Numerical analysis on the torque characteristics of hybrid hydrokinetic turbine for different configurations and operating conditions

Abstract

A hybrid hydrokinetic turbine can become an efficient converter to harness the untapped hydrokinetic energy of small-scale hydro potentials sites such as canals and rivers, determining the optimal performance parameters becomes necessary. As the torque of a hydrokinetic turbine is considered one of the important performance parameters, an extensive numerical investigation has been carried out to analyse the torque characteristics of a hybrid HKT having a different value of radius ratio and attachment angle operated under different RPM and flow velocity. Under the present study, CFD analysis of four different configurations of hybrid hydrokinetic turbines covering the range of radius ratio from 0.2 to 0.8 and attachment angle from 30° to 150° have been carried out. A URANS with the conjunction of RNG k-ε has been exercised to accomplish the objectives of the present investigation. Based on the numerical results, the best configuration is found to have an optimum radius ratio value and attachment angle obtained as 0.4 and 90°, respectively. For the best-configured hybrid HKT, the average torque developed is improved by 51%, 20%, 19%, 6% and 24% compared to other hybrid configurations, corresponding to a TSR of 0.9 and Reynolds number of 1.12 × 105. The self-starting characteristics of the hybrid configuration with a 0.4 radius ratio and 90° attachment angle are better than the other considered hybrid configurations. Further, the instantaneous torque developed by the hybrid configuration with a 0.4 radius ratio and 90° attachment angle was found to be positive at each rotor angle during one cycle of revolution. Moreover, the least rate of torque pulsation is found for the hybrid HKTs operated at low RPM and Reynolds number.