Session: 18-02 HelioCon Windload

Paper Number: 142141

142141 - Impact of Heliostat Array Density on Boundary Layer Characteristics and Wind Loading 

Abstract: 

This paper investigates the impact of heliostat array density on boundary layer turbulence parameters within the array and develops a correlation between the local flow characteristics and the wind loads on heliostats in different rows of the array. A linearly staggered array of 42 heliostats in 7 rows was tested in the University of Adelaide wind tunnel at elevation angles in increments of 15° between 0° and 90° for two different field densities of 12.5% and 37.5%. Wind loads were measured using four three-axis ME Systeme K3D40 load cells mounted beneath the rectangular platform. The position of the load cells could be adjusted to different rows within the field to analyze the forces measured on individual heliostats in each of the seven rows of the staggered array. A set of spires at the test section inlet were used to generate incoming ABL profile of grassy plains. Three-dimensional flow measurements were taken with a Turbulent Flow Instrumentation (TFI) multi-hole pressure (Cobra) probe at a sampling rate of 1000 Hz.

Wind loads on heliostats in the seven rows of the array for two array densities were normalized to a single isolated heliostat. The variation of mean load coefficients showed a steady decrease in both drag and lift forces on heliostats with increasing row at all operating elevation angles above 30°. The magnitude of load reduction tends to be larger for the high-density case and the loads stabilize and approach a constant value at rows 4-5 and beyond in agreement with previous wind tunnel studies by Peterka et al. (1986,1987). Peak load coefficients show a similar trend to mean coefficients, except that the peak drag coefficients at elevation angles of 15° and 30° from row 2 onwards exceed single heliostat coefficients at a 90° elevation for the row, and peak lift coefficients at elevation angle of 15° at all positions downstream of the first row exceed single heliostat coefficients at this angle. The maximum coefficients for these operating angles were shown to be due to the amplification of streamwise component of turbulence intensity for drag coefficients, and the vertical component of velocity for lift forces. The results indicate the feasibility of designing lighter heliostat components in shielded in-field regions with reduced loads compared to the design operating load of a single heliostat. For instance, the first two rows are highly loaded and at some angles exceed the isolated heliostat load, however from the fourth staggered row and with increasing distance into the field, mean and peak loads at elevation angles above 30° are reduced by up to 50%. Amplification of peak lift forces at elevation angles of 30° and lower in downstream rows of the field present a larger risk to operating accuracy and stability and should therefore be carefully considered for in-field load amplification.

To relate the wind loads in different rows of the array to the in-field flow characteristics and heliostat array density and blockage parameters, spanwise and vertical profiles were measured to correlate the variation in loads to the local flow characteristics. The variations of flow in the spanwise direction show shielding and blocking effects by upstream heliostats with deficits in velocity, along with flow channelling between adjacent heliostats leading to increased velocity impacting the second row and third row in the high-density array.

Presenting Author: Matthew Marano The University of Adelaide

Presenting Author Biography: To be presented by Matthew Emes if possible.

Authors:

Matthew Marano The University of Adelaide
Matthew Emes The University of Adelaide
Azadeh Jafari The University of Adelaide
Maziar Arjomandi The University of Adelaide