Unsteadiness in Flow over a Flat Plate at Angle-of-Attack at Low Reynolds Numbers

Abstract

Flow over an impulsively started low-aspect-ratio flat plate at angle-of-attack is investigated for a Reynolds number of 300. Numerical simulations, validated by a companion experiment, are performed to study the influence of aspect ratio, angle of attack, and planform geometry on the interaction of the leading-edge and tip vortices and resulting lift and drag coefficients. Aspect ratio is found to significantly influence the wake pattern and the force experienced by the plate. For large aspect ratio plates, leading-edge vortices evolved into hairpin vortices that eventually detached from the plate, interacting with the tip vortices in a complex manner. Separation of the leading-edge vortex is delayed to some extent by having convective transport of the spanwise vorticity as observed in flow over elliptic, semicircular, and delta-shaped planforms. The time at which lift achieves its maximum is observed to be fairly constant over different aspect ratios, angles of attack, and planform geometries during the initial transient. Preliminary results are also presented for flow over plates with steady actuation near the leading edge.

Effect of Tip Vortices in Low-Reynolds-Number Poststall Flow Control

“…The regularization has not been observed to influence the flowfield and the body force in any significant manner [27]. The side force generated at high angles of attack in asymmetric flow (about the midspan) is found to be at least an order of magnitude smaller than the preceding two forces and is not focused upon in the current study.…”

“…The velocity boundary condition of uniform flow is specified at the computational boundary, except for the outlet, at which the convective boundary condition @u=@t U 1 @u=@x 0 is applied. Validation of the computational setup is offered in [13,27], showing good agreement between the current simulation and the experiment for steady and unsteady flows around an impulsively started plate of AR 2 at Re 100.…”

On the role of thickness ratio and location of axis of rotation in the flat plate motions

“…Similar to other quasi-steady models (Amandolese et al, 2013;Fernandes and Mirzaeisefat, 2015), we consider that these components are uncoupled, and can be expressed as a function of α. Previous studies have shown that compared to the lift force, the drag under small attack angles is much smaller and can be neglected (Taira et al, 2007;Ortiz et al, 2015). Also, M re is ignored here for estimating the dominating pitch frequency, so are the damping terms considering that they are comparatively small (see Part A).…”

Vortex separation and interaction in the wake of inclined trapezoidal plates

“…Following that study, the flows over rectangular plates under actuation (Taira et al 2007) and periodic excitation were investigated as a means to control the flow.…”

“…Notably, in a wind-tunnel study, Torres & Mueller (2004) documented the aerodynamic performance of 28 different planforms based on four shapes with different aspect ratios, including the rectangle and ellipse. Subsequently, an analysis of different wing shapes was provided by Taira, Dickson & Colonius (2007). They compared the force on plates with the same area but different shapes (rectangular, elliptic, semicircular and delta shaped).…”