Wind Characteristics in the Wake of a Non-Rotating Wind Turbine close to a Hill

Abstract

Hilly terrain may considerably influence energy yield and structural loading of wind turbines. Wind energy developers are therefore required to accurately predict wind characteristics at the wind farm site already in the designing phase. It is necessary to determine how particular hill shape and size affect wind characteristics at the location of wind turbines operating in the wake of a hill. In order to address this complex issue, small-scale laboratory experiments were carried out in a boundary layer wind tunnel (BLWT). The focus was on characteristics of the flow at the same position downstream of the hill and the wind turbine models studied on various sizes and shapes of the hill model. Three hill models (a small and a large hill with laterally uniform heights and a hill with a bay) were exposed to the thermally neutrally stratified atmospheric boundary layer (ABL) simulation. In each experiment, there was only one hill model in the BLWT test section. The configuration without the hill, i.e. the flat terrain model, was tested as a reference case. Downstream of the hill model, there was a single (alone-standing) wind turbine model. Flow characteristics were studied downstream (behind) the wind turbine model. The wind turbine model was in the parking position in order to study wind characteristics in the situation with a strong wind when there is no rotation of rotor blades. The experimental results indicate a velocity decrease and stronger turbulence in the wind turbine wake in the presence of a hill, which trend is more pronounced in the case of larger hills. Strong velocity gradients are observed around the hub height in the large hill configuration, while this velocity deficit is the smallest in the hill with a bay configuration due to flow channeling. The velocity power spectra reveal the characteristic peak due to the vortex shedding from the hill ridge. The obtained results provide a new insight into the turbulent wake characteristics of a single wind turbine placed downstream of a hill with a potential to serve as a validation tool for computational studies.

The effect of parked wind turbines on wind flow and turbulence over a complex terrain

“…An attempt was also made to distinguish between the effects of parked wind turbines and hill orography on the wind characteristics over a complex terrain. This analysis complements previous findings concerning the wind characteristics related to wind turbines standing alone, 7,8 those embedded in wind farms, 9 and other aerodynamic aspects of parked wind turbines, Xu and Ishihara, 10 Shirzadeh et al, 11 and Tang et al 12 …”

Numerical simulation of the boundary layer development behind a single quarter elliptic-wedge spire

“…Hagishima et al (2009) and Zaki et al (2011Zaki et al ( & 2012) used a set of quarter elliptic-wedge spires as a vortex generator to identify the measured drag coefficient (Cd) which is produced by the rough walls consisting of cubes in the furious pattern of arrangement [14][15][16]. Kozmar (2016) used a set of quarter elliptic-wedge spires completed with the castellated barrier wall as a vortex generator followed by the roughness wall consisting of arranged cubes to observe the wind turbine wake downwind of a mountain [17,18].…”