THE RANDOM SWEEPING DECORRELATION HYPOTHESIS IN STRATIFIED TURBULENT FLOWS

Longitudinal velocity measurements above a uniform dry lakebed were ca rried out to investigate the applicability of the random sweeping deco rrelation hypothesis to thermally stratified turbulent flow. The highe r order velocity structure functions of order m were measured and mode led using the sweeping decorrelation hypothesis. In order to reduce th e influence of Taylor's frozen hypothesis on the assessment of the swe eping decorrelation hypothesis, two dimensionless quantities, develope d by Praskovsky et al. (1993), were used. Based on these dimensionless quantities, the sweeping decorrelation hypothesis predictions agreed well with the higher order structure function measurements. Assumption s inherent in the sweeping decorrelation hypothesis were also consider ed. It was found that strong interaction existed between the energy co ntaining scales and the inertial subrange scales, indicating that the sweeping action alone does not fully describe the higher order structu re function. Also, local temperature-velocity interactions were measur ed and found to be significant thus weakening the validity of the swee ping decorrelation hypothesis. However, these two interaction mechanis ms appeared to be opposite in sign and counteracted each other.