Aeroacoustic Performance of an Airfoil with Circulation Control

Aerodynamic noise originating from slotted slats represents the major component of high-lift related airframe noise. Therefore slatless high-lift systems are considered effective means to reduce airframe noise. The major challenge within the design of such systems is to compensate the deficit in maximum lift performance for slatless wings, and the possibility to remove the gap between main airfoil and Fowler flap. One way to achieve the required high-lift capabilities is active flow control, like e.g. wing trailing edge blowing. Such a circulation control technology was investigated in the EU co-financed research project TimpAN (Technology to improve Airframe Noise). Both numerically and experimentally obtained results showed the expected good aerodynamic performance. High lift coefficients could be achieved with a limited fraction of the cold engine flow used for blowing. In this paper the results from noise measurements on a wing-flap configuration using circulation control to generate high lift are documented. Noise tests were performed in the open test section of the Acoustic Wind Tunnel Braunschweig for predefined operational conditions. A comparison of noise data for the 3-element DLR F16 high-lift model of the same profile geometry and for the same lift performance shows that a noise reduction in the order of 3dB to 6dB is achieved for the 2-element high-lift wing with flow control in the frequency range between 2kHz and 20kHz (at model scale), while a noise increase is observed to occur at low frequencies. The latter, however, might be due to excess installation noise originating from the current test set-up