Effects of Applied Acoustic Fields on Attached Jet Flows

1971 ◽  
Vol 93 (1) ◽  
pp. 63-73 ◽  
Author(s):  
Donald O. Rockwell ◽  
Kenji Toda
Keyword(s):  
Reynolds Numbers ◽  
Jet Flows ◽  
Design Criteria ◽  
Arc Length ◽  
Hot Wire ◽  
Applied Frequency ◽  
Smoke Visualization ◽  
The Third ◽  
Severe Effect ◽  
Jet Nozzle

The effects of application of sound of a spectrum of frequencies and amplitudes to bounded attached jets of a range of Reynolds numbers flowing over surfaces of various radii of curvature have been examined using hot-wire anemometry, smoke visualization, and tuft-deflection techniques. Frequencies of sound to which the jet is sensitive, results of changes in sound amplitude at a given frequency, and the growth of the effects of applied sound with arc length from the nozzle exit were investigated to provide some qualitative design criteria for controlling the sensitivity of flueric elements to externally applied sound. Frequencies of sound which are related to the jet nozzle resonance characteristics have the most severe effect on the attached jet. For a given applied frequency, the flow field of the jet can be altered for a much wider range of jet Reynolds number at higher amplitudes of applied sound than at relatively low amplitudes of applied sound. Four Reynolds numbers regimes can be established to describe the behavior of the attached jet with applied sound, Frequency- and amplitude-dependent jumps in angle of detachment of the jet are attainable in the first two regimes, and deflections of the jet proportional to the applied frequency and amplitude are attainable in the third and fourth regimes.

A time-domain evaluation of the large-scale flow structure in a turbulent jet

1979 ◽  
Vol 367 (1729) ◽  
pp. 193-218 ◽  
Keyword(s):  
Flow Structure ◽  
Time Domain ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Turbulent Jet ◽  
Flow Structures ◽  
Jet Flows ◽  
Hot Wire ◽  
Potential Core ◽  
Large Scale Flow

This paper describes an investigation of the large-scale flow processes which occur in turbulent circular jet flows ( Re > 10 5 ). The existence of regular large-scale flow structures at low and moderate Reynolds numbers ( Re < 5 x 10 4 ) has clearly been demonstrated by flow-visualization experi­ments, but visual evidence for order in jet turbulence becomes ambiguous at a Reynolds number around 7 x 10 4 . A new time-domain technique for the study of two-dimensional large-scale flow structures has been developed by Bruun (1977). In this paper this technique is extended to the study of three-dimensional large-scale flow structures by the inclusion of X hot-wire and circumferential eductions. The evaluated large-scale structures in the turbulent jet ( Re = 2 x 10 5 ) are shown to deviate considerably from the axi-symmetric flow structures which occurs at low and moderate Reynolds numbers ( Re < 5 x 10 4 ). We observe a much smaller deformation rate of the semi-regular flow structure in the potential core in the turbulent jet case, and also the circumferential eductions reveal a rapid radial decrease in the circumferential coherence of the related large-scale flow structure in the mixing region. Further-­more, combining these results with the X hot-wire eductions in the mixing region proved that the major contributions to the shear stress uv is caused by circumferentially-narrow tongues of ‘fast moving ejected’ and ‘slow moving entrained ’fluid, similar to the ‘burst’ and ‘sweep’ events observed previously in turbulent wall boundary layers.

scholarly journals LDV measurements of orifice jet flows at low Reynolds numbers.

1991 ◽  
Vol 57 (534) ◽  
pp. 508-515
Author(s):  
Seiichi WASHIO ◽  
Tadataka KONISHI ◽  
Mitsuru BABA ◽  
Tadashi SAKAGUCHI ◽  
Masato KAMIYA
Keyword(s):  
Reynolds Numbers ◽  
Jet Flows ◽  
Low Reynolds Numbers ◽  
Low Reynolds

scholarly journals Control of a Round Jet Intermittency and Transition to Turbulence by Means of an Annular Synthetic Jet

Actuators ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 185
Author(s):  
Zuzana Antošová ◽  
Zdeněk Trávníček
Keyword(s):  
Reynolds Number ◽  
Active Control ◽  
Flow Regimes ◽  
Velocity Profiles ◽  
Synthetic Jet ◽  
Transition To Turbulence ◽  
Jet Flows ◽  
Maximal Effect ◽  
Hot Wire ◽  
Round Jet

This paper deals with active control of a continuous jet issuing from a long pipe nozzle by means of a concentrically placed annular synthetic jet. The experiments in air cover regimes of laminar, transitional, and turbulent main jet flows (Reynolds number ranges 1082–5181). The velocity profiles (time-mean and fluctuation components) of unforced and forced jets were measured using hot-wire anemometry. Six flow regimes are distinguished, and their parameter map is proposed. The possibility of turbulence reduction by forcing in transitional jets is demonstrated, and the maximal effect is revealed at Re = 2555, where the ratio of the turbulence intensities of the forced and unforced jets is decreased up to 0.45.

