INFLUENCE OF SEMICYLINDRICAL CAVITY ON INTEGRAL CHARACTERISTICS OF WALL BOUNDARY LAYER
DOI:
https://doi.org/10.20535/2305-9001.2012.64.53196Keywords:
boundary layer, boundary conditions, cavity, indentation, velocity defects, displacement thickness, momentum thickness, shape factor, coherent vortex structuresAbstract
Process control of mass and heat transfer in liquid and gas flows by means of cavities at the streamlined surfaces is one of the most promising ways to save energy in industrial, transport and power units and machines. The cause of this experimental study setting was deficit of information about coherent vortex structures (CVS) formation and emission from the grooves in the wake flow. To obtain this information in this work we investigate the profiles of the defects of the longitudinal velocity, displacement thickness, momentum thickness and shape factor in the boundary layer of air flow in front, above and behind the surface semi-cylindrical indentation on a flat plate. Analysis of these data shows that they reflect the influence of dissipative and inertial effects on the structure of the flow and allow us to determine the location of the CVS zones in the cavity of the groove and to better understand the conditions and nature of their beginning. Quantitative and qualitative changes of shape factor along the longitudinal coordinate as a function of flow velocity are significantly differ from traditional notions about weak dependence of this characteristic from Reynolds number, that is peculiar to flow over the plates and wing profiles without indentations. The proposed organization and implementation of experiments allow to receive sufficiently effective data by using per single hot-wire sensor of thermoanemometer. Pictures of the formation and evolution of the CVS expend complementary to the boundary conditions database for numerical calculations of heat transfer and aerodynamic drag in the flow with small Mach numbers over surface indentations. Results of investigation may be useful in designing of surfaces for aircrafts, ships and ground transports, as well as efficient compact heat exchangers.References
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