TURBULENT-FLOW FRICTION AND HEAT-TRANSFER CHARACTERISTICS FOR SPHERICAL CAVITIES ON A FLAT-PLATE

Experimental investigations were made of friction and heat transfer on surfaces shaped by systems of spherical cavities streamlined by a turbulent flow. The experiments were run on a special aerodynamic test bed using a traditional procedure for diagnosing a boundary layer in conditions of outer flow. Ten plates were used as prototypes. nine of which had surfaces shaped by staggered ordered systems of spherical cavities at various densities and geometries, and one smooth surface for test experiments. All measurements were made with a DISA-55M thermoanemometric set and direct-acting standard transducers with 2.5 mum diameter filaments. For direct measurement of heat flux on a smooth surface, DTP-05 transducers were used. which did not produce any significant changes in the temperature field of the specimen. From the results obtained we conclude that such a shaping of a heating surface has no appreciable effect on the hydrodynamics of a flow with considerable (up to 30-40%) heat transfer enhancement. Experimental data on heat transfer are generalized, and a relationship suitable for engineering estimation of heat transfer on surfaces shaped by a regular relief of spherical cavities and valid for the investigated geometric parameters of shaping and flow regimes has been obtained.