Estimation of blade loads for a variable pitch vertical axis wind turbine from particle image velocimetry

Abstract

This paper presents the flow fields and aerodynamic loading of a two bladed H‐type vertical axis wind turbine with active variable pitch for load and circulation control. Particle Image Velocimetry is used to capture flow fields at six azimuthal positions of the blades during operation, three upwind and three downwind. Flow phenomena such as dynamic stall and tower shadow are captured in the flow fields. The phase‐averaged velocity fields and their time and spatial derivatives are used to calculate the normal and tangential loading at each position for each pitching configuration using the Noca formulation of the flux equations. The results show the effect of load shifting from the upwind to downwind region of the actuator using pitch and the effects of dynamic stall on the blades. The results also provide an unique database for model validation.

On the wake deflection of vertical axis wind turbines by pitched blades

“…Here, we introduce the idealization of a VAWT based on the three‐dimensional AC model, which has been verified as a good representation of an H‐type VAWT 42 . The AC has a height‐to‐diameter ratio of one, the same as the VAWTs investigated in the literature (e.g., Tescione et al 34 and LeBlanc and Ferreira 44 ). For simplicity, assume the load is uniformly distributed in the upwind and downwind locations, respectively, with the upwind half loaded more heavily (Figure 1).…”

“…Such phenomenon has been confirmed by both load and flow field measurements performed on the blades of a larger H-type VAWT. 44 In contrast, positive pitch increases both streamwise and lateral force by 25% and 180%, respectively. Besides that, LeBlanc and Ferreira (2021) 44 reported significantly increased blade load in the upwind-windward region, and a sudden drop in the upwind-leeward region.…”

“…44 In contrast, positive pitch increases both streamwise and lateral force by 25% and 180%, respectively. Besides that, LeBlanc and Ferreira (2021) 44 reported significantly increased blade load in the upwind-windward region, and a sudden drop in the upwind-leeward region. The same happens in the current measurement, which can be justified by the averaged velocity deficit fields presented in Section 4.1.…”

“…Ferreira (2009) 43 first proposed that by shifting the pitching axis of a VAWT, the blade load can be shifted upwind or downwind of the swept area of the rotor. Recently, LeBlanc and Ferreira (2021) 44 measured the blade load with an in‐house designed VAWT that can perform active pitch control, showing that a fixed blade pitch can modify the blade load effectively. A few studies can also be found in the literature using the pitched blades on the deflection of VAWTs' wake.…”

Estimation of blade loads for a variable pitch Vertical Axis Wind Turbine with strain gage measurements

“…While data were only collected at a handful of locations around the azimuth, it provides excellent detail of the potential presence of dynamic stall at tip speed ratios lower than 3.5 for said solidity ratio. More recently, measurements have been made using flow analysis techniques such as Particle Image Velocimetry, 6 previously used by Ferreira, 7 Castelein et al, 8 and Castelein 9 . While very useful, these measurements are limited in temporal and azimuthal resolution and are difficult to conduct.…”