scholarly journals Intermittency, Moments, and Friction Coefficient during the Subcritical Transition of Channel Flow

Entropy ◽  
2020 ◽  
Vol 22 (12) ◽  
pp. 1399
Author(s):  
Jinsheng Liu ◽  
Yue Xiao ◽  
Mogeng Li ◽  
Jianjun Tao ◽  
Shengjin Xu
Keyword(s):  
Friction Coefficient ◽  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Test Case ◽  
Structure Model ◽  
Turbulent Structures ◽  
Third Order ◽  
Low Reynolds Numbers ◽  
The Third ◽  
High Turbulence

The intermittent distribution of localized turbulent structures is a key feature of the subcritical transitions in channel flows, which are studied in this paper with a wind channel and theoretical modeling. Entrance disturbances are introduced by small beads, and localized turbulent patches can be triggered at low Reynolds numbers (Re). High turbulence intensity represents strong ability of perturbation spread, and a maximum turbulence intensity is found for every test case as Re ≥ 950, where the turbulence fraction increases abruptly with Re. Skewness can reflect the velocity defects of localized turbulent patches and is revealed to become negative when Re is as low as about 660. It is shown that the third-order moments of the midplane streamwise velocities have minima, while the corresponding forth-order moments have maxima during the transition. These kinematic extremes and different variation scenarios of the friction coefficient during the transition are explained with an intermittent structure model, where the robust localized turbulent structure is simplified as a turbulence unit, a structure whose statistical properties are only weak functions of the Reynolds number.

An experimental study of round jets in cross-flow

1996 ◽  
Vol 306 ◽  
pp. 111-144 ◽  
Author(s):  
R. M. Kelso ◽  
T. T. Lim ◽  
A. E. Perry
Keyword(s):  
Flow Visualization ◽  
Shear Layer ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Stream Velocity ◽  
Hot Wire ◽  
Vortex System ◽  
Freestream Velocity ◽  
Round Jets ◽  
Topological Features

The structure of round jets in cross-flow was studied using flow visualization techniques and flying-hot-wire measurements. The study was restricted to jet to freestream velocity ratios ranging from 2.0 to 6.0 and Reynolds numbers based on the jet diameter and free-stream velocity in the range of 440 to 6200.Flow visualization studies, together with time-averaged flying-hot-wire measurements in both vertical and horizontal sectional planes, have allowed the mean topological features of the jet in cross-flow to be identified using critical point theory. These features include the horseshoe (or necklace) vortex system originating just upstream of the jet, a separation region inside the pipe upstream of the pipe exit, the roll-up of the jet shear layer which initiates the counter-rotating vortex pair and the separation of the flat-wall boundary layer leading to the formation of the wake vortex system beneath the downstream side of the jet.The topology of the vortex ring roll-up of the jet shear layer was studied in detail using phase-averaged flying-hot-wire measurements of the velocity field when the roll-up was forced. From these data it is possible to examine the evolution of the shear layer topology. These results are supported by the flow visualization studies which also aid in their interpretation.The study also shows that, for velocity ratios ranging from 4.0 to 6.0, the unsteady upright vortices in the wake may form by different mechanisms, depending on the Reynolds number. It is found that at high Reynolds numbers, the upright vortex orientation in the wake may change intermittently from one configuration of vortex street to another. Three mechanisms are proposed to explain these observations.

Vortex Shedding from Smooth and Roughened Cylinders in Cross-Flow near a Plane Surface

1979 ◽  
Vol 30 (1) ◽  
pp. 305-321 ◽  
Author(s):  
G. Buresti ◽  
A. Lanciotti
Keyword(s):  
Vortex Shedding ◽  
Plane Surface ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Cylinder Surface ◽  
Hot Wire ◽  
Cylinder Axis ◽  
Supercritical Regime ◽  
Subcritical Regime ◽  
Smooth Cylinder

SummaryThe characteristics of the flow field around a circular cylinder in cross-flow placed at various distances from a plane, parallel both to the flow and to the cylinder axis, were analysed using a hot wire anemometer. Experiments were performed in a wind tunnel with Reynolds numbers ranging from 0.85×105 to 3×105. The spectra of the hot wire signals were obtained using a Fast Fourier Transform technique programmed on a PDP 11/40 computer. As regards a smooth cylinder, the main features of the vortex shedding mechanism in the subcritical regime remained unaltered for distances from the plane greater than approximately 0.4 diameters; in particular the Strouhal frequency did not show any significant variation relative to the typical value for an isolated cylinder. As for lower values of the distance from the plane, the regular vortex shedding disappeared and the hot wire spectra showed typical turbulent features. The possibility of obtaining supercritical conditions by roughening the cylinder surface was confirmed together with the importance of the Reynolds number based on the typical roughness size, Rk, in the evaluation of the flow regime around the cylinder. In the case of roughened cylinders, and with values of Rk below-350, the regular vortex shedding disappeared at a distance from the plane smaller than 0.3 diameters. This fact suggests that, at least in part of the supercritical regime, the influence of the plane can be smaller than in the subcritical regime.

