| dc.description.abstract | The National Aeronautics and Space Administration (NASA) Aeronautics Research Mission Directorate (ARMD) vision for aeronautical research has defined the goal of creating an ultra-efficient subsonic transport flight vehicle. In order to create such a vehicle, the Advanced Aerodynamic Design Center for Ultra-Efficient Vehicles was established. This center is developing a new airfoil capable of maintaining laminar flow. At Texas A&M’s Computational Stability and Transition Laboratory, I am working to define the allowable sweep and twist for a new slotted, natural-laminar-flow (SNLF) airfoil, the S207. Setting the limits for these sweep and twist parameters will allow for proper implementation into Boeing’s subsonic ultra green aircraft configuration.
The goal of this thesis is to identity the maximum sweep angle for which the crossflow instability does not negate the benefits of the natural-laminar-flow (NLF) design of the S207 airfoil, for a range of angles of attack.
To determine this angle, the amplification of all expected disturbances is calculated using the Linear Parabolized Stability Equations (LPSE) on a multitude of sweep angles. In addition to sweep, the effects of angle of attack variation are also examined. For sweep angles ≥ 20◦ and cl ≈ 0.65, crossflow disturbances exceed their critical N-factor value of 5, and therefore crossflow is presumed to onset transition. Lowering the sweep angle to Λ = 15◦ and considering an angle of attack variation, the crossflow N-factors reach 4.6 units. This is below the critical value, but does not allow for much margin of error. Additionally, this critical value does not account for any interaction between the mechanisms, which lowers the N-factor necessary to induce transition. Therefore, a reduced sweep angle of 12.5◦ is analyzed. For a 12.5◦ sweep angle, the maximum N-factors achieved are well below the critical values, for all studied angles of attack. Considering the interaction between the Tollmien-Schlichting and crossflow mechanisms, flow over the 12.5◦ sweep case is still predicted to be laminar. Therefore, the crossflow instability does not appear to negate the benefits of the S207’s SNLF design for sweep angles up to and including 12.5◦ for an angle of attack range of -1.772◦ to -1.272◦ | en |
