UNDERSTANDING BYPASS TRANSITION ON LAMINAR-FLOW AIRFOILS CAUSED BY ADVERSE WEATHER CONDITIONS

Laminar flow airfoils represent a possible method of greatly increasing the efficiency and thus flight time of small civilian aircraft and drones. This is theoretically accomplished by allowing the boundary layer to remain laminar and attached over a wing, thus reducing the effects of drag over the wing. Unfortunately, laminar flow boundary layers are easily disturbed by a variety of outside effects, including particles, rainfall, transient pressure changes, and other phenomena. Disruptions to flow are able to cause transient or lasting disturbances, both of these scenarios working to prematurely trigger transition over a surface. For this reason it is important to understand the impact these conditions have on boundary layers, and to discover possible methods of mitigation. The focus of these studies lies in examining the differences of behavior and interactions between spots and wedges created by a variety of scenarios.These scenarios may be divided into the ricochet and the adhesion scenarios. The difference being that within the ricochet scenario the droplet rebounds from the surface while in the adhesion scenario some amount of the droplet volume remains attached. The ricochet scenario serves as comparison to a spot initiated by an impulsive disturbance, with the aim to investigate the importance of methodology to the disturbance creation. The adhesion scenarios investigate the interaction between the initial disturbance and the lasting disturbance that follows, and has three subcategories in which the droplet:1) retains sufficient mass to instigate a turbulent wedge.2) loses sufficient mass to only form a low-speed streak.3) retains sufficient mass to create an unstable low speed streak, capable of turning into a wedge. Raindrops will be abstracted into time-evolving body forces moving through channel flow making use of an in-house direct numerical simulation code. This code solves the Navier Stokes equations without utilizing any turbulencemodels by resolving the relevant length and time scales using a pseudo spectral algorithm based on the channel code algorithm of Kim Moin and Moser. The simulations will be examined through a turbulence and vorticity field of view, analysis of both large turbulent structures and smaller phenomena.