Viscous sublayer flow visualizations at Rθ≂1 500 000

Abstract

Plan view flow visualization experiments were conducted in the atmospheric surface layer that flows over the Great Salt Lake Desert at the U.S. Army Dugway Proving Ground, Dugway, Utah. Measurements were acquired on a nonconductive, polyethylene platform made flush with the desert floor. Surface conditions upstream of the measurement site were flat, devoid of vegetation, and because of the dried mud/clay/salt composition, essentially dust free. Local surface variations ranged between 1 and 3 mm, which corresponded to three to ten viscous units during the experiments. Flow visualizations were accomplished by continuously injecting theatrical fog through a tangential slit covering a smoke reservoir buried under the platform. During the visualizations, the atmospheric surface layer flow was near neutral thermal stability. Flow velocities at 2.0 m above the surface maintained directional constancy, with a magnitude of about 1.5 m/s. A single element hot-wire probe positioned near y+=3.4 was used to measure the wall shear. Visualization results indicate the existence of the pocket and streak motions seen at much lower Reynolds number. The average inner normalized streak spacing was found to be λ+=93.1, with a positively skewed, nearly lognormal distribution. The average maximum inner normalized pocket width was found to be w+=127.2, with a positively skewed distribution. The average time between pockets was determined to be T+=36.6. Comparisons are made with existing low Reynolds number results, and a brief discussion is provided regarding the physics underlying the present observations.

Scaling properties of velocity and temperature spectra above the surface friction layer in a convective atmospheric boundary layer

“…The site is described by Klewicki et al (1995). Figure 1 shows the site and the array of sonic anemometers.…”

Experimental manipulation of wall turbulence: A systems approach

“…The structure and dominant dimensions associated with the autonomous, near-wall cycle of turbulence have been known since the seminal experiments of Kline et al 45 Significant study of the dynamics of the flow in this region, performed by, e.g., Waleffe, 46 Jiménez and Pinelli, 47 and Schoppa and Hussain 48 using low Reynolds number data, revealed the well-known quasi-streamwise vortex and streamwise velocity streak structure, while experiments in the atmospheric surface layer 49 have demonstrated the Reynolds number independence of the streak spacing in viscous units at the near-wall scales identified above, namely, λ + x ≈ 1000 and λ + z ≈ 100. Comparison with the structure arising from our analysis requires the specification of an additional parameter, the phase velocity, c. For the dominant wavelengths associated with the near-wall cycle, the first singular mode is critical and attached to the wall, as identified in Figure 7, when c + = 10 − 15, the minimum convection velocity associated with energetic disturbances.…”

Formation and behavior of aeolian streamers

“…Some measurements have been gathered in atmospheric boundary layers [e.g., Klewicki et al, 1995], but interactions with sediment transport processes have not been established. Such vortices are usually associated with flow over curved surfaces in the form of Taylor-Görtler vortices [Floryan and Saric, 1982] or may be associated with the curvature of individual eddies and hairpin vortices shed by burst sweep events [Blackwelder, 1983;Myose and Blackwelder, 1991].…”