Full-scale investigation of heliostat aerodynamics through wind and pressure measurements at a pentagonal heliostat

Wind loads on heliostats are often investigated through experimental wind tunnel studies or numerical simulations. However, these approaches cannot consider the full-scale conditions but require a reproduction and simulation of both the heliostat structure and the wind conditions. Complementary full-scale investigations are therefore crucial but are at the same time relatively costly, as it is cumbersome to set up large heliostats with measurement devices. This paper introduces a new pressure measurement system which is easy-to-apply to a real-scale heliostat and enables full-scale investigations with minimized effort. The results of a first field study are presented during which wind and pressure measurements were taken simultaneously over periods of 10 min at a 48.5 m2 pentagonal Stellio heliostat. The non-dimensional pressure distributions are investigated and it is shown that the mean cp-values are very consistent amongst the measurement periods and reach values between 2.2 and 2.6. These values, in turn, are found to agree well with results of a wind tunnel study. Moreover, the behavior of the load coefficients with varying angles of attack is studied and the aerodynamic admittance functions are evaluated which give in-depth insight into the generation of aerodynamic loads. The admittance functions are found to start decreasing at a non-dimensional frequency of approximately 0.2. This finding indicates that eddies which are about the size of the heliostat or larger are fully effective in generating aerodynamic loads while the effectiveness of smaller eddies is reduced.