Roberts, Matthew William (2012-05). Computational Evaluation of a Transonic Laminar-Flow Wing Glove Design. Master's Thesis.
The aerodynamic benefits of laminar flow have long made it a sought-after attribute in aircraft design. By laminarizing portions of an aircraft, such as the wing or empennage, significant reductions in drag could be achieved, reducing fuel burn rate and increasing range. In addition to environmental benefits, the economic implications of improved fuel efficiency could be substantial due to the upward trend of fuel prices. This is especially true for the commercial aviation industry, where fuel usage is high and fuel expense as a percent of total operating cost is high. Transition from laminar to turbulent flow can be caused by several different transition mechanisms, but the crossflow instability present in swept-wing boundary layers remains the primary obstacle to overcome. One promising technique that could be used to control the crossflow instability is the use of spanwise-periodic discrete roughness elements (DREs). The Flight Research Laboratory (FRL) at Texas A&M University has already shown that an array of DREs can successfully delay transition beyond its natural location in flight at chord Reynolds numbers of 8.0x10^6. The next step is to apply DRE technology at Reynolds numbers between 20x10^6 and 30x10^6, characteristic of transport aircraft. NASA's Environmentally Responsible Aviation Project has sponsored a transonic laminar-flow wing glove experiment further exploring the capabilities of DRE technology. The experiment will be carried out jointly by FRL, the NASA Langley Research Center, and the NASA Dryden Flight Research Center. Upon completion of a wing glove design, a thorough computational evaluation was necessary to determine if the design can meet the experimental requirements. First, representative CAD models of the testbed aircraft and wing glove were created. Next, a computational grid was generated employing these CAD models. Following this step, full-aircraft CFD flowfield calculations were completed at a variety of flight conditions. Finally, these flowfield data were used to perform boundary-layer stability calculations for the wing glove. Based on the results generated by flowfield and stability calculations, conclusions and recommendations regarding design effectiveness were made, providing guidance for the experiment as it moved beyond the design phase.