20th Australasian Fluid Mechanics Conference Perth, Australia 5-8 December 2016 Wake Structure of Airfoil with Serrated Trailing Edge M. Awasthi1, C.J. Doolan1and D.J. Moreau1 1School of Mechanical and Manufacturing Engineering, UNSW Australia, Sydney, 2052, Australia Abstract This work presents a detailed wake survey of a NACA 0012 airfoil with sawtooth type trailing edge serrations. Two different serrations with wavelengths of 0.035 and 0.052 chord lengths and each with an amplitude of 0.16 chord length were considered. The measurements were performed in an open-jet facility at a chord based Reynolds number of approximately 308,000. For each configuration, five different geometric angles of attack between 0° and 15° were also considered. The wake profiles were measured between 1% and 150% chord lengths downstream of the serrated and straight trailing edge. Results show that addition of serrations on the airfoil leads to a lower velocity deficit along the serration root possibly due to enhanced turbulent mixing and three-dimensional flow near the serrations. At lifting conditions, the serrated wake, compared to the un-serrated airfoil, shows less deflection towards the pressure side of the airfoil. Lastly, the near and far-wake structure are shown to be nearly independent of the serration wavelength. IntroductionThe trailing edge noise problem has gained much attention recently due to myriad applications ranging from airframe to wind turbine noise. While several attempts which include both active and passive devices have been made to tackle this problem, it appears that addition of trailing edge (te) extensions such as serrations is the most widely employed method. Despite of their widespread use however, little is known about the mechanism through which serrations reduce the noise. The present work is part of an ongoing attempt to understand the flow physics of serrated te’s in order to develop efficient devices to aid noise reduction efforts. One of the earliest work on serrations was a theoretical study by Howe  who proposed that the use of sawtooth serrations can attenuate the te noise at frequencies greater than those associated with length scales smaller than the amplitude of the serrations. This theory however assumes that the turbulence is frozen and the serrations reduce noise through a reduction in the scattering efficiency of the te. However, recent works such (, ) have found that the serrations lead to a noise attenuation at lower frequencies and can increase the high frequency noise. It has also been found that the serrations can supress vortex shedding noise through a reduction in the strength of the te vortex shedding . These results suggest that, in addition to the scattering efficiency, the modification of the near-field hydrodynamic sources by the serrations must play a role in noise suppression mechanism.
- Spring '17
- Airfoil, Serrations, wake structure