Boundary Layer Transition due to Free Stream Particles - A Simple Experimental Approach

Application of drag reduction technology based on laminar flow in a commercial environment is still being hindered by unanswered questions regarding its operational reliability. The encounter of ice crystals, as occurring in cirrus cloud, is known to result in performance degradations or even a temporary complete loss of laminar flow. Actually occurring mechanisms are not well understood and previously proposed critical parameters have not yet been verified experimentally. Difficulties encountered while attempting to recreate conditions in the laboratory that are representative of the real occurrences have led to the development and design of several alternative experimental methods. This study presents results from a relatively simple method, in terms of its complexity, providing for further insight into the phenomenon of a small particle being capable of producing a turbulent event while passing through an initially laminar boundary layer. Using this method, for a smooth spherical particle, a critical Reynolds number of approximately 300 has been determined above which the generation of a turbulent-spot-like disturbance will occur.