Growing concerns about the environmental impact of fossil fuel energy and improvements in both the cost and performance of wind turbine technologies has spurred a sharp expansion in wind energy generation. However, both the increasing size of wind farms and the increased contribution of wind energy to the overall electricity generation market has created new challenges. As wind farms grow in si...

Numerical investigation of vortex dynamics in near wake of a hovering hawkmoth and hovering aerodynamics is conducted with a biology-inspired dynamic flight simulator. This simulator is developed to be capable of ‘flying’ an insect on a basis of realistic wing-body morphologies and kinematics. The computed results show a three-dimensional mechanism of vortical structures in hawkmoth hovering. A...

A potential flow model is used to study the unsteady flow past two airfoils in configuration, each of which is suddenly set into motion. The airfoil bound vortices are modeled using lumped vortex elements and the wake behind the airfoil is modeled by discrete vortices. This consists of solving a steady state flow problem at each time-step where unsteadiness is incorporated through the “zero nor...

The fluid dynamics of many swimming and flying animals involves the generation and shedding of vortices into the wake. Here we studied the dynamics of similar vortices shed by a simple two-dimensional flapping foil in a soap-film tunnel. The flapping foil models an animal wing, fin or tail in forward locomotion. The vortical flow induced by the foil is correlated to (the resulting) thickness va...

When a plane crosses the wake generated by a preceding aircraft, large dynamical loads in the order of the design loads may be induced. Loads analysis models for such wake vortex encounters need to consider aspects important for manoeuvre, as well as gust type responses. If the angle between the path and the trailing vortices is small, the encounter is manoeuvre like due to large induced roll m...

1 Lagrangian analysis is capable of revealing the underlying structure and complex phenomena in unsteady flows. We present Particle-Image Velocimetry measurements of the wake of a cylinder undergoing streamwise vortex-induced vibrations and calculate the Finite-Time Lyapunov Exponents (FTLE) in backward-and forward-time. The FTLE fields are compared to the phase-averaged vorticity fields for th...

An experimental study of the effect of wake disturbance frequency on the secondary flow vortices in a two-dimensional linear cascade is presented. The flow Reynolds numbers, based on exit velocity and suction side surface length were 25,000, 50,000 and 85,000. Secondary flow was visualized by injecting smoke into the boundary layer and illuminating it with a laser light sheet located at the exi...

Understanding how moving organisms generate locomotor forces is fundamental to the analysis of aerodynamic and hydrodynamic flow patterns that are generated during body and appendage oscillation. In the past, this has been accomplished using two-dimensional planar techniques that require reconstruction of three-dimensional flow patterns. We have applied a new, fully three-dimensional, volumetri...

Flow around square cylinders with cut-corners at the front edges is investigated using particle image velocimetry. It is found that drag reduction can be achieved for the tested cut-corner dimensions. The mechanism for the drag reduction is explored on the statistical and structural aspects of the flow. After cutting the corners, the fluctuation intensity of the wake is weakened, the length of ...

The potential hazard of one aircraft encountering the trailing vortex wake of another aircraft during either take-off or landing is well known. The wake vortex hazard in the terminal area has been virtually eliminated using the operational procedures and aircraft separation criteria mandated by the air traffic authorities. This paper presents arguments that wake encounters at cruise altitude ar...