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A two-dimensional synthetic jet is studied numerically by solving the incompressible, unsteady, Reynolds-averaged, Navier-Stokes equations and using a k-⑀ turbulence model. Rather than a resonant cavity, the synthetic jet is supplied by a fully developed channel flow. Results for two exit geometries, a sharp exit and a rounded exit, and several dimensionless stroke lengths are compared. This study focuses on the effect of the displacement amplitude ͑stroke length͒ on the power required to form the jet, the net momentum flux downstream of the exit, the formation threshold, and the spatial development of the synthetic jet. It is shown that the channel flow development length, the self-similar region, and the region from which the jet draws fluid all scale on the stroke length. It is also demonstrated that the power required to form the jet increases with stroke length as does the resultant momentum flux. Finally, the power required to form a synthetic jet is significantly smaller for a rounded exit compared to a sharp-edged exit.

Three model problems associated with aerodynamic drag minimizations are studied. These test cases have been proposed by the aerodynamic design optimization discussion group, and they include an inviscid NACA0012 nonlifting airfoil, a viscous RAE2822 lifting airfoil, and a viscous lifting wing based on the NASA Common Research Model. Various optimization methods are used, including MDOPT, TRANAIR, SYN83, and SYN107. The resulting designed and associated baseline geometries are cross analyzed by several computational fluid dynamics codes, including OVERFLOW, TRANAIR, GGNS, and FLO82. Pathological issues are unveiled in both of the simple airfoil model problems. Designed geometries for the inviscid symmetric test case exhibit strong tendencies to permit nonsymmetric flow solutions. Designed airfoils for the viscous lifting case also support nonunique solutions and hysteresis loops at or near the design point in Reynolds-averaged Navier-Stokes and integral boundary-layer method simulations. These results provide further evidence that single-point aerodynamic optimization is often ill posed. In extreme cases, it can yield designs with very undesirable aerodynamic characteristics, at least as analyzed by Reynolds-averaged Navier-Stokes and integral boundary-layer methods occurring at offdesign, and even ondesign, conditions. These examples are used to further document the multiple-solution and pseudosolution phenomena for steady-state Reynolds-averaged Navier-Stokes. This provides evidence that, even in practical engineering settings, numerical methods to assess stability and uniqueness of steady-state solutions and/or predict the bifurcations of these solutions have value. The single-point wing design problem is likewise ill posed in the spanwise direction. A multipoint design with a potentially large number of points or the inclusion of inequality constraints can regularize the problem.wing reference chord, which is approximately equal to the mean aerodynamic chord M = Mach number; V∕a P 0 = total pressure q = dynamic pressure; 1 2 ρV 2 Re = Reynolds number; ρ ∞ V ∞ C ref ∕μ ∞ S ref = reference area t = thickness of an airfoil α = angle of attack Δ = difference in quantity (new-baseline) η = fraction of wing semispan κ = curvature ρ = radius of curvature τ = trailing-edge-included angle ∞ = freestream conditions

A two-phase study is described that designs and validates a supersonic airliner feasible for entry into service in the 2018 to 2020 timeframe (NASA N+2 generation). A Mach 1.6 to 1.8 low sonic-boom aircraft configuration is developed that meets aggressive sonic-boom and performance goals. The concept and the tools utilized for its design are validated through a series of wind-tunnel tests at the NASA Ames 9 ft x 7 ft Supersonic Wind Tunnel, NASA Ames 11 ft Transonic Wind Tunnel, and NASA Glenn 8 ft x 6 ft Supersonic Wind Tunnel. Comparisons between CFD and wind-tunnel near-field pressure distributions are made. Sonic-boom test techniques are described and investigated. Results from spatial-averaging show the best agreement with CFD.

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