The Effect of Moderate Freestream Turbulence on Crossflow Instability and Transition

Previous research indicates that the generation of stationary and traveling crossflow modes is dependent on the level of freestream turbulence, \textit{Tu}. Recent experiments in low turbulence environments have also shown that the initial amplitudes of stationary crossflow disturbances arising from surface roughness are influenced by small variations in \textit{Tu}. Preliminary results are presented concerning experimental investigation into the role of moderate levels of freestream turbulence (\textit{Tu }= 0.025{\%} - 0.2{\%}) in boundary layer receptivity to surface roughness. Transition induced by crossflow instability is studied using a 45-degree swept wing model in the low turbulence Klebanoff-Saric Wind Tunnel. Naphthalene flow visualization is used to assess transition location and detailed hotwire anemometry measurements are made to quantify these initial disturbance amplitudes.