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.

Evaporation from an extended meniscus for nonisothermal interfacial conditions

Abstract: A study is presented to determine the effects of evaporation from the thin film region of a liquid-vapor meniscus within the micropores of a heat pipe porous or grooved wick on the interfacial shape, temperature distribution, and pressure distribution. Wayner's theoretical treatment of evaporating thin films is applied to the problem of an evaporating extended meniscus within circular or slotted pores. In this application of Wayner's model, the nondimensional momentum equation is uniquely scaled in terms of the capillary number, to justify the use of the static meniscus curvature as a boundary condition for the extended meniscus profile even for the dynamic evaporating conditions studied herein. This boundary condition for small capillary numbers is consistent with the observation of the nearly constant meniscus curvature with evaporation rate that the thin film must asymptotically approach. From these basic tenets, the mechanical and thermal behavior of a stably, evaporating, nonisothermal extended meniscus is predicted. The resulting predictions are qualitatively consistent with the experimental findings of Wayner and the previous theoretical studies. They further support the claims that for the cases studied herein, both thermocapillary stresses and vapor recoil stresses at the liquid-vapor interface are negligible. However, scaling arguments are presented that identify the conditions necessary for these terms to be important.

A Large-Area, Mushroom-Capped Plasmonic Perfect Absorber: Refractive Index Sensing and Fabry–Perot Cavity Mechanism

Abstract: In most plasmon resonance based sensor to date, only the surface of the sensor is accessible to the gas or liquid as the sensing target. In this work, an interferometric, lithographically fabricated, large-area, mushroom-capped plasmonic perfect absorber whose dielectric spacer is partially removed by a reactive-ion-etch process, thereby enabling the liquid to permeate into the sensitive region to a refractive index change, is demonstrated. Findings of this paper demonstrate experimentally and numerically that etching the spacer below the metamaterial resonator increases the spectral shift of the resonance wavelengths as the surrounding refractive index changes. The sensitivity and the figure of merit, as the measure of the sensor performance, are significantly improved. In this paper, it is shown that the plasmonic perfect absorber can be understood as a Fabry–Perot cavity bounded by a “resonator” mirror and metallic film, where the former exhibits a “quasi-open” boundary condition and leads to the characteristic feature of subwavelength thickness.

Micromechanical Modeling of Viscoelastic Properties of Carbon Nanotube-Reinforced Polymer Composites

Abstract: A micromechanics model is developed for predicting the linearly viscoelastic properties of carbon nanotube-reinforced polymer composites. By employing the Correspondence Principle in viscoelasticity, the Mori-Tanaka method is extended to the Carson domain. The inversion of the creep compliances from the Carson (transformed) domain to the time (physical) domain is accomplished numerically by using a recently developed multi-precision algorithm. The new micromechanics model is validated by comparing with existing experimental data. By applying the presently developed model, a parametric study for the creep behavior of carbon nanotube-reinforced polymer composites is conducted, with testing temperature, nanotube aspect ratio, nanotube volume fraction and nanotube orientation as the controlling parameters. For composites having unidirectionally aligned nanotubes, numerical results indicate that the increase of the nanotube aspect ratio significantly enhances their axial creep resistance but has insignificant ...

Laser-based investigations in gas turbine model combustors

Abstract: Dynamic processes in gas turbine (GT) combustors play a key role in flame stabilization and extinction, combustion instabilities and pollutant formation, and present a challenge for experimental as well as numerical investigations. These phenomena were investigated in two gas turbine model combustors for premixed and partially premixed CH4/air swirl flames at atmospheric pressure. Optical access through large quartz windows enabled the application of laser Raman scattering, planar laser-induced fluorescence (PLIF) of OH, particle image velocimetry (PIV) at repetition rates up to 10 kHz and the simultaneous application of OH PLIF and PIV at a repetition rate of 5 kHz. Effects of unmixedness and reaction progress in lean premixed GT flames were revealed and quantified by Raman scattering. In a thermo-acoustically unstable flame, the cyclic variation in mixture fraction and its role for the feedback mechanism of the instability are addressed. In a partially premixed oscillating swirl flame, the cyclic variations of the heat release and the flow field were characterized by chemiluminescence imaging and PIV, respectively. Using phase-correlated Raman scattering measurements, significant phase-dependent variations of the mixture fraction and fuel distributions were revealed. The flame structures and the shape of the reaction zones were visualized by planar imaging of OH distribution. The simultaneous OH PLIF/PIV high-speed measurements revealed the time history of the flow field–flame interaction and demonstrated the development of a local flame extinction event. Further, the influence of a precessing vortex core on the flame topology and its dynamics is discussed.