Velocity measurements in the field of an internal gravity wave by means of speckle photography

Gärtner, Uwe; Wernekinck, U.; Merzkirch, W.

doi:10.1007/bf00369121

Cited by 16 publications

(3 citation statements)

References 7 publications

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“…This phase pattern is identical to that predicted by Lighthill [8] and Mowbray and Rarity [24] for internal waves produced by the vertical translation of a line or point source in a density-stratified fluid (see also Refs. [25][26][27][28]). Note that ϕ 0 is the phase relative to the phase at emission ϕ e which remains unspecified here.…”

Section: A Inviscid Wake Of a Line Objectmentioning

confidence: 99%

Wake of inertial waves of a horizontal cylinder in horizontal translation

et al. 2018

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We analyze theoretically and experimentally the wake behind a horizontal cylinder of diameter d horizontally translated at constant velocity U in a fluid rotating about the vertical axis at a rate Ω. Using particle image velocimetry measurements in the rotating frame, we show that the wake is stabilized by rotation for Reynolds number Re = U d/ν much larger than in a non-rotating fluid. Over the explored range of parameters, the limit of stability is Re (275 ± 25)/Ro, with Ro = U/2Ωd the Rossby number, indicating that the stabilizing process is governed by the Ekman pumping in the boundary layer. At low Rossby number, the wake takes the form of a stationary pattern of inertial waves, similar to the wake of surface gravity waves behind a ship. We compare this steady wake pattern to a model, originally developed by [Johnson, J. Fluid Mech. 120, 359 (1982)], assuming a free-slip boundary condition and a weak streamwise perturbation. Our measurements show a quantitative agreement with this model for Ro 0.3. At larger Rossby number, the phase pattern of the wake is close to the prediction for an infinitely small line object. However, the wake amplitude and phase origin are not correctly described by the weak-streamwise-perturbation model, calling for an alternative model for the boundary condition at moderate rotation rate.

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Section: A Inviscid Wake Of a Line Objectmentioning

confidence: 99%

Wake of inertial waves of a horizontal cylinder in horizontal translation

et al. 2018

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“…Experiments have involved a wide range of bodies and motions. This includes: a cylinder, in uniform horizontal (Stevenson (Stevenson et al 1983;Gartner 1983u, b ;Gartner, Wernekinck & Merzkirch 1986) or inclined (Stevenson 1968) motion, or in uniform horizontal or inclined motion with 0scillations (Stevenson & Thomas 1969), or in accelerated or curved motion (Stevenson 1973;Peat & Stevenson 1975; a sphere, in uniform horizontal (Peat & Stevenson 1975;Makarov & Chashechkin 1981Chashechkin 1989;Hopfinger et al 1991;Bonneton, Chomaz & Hopfinger 1993), vertical (Mowbray & Rarity 1967) or inclined (Peat & Stevenson 1975) motion, or in uniform vertical (Stevenson 1969) or horizontal or inclined (Peat & Stevenson 1975) motion with oscillations; a slender ellipsoid (Gilreath & Brandt 1985), a triangular ridge of finite width (Castro, Snyder & Marsh 1983;Castro 1987), and two-dimensional obstacles (Baines & Hoinka 1985), all of which in uniform horizontal motion. Numerical simulations are comparatively few.…”

Section: Experiments and Numerical Simulationsmentioning

confidence: 99%

Internal wave generation in uniformly stratified fluids. Part 2. Moving point sources

Voisin

1994

J. Fluid Mech.

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The Green's function method is applied to the generation of internal gravity waves by a moving point mass source. Arbitrary motion of a source of arbitrary time dependence is treated using the impulsive Green's function, while ‘classical’ approaches of uniform motion of a steady or oscillatory source are recovered using the monochromatic Green's function. Waves have locally the structure of impulsive waves, emitted at the retarded time tr, and having propagated with the group velocity; at each position and time an implicit equation defines tr, in terms of which the waves are written. A source both oscillating and moving generates two systems of waves, with respectively positive and negative frequencies, and when oscillations vanish these systems merge into one.Three particular cases are considered: the uniform horizontal and vertical motions of a steady source, and the uniform horizontal motion of an oscillatory source. Waves spread downstream of the steady source. For the oscillatory source they can extend both upstream and downstream, depending on the ratio of the source frequency to the buoyancy frequency, and are contained inside conical wavefronts, parts of which are caustics. For horizontal motion, moreover, the steady analysis (based on the monochromatic Green's function) reveals the presence of two insignificant contributions overlooked by the unsteady analysis (based on the impulsive Green's function), but which for an extended source may become of the same order as the main contribution. Among those is an upstream columnar disturbance associated with blocking.

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“…Meynart (1979) first applied the spatial frequency filtering technique in the velocity field measurement of fluid flows to obtain a velocity contour map of Benard convection. After that this technique was applied to an internal gravity wave by Gartner et al (1986), a convection in a liquid by Meynart et al (1987), a Couette flow by Narumi et al (1988), and some types of flow by the author (Suzuki et al, 1983;Kawahashi et al, 1986). Digital filtering on the basis of numerical convolution integral was presented by Grant & Qiu (1990).…”

Section: Introductionmentioning

confidence: 99%

Whole field spatial frequency analysis of double-or multiple-exposed PIV images

Kawahashi

Kamimura

Hirahara

1998

J Vis

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Speckle Velocimetry or high-image density PIV gives a velocity vector map of a twodimensional flow field by point-by-point spatial frequency analysis of local pattern at an interrogation spot in a double-or a multiple-exposed image of laser speckle or pseudo-speckle pattern generated by pulsed laser-light-sheet illuminations of a plane in the flow densely seeded with fine particles. The whole field spatial frequency analysis of the double-or multiple-exposed PIV image gives more useful information of the flow field. Optical Fourier transform is a conventional technique not only for the local spatial frequency analysis but for the whole field analysis. Filtering of spatial frequency is one of the typical techniques for the latter which can reconstruct a velocity contour or a component velocity contour map of the flow. Fundamentally this technique is a simple and efficient analogue method to get more information in the velocity field analysis of the flow than a digital image processing, but in practical applications the measurement is restricted to simple flows because of optical noise and low spatial resolution. In order to improve the technique, the fundamental characteristics of the filtering and the noise yielded in the filtering process must be investigated. Meanwhile, wavelet analysis can also be applied to the whole field spatial frequency analysis of PIV image. In this paper the filtering technique is examined by numerical convolution integral, and the results obtained are compared with ones obtained by the wavelet analysis.

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Velocity measurements in the field of an internal gravity wave by means of speckle photography

Cited by 16 publications

References 7 publications

Wake of inertial waves of a horizontal cylinder in horizontal translation

Wake of inertial waves of a horizontal cylinder in horizontal translation

Internal wave generation in uniformly stratified fluids. Part 2. Moving point sources

Whole field spatial frequency analysis of double-or multiple-exposed PIV images

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