Inflight Investigations of Atmospheric Turbulence

Abstract

One of the key technologies in aeronautics offering substantial improvements in the fields of economy is the laminar flow technology. The sensitivity of the laminar boundary layer flow over aerodynamically smooth surfaces to the effects of disturbances, like noise, vibration and insect-contamination as well as the atmospheric conditions call for a thorough study of these aspects. This paper deals with one important element of the atmospheric state, that is the atmospheric turbulence. Inflight measurements of the atmospheric turbulence intensity were undertaken within the framework of a European collaborative 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 is compared with the results of in-flight measurement from other sources, most of which also stem from investigations related to the laminar flow technology. A corresponding comparison is made as regards the freestream turbulence intensities determined in 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.