Vortex dislocation in wake-type flow caused by local spanwise nonuniformity

DNS of spatiotemporal evolution of a wake-type flow is performed. In the incoming flow, a local spanwise nonuniformity in momentum defect is initially imposed. Results show that the spanwise nonuniformity leads to a series of symmetric twist vortex dislocation in downstream of the flow. Vortex line variations and substantial transition of vorticity from spanwise to the streamwise and vertical directions clearly feature the generation of a vortex dislocation and the real vortex linking in the dislocation. Dynamical process and the mechanism responsible for the vortex dislocation are described.

Simulation of Vortex-dominant and Turbulent Flows in Natural Environment

In the present talk, the simulation of vortex dominant and turbulent flows are primarily addressed. To cope with complicated circumstances in environmental flows we illustrate the strategy of combining simplified physical model and suitable algorithm by a few examples.

A Breakdown Criterion of Free Molecular Flows and an Optimum Analysis of EBPVD

Two important issues in electron beam physical vapor deposition (EBPVD) are addressed. The first issue is a validity condition of the classical cosine law widely used in the engineering context. This requires a breakdown criterion of the free molecular assumption on which the cosine law is established. Using the analytical solution of free molecular effusion flow, the number of collisions (N-c) for a particle moving from an evaporative source to a substrate is estimated that is proven inversely proportional to the local Knudsen number at the evaporation surface. N-c = 1 is adopted as a breakdown criterion of the free molecular assumption, and it is verified by experimental data and DSMC results. The second issue is how to realize the uniform distributions of thickness and component over a large-area thin film. Our analysis shows that at relatively low evaporation rates the goal is easy achieved through arranging the evaporative source positions properly and rotating the substrate.

Parametric Study of the Device Angle Dependency of a Single Vortex Generator on a Flat Plate

Ponencia presentada en el 10th World Congress on Computational Mechanics (WCCM 2012), Sao Paulo (Brazil).Publicados los abstracts en documento con ISBN: 978-85-86686-69-6.

Nonlinear Fluid Damping In Structure-Wake Oscillators In Modeling Vortex-Induced Vibrations

A Nonlinear Fluid Damping (NFD) in the form of the square-velocity is applied in the response analysis of Vortex-induced Vibrations (VIV). Its nonlinear hydrodynamic effects oil the coupled wake and structure oscillators are investigated. A comparison between the coupled systems with the linear and nonlinear fluid dampings and experiments shows that the NFD model can well describe response characteristics, such as the amplification of body displacement at lock-in and frequency lock-ill, both at high and low mass ratios. Particularly, the predicted peak amplitude of the body in the Griffin plot is ill good agreement with experimental data and empirical equation, indicating the significant effect of the NFD on the structure motion.