A numerical analysis to determine wake recovery distance for the longitudinal arrangement of hydrokinetic turbine in the channel system

Abstract

ABSTRACT Hydrokinetic technology is developing rapidly from model to prototype testing. The principle of hydrokinetic technology involves the passage of flow through the hydrokinetic turbine, which reduces the velocity downstream of turbine due to the energy extraction and obstruction created by turbine operation. This reduced velocity regains its initial velocity after certain distance known as wake recovery distance due to mixing regime and available discharge. This study aims to analyze the wake recovery distance under different flow velocities considering various dimensions of turbine. In order to study the impact of turbine operation on the flow condition, a 3D unsteady and rotational numerical analysis has been carried out by incorporating free surface effect. It is a first prototype based study and the analysis has been carried out on actual dimensions of the turbine taking 0.5, 1.0, 1.5, and 2.0 m dia. operating at varying water depth (2, 3, 4, 5, 6, and 7 m). Impact of velocity, turbine diameter and water depth on wake recovery distance is analyzed in the study to define the distance between two units along the channel length under different operating conditions. The distance between two units should be the summation of upstream (back water effect) and downstream (wake recovery distance) disturbance created by the turbine operation. It is observed that more than 90% of initial flow velocity gets recovered at ‘25D’ downstream of rotor.