Excited Air Jet With a Confined Hot Crossflow

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2906306 ◽

1992 ◽

Vol 114 (1) ◽

pp. 46-54 ◽

Cited By ~ 28

Author(s):

P. J. Vermeulen ◽

P. Grabinski ◽

V. Ramesh

Keyword(s):

Strouhal Number ◽

Temperature Profiles ◽

Measured Temperature ◽

Mixing Zone ◽

Wake Region ◽

Mixing Processes ◽

Jet Mixing ◽

Air Jet ◽

Percent Increase ◽

Jet Structure

The mixing of an acoustically pulsed air jet with a confined hot crossflow has been assessed by temperature profile measurements. These novel experiments were designed to examine the effects of acoustic driver power and Strouhal number on jet structure, penetration, and mixing. The results showed that excitation produced strong changes in the measured temperature profiles. This resulted in significant increases in mixing zone size, penetration (at least 100 percent increase), and mixing, and the length to achieve a given mixed state was shortened by at least 70 percent. There was strong modification to the jet-wake region. The increase in jet penetration and mixing was saturating near 90 W, the largest driving power tested. The jet response as determined by penetration and mixing was optimum at a Strouhal number of 0.27. Overall, pulsating the jet flow significantly improved the jet mixing processes in a controllable manner.

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Strouhal Number for VIV Excitation of Long Slender Structures

Volume 5: Pipelines, Risers, and Subsea Systems ◽

10.1115/omae2018-77433 ◽

2018 ◽

Author(s):

Andrew E. Potts ◽

Douglas A. Potts ◽

Hayden Marcollo ◽

Kanishka Jayasinghe

Keyword(s):

Reynolds Number ◽

Strouhal Number ◽

Degrees Of Freedom ◽

Measurement Techniques ◽

Cross Flow ◽

Degree Of Freedom ◽

Circular Cylinders ◽

Two Degrees Of Freedom ◽

Shedding Frequency ◽

Eddy Shedding

The prediction of Vortex-Induced Vibration (VIV) of cylinders under fluid flow conditions depends upon the eddy shedding frequency, conventionally described by the Strouhal Number. The most commonly cited relationship between Strouhal Number and Reynolds Number for circular cylinders was developed by Lienhard [1], whereby the Strouhal Number exhibits a consistent narrow band of about 0.2 (conventional across the sub-critical Re range), with a pronounced hump peaking at about 0.5 within the critical flow regime. The source data underlying this relationship is re-examined, wherein it was found to be predominantly associated with eddy shedding frequency about fixed or stationary cylinders. The pronounced hump appears to be an artefact of the measurement techniques employed by various investigators to detect eddy-shedding frequency in the wake of the cylinder. A variety of contemporary test data for elastically mounted cylinders, with freedom to oscillate under one degree of freedom (i.e. cross flow) and two degrees of freedom (i.e. cross flow and in-line) were evaluated and compared against the conventional Strouhal Number relationship. It is well established for VIV that the eddy shedding frequency will synchronise with the near resonant motions of a dynamically oscillating cylinder, such that the resultant bandwidth of lock-in exhibits a wider range of effective Strouhal Numbers than that reflected in the narrow-banded relationship about a mean of 0.2. However, whilst cylinders oscillating under one degree of freedom exhibit a mean Strouhal Number of 0.2 consistent with fixed/stationary cylinders, cylinders with two degrees of freedom exhibit a much lower mean Strouhal Number of around 0.14–0.15. Data supports the relationship that Strouhal Number does slightly diminish with increasing Reynolds Number. For oscillating cylinders, the bandwidth about the mean Strouhal Number value appears to remain largely consistent. For many practical structures in the marine environment subject to VIV excitation, such as long span, slender risers, mooring lines, pipeline spans, towed array sonar strings, and alike, the long flexible cylinders will respond in two degrees of freedom, where the identified difference in Strouhal Number is a significant aspect to be accounted for in the modelling of its dynamic behaviour.

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