| Performance capabilities of future "flight" vehicles will be significantly enhanced by the use of "smart" or adaptive structures. For example, advanced submarine stern configurations will require a variety of control surfaces to actively manage aftbody boundary layer flow, vorticity, propulsor inflow and intrapropulsor flow, as well as vehicle attitude. More specifically, real-time sensing of flow conditions over attitude control surfaces might be utilized to implement advanced camber control algorithms for increased lift without flow separation and improved tactical maneuvering performance with reduced acoustic signature. Thus, two necessary attributes of advanced control surfaces will be (1) integrated actuation to provide placement flexibility at remote locations with minimal structural interfacing and control interconnects, and (2) improved lift efficiency and associated flow characteristics using variable-camber control.; The objective of this research effort was to develop a variable-camber airfoil, measure its performance in a wind tunnel, and assess the feasibility of implementing real-time camber optimization algorithms by using surface pressure readings. To begin, a numerical vortex blob method with integral boundary layer solvers was used to compare predicted lift performance between a variable-camber NACA 0012 airfoil fixed at 1/4 chord and its rigid full-flying baseline counterpart. Results at Re = 10,000,000 show a factor of two increase in maximum lift possible using variable-camber with a fixed wingbox. Subsequently, a 610 mm spanwise uniform test article, measuring 508 mm in chord and bilaterally capable of 18% camber at 21 degrees angle-of-attack, was developed using pneumatic actuation (with co-located servovalves, actuation cells, and displacement sensors) to control four discrete chordwise foil segments. Wind tunnel testing of the active and rigid 0012 foil sections (albeit limited to Re = 276,000 and associated dominance of laminar over turbulent flow separation) demonstrated an 80% increase in maximum lift possible with the variable-camber foil. Lastly, a camber optimization approach was identified and simulated using a Simplex algorithm to minimize error between prescribed and measured foil surface pressure distributions, thereby providing a means to control boundary layer development and its impact on flow transition and separation. |
