FEDSM2006-98021 A MEAN-FIELD FREE-ENERGY LATTICE BOLTZMANN MODEL FOR LIQUID-VAPOR INTERFACES

ABSTRACT A nonlocal pressure equation is proposed for liquid-vapor interfaces based on mean-field theory. The new nonlocal pressure equation is shown to be a generalized form of the nonlocal pressure equation of the van der Waals theory or the "squaregradient theory". The proposed nonlocal pressure is implemented in the mean-field free-energy lattice Boltzmann method (LBM) proposed b

HT2008-56155 EFFECTS OF SYNGAS ASH PARTICLE SIZE ON DEPOSITION AND EROSION OF A FILM COOLED LEADING EDGE

Abstract The paper investigates the deposition and erosion caused by Syngas ash particles in a film cooled leading edge region of a representative turbine vane. The carrier phase is predicted using Large Eddy Simulation for three blowing ratios of 0.4, 0.8 and 1.2. Three ash particle sizes of 1, 5, and 10 microns are investigated using Lagrangian dynamics. The 1 micron particles with momentum Stokes number St = 0.03 (based on approach velocity and cylinder diameter), follow the flow streamlines around the leading edge and few particles reach the blade surface. The 10 micron particles, on the other hand with a high momentum Stokes number, St = 3, directly impinge on the surface, with blowing ratio having a minimal effect. The 5 micron particles with St = 0.8, show the largest receptivity to coolant flow and blowing ratio. On a number basis, 85-90% of the 10 micron particles, 40-50% of 5 micron particles and less than 1% of 1 micron particles deposit on the surface. Overall there is a slight decrease in percentage of particles deposited with increase in blowing ratio. On the other hand, the potential for erosive wear is highest in the coolant hole and is mostly attributed to 5 micron particles. It is only at B.R.=1.2 that 10 micron particles contribute to erosive wear in the coolant hole

Analysis of a 180-degree U-turn maneuver executed by a hipposiderid bat.

Bats possess wings comprised of a flexible membrane and a jointed skeletal structure allowing them to execute complex flight maneuvers such as rapid tight turns. The extent of a bat's tight turning capability can be explored by analyzing a 180-degree U-turn. Prior studies have investigated more subtle flight maneuvers, but the kinematic and aerodynamic mechanisms of a U-turn have not been characterized. In this work, we use 3D optical motion capture and aerodynamic simulations to investigate a U-turn maneuver executed by a great roundleaf bat (Hipposideros armiger: mass = 55 g, span = 51 cm). The bat was observed to decrease its flight velocity and gain approximately 20 cm of altitude entering the U-turn. By lowering its velocity from 2.0 m/s to 0.5 m/s, the centripetal force requirement to execute a tight turn was substantially reduced. Centripetal force was generated by tilting the lift force vector laterally through banking. During the initiation of the U-turn, the bank angle increased from 20 degrees to 40 degrees. During the initiation and persisting throughout the U-turn, the flap amplitude of the right wing (inside of the turn) increased relative to the left wing. In addition, the right wing moved more laterally closer to the centerline of the body during the end of the downstroke and the beginning of the upstroke compared to the left wing. Reorientation of the body into the turn happened prior to a change in the flight path of the bat. Once the bat entered the U-turn and the bank angle increased, the change in flight path of the bat began to change rapidly as the bat negotiated the apex of the turn. During this phase of the turn, the minimum radius of curvature of the bat was 5.5 cm. During the egress of the turn, the bat accelerated and expended stored potential energy by descending. The cycle averaged total power expenditure by the bat during the six wingbeat cycle U-turn maneuver was 0.51 W which was approximately 40% above the power expenditure calculated for a nominally straight flight by the same bat. Future work on the topic of bat maneuverability may investigate a broader array of maneuvering flights characterizing the commonalities and differences across flights. In addition, the interplay between aerodynamic moments and inertial moments are of interest in order to more robustly characterize maneuvering mechanisms