Turbulent contamination of laminar flow due to free stream particles

Laminar Flow technology is known to be detrimentally affected when encountering ice crystals as occurring in cirrus cloud. However, the principle mechanisms leading to the transition of a laminar boundary layer due to a small particle travelling through it are not well understood. Moreover, a previously-proposed critical particle parameter had not been experimentally verified. Difficulties encountered during efforts to re-create the naturally occurring mechanisms in a laboratory led to the development of an alternative approach. This is based on a surface moving within a fluid that is otherwise at rest, thus reversing the conventional approach of a wind tunnel. Proceeding as such alleviates investigations on particles that are in equilibrium to the free stream before entering a laminar boundary layer, since it allows for positioning the particle at a fixed location while involved processes are slowed down. Preliminary computational analysis resulted in encouraging data with regard to the feasibility of the proposed method. Although, the first practical investigations involving the newly-developed test facility showed some differences to the numerical prediction, an equilibrium flow field was obtained, representing a workable environment for this purpose. Subsequent more detailed measurements resulted in a surprisingly close match of the obtained velocity profile when compared to the Blasius solution. Both single hot wires and smoke flow visualisation were proven to be unsuitable to conducting the desired particle investigations. Subject to an upgrade of the employed measurement techniques (e.g. crossed hot wires or PIV) the fabricated test facility is likely to produce some of the missing answers on the particle wake development within a wall-bounded non-uniform flow.