In-flight Investigations of Atmospheric Turbulence

Abstract

The laminar flow technology is one of the key technologies in aeronautics offering substantial improvements in the fields of economy and ecology. Owing to the sensitivity of laminar boundary layer flow over aerodynamically smooth surfaces to effects of disturbances as for example insect contamination, noise and vibration as well as the atmospheric conditions, all these aspects of the receptivity problem have to be taken into account in the application of the laminar flow technolog. In this context one important element is the atmospheric turbulence. In-flight measurements of the atmospheric turbulence intensity have been undertaken within the framework of a European collabrative programme to flight test a natural laminar flow nacelle. The measurement of the atmospheric turbulence intensity was one of the tasks of the University of Oxford. The knowledge gained concerning the turbulence intensity has been compared with the results of in-flight measurements in Europe from other sources, most of which also stem from investigations related to the laminar flow technology. In contrast investigations specifically addressing the atmospheric turbulence ranging from still air and cumulus cloud to thunderstorm have been conducted in the United States of America by NASA. A comparison is made of the freestream turbulence intensities obtained in flight with results for some wind tunnels. The in-flight measurements have yielded turbulence intensities for the still air atmosphere which are less than 0.05%, a figure that for the wind tunnels examined is only reached in the low speed regime.