Author: Andre Chang, Peter Dewey, Antony Jameson, Chunlei Liang, Alexander SmitsPublication: Stanford UniversityYear Published: 2011 The flow over a pair of counter-rotating cylinders is investigated numerically and experimentally. It is demonstrated that it is possible to suppress unsteady vortex shedding for gap sizes from one to five cylinder diameters, at Reynolds numbers from 100 to…
Author: F. Diaz, J. Gavalda, J. G Kawall, J.F. Keffer, and F. GiraltPublication: Universitat de BarcelonaYear Published: 1983 Wind turbines must withstand harsh environments that induce many stress cycles into their components. A numerical analysis package is used to illustrate the sobering variability in predicted fatigue life with relatively small changes in inputs. The variability…
Author: Lydia Ruiz, Robert Whittlesey, John DabiriPublication: Cambridge UniversityYear Published: 2010 It has been previously suggested that the generation of coherent vortical structures in the near-wake of a self-propelled vehicle can improve its propulsive efficiency by manipulating the local pressure field and entrainment kinematics. This paper investigates these unsteady mechanisms analytically and in experiments. A…
Author: Matthias Kinzel, Daniel Araya and John DabiriPublication: Physics of FluidsYear Published: 2015 Experimental results from three different full scale arrays of vertical-axis wind turbines (VAWTs) under natural wind conditions are presented. The wind velocities throughout the turbine arrays are measured using a portable meteorological tower with seven, vertically staggered, three-component ultrasonic anemometers. The power…
Author: Daniel Araya, Tim Colonius and John DabiriPublication: J. Fluid Mech.Year Published: 2017 We present experimental data to demonstrate that the far wake of a vertical-axis wind turbine (VAWT) exhibits features that are quantitatively similar to that of a circular cylinder with the same aspect ratio. For a fixed Reynolds number (Re ≈ 0.8 ×…
Author: Kristian DixonPublication: Delft University of Tech.Year Published: 2008 A 3D unsteady multi-body panel method is developed that can model arbitrary geometries. The method has been specifically designed so that it can handle the blade-wake interactions and viscous wake effects that are important for modelling a vertical axis wind turbine (VAWT). A systematic validation and…
Author: John DabiriPublication: IOPScienceYear Published: 2007 Aquatic animals swimming in isolation and in groups are known to extract energy from the vortices in environmental flows, significantly reducing muscle activity required for locomotion. A model for the vortex dynamics associated with this phenomenon is developed, showing that the energy extraction mechanism can be described by simple…
Author: John DabiriPublication: J. Renewable and Sustainable EnergyYear Published: 2011 Modern wind farms comprised of horizontal-axis wind turbines (HAWTs) require significant land resources to separate each wind turbine from the adjacent turbine wakes. This aerodynamic constraint limits the amount of power that can be extracted from a given wind farm footprint. The resulting inefficiency of…
Author: Clara O’Farrell and John O. DabiriPublication: Cambridge UniversityYear Published: 2014 The formation and pinch-off of non-axisymmetric vortex rings is considered experimentally. Vortex rings are generated using a non-circular piston–cylinder arrangement, and the resulting velocity fields are measured using digital particle image velocimetry. Three different nozzle geometries are considered: an elliptical nozzle with an aspect…
Author: Clara O’Farrell and John O. DabiriPublication: Cambridge UniversityYear Published: 2012 The nonlinear perturbation response of two families of vortices, the Norbury family of axisymmetric vortex rings and the Pierrehumbert family of two-dimensional vortex pairs, is considered. Members of both families are subjected to prolate shape perturbations similar to those previously introduced to Hill’s spherical…