Experimental Studies of an Accelerating, Pitching, Flat-Plate at Low Reynolds Number

Abstract

The understanding of low Reynolds number aerodynamics is becoming increasingly prevalent with the recent surge in interest in advanced Micro-Air Vehicle (MAV) technology. Research in this area has been primarily stimulated by a military need for smaller, more versatile, autonomous, surveillance aircraft. The mechanism for providing the high lift coe cient required for MAV applications is thought to be largely influenced by the formation of a Leading Edge Vortex (LEV). This paper analyses experimentally, the influence of the LEV e↵ect for a flat plate wing (A = 4) under fast and slow pitch-up motions at Re =10,000 using a combination of dye flow visualisation and PIV measurements. It is found that a fast pitch over 1c shows a flow topology dominant LEV, while for a slow pitch case over 6c, the flow is largely separated. The development of the suction surface flow and the LEV was strongly correlated with the kinematics of the leading edge, suggesting that the e↵ective local angle of incidence at the Leading Edge (LE) is of considerable significance in unsteady pitching motions. NomenclatureA Aspect Ratio b Wing span, m c Wing chord, m c max Maximum number of chords travelled k Reduced frequency LE Leading Edge LEV Leading Edge Vortex Q Q-criterion vortex detection parameter s Distance travelled in chord lengths, m TE Trailing Edge TEV Trailing Edge Vortex t Time, s U inf Reference velocity, ms 1 ↵ Angle of incidence, ↵ Pitch rate, rad/s ✏ Error ci Swirling Strength ⇢ Density, kg/m 3

Exploring the Impact of Rapidly Actuated Control Surfaces on Drone Aerodynamics

“…The study by [31], where TECS was dynamically actuated from 0 • to 30 • , addressed this particular question and found the transient lift/pitching moment response to be similar, whether the fore element was at an incidence of 0 • or 20 • . Investigations of the effect of actuation rates on the LEV size were also previously carried out by [33][34][35][36][37][38]. In these investigations, it was found that increasing the pitch rate delayed the formation of LEVs on the upper surface and made the LEVs more compact and stronger, thus producing a much larger transient C L .…”

Low Reynolds Number Experimental Studies on Flat Plates

“…The system employs a CCD high-speed camera, which has a frame rate capability of more than 5x10 4 Hz, at a resolution of 1024 x 1024 pixels. The frame rate is selected to give a pixel displacement between images of between 2 and 5 pixels.…”

“…Stevens et al 4 used a simple kinematic argument to interpret PIV and flow visualisation data. For a wing pitched about the mid-chord, the development of the suction surface flow and the Leading Edge Vortex (LEV) was strongly correlated with the kinematics of the Leading Edge (LE), suggesting that the e↵ective local angle of incidence is of considerable significance in unsteady pitching motions.…”

Vortex dynamics around pitching plates

“…Study of the vortex dynamics around plates undergoing unsteady motions has been identified as an international research task by the NATO AVT-202 Group and the AIAA Fluid Dynamics Technical Committee's Low Reynolds Number Discussion Group. The identified research task encompasses a wide variety of motions, including pitching 8,9 , rotation 10,11 , various acceleration profiles 12,13 , and the combination thereof 14 .…”