Active Flow Control for Aircrafts and Heavy Vehicles

Licentiate thesis, 2009

Bluff-body flows are dominated by large dissipative vortex-shedding wakes with low mean pressure compared to the high pressure on their frontal area. This induced pressure difference is the major contribution to the total aerodynamic drag. The objective of the present work is to apply Active and Passive Flow Control (AFC) strategies to reduce the typically large base drag on bluff-bodies. Two main cases are investigated: A tilt-rotor aircraft wing during hover and a simplified truck-trailer model. Numerical computations using large-eddy simulation of the turbulent flow are carried out with and without AFC in order to evaluate the achieved drag reduction. A thorough parameter study of a novel rear-end trailer geometry and the parameters of AFC is carried out and also optimized using Response Surface Methodology. Flow reattachment process, dynamics of the flow with and without AFC and corresponding wake structures are discussed and analyzed. Experimental investigation of a typical synthetic-jet actuator is also carried out in order to evaluate the order of magnitude of maximum possible momentum coefficient Cμ. It is shown for with AFC the separated flow on the mounted flaps is reattached in the tilt-rotor aircraft wing and the truck-trailer model. The large dissipative wake size is narrowed and its intensity weakened. The base pressure is increased a great deal and the corresponding drag reduction is about 30% in both cases. The maximum possible momentum coefficient is Cμ=1% which is enough in order to achieve the desired drag reduction.