Control of Transition in Swept-Wing Boundary Layers using MEMS Devices as Distributed Roughness

摘要

Active flow control using MEMS-based microactuators holds tremendous promise for achieving laminar flow control and drag reduction for a wide class of aircraft. In order to achieve effective control it is necessary to have a complete understanding of the fundamental instability processes that apply to a particular boundary layer and to develop a sensor and actuator system that is capable of providing an appropriate control input to that boundary layer. In the present work, crossflow-dominated swept-wing boundary layers are the primary interest. These boundary layers are known to undergo a highly nonlinear transition process that involves, in low-disturbance environments, stationary waves of longitudinal vorticity. These stationary waves have to potential to be controlled or suppressed by an appropriate surface roughness configurations that could be provided by MEMS-based actuators. The work performed here consists of a parallel experimental and hardware development efforts. The breakdown phase of the crossflow instability is investigated in the experiments in an effort to determine an appropriate control input. A MEMS-based roughness actuator system is developed to provide controlled roughness inputs. The results of the experimental phase conclusively demonstrate that the destabilization of a high- frequency secondary instability is responsible or breakdown. The MEMS development effort did not produce a useful control device because of certain shortcomings in the present state of MEMS fabrication quality control and overall system integration.