A comparative analysis of hydrokinetic turbine performance at low chord-based Reynolds number

Most hydrokinetic devices are rated for operation in mean streamwise flow velocities outside the range encountered in most rivers, making very few riverine sites suitable for hydrokinetic energy applications. Should the application of such devices be expanded, it is imperative to investigate potential solutions. Hence, this study aims to quantify and compare the performance of two types of hydrokinetic devices in flows representative of realistic riverine conditions. Four devices were tested: two Gorlov vertical axis devices and two horizontal axis hydrokinetic turbines (HAHTs). One Gorlov and one HAHT were representative of typical riverine design and the others were designed using the 20-32c aerofoil to allow for clear comparison between the device orientations. Experiments were conducted in the Aberdeen Open Channel Facility. Measurements of rotor torque and drag were taken using specially manufactured devices designed to deflect under operating conditions, where these deflections were measured using capacitive sensors such that torque and drag may be calculated as proportional to recorded deflection. Neither of the Gorlov devices succeeded in producing positive torque, with the 20-32c rotor reducing parasitic load slightly. The HAHT rotor representing a typical design produced a maximum C_p of 0.13, while the 20-32c HAHT design produced a maximum C_p of 0.40. It was concluded that Gorlov devices do not appear well suited for operation at studied flow conditions while HAHT design significantly impacts output torque, where focus should be given to higher performing aerofoils and prioritising greater chord lengths, although this does have implications for the thrust coefficient.