Hot-wire spatial resolution issues in wall-bounded turbulence

2009 ◽  
Vol 635 ◽  
pp. 103-136 ◽  
Author(s):  
N. HUTCHINS ◽  
T. B. NICKELS ◽  
I. MARUSIC ◽  
M. S. CHONG
Keyword(s):  
Reynolds Number ◽  
Boundary Layers ◽  
Spatial Resolution ◽  
Reynolds Numbers ◽  
Energy Spectra ◽  
Small Scale ◽  
Wire Length ◽  
Hot Wire ◽  
Wide Range ◽  
Near Wall

Careful reassessment of new and pre-existing data shows that recorded scatter in the hot-wire-measured near-wall peak in viscous-scaled streamwise turbulence intensity is due in large part to the simultaneous competing effects of the Reynolds number and viscous-scaled wire length l+. An empirical expression is given to account for these effects. These competing factors can explain much of the disparity in existing literature, in particular explaining how previous studies have incorrectly concluded that the inner-scaled near-wall peak is independent of the Reynolds number. We also investigate the appearance of the so-called outer peak in the broadband streamwise intensity, found by some researchers to occur within the log region of high-Reynolds-number boundary layers. We show that the ‘outer peak’ is consistent with the attenuation of small scales due to large l+. For turbulent boundary layers, in the absence of spatial resolution problems, there is no outer peak up to the Reynolds numbers investigated here (Reτ = 18830). Beyond these Reynolds numbers – and for internal geometries – the existence of such peaks remains open to debate. Fully mapped energy spectra, obtained with a range of l+, are used to demonstrate this phenomenon. We also establish the basis for a ‘maximum flow frequency’, a minimum time scale that the full experimental system must be capable of resolving, in order to ensure that the energetic scales are not attenuated. It is shown that where this criterion is not met (in this instance due to insufficient anemometer/probe response), an outer peak can be reproduced in the streamwise intensity even in the absence of spatial resolution problems. It is also shown that attenuation due to wire length can erode the region of the streamwise energy spectra in which we would normally expect to see kx−1 scaling. In doing so, we are able to rationalize much of the disparity in pre-existing literature over the kx−1 region of self-similarity. Not surprisingly, the attenuated spectra also indicate that Kolmogorov-scaled spectra are subject to substantial errors due to wire spatial resolution issues. These errors persist to wavelengths far beyond those which we might otherwise assume from simple isotropic assumptions of small-scale motions. The effects of hot-wire length-to-diameter ratio (l/d) are also briefly investigated. For the moderate wire Reynolds numbers investigated here, reducing l/d from 200 to 100 has a detrimental effect on measured turbulent fluctuations at a wide range of energetic scales, affecting both the broadband intensity and the energy spectra.

A Convection Heat Transfer Correlation for a Binary Air-Helium Mixture at Low Reynolds Number

2007 ◽  
Vol 129 (11) ◽  
pp. 1494-1505 ◽  
Author(s):  
Arindam Banerjee ◽  
Malcolm J. Andrews
Keyword(s):  
Heat Transfer ◽  
Mixing Layer ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Gas Mixtures ◽  
Correlation Technique ◽  
Hot Wire ◽  
Nusselt Numbers ◽  
Low Reynolds ◽  
Constant Temperature Anemometer

The results of experiments investigating heat transfer from a hot wire in a binary mixture of air and helium are reported. The measurements were made with a constant temperature anemometer at low Reynolds numbers (0.25<Re<1.2) and correlated by treating the data in terms of a suitably defined Reynolds and Nusselt numbers based on the wire diameter. The correlation was obtained by taking into account the temperature dependency of gas properties, properties of binary gas mixtures, and the fluid slip at the probe surfaces as well as gas accommodation effects. The correlation has been used to measure velocity and velocity-density statistics across a buoyancy driven Rayleigh–Taylor mixing layer with a hot wire. The measured values obtained with the correlation agree well with measurements obtained with a more rigorous and extensive calibration technique (at two different overheat ratios). The reported correlation technique can be used as a faster and less expensive method for calibrating hot wires in binary gas mixtures.

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