Author(s): Tom Harries; James Brammer; Bettina Bockelmann-Evans; Alan Kwan
Linked Author(s):
Keywords: Savonius; Vertical-axis turbine; PIV; Wake; Blockage effect
Abstract: Aninvestigation has been undertaken into the blockage and wake characteristics of various scaled Savonius turbines. The Savonius turbine is a vertical axis turbine which can be utilised in either an aero or hydro environment; however, this study will focus on the Savonius turbine in the water environment. Many studies have been compiled which examine the performance characteristics of the turbine in a closed test section in a laboratory flume, with the aim to improve design efficiency, power output etc. Blockage effects result in local flow acceleration on either side of the turbine due to the constriction caused by the flume walls in relation to the turbine scale. This phenomenon is absent when the turbine is placed unobstructed in an open marine scenario (i. e. no side wall effects). Since the power output of a turbine is proportional to the cube of the inflow velocity, the inability to quantify the blockage effect can lead to an over-estimation of the performance of a turbine in the laboratory environment. This study aims to use the non-intrusiveparticle image velocimetry (PIV) technique to obtain the time averaged flow field surrounding four various scaled Savonius turbines at two different azimuth angles 0° and 90°, representing different degrees of blockage. The PIV analysis was performed in 2D, on a horizontal plane atthe mid-depth of the flow and turbine. Wake characteristics of the various scaled turbines were examined and compared. The study revealed that an increase in blockage factor results in a decrease in the length of the turbine wake. The turbine with the smallest blockage factor of 20% at 0° and 90°resulted in wake lengths X/D = 13. 4 and 20. 4, whilst the turbine with the largest blockage factor of 50% at 0° and 90° resulted in wake length X/D = 4. 22 and 3. 055, respectively.
Year: 2013