Physical Insights, Steady Aerodynamic Effects, and a Design Tool for Low-Pressure Turbine Flutter

The successful, efficient, and safe turbine design requires a thorough understanding of the underlying physical phenomena. This research investigates the physical understanding and parameters highly correlated to flutter, an aeroelastic instability prevalent among low pressure turbine (LPT) blades in both aircraft engines and power turbines. The modern way of determining whether a certain cascade of LPT blades is susceptible to flutter is through time-expensive computational fluid dynamics (CFD) codes. These codes converge to solution satisfying the Eulerian conservation equations subject to the boundary conditions of a nodal domain consisting fluid and solid wall particles. Most detailed CFD codes are accompanied by cryptic turbulence models, meticulous grid constructions, and elegant boundary condition enforcements all with one goal in mind: determine the sign (and therefore stability) of the aerodynamic damping. The main question being asked by the aeroelastician, ``is it positive or negative?'' This type of thought-process eventually gives rise to a black-box effect, leaving physical understanding behind. Therefore, the first part of this research aims to understand and reveal the physics behind LPT flutter in addition to several related topics including acoustic resonance effects. A percentage of this initial numerical investigation is completed using an influence coefficient approach to study the variation the work-per-cycle contributions of neighboring cascade blades to a reference airfoil. The second part of this research introduces new discoveries regarding the relationship between steady aerodynamic loading and negative aerodynamic damping. Using validated CFD codes as computational wind tunnels, a multitude of low-pressure turbine flutter parameters, such as reduced frequency, mode shape, and interblade phase angle, will be scrutinized across various airfoil geometries and steady operating conditions to reach new design guidelines regarding the influence of steady aerodynamic loading and LPT flutter. Many pressing topics influencing LPT flutter including shocks, their nonlinearity, and three-dimensionality are also addressed along the way. The work is concluded by introducing a useful preliminary design tool that can estimate within seconds the entire aerodynamic damping versus nodal diameter curve for a given three-dimensional cascade.

RIR-MAPLE deposition of plasmonic silver nanoparticles

© 2016, Springer-Verlag Berlin Heidelberg.Nanoparticles are being explored in many different applications due to the unique properties offered by quantum effects. To broaden the scope of these applications, the deposition of nanoparticles onto substrates in a simple and controlled way is highly desired. In this study, we use resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) for the deposition of metallic, silver nanoparticles for plasmonic applications. We find that RIR-MAPLE, a simple and versatile approach, is able to deposit silver nanoparticles as large as 80 nm onto different substrates with good adhesion, regardless of substrate properties. In addition, the nanoparticle surface coverage of the substrates, which result from the random distribution of nanoparticles across the substrate per laser pulse, can be simply and precisely controlled by RIR-MAPLE. Polymer films of poly(3-hexylthiophene-2,5-diyl) (P3HT) are also deposited by RIR-MAPLE on top of the deposited silver nanoparticles in order to demonstrate enhanced absorption due to the localized surface plasmon resonance effect. The reported features of RIR-MAPLE nanoparticle deposition indicate that this tool can enable efficient processing of nanoparticle thin films for applications that require specific substrates or configurations that are not easily achieved using solution-based approaches.