Experimental-numerical investigation of a pitching airfoil in deep dynamic stall

Abstract

The results of a comprehensive experimental campaign are compared to computational fluid dynamics simulations results to assess the modelling capabilities for a NACA 23012 pitching airfoil in deep dynamic stall regime. The experimental campaign involved fast unsteady pressure measurements and particle image velocimetry. Two-dimensional simulations were carried out with EDGE, developed by FOI. The investigated test case consists in a sinusoidal pitching motion with a 10 amplitude and a reduced frequency of 0.1 around a mean angle of attack of 10 . The behaviour of the experimental lift and pitching moment coefficients is in close agreement with the two-dimensional simulations results, also during the downstroke motion where the flow field is characterised by severe unsteadiness conditions. A three-dimensional numerical model was built to evaluate the relevance of three-dimensional effects on the experiments. Three-dimensional simulations were carried out using the commercial code FLUENT. During upstroke motion, three-dimensional simulations results are in better agreement with the experiments, in particular in terms of the lift coefficient curve slope and of the pitching moment coefficient peak. The flow fields evaluated by particle image velocimetry surveys show strong vortical structures moving on the airfoil upper surface during the downstroke motion that are captured only by the three-dimensional model; then, the flow fields comparison demonstrates the importance of three-dimensional effects for a deep dynamic stall condition.

Wake Measurements behind an Oscillating Airfoil in Dynamic Stall Conditions

“…In particular, the bulk velocity defect observed in the deep dynamic stall curve from 12 ∘ < < 18 ∘ in downstroke demonstrates that the flow is quite three dimensional in this range of angles of attack. The results of the threedimensional numerical simulations reported in Zanotti et al [24,25] carried out for the tested deep dynamic stall condition support this consideration. On the other hand, the quite flat behavior of the bulk velocity observed for the tested light dynamic stall condition suggests that in this regime three-dimensional flow effects are negligible during the whole pitching cycle.…”

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.…”

Numerical Simulation of the Wake Structure and Thrust/Lift Generation of a Pitching Airfoil at Low Reynolds number via an Immersed Boundary Method

“…They have also reported the transition point at which the KVS regime turns to the RKVS one. Zanotti et al (2014) studied, both experimentally and numerically, a pitching airfoil in deep dynamic stall condition. They reported that, during upstroke motion, 3-D numerical models are in better agreement with the experiments as compared to 2-D models.…”