Abstract
Abstract. We present shelter measurements of a fence from a field experiment in Denmark. The measurements were performed with three lidars scanning on a vertical plane downwind of the fence. Inflow conditions are based on sonic anemometer observations of a nearby mast. For fence-undisturbed conditions, the lidars' measurements agree well with those from the sonic anemometers and, at the mast position, the average inflow conditions are well described by the logarithmic profile. Seven cases are defined based on the relative wind direction to the fence, the fence porosity, and the inflow conditions. The larger the relative direction, the lower the effect of the shelter. For the case with the largest relative directions, no sheltering effect is observed in the far wake (distances ⪆ 6 fence heights downwind of the fence). When comparing a near-neutral to a stable case, a stronger shelter effect is noticed. The shelter is highest below ≈ 1.46 fence heights and can sometimes be observed at all downwind positions (up to 11 fence heights downwind). Below the fence height, the porous fence has a lower impact on the flow close to the fence compared to the solid fence. Velocity profiles in the far wake converge onto each other using the self-preserving forms from two-dimensional wake analysis.
Highlights
The flow around obstacles is difficult to observe and model because of the turbulence characteristics and velocity shears
The measurements were conducted by the WS and agree well with sonic anemometer measurements from a nearby mast when the wind is not largely disturbed by the fence
Simulation of the WS measurements reveals that the WS tends to underestimate the magnitude of the u component at x/ h 4 and z/ h > 1
Summary
The flow around obstacles is difficult to observe and model because of the turbulence characteristics and velocity shears Such flow has not received much attention in wind energy partly due to the urge to decrease the cost of energy, narrowing the research on flow characteristics to large-turbine operating conditions. Computational fluid dynamics (CFD) methods, e.g. those solving the Reynolds-averaged Navier–Stokes (RANS) equations, can accurately describe the flow around obstacles and are used to study specific flow conditions (Iaccarino et al, 2003). They are often too expensive to be implemented in wind-resource assessment tools. Where g is the gravitational acceleration, T a reference temperature, v the virtual potential temperature; the primes denote fluctuations around the time average, and the overbar a time average
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