Free Convection Similarity and Measurements in Flows With and Without Shear

Abstract

The free convection similarity theory is examined in the light of recent observations in the atmosphere, convection chambers and wind tunnels. The theory describes the fluctuations of temperature and vertical velocity fairly well, but only in flows with finite shear. The horizontal components of velocity and mean temperature may not be scaled by the same in the range of stability ordinarily encountered in the surface layer of the atmosphere. Free convection similarity scaling of the outer layer is expected to be more successful, although sufficient atmospheric data are not available to test this assertion. Preliminary results of numerical calculations by Deardorff are very encouraging, and so are our limited observations in a wind tunnel boundary layer. Because of extremely variable conditions in the atmosphere under free convection, some aspects of this flow may be better studied in the laboratory under carefully controlled conditions. Both convection chamber (no shear) and wind tunnel (finite shear) flows have been used for this purpose; the latter is shown to give better similarity with the atmospheric boundary layer.