Abstract

The mean and spectral characteristics of turbulence in the wake flow of a flat plate model resembling a heliostat in the atmospheric boundary layer flow are investigated in a wind tunnel experiment. Mean velocity and turbulence kinetic energy were characterized in the wake of a heliostat model at three elevation angles up to a distance of eight times the characteristic dimension of the heliostat panel. An increase in turbulence intensity and kinetic energy was found in the wake flow, reaching a peak at a distance equal to approximately twice the characteristic dimension of the heliostat panel. Furthermore, spectral and wavelet analysis of velocity fluctuations in the wake showed that the dominant mechanism in the immediate downstream of the plate was the breakdown of large inflow turbulence structures to smaller scales. In the end, the wake-induced turbulence patterns and wind loads in a heliostat field were discussed. It was found that compared to a heliostat at the front row, the heliostats positioned in high-density regions of a field were subjected to a higher turbulence intensity and, consequently, larger dynamic wind loading. The results show that it is necessary to consider the increased unsteady wind loads for the design of a heliostat in high-density regions of a field, where the gap between the rows is less than three-times the characteristic length of the heliostat panel.

Highlights

  • Understanding the flow characteristics in the wake of a heliostat is a fundamental step for analysis of the flow turbulence within a heliostat field which has several complexities including its dependence on the field arrangement and density

  • This study focuses on the wake of a heliostat in an atmospheric boundary layer and aims to develop an understanding of how the statistical and spectral characteristics of turbulence change in the wake of the heliostat

  • The increase in the unsteady wind loads on the inner field heliostats is expected to be less in regions of the field with a very low density, x/c >6, as the increase in the turbulence intensity is less than 20%, where the 20% increase is for α=90°

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Summary

Introduction

Understanding the flow characteristics in the wake of a heliostat is a fundamental step for analysis of the flow turbulence within a heliostat field which has several complexities including its dependence on the field arrangement and density. An experimental study of the effect of grid-generated turbulence, with turbulence intensities between 0.8% and 4.3%, on the wake of a disk normal to the flow found that the inflow turbulence weakened vortex shedding in the near wake and reduced its strength (Rind and Castro, 2012). The inflow turbulent boundary layer alters the wake of a heliostat from a flat plate developed in a uniform flow Another parameter, in addition to the inflow turbulence, which affects the wake of a heliostat is the ground effect. Extensive velocity measurements were conducted in the wake of a flat plate model representing a heliostat in two simulated neutral atmospheric boundary layer flows in the University of Adelaide large-scale wind tunnel to characterise turbulence in the wake flow.

Methodology
Wake Flow Characteristics
Wake-induced wind loads in a heliostat field
Findings
Conclusions
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