Eleanor Praskovskaya

Fractal Geometry of Isoconcentration Surfaces in a Smoke Plume

Abstract The fractal properties of isoconcentration surfaces in a smoke plume are studied in an atmospheric boundary layer wind tunnel. Instantaneous high-resolution two-dimensional images of the fine particle concentration at Schmidt number Sc → ∞ were obtained in three plume cross sections with a video imaging technique. The fractal dimension D of isoconcentration contours is estimated with box-counting and area-perimeter methods; the range of thresholds is 0.5 ≤ c*/c ≤ 1.5, where c is the mean particle concentration for a particular image and c* is the threshold. Using the box-counting method, the local values of D = −d(log Nϵ)/d(log ϵ) are found to be constant over variations in ϵ that are more than a decade, where Nϵ, is the number of boxes with size ϵ required to cover an isoconcentration curve. Using the area-perimeter method, the fractal dimension is estimated with the relation P ∼ AD/2, where P and A denote the perimeter and area of the individual closed isoconcentration curves. The noise influ...

Further experimental support for the Kolmogorov refined similarity hypothesis

The validity of the Kolmogorov refined similarity hypothesis (RSH) is tested experimentally in the mixing layer and in the return channel of a large wind tunnel, at Rλ≈2.0×103 and 3.2×103, respectively. The energy dissipation rate is estimated from the longitudinal gradient of both the longitudinal ∂u/∂x and transverse ∂w/∂x velocity components, and the results are in good agreement with RSH in both cases.

Spatial-Temporal Differential Analysis for Profiling the Atmosphere, 2, Experimental Results

We consider an application of the spatial-temporal differential analysis (STDA) to measuring characteristics of the atmosphere with spaced antenna wind profilers. STDA is a new method for processing multiple signals which utilizes spatial and temporal scintillations in the instantaneous signal power on the radar antenna. To test the practical potential of STDA, we used actual signals from the multiple antennas profiling radar (MAPR). The goal was to measure mean horizontal winds and characteristics of atmospheric turbulence in the presence of intensive ground clutter. The STDA results in the atmospheric boundary layer at a height of 300 m above the ground are compared with simultaneous measurements by a sonic anemometer located atop a 300-m tower 600 m distant from MAPR. Second-order structure functions for multiple radar signals were used for the processing. We demonstrate that this simplified STDA technique provides a good performance by reliably measuring mean winds in cluttered environment It also enables comprehensive measurements of atmospheric turbulence which no other known methodology is able to provide