Measurements of the shear-stress variation along and the velocity profiles above a solid wavy wall bounding a turbulent flow are presented for waves with height-to-length ratios of 2a/λ = 0·0312 and 0·05. These are compared with previous measurements of the wall shear stress reported by Thorsness (1975) and by Morrisroe (1970) for 2a/λ = 0·012. The investigation covered a range of conditions from those for which a linear behaviour is observed to those for which a separated flow is just being initiated.Pressure measurements indicate a linear response in that the spatial variation is described quite well by a single harmonic with a wavelength equal to that of the surface. However, the variation of τw for waves with 2a/λ = 0·0312 and 0·05 can be more rapid on the leeward side of the wave. The degree of departure from a sinusoidal variation increases with increasing wave height and fluid velocity and, from the results reported in this paper, it is suggested that nonlinear behaviour will become evident when au*/v [ges ] 27.Many aspects of the flow for all three waves are described by a solution of the linear momentum equations previously presented by Thorsness (1975) and by Thorsness & Hanratty (1977). These include the phase and amplitude of the pressure profile and the first harmonic of the shear-stress profile and the velocity field outside the viscous wall region.These results suggest that up to separation the flow is approximated quite well by linear theory. Nonlinearities affect the flow only in a region very close to the wave surface and are manifested by the appearance of higher harmonics in the variation of τw.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112079002196

Influence of the amplitude of a solid wavy wall on a turbulent flow. Part 1. Non-separated flows

: Measurements were made of the variation of wall shear stress and of the root mean square level of the fluctuating shear stress along a solid wavy surface with an amplitude of 0.014 in. and a wavelength of 2 in. The phase angle associated with the spatial variation of the wave-induced shear stress passes through a well defined maximum when measured as a function of the dimensionless wave number, alpha = 2 pi nu/lambda u star. Measurements of the wall shear stress and in particular the location of this maximum provide an extremely sensitive test of turbulence models which pay particular attention to the viscous wall region. The use of a quasi-laminar assumption, whereby the wave induced changes of the Reynolds stresses are ignored, gives good agreement with the measurements of the variation of the wall shear stress for large values of alpha. An equilibrium turbulence assumption in which the wave induced Reynolds stresses are assumed to adjust instantaneously to changes in flow conditions along the wave surface is valid for only small values of alpha. In the range of 0.0005 alpha 0.2 it is necessary to use a model for wave induced Reynolds stresses which takes account of the fact that the turbulence does not respond immediately to changes in the flow conditions. The mixing length model of Loyd et al. provides the best fit of the data. A modification of this model which takes into account the effect of streamline curvature on the mixing length provides an improved fit of the available pressure measurements over a wavy surface.

Turbulent Flow over Small Amplitude Solid Waves

Interfacial instabilities of air-driven liquid films

The rate of the energy dissipation in wind-generated waves is evaluated as the difference between the rate of the energy received from the wind, and the rate of development of the wave energy An equation is derived from the rate of the energy dissipation in terms of wave characteritics, broadness of the directional distribution of spectral compoennts, and a coeffciient of turbulent viscosity A hypothesis is made that the latter is composed of two parts, the one directly produced by the wind drag, and the other by the wave formation The first is evaluated on basis of Ekman's theory of ocean currents, and of Richardson-Kolmogorov 4/3 power scaling law The the functional form of the second part is obtained by dimesnional reasoning, and a universal empirical coefficient is computed, which has a constant value for all wind velocities, and alls stages of the wave development

The dissipation of energy in wind-generated waves: a hypothesis

/pdf/recherches-en-soufflerie-sur-l-action-relative-de-la-houle-4y5k5025qq.pdf

Recherches en soufflerie sur l'action relative de la houle et du vent

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Recherches en soufflerie sur l'action relative de la houle et du vent