Drag reduction on a large-scale nacelle using a micro-blowing technique

An experimental study has been carried out to evaluate the micro-blowing turbulent drag reduction concept on an aircraft engine nacelle. A traversable hot wire probe was used to survey the boundary layer on a large-scale nacelle model in the United Technologies Research Center (UTRC) Acoustic Research Tunnel (ART). Control volume analysis was employed to deduce the model skin friction drag from the boundary layer survey data. The wind tunnel was operated at a unit Reynolds number of 2 million per foot, which simulated nacelle cruise operation at 0.8 Mach number and an altitude of 35,000 feet. The ART test section was configured such that axial pressure distributions typical of full-scale engine nacelles were produced over the model, and the ART freestream turbulence levels were low enough so as to provide an adequate simulation of conditions at altitude (ART freestream turbulence levels were measured at 0.05 0.07% of the freestream velocity). Results of the present study indicate that skin friction drag reductions of 50 70% are possible over portions of the nacelle, with the addition of only small amounts of blowing air (blowing coefficients on the order of 0.002 and smaller). Skin friction drag reduction levels are referenced to the skin friction drag of a solid, non-porous panel, which was also measured as part of the current experiment. For the present skin and nacelle geometry, drag reduction was seen to increase with decreasing unit Reynolds number. The largest drag reductions were seen to occur within regions of adverse pressure gradient. * Senior Research Engineer. Senior Member AIAA. *I Research Engineer. Member AIAA. Copyright