Herein is introduced the mechanism for active control influencing the generation of the near-wall streamwise vortices,which are closely related to the production of high skin friction in wall-bounded turbulent flows.A...Herein is introduced the mechanism for active control influencing the generation of the near-wall streamwise vortices,which are closely related to the production of high skin friction in wall-bounded turbulent flows.A new opposition control scheme with adjusting control amplitude is proposed and evaluated in turbulent channel flow by direct numerical simulations.The maximum drag reduction rate can be greatly enhanced