Experimental study of dynamic wind loads on heliostats

Abstract

The fluctuating behaviour of wind load on a heliostat model at different ground clearance ratios and elevation angles under low and high turbulence flow conditions are reported in this paper. The experiments were conducted in a wind tunnel. An instrumented heliostat model contains differential pressure sensors at the front and back of the heliostat panel, which is exposed to the flow. The power spectral density of the fluctuating pressure measured by the pressure sensors was used to calculate the Strouhal number and the frequency of the wind load fluctuations on the heliostat model at different ground clearance ratios of 0.106–0.485 and different elevation angles of 15°–88°. It was observed that for elevation angles larger than 45°, the Strouhal number of the heliostat model is insensitive to flow turbulence, but at lower than 45°, it is significantly influenced by the flow turbulence parameters when the turbulence intensity at the hinge height of the heliostat is approximately 14 %. Additionally, it was shown that when the heliostat ground clearance ratio reduces, an asymmetric wake is formed in the vertical plane, and the Strouhal number increases, while for higher values of ground clearance ratio, a symmetric wake is formed and the Strouhal number stabilises at a constant value of 0.135. Increasing turbulence intensity from 2 % to 14 % leads to decrease in the Strouhal number for a ground clearance ratio of 0.333 or less. In contrast, for a ground clearance ratio of 0.409 or larger, it stays almost constant at 0.15.