A near-wall control approach to suppress the log-law energy containing structures to obtain frictional drag reduction at relatively high Reynolds numbers

The energy consumption in an aircraft is mainly due to the aerodynamic drag force that opposes an aircrafts motion through the air. Almost 50% of total drag is due to the viscous drag, which is directly related to the friction drag of the aircraft caused by the interaction of the turbulent boundary layer flow with the aircraft surface. Studies on the aircraft and turbulent boundary layer interactions, together with developments of advanced flow control technologies, can effectively reduce more
more » ... han 40% of the viscous drag, which is equivalent to about 15% of the total drag and has, therefore, major implications to the energy consumption of commercial aircraft. Saving 1% of fuel on a Boeing 737 - 800 would result in a 100 metric tons yearly fuel reduction. It would also decrease the emission of pollutants by 318.7 tons of CO2 , 123.9 tons of H2O, 2.122 tons of NOx , 98 kg of SO2 and 56 kg of CO. Hence, even a small drag reduction gives significant benefits [1]. Many studies have addressed the existence of large-scale (LS) motions that are very important for wall turbulence at high Reynolds numbers [2, 3]. The streamwise lengths of the large eddies can be in an order of 10-20 boundary-layer thicknesses in the logarithmic region of wall-bounded flows [4]. These large eddies involve mostly streamwise velocity fluctuations and contain most of the streamwise kinetic energy. Many subsequent studies have reported that log-law LS motions strongly influence near-wall turbulent structures [3,5]. Therefore, to control the log-law large-scale structures is important to obtain frictional drag reduction at high Reynolds numbers. However, the general approach to control those log-law structures is to apply a flow control method on those relatively high wall-normal locations; this is not a feasible method when it comes to real-world applications. In this study, we suppressed positive wall-normal velocity near the wall, at y+ 20. By doing so we aimed to suppress the formation or interaction of organized flow structures in the log- [...]
doi:10.13009/eucass2022-4753 fatcat:irtkrqjzmza3vni55rsktkys7e