High-Reynolds-number turbulent-boundary-layer wall pressure fluctuations with skin-friction reduction by air injection.
The hydrodynamic pressure fluctuations that occur on the solid surface beneath a turbulent boundary layer are a common source of flow noise. This paper reports multipoint surface pressure fluctuation measurements in water beneath a high-Reynolds-number turbulent boundary layer with wall injection of air to reduce skin-friction drag. The experiments were conducted in the U.S. Navy's Large Cavitation Channel on a 12.9-m-long, 3.05-m-wide hydrodynamically smooth flat plate at freestream speeds up to 20 ms and downstream-distance-based Reynolds numbers exceeding 200 x 10(6). Air was injected from one of two spanwise slots through flush-mounted porous stainless steel frits (approximately 40 microm mean pore diameter) at volume flow rates from 17.8 to 142.5 l/s per meter span. The two injectors were located 1.32 and 9.78 m from the model's leading edge and spanned the center 87% of the test model. Surface pressure measurements were made with 16 flush-mounted transducers in an "L-shaped" array located 10.7 m from the plate's leading edge. When compared to no-injection conditions, the observed wall-pressure variance was reduced by as much as 87% with air injection. In addition, air injection altered the inferred convection speed of pressure fluctuation sources and the streamwise coherence of pressure fluctuations.
Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
Eric S
ES
Winkel
Brian R
BR
Elbing
Steven L
SL
Ceccio
Marc
M
Perlin
David R
DR
Dowling
D000388:Air / Q000032:analysis*; D017276:Friction; D006801:Humans; D007267:Injections; D007700:Kinetics; D045423:Microbubbles; D008954:Models, Biological; D011312:Pressure; D012879:Skin Physiological Phenomena