On the influence of wind on cavity receivers for solar power towers: Flow visualisation by means of background oriented schlieren imaging

Kurzfassung

In previous studies the influence of wind on convective losses of a solar cavity receiver has been investigated experimentally and numerically. It was found that in the backward facing cavity a reduction of convective losses with increasing wind speed can occur. In this short communication we give an explanation for these results by analysing the flow structure with the background oriented schlieren (BOS) method. For image analysis a gradient-based approach following Lucas and Kanade (1981) has been implemented. With a coarse to fine iterative strategy density gradients resulting in pixel shifts of several pixels in the image plane are determinable. The results show good agreement with theoretical analyses. The developing plume is well defined and with increasing wind speed disturbances of the plume structure are clearly resolved. Moreover, in the natural convection cases the transition from laminar to turbulent flow has been made visible