To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

Interest in the advancement of hydrokinetic energy conversion (HEC) technology has grown substantially in recent years. The hydrokinetic industry has advanced beyond the initial testing phase and will soon install demonstration projects with arrays of full-scale devices. By reviewing the current state of the industry and the cutting edge research this paper identifies the key advancements required for HEC technology to become commercially successful at the utility scale. The primary hurdles are: (i) reducing the cost of energy, (ii) optimizing individual turbines to work in concert considering array and bathymetry effects, (iii) balancing energy extraction with environmental impact, and (iv) addressing socioeconomic concerns. This review is split into three primary sections. The first section provides an overview of the HEC technology systems that are most likely to be installed in commercial arrays. The second section is an in-depth literature review. The literature review is sub-divided into five areas that are positioned to significantly impact the viability of HEC technology: (i) site assessment, (ii) turbine design, (iii) turbine wake modeling, (iv) array performance, and (v) environmental impact. The final section presents an outlook for the HEC industry and future research.

Hydrokinetic energy conversion: Technology, research, and outlook

A review on fluid dynamics of flapping foils

https://pure.tue.nl/ws/files/109101582/1_s2.0_S0360544218319704_main.pdf

Towards optimal aerodynamic design of vertical axis wind turbines: Impact of solidity and number of blades

Starting torque improvement using J-shaped straight-bladed Darrieus vertical axis wind turbine by means of numerical simulation

Simulation of power extraction from tidal currents by flapping foil hydrokinetic turbines in tandem formation

Numerical investigations on flow structure and behavior of vortices in the dynamic stall of an oscillating pitching hydrofoil

The power extraction by flapping foil hydrokinetic turbine in swing arm mode

Fluid structures of flapping airfoil with elliptical motion trajectory

In this paper the effect of accelerated flow over a moving airfoil is considered and based on the flow field around the airfoil the dynamic stall is evaluated. In contrast to ordinary pitching motion, the dynamic stall evaluation in this study is performed with a different motion pattern, in which the airfoil has a heaving motion in one direction. This motion pattern is also similar to rotation of an element of blade in horizontal axis wind turbines (HAWTs). In present investigation, the Reynolds number is changed during simulation time and variations of this parameter from initial to final values are shown by acceleration parameter. The operating Reynolds number is more than 106, and a S809 airfoil is selected to move with accelerations of 1, 4 and 6 m/s2 in normal direction to free stream. To resolve accelerated flow filed in the two-dimensional computational domain and to achieve results within a reasonable computation time, the unsteady Reynolds-Averaged Navier–Stokes (URANS) equations are employed. The governing equations are discretized based on the finite volume approach and semi-implicit method for pressure linked equations algorithm is used for pressure–velocity coupling. Furthermore, turbulence effect on flow field is accounted using shear stress transport (SST) k-ω model. It is shown that the accelerated flow can significantly influence on the aerodynamic loads and dynamic stall trend. This study may introduce a new concept regarding dynamic stall and aerodynamic loads when the rotational acceleration is involved in HAWTs. Copyright © 2014 John Wiley & Sons, Ltd.

Hamid Reza Karbasian

Papers

Simulation of power extraction from tidal currents by flapping foil hydrokinetic turbines in tandem formation

Numerical investigations on flow structure and behavior of vortices in the dynamic stall of an oscillating pitching hydrofoil

The power extraction by flapping foil hydrokinetic turbine in swing arm mode

Fluid structures of flapping airfoil with elliptical motion trajectory

Effect of acceleration on dynamic stall of airfoil in unsteady operating conditions