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.

Laminar-Turbulent Transition in a Mach 8 Elliptic Cone Flow

Abstract: To examine the influence of crossflow on transition in a hypersonic boundary layer, an experimental and computational study was made of a Mach 8 flow over a sharp-nosed elliptic cone of 2:1 cross section. Extensive flow visualization was carried out experimentally, including schlieren photography and surface oil-flow visualization. Mean pressure and heat flux were measured at the wall of the wind-tunnel model. For comparison with the experiments, a computation of the basic state flow was carried out using the parabolized Navier-Stokes equations. The basic state laminar flow was found to be relatively complex, with highly skewed velocity profiles and a pair of symmetric vortices on the top centerline of the cone. Transition in the elliptic cone flow was found to be significantly different than transition in hypersonic flow over planar and axisymmetric configurations, which is driven by the second mode instability. In the elliptic cone flow the transition front was nonuniform, with early transition near the top centerline and delayed transition near the leading edge. Rope waves were observed on both the leading edge and top centerline; unusual elongated streaks were observed on the top centerline

General Crystalline Hartree-Fock Formalism: Diamond Results

Abstract: A method is presented for performing crystalline Hartree-Fock calculations with a wave-function basis consisting of Gaussian lobe functions. The most important concepts involve (i) the utilization of crystal symmetry in characterizing the first-order density matrix, and in selective computation and efficient storage of the one- and two-electron integrals; (ii) the introduction of a charge-conserving approximation for some of the less important three- and four-center integrals over contracted Gaussian basis functions; and (iii) the imposition of monopole and dipole compensation for the most important neglected two-electron Coulomb integrals. The method is applied to diamond, and calculational results are given for various sets of parameters. The best results include a Hartree-Fock cohesive energy of 0.38 Ry/atom, a virial coefficient ($\ensuremath{-}\frac{2T}{V}$) of 1.0005 for a lattice constant of 3.56 \AA{}, a direct band gap at $\ensuremath{\Gamma}$ of 15 eV, and an indirect band gap from $\ensuremath{\Gamma}$ to $\ensuremath{\Delta}$ of 13.7 eV. The(111) Fourier transform of the charge density is 3.29 electrons per crystallographic unit cell.

Study on Trapped-Vortex Combustor-Effect of Injection on Flow Dynamics

Abstract: Low-velocity  ows in the cavities of a combustor can aid in establishing stable  ames. However, unsteady  ows in and around cavities may destabilize these  ames. By proper cavity design it is possible to lock (trap) the vortices spatially and, thereby, stabilize the  ames. The spatially locked vortices restrict the entrainment of main air into the cavity. For obtaining good performance characteristics with a trapped-vortex combustor, a sufŽ cient amount of fuel and air must be injected directly into the cavity. This mass injection can alter the dynamic characteristics of the  ow inside and around the cavity. The present study employed a numerical simulation to investigate the vortex dynamics of a cavity into which  uid mass is directly injected through jets. A third-order-accurate, time-dependent, computational  uid dynamics with chemistry code was used for simulating the dynamic  ows associated with an axisymmetric, centerbody trapped-vortex combustor under nonreacting and reacting conditions. It was found that mass injection increases the optimum size (width-to-diameter ratio) of the cavity. Injection of small amounts of  uid into a nonoptimum cavity increases the unsteadiness of the  ow. Fluid injected into the optimumsize cavity is transported along the outer core of the vortex, providing more efŽ cient mixing and a longer residence time for the fuel/air mixture. It was also found that use of thinner afterbodies results in the cavity  ow being more dynamic. Calculations made with a global-chemistry model revealed that at higher annulus air velocities, combustion is limited to the cavity region. As in the case of cold  ows, the injection jets in reacting  ows are pushed outward from the center when the cavity size is small.

Reconfigurable tracking control with saturation

Abstract: On-line system identification and on-line optimization is used to maximize aircraft tracking performance before and after control surface failure, yet prevent instability and departure. The on-line optimization consists of receding horizon/model predictive optimal control with one-step-ahead actuator rate constraint enforcement. Such hard constraint enforcement is rigorous through use of a linear programming algorithm to include rate saturation in the design. The paper demonstrates that the full, infinity norm solution with one-step-ahead constraint enforcement is equivalent to a simple one-dimensional optimization whose solution is attainable in closed form. This equivalence allows for an efficient on-line implementation of reconfigurable control with hard actuator rate constraints. Good tracking performance after severe failure is demonstrated in realistic simulations.