Experimental investigation of the dynamic stall phenomenon on a NACA 23012 oscillating airfoil

Abstract

An extensive experimental investigation was conducted on an oscillating NACA 23012 airfoil to study the flow structures and the consequent performances in dynamic stall conditions. The testing activity involved two different measurement techniques: fast unsteady pressure measurements and particle image velocimetry. The analysis of the experimental data set made possible to achieve a deep insight in the mechanism of the dynamic stall phenomena for the NACA 23012 airfoil in the different dynamic stall regimes. In particular, the flow velocity field measured on the airfoil upper surface described in detail the mechanism of the formation, migration and shedding of strong vortical structures characteristic of the deep dynamic stall. In addition, Gurney flap effects were investigated. The experimental results showed that it would be advantageous to deploy active Gurney flaps to improve helicopter rotor blade performances. The whole set of experimental results can be considered as a reference to validate computational fluid dynamics tools.

Experimental investigation of a trailing edge L-shaped tab on a pitching airfoil in deep dynamic stall conditions

“…Small discrepancies between the pitching moment curves can be observed just in the range between 16 5 5 18 in downstroke. In fact, the flow field in this incidence range is characterised by severe unsteadiness, as it was shown in the works by Zanotti and Gibertini 15 and Zanotti et al 16 Figures 7 and 8 show the comparison of the lift and quarter chord moment coefficients evaluated with the L-shaped tab deployed and retracted with respect to the clean airfoil configuration. The standard deviation of the airloads coefficients is plotted on all the airloads coefficients curves.…”

“…16,31 Thus, the flow fields presented in Figure 15 have to be taken in account just for giving an indication about the local effects introduced by the L-shaped tab, as they represent planar cuts through a strongly 3D flow field.…”

“…[14][15][16][17] The blade section model, with a c ¼ 0.3 m chord and a b ¼ 0.93 m span, is composed of three aluminium machined sections attached to an internal metallic structure. The model central section is interchangeable depending on the measurement technique involved.…”

Design, Manufacturing and Wind Tunnel Validation of a Morphing Compliant Wing

“…The Sergio De Ponte wind tunnel at POLIMI is shown in Fig. 13 together with the oscillating system used for the precision positioning of the morphing wing model in terms of angle of attack [33]. As already mentioned, the morphing wing model has a span of 930 mm and a chord of 418 mm.…”

Wake Measurements behind an Oscillating Airfoil in Dynamic Stall Conditions

“…In fact, several research activities both in experimental and numerical fields investigated the effectiveness of different dynamic stall control systems integrated into the blade section (e.g., [4][5][6]). Moreover, the study of the fine details involved in the physics of this phenomenon was widely investigated in the recent years, as, for instance, in [7][8][9]. In this research area, the study of the unsteady wake of an oscillating airfoil features a relatively low attention by the literature with respect to the evaluation of the characteristic flow field and the measurement of the airloads on oscillating airfoils in dynamic stall conditions, as demonstrated by the large number of research activities focused on this topic (e.g., [9][10][11][12]).…”