A study of unsteady wake-induced boundary-layer transition with thermochromic liquid crystals

Abstract A method of using thermochromic liquid crystals has been developed to visualize the thermal footprints of artificially created turbulent spots as they propagate downstream in an otherwise laminar boundary layer. In the present study, this technique was employed to study the turbulent events, which were generated spontaneously by turbulent wakes of circular cylinders convecting in a laminar boundary layer over a heated flat plate. The experiment was conducted in a water tunnel at a free-stream velocity of 0.2 m/s. The purpose of the experiment was to simulate the unsteady wake-induced boundary-layer transition typically occurring in multistage turbomachines. The location of the onset of transition and the turbulent spot formation rate were obtained by processing the recorded colour change of thermochromic liquid crystals for the first time. The results were compared with those predicted from standard correlations.