Wright-Patterson Air Force Base

About: Wright-Patterson Air Force Base is a other organization based out in Wright-Patterson AFB, Ohio, United States. It is known for research contribution in the topics: Laser & Mach number. The organization has 5817 authors who have published 9157 publications receiving 292559 citations. The organization is also known as: Wright-Patterson AFB & FFO.

Large-Eddy Simulation of Plasma-Based Turbulent Boundary-Layer Separation Control

Abstract: A large-eddy simulation (LES) was carried out in order to numerically describe the use of plasma-based actuation for the control of turbulent boundary-layer separation. The configuration consisted of a flat plate section over which the boundary layer developed, followed by a curved convex rearward-facing ramp, corresponding to an experimental arrangement. A single dielectric-barrier-discharge (DBD) plasma actuator was then employed to reduce the extent of the separated flow region. Solutions were obtained to the Navier-Stokes equations, that were augmented by source terms used to represent plasma-induced body forces imparted by the actuator on the fluid. A simple phenomenological model provided the electric field generated by the plasma, resulting in the body forces. The numerical method utilized a high-fidelity time-implicit scheme, employing domain decomposition in order to perform calculations on a parallel computing platform. Simulations were first conducted for an isolated actuator in the absence of external flow, which were used to optimize the choice of parameters inherent in the plasma model. Subsequently, actuation was applied to the plate development section without the downstream ramp section. Following these computations, the complete plate/ramp configuration was simulated. In all cases, both continuous and pulsed operation of the actuator was considered. Comparisons are made with available experimental data, and with baseline flows where no control was enforced. The large separated flow region characterizing the baseline flow for the plate/ramp configuration was well captured by the simulation. When continuous control was applied, separation was almost entirely eliminated. Pulsing operation of the actuator using a 40% duty cycle was not as eective, but did result in a considerable reduction of the recirculating zone. The control cases compared reasonably well with experimental measurements. Although deficiencies in the plasma model were apparent in the near-wall region, it appeared to be adequate for use with LES in the exploration of plasma-based control for turbulent wall-bounded flows.

Coordinated Control of Multisatellite Systems

Abstract: The problem of formation and reconŽ guration of multiple microsatellite systems is addressed A control scheme called the perceptive frame is adopted that integrates the decentralized feedback of each satellite with online sensor information to achieve the goal of formation keeping and intersatellite coordination The proposed design algorithm has the advantage of relative position keeping and easy formation reconŽ guration

Titanium alloy fatigue fracture facet investigation by selected area electron channeling

Abstract: Flat regions (facets) found on fracture surfaces caused by initiation and propagation of fatigue cracks through the titanium alloys IMI-685 tested with and without a 5 min load dwell and Ti-11 have been examined using selected area electron channeling. The crystallographic planes of the facets have been identified as being near basal for the IMI-685 and more random for the Ti-11. None of the dwell specimens showed a pure basal facet orientation. The plastic zone size was also assessed and found to correlate approximately with stress intensity, allowing confirmation of crack initiation sites as determined by fractography. One case of beta to alpha-beta transformation crystallography is also examined. A partial channeling map for titanium is presented.

Refractive‐index anisotropy and optical dispersion in films of deoxyribonucleic acid

Abstract: Received 12 May 2006; accepted 29 July 2006DOI 10.1002/app.26082Published online in Wiley InterScience (www.interscience.wiley.com).ABSTRACT: We have determined the refractive indicesin the directions parallel and perpendicular to the surfaceplane of films of deoxyribonucleic acid (DNA) and theirwavelength dispersion. These parameters are fundamen-tal for understanding the properties of waveguidingstructures containing DNA-based photonic materials. Theorientation of DNA molecules in films and their opticalproperties are sensitive to the film fabrication and envi-ronmental conditions influencing the structure. Prismcoupling measurements show ambient-humidity-relatedchanges in the refractive index, birefringence, and anisot-ropy of the alignment of the DNA molecules in the filmsstudied. These films were 0.5–5 mm thick, were preparedby both spin coating and casting from aqueous solutionscontaining 0.1–3 wt % DNA, and were measured inambient air with relative humidities of 37–58%. Theoptical properties of the films and the orientation of theDNA molecules are discussed with respect to the mech-anism for the formation of the polymer liquid-crystallinephases during film deposition. The dispersion of the re-fractive indices in films of native DNA has been derivedfrom interference fringes in absorption and reflectionspectra in the wavelength range of 350–2700 nm throughthe fitting of the positions of the fringes with the Sellme-ier dispersion formula in combination with the prismcoupling data.