Experimental and numerical investigations of controlled transition in low-speed free flight

Abstract

This paper reports on the joint work of several university research groups, where scientists of five German universities tackled the problem of controlled laminar-turbulent transition on an unswept motor-glider wing with different low disturbance measurement methods on respective wing-gloves as well as with Direct Numerical Simulations. To establish a comparable measurement environment for the different measurement methods as well as to facilitate the comparison between measurement and numerical results, a controlled continuous disturbance wave train excited by a harmonic point source was introduced into the boundary-layer flow. A successful comparison between the controlled experiment and simultaneous computations is an essential step towards the understanding of more complex transition scenarios like natural transition. The investigation of the downstream development of the three-dimensional point-source disturbance was the main objective of the mutual research effort.