Effect of cylindrical trip devices on the swept-wing boundary layer. 1. Turbulization scenarios and efficiency

The main goal of the present study is to investigate the mechanism of forced turbulization of the laminar boundary layer on a swept wing with domination of crossflow instability by means of using spanwise-periodic cylindrical trip devices. The experiments are performed with hot-wire anemometry in a low-turbulence wind tunnel based at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk) at low subsonic free-stream velocities; a 25-degree swept wing is chosen as a model. Results of detailed precision measurements of the mean and fluctuating structure of the flow are obtained in a broad space range in 12 different regimes of measurements for five types of trip devices (and also without them) for two flow velocities. The range of the Reynolds numbers based on the trip height is from 565 and 3613. The present paper describes the first part of the study, i.e., the main scenarios of the transition to turbulence induced by trip devices. They are demonstrated to be highly effective. Subsequent studies will be described in Part 2 of the paper.