VISCOUS AERODYNAMIC DRAG ACCOUNTS FOR ABOUT HALF OF THE TOTAL DRAG ON COMMERCIAL AIRCRAFT AT SUBSONIC CRUISE CONDITIONS.

VISCOUS AERODYNAMIC DRAG ACCOUNTS FOR ABOUT HALF OF THE TOTAL DRAG ON COMMERCIAL AIRCRAFT AT SUBSONIC CRUISE CONDITIONS. TWO AVENUES ARE AVAILABLE TO ACHIEVE SUBSTANIALDRAG REDUCTION: EITHER LAMINAR FLOW CONTROL OR TURBULENCE MANIPULATION. THIS PROPOSAL CONCERNS THE LATTER APPROACH. A NEW TECHNIQUE TO REDUCE SKIN FRICTION DRAG IN A TURBULENT BOUNDARY LAYER IS PROPOSED. THE TECHNIQUE COMBINES THE BENEFICIAL EFFECTS OF A LONGITUDINALLY RIBBED SURFACE AND SUCTION. THE SUCTION WILL BE APPLIED SELECTIVELY IN SPACE AND TIME TO MINIMIZE THE PUMPING ENERGY REQUIREMENTS AND TO ALLEVIATE THE NEED FOR USING A POROUS WALL. IT IS ANTICIPATED THAT THE NET DRAG REDUCTION USING THE PROPOSED METHOD WILL FAR EXCEED THAT ATTAINED USING SUCTION ALONE OR LONGITUDINAL GROOVES ALONE. THE FEASIBILITY OF THE PROPOSEDTECHNIQUE WILL BE DETERMINED BY CONDUCTING A SET OF WELL-CONTROLLED EXPERIMENTS USING A ZERO-PRESSURE-GRADIENT BOUNDARY LAYER THAT DEVELOPS ON A FLAT PLATE TOWED IN AN 18-METER WATER CHANNEL. FLOW VISUALIZATION AND FAST-RESPONSE PROBE MEASUREMENTS WILL BE CONDUCTED TO DETERMINE THE EFFECT OF THE DEVICE ON THE FLOW FIELD. THE DRAG WILL BE DIRECTLY MEASURED TO INDICATE THE REDUCTION ACHIEVED BY USING THE PROPOSED TECHNIQUE.