Air trapping at impact of a rigid sphere onto a liquid

AbstractAn experimental and theoretical investigation of the air trapping by a blunt, locally spherical body impacting onto the free surface of water is conducted. In the parameter regime previously studied theoretically by Hicks &amp; Purvis (J. Fluid Mech., vol. 649, 2010, pp. 135–163), excellent agreement between experimental data and theoretical modelling is obtained. Earlier predictions of the radius of the trapped air pocket are confirmed. A boundary element method is used to consider air cushioning of an impact of an axisymmetric body into water. Efficient computational methods are obtained by analytically integrating the boundary integral equation over the azimuthal variable. The resulting numerically computed free-surface profiles predict an annular touchdown region in excellent agreement with the experiments.</jats:p

Internal wave attractors examined using laboratory experiments and 3D numerical simulations

In the present paper, we combine numerical and experimental approaches to study the dynamics of stable and unstable internal wave attractors. The problem is considered in a classic trapezoidal setup filled with a uniformly stratified fluid. Energy is injected into the system at global scale by the small-amplitude motion of a vertical wall. Wave motion in the test tank is measured with the help of conventional synthetic schlieren and PIV techniques. The numerical setup closely reproduces the experimental one in terms of geometry and the operational range of the Reynolds and Schmidt numbers. The spectral element method is used as a numerical tool to simulate the nonlinear dynamics of a viscous salt-stratified fluid. We show that the results of three-dimensional calculations are in excellent qualitative and quantitative agreement with the experimental data, including the spatial and temporal parameters of the secondary waves produced by triadic resonance instability. Further, we explore experimentally and numerically the effect of lateral walls on secondary currents and spanwise distribution of velocity amplitudes in the wave beams. Finally, we test the assumption of a bidimensional flow and estimate the error made in synthetic schlieren measurements due to this assumption

Generation of internal gravity waves by a katabatic wind in an idealized alpine valley

“The original publication is available at www.springerlink.com”. Copyright Springer. DOI: 10.1007/s00703-009-0349-4The dynamics of the atmospheric boundary layer in an alpine valley at night or in winter is dominated by katabatic (or down-slope) flows. As predicted by McNider (1982) oscillations along the slope are expected to occur if the fluid is stably-stratified, as a result of buoyancy and adiabatic cooling/warming effects. Internal gravity waves must also be generated by the katabatic flows because of the stable stratification. The aim of the present paper is to identify and characterize the oscillations in the katabatic flow as well as the internal gravity wave field emitted by this flow. Numerical simulations with the ARPS code are performed for this purpose, for an idealized configuration of the Chamonix valley. We show that the oscillations near the slope are non propagating motions, whose period is well predicted by the single particle model of McNider (1982) and equal to 10 to 11 mn. As for the wave field, its frequency is close to 0.85 N, where N is the value of the Brunt-Väisälä frequency in the generation region of the waves, consistently with previous academic studies of wave emission by turbulent motions in a stratified fluid. This leads to a wave period of 7 to 8 mn.Peer reviewe