Experimental investigation on the aerodynamic behavior of square cylinders with rounded corners

The influence of corner shaping on the aerodynamic behavior of square cylinders is studied through wind tunnel tests. Beside the sharp-edge corner condition considered as a benchmark, two different rounded-corner radii (r/b=1/15 and 2/15) are studied. Global forces and surface pressure are simultaneously measured in the Reynolds number range between 1.7×10⁴ and 2.3×10⁵. The measurements are extended to angles of incidence between 0° and 45°, but the analysis and the discussion presented herein is focused on the low angle of incidence range. It is found that the critical angle of incidence, corresponding to the flow reattachment on the lateral face exposed to the flow, decreases as r/b increases and that an intermittent flow condition exists. In the case of turbulent incoming flow, two different aerodynamic regimes governed by the Reynolds number have been recognized.     

Extension of the Kida law in turbulenceExtension de la loi de Kida en turbulence

We extend the validity range of Kida's log-stable law of stability index α=1.65 and intermittency parameter μ=0.2 to a new range of Reynolds number. This law describes intermittencies in fully developed turbulent flows or more precisely the p.d.f. of turbulence dissipation. Former measurements of the hyper-flatness factors of order 4, 5, 6 of turbulent velocity increments, coming from both experimental works and numerical simulations are used. We show that the power-law variation of these hyper-flatness factors with Taylor scale based Reynolds numbers Re_λ can be fitted, for Re_λ ranging from 35 to 750, by a log-stable law of stability index α=1.65 and intermittency parameter μ=0.21. To cite this article: N. Rimbert, O. Séro-Guillaume, C. R. Mecanique 331 (2003).     

A case of strong nonlinearity: Intermittency in highly turbulent flows

It has long been suspected that flows of incompressible fluids at large or infinite Reynolds number (namely at small or zero viscosity) may present finite time singularities. We review briefly the theoretical situation on this point. We discuss the effect of a small viscosity on the self-similar solution to the Euler equations for inviscid fluids. Then we show that single-point records of velocity fluctuations in the Modane wind tunnel display correlations between large velocities and large accelerations in full agreement with scaling laws derived from Leray's equations (1934) for self-similar singular solutions to the fluid equations. Conversely, those experimental velocity–acceleration correlations are contradictory to the Kolmogorov scaling laws.     

Lévy models and scale invariance properties applied to Geophysics

In this work we study scale invariant functions and stochastic Lévy models and we apply them to geophysical data. We show that a pattern arises from the scale invariance property and Lévy flight models that may be used to estimate parameters related to some major event–major earthquakes.     

间歇性排气噪声源的特性及消声器结构的研究

排气噪声可分为稳定排气噪声，周期性排气噪声和间歇性排气噪声，通过对锻压机离合器与制动器的排气噪声源的特性研究，指出间歇性气噪声是由管道噪声，阀门噪声和喷口噪声所组成，首次指出了间歇性排气噪声存在单极子噪声及爆炸声。通过理论计算及试验建立了一种有效的滤波了噪消声器结构。