Drag-reduction techniques capable of reducing the level of turbulent friction through wall-parallel movement of the wall are described, with special emphasis placed on spanwise movement. The discussion is confined to active open-loop control strategies, although feedback control is briefly mentioned with regard to peculiarities of spanwise sensing and/or actuation. Theoretical considerations ar...

The drag-reduction mechanism of spanwise wall oscillation in a turbulent channel was investigated as an extension the work Yakeno et al. [“Modification quasi-streamwise vortical structure drag-reduced flow with oscillation,” Phys. Fluids 26, 085109 (2014)] at low Reynolds number. Flow instability evaluated by computing transient energy growth under oscillating base which governed generation nea...

The presence of large-scale vortices with high spanwise coherence has been observed in the atmospheric boundary layer (ABL). This study investigates an innovative technique to generate a large-scale spanwise vortex from the oscillation of a surface-mounted fence in a wind tunnel. Characteristics of the large vortex with a well-defined length scale and its development with downstream distance be...

In the present paper laminar separation bubbles are investigated by means of direct numerical simulations with respect to steady and unsteady 2D and 3D Tollmien-Schlichting (TS) like boundary layer disturbances. The specific influence of several disturbance modes on the size and shape of the laminar separation bubble are considered to allow for an effective reduction of the region of separated ...

The drag reduction properties of a turbulent channel flow modified by spanwise sinusoidal oscillations of the walls are investigated by direct numerical simulations. The work is based on the linear relation between the drag reduction and the parameter S, function of the maximum wall velocity and the period of the oscillation. This quantity, first determined by JI-Choi et al. (2002) and later st...

Direct numerical simulation data of a Mach 2.9, 24◦ compression ramp configuration are used to analyse the shock motion. The motion can be observed from the animated DNS data available with the online version of the paper and from wall-pressure and mass-flux signals measured in the free stream. The characteristic low frequency is in the range of (0.007–0.013) U∞/δ, as found previously. The shoc...

Weidan Ni 1,†, Lipeng Lu 1,†, Catherine Le Ribault 2,† and Jian Fang 1,3,*,† 1 National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, School of Energy and Power Engineering, Beihang University, 37 Xueyuan Road, Haidian District, Beijing 100191, China; [email protected] (W.N.); [email protected] (L.L.) 2 Laboratoire de Mécanique Des Fluides (LMFA), Ecole Centrale...

Subjecting a boundary layer to sudden or changing strain can have a profound effect on the flow. In turbulent boundary layers, oscillating the wall has been shown in previous studies as a viable mechanism to reduce drag. At lower Reynolds numbers, and in particular in the transition regime, the flow response is complex. On the one hand, the three dimensionality of the base state can lead to new...