The Effect of Cross Flow and Isolated Roughness Elements on the Boundary Layer and Wall Pressure Fluctuations on Circular Cylinders
Abstract : In this paper pressure fluctuation measurements on smooth cylinders aligned with the flow have been extended to include the effect of slight cross flow and isolated roughness elements. A yaw angle of a few degrees is sufficient to produce severe asymmetry of the outer portion of the boundary layer as deduced from impact pressure measurements using computer controlled traversing gear. The root-mean-square surface pressure fluctuations are a maximum on the windward surface but only slightly larger than with no yaw. On the leeward surface they are much lower. The power spectrum of the pressure has greater energy density at high frequencies on the windward surface and at low frequencies on the leeward side. With no cross flow the root-mean-square surface pressure is greatly increased by a cylindrical collar placed around the cylinder. A collar which increases the diameter by 50% more than doubles the wall pressure three diameters downstream. The spectra of the pressure scale with collar thickness and the intensity of the surface pressure fluctuations scales with the ratio of collar thickness to distance downstream. (Author)
High Reynolds number thick axisymmetric turbulent boundary layer measurements
Experimental measurements of the wall shear stress and momentum thickness for thick axisymmetric turbulent boundary layers are presented. The use of a full-scale towing tank allowed zero pressure gradient turbulent boundary layers to be developed on cylinders with diameters of 0.61, 0.89, and 2.5 mm and lengths ranging from 30 m to 150 m. Moderate to high Reynolds numbers (104<Reθ<105, 108<ReL<109) are considered. The relationship between the mean wall shear stress, cylinder diameter, cylinder length, and speed was investigated, and the spatial growth of the momentum thickness was determined. The wall shear stress is significantly higher, and the spatial growth of the boundary layers is shown to be lower than for a comparable flat-plate case. The mean wall shear stress exhibits variations with length that are not seen in zero pressure gradient flat plate turbulent boundary layers. The ratio of outer to inner boundary layer length scales is found to vary linearly with Reθ, which is qualitatively similar to a flat plate turbulent boundary layer. The quantitative effect of a riblet cylindrical cross-sectional geometry scaled for drag reduction based on flat plate criteria was also measured. The flat plate criteria do not lead to drag reduction for this class of boundary layer shear flows.
Turkish Political Culture and Civil Society : an Unsettling Coupling?
This paper attempts to analyze Turkish politics in the post-1980 period with a special reference to the relationship among the state elites, political elites and societal actors and its impact on the constitution of civil society in Turkey. After the 1980 military intervention, the political and economic realms of Turkey witnessed a relative degree of liberalization through Uzal's neo-liberal policies. The January 24 economic decisions paved the way for economic liberalization as well as letting new economic and societal actors emerge. These new economic actors were different from the prevailing economic actors which used to enjoy having a considerable amount of opportunity spaces in the economic sphere. Together with the Uzal governments, Islamic segments started to become powerful in both political and economic realms. This paper analyses the chief traits of Turkish politics and economics and their impact upon civil society aftermath the 1980 coup in general, and the relationship and/or interaction among the state elites, political elites and societal actors in particular. The engagements of newly-emerging societal and economic actors into Turkish political scene and the challenge of these actors against the so-called 'Kemalist-Republican' elites are also illustrated in the paper. Moreover, state-Islam interaction, politics-Islam interaction as well as Kemalism-newly-emerging societal and economic actors interaction will be studied with a special emphasis to the post-1980 period. The major argument of the paper is that, in Turkey, both civil society issues and political issues reveal outcomes which are primarily shaped by the nature of the relationship between state elites and political elites in general and by Turkish political culture in particular.