About Coherent Structures and Noise at High-Lift Configurations

Kurzfassung

In order to contribute to the understanding of the noise-source mechanism at high-lift configurations, a detailed experimental study is performed at the slat of the DLR-F16 configuration. It is a multi-element 2D high-lift airfoil with a modular design. The study includes PIV-measurements in the vicinity of the slat and the leading edge of the main-wing, surface pressure and far-field pressure measurements at the suction and pressure side of the model. A detailed description of the experimental setup can be found in [1]. The free stream velocity and angle of attack is varied and it can be shown, that the intensity of the tonal components in the far field spectrum varies with both parameters. The study presented here is focused on the application of the so called “causality correlation” method. The aim of this method is to find a linear relation between the cause: the flow field and the effect: the sound field by means of correlating the measured velocity fluctuations in the flow and the pressure fluctuations in the far-field. Parts of the correlation results are presented in [1,2], comparing the spatial and temporal distribution of the correlation coefficients for different angles of attack. In these papers significant correlation coefficients are observed between the far-field pressure signals and the flow structures in the slat region of the high-lift configuration. The temporal and spatial distribution of the coefficients depends strongly on the angle of attack. Alternating structures in the spatial distribution together with a periodicity in the temporal evolution are observed in case of low angles of attack. In case of higher angles of attack the temporal evolution shows only a short event and a comparatively small region of significant values downstream of the slat-gap.