Forces and Moments on Flat Plates of Small Aspect Ratio with Application to PV Wind Loads and Small Wind Turbine Blades

Abstract

Abstract:To improve knowledge of the wind loads on photovoltaic structures mounted on flat roofs at the high angles required in high latitudes, and to study starting flow on low aspect ratio wind turbine blades, a series of wind tunnel tests were undertaken. Thin flat plates of aspect ratios between 0.4 and 9.0 were mounted on a sensitive three-component instantaneous force and moment sensor. The Reynolds numbers varied from 6 × 10 4 to 2 × 10 5 . Measurements were made for angles of attack between 0° and 90° both in the free stream and in wall proximity with increased turbulence and mean shear. The ratio of drag to lift closely follows the inverse tangent of the angle of incidence for virtually all measurements. This implies that the forces of interest are due largely to the instantaneous pressure distribution around the plate and are not significantly influenced by shear stresses. The instantaneous forces appear most complex for the smaller aspect ratios but the intensity of the normal force fluctuations is between 10% and 20% in the free-steam but can exceed 30% near the wall. As the wind tunnel floor is approached, the lift and drag reduce with increasing aspect ratio, and there is a reduction in the high frequency components of the forces. It is shown that the centre of pressure is closer to the centre of the plates than the quarter-chord position for nearly all cases.

Low Reynolds Number Numerical Simulation of the Aerodynamic Coefficients of a 3D Wing

“…The behavior of a 3D wing, analyzing the forces (lift, drag & normal) on several finite wings of small to large aspect ratio has been experimentally investigated at low Reynolds number (Ortiz et al, 2015). Their results stated that lift to drag ratio (L/D ratio) follows the inverse tangent of the angle of incidence for almost all experimental cases.…”

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).…”

Energetic design of a new autogyro aircraft with cyclorotors with possibility of energy harvesting

“…According to [8] and [9], it can be possible to use the following empirical relations for CD and CL at different angles of attach.…”

“…The experimental results by Ortiz [9] allow also considering experimental values that can be easily interpolated. Figure 11.…”