An experimental investigation of unsteady pressure distribution on tandem heliostats

The unsteady surface pressure distribution on heliostats in a tandem arrangement is investigated in this experimental study. The differential pressure on the panel of a heliostat model is measured for a range of gaps between the two tandem heliostats, varying from 1 to 7 times the chord length dimension of the panel. The heliostat models are placed in a simulated turbulent atmospheric boundary layer in the University of Adelaide wind tunnel. The measured surface pressures are analysed and compared with those of a single heliostat, at three elevation angles of 30°, 60° and 90°. The results showed that the peak pressure distribution on the tandem heliostat differs significantly from the single heliostat. Regions of large-magnitude pressure occur near the edges of the panel at smaller gap ratios. Large unsteady variations of the position of the centre of pressure are found for the tandem heliostat at gap ratios equal to and less than 5, which lead to an increase of the hinge moment relative to the single heliostat. The peak hinge moment coefficient on a tandem heliostat is found to be 40% and 70% larger than the coefficient on the single heliostat at elevation angles of 30° and 60°, respectively. The results therefore indicate the importance of the unsteady wind loads in different rows of a field for the design of heliostats as they vary significantly from the loads on a single heliostat dependent on the field arrangement.