A detailed insight of the typical features involved in the dynamic stall phenomenon for a NACA 23012 airfoil was obtained through a comprehensive experimental campaign. The experimental rig designed for testing pitching blade section models enabled to reproduce the typical conditions of the flight envelope of a full-scale retreating rotor blade section at high forward flight speed. The use of both fast pressure transducers and PIV allowed to relate the load distributions to the flow phenomena. In fact, the PIV flow field surveys, performed with a high spatial resolution, illustrated the detailed flow physics that characterise the different phases of the blade stall process and in particular the formation of the DSV typical of the deep dynamic stall regime. The comprehensive data set produced by the experimental activity could be considered as a reference data base for the validation of numerical models. In fact, an ongoing activity at Politecnico di Milano is evaluating the modelling capabilities for this peculiar flow conditions comparing different 2D and 3D CFD models against the experimental results presented in this study, in particular for the deep dynamic stall condition. The test with a Gurney flap demonstrated an appreciable effect on the airfoil performance and demonstrated that a cyclically deployed Gurney flaps could be used to improve the helicopter main rotor performances. In particular, these results suggest that the flap has to be deployed downward during the upstroke phase (retreating blade) and retreated in the down-stroke phase (advancing blade) in order to increase the retreating blade lift and, at the same time, to reduce the risk reduction of stall flutter occurrence. Hence, the results obtained from the experiments with the fixed Gurney flap encourage the research activity on the use of an active Gurney flap for dynamic stall control purposes. An other interesting topic that should be further investigated is about the effects of higher-order pitching motion. A preliminary test carried out in this study (similarly to what done by Gardner et al.) has shown sensible effects for a 1° 5/rev oscillation superimposed to the main 1/rev oscillation.
Experimental investigation of the dynamic stall phenomenon on a NACA 23012 oscillating airfoil
Experimentelle Untersuchung des dynamischen Stall-Phänomens bei einem schwingenden NACA 23012 Profil
2013
14 Seiten, 13 Bilder, 1 Tabelle, 22 Quellen
Article (Journal)
English
Experimental investigation of the dynamic stall phenomenon on a NACA 23012 oscillating airfoil
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