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.
Winkel
Eric S
ES
Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
Elbing
Brian R
BR
Ceccio
Steven L
SL
Perlin
Marc
M
Dowling
David R
DR
D000388:Air / Q000032:analysis*; D017276:Friction; D006801:Humans; D007267:Injections; D007700:Kinetics; D045423:Microbubbles; D008954:Models, Biological; D011312:Pressure; D012879:Skin Physiological Phenomena