Effects of Wall Tangential Zero-mass Jets on Turbulent Drag Reduction

Skin friction drag accounts for 40-45% of the total drag for commercial flights. Drag reduction is one of the aims of the aeronautical industry, as it would increase the efficiency of the aircraft, reduce costs and make the air transportation greener. The objective of this thesis is to study in detail the technique of the Wall Tangential Zero-Mass Jets (WT-ZMJ) for turbulent boundary layer drag reduction, which is a developing active flow control system. For that, the contributing components of the skin friction drag are identified by means of a novel extension of the method introduced by Fukagata et al. (2002). In this extension, the boundary condition of a jet is introduced and applied to the WT-ZMJ. The mechanism proposed to operate the jets is studied as well as its power efficiency. Different configurations and flow control parameters of the WT-ZMJ are explored and further analysed with the extended FIK (FIK-E). This is done to identify the contributions that are affected by each parameter. The findings show that even though the Reynolds stress contribution increases the skin friction, the inhomogeneous contribution reduces it, which relates to the velocity gradient modification in the flow field. Moreover, a turbulence model based on the one developed by Spalart and Allmaras (1992) is obtained to explore the potential benefits of WT-ZMJ for practical applications.