Investigation of the near and far wake of a bluff airfoil model with trailing edge modifications using time-resolved particle image velocimetry

Abstract

Experimental investigations on the topology and the structure of the near and far wake of a quasi-2D blunt NACA0012 airfoil cut at 80 % of the original chord length cmaster have been performed by means of time-resolved particle image velocimetry. The experiments took place in a closed-loop water tunnel at a model-thickness H-based Reynolds number of ReH = 44,000. The periodic and alternating vortex formation process at the base of the bluff model with a dimensionless frequency of Srh = 0.2 (relating to the trailing edge height h) was investigated in detail. Subsequently, four modifications of the trailing edge geometry (broken trailing edge, square-wave base, stepped afterbody and extension of the reference model by \(\Delta c/c_{\rm master} = 7.5\,\%\)) have been investigated in order to mitigate the periodic vortex formation and the alternating shedding process. In the far wake, a considerable decrease in momentum loss and resulting drag force in the range of 29 % has been achieved for this specific Reynolds number. Investigations of the time-resolved flow field proved that the periodic, alternating flow separation can be attenuated resulting in an optimized recirculation region and a low-loss wake. It can be inferred that passive flow control means like modifications of the rear end geometry of quasi-2D blunt models are a capable method to improve the flow field with respect to a minimization of momentum losses in the wake.