Flat-Plate Drag Reduction with Streamwise Noncontinuous Microblowing

Abstract

The efficiency of air microblowing through a wall consisting of alternating permeable and impermeable sections to reduce the turbulent skin-friction drag of a flat plate in a nominally gradientless incompressible flow was studied experimentally. The mass flow rate of the air per unit area was varied in the range from 0 to , which corresponds to the maximum blowing coefficient equal to 0.00287. In the previous study of the authors (Kornilov, V. I., and Boiko, A. V., “Efficiency of Air Microblowing Through Microperforated Wall for Flat Plate Drag Reduction,” AIAA Journal, Vol. 50, No. 3, 2012, pp. 724–732.), it was found in particular that there exists a wide flow region of reduced skin friction downstream from the microperforated insert. Therefore, the main attention in the present study is paid to distributed boundary-layer characteristics and efficiency of the given control technique supplemented with forced impermeable surface sections to reduce energy cost. Excluding the impermeable sections, a consistent reduction of the skin-friction coefficient along the chord of the perforated insert was found, the reduction achieving 71% at maximum value of the blowing coefficient. It is also shown that the microblowing with the same airflow rate as at completely permeable surface is able to provide the flat-plate total drag reduction of about 15–25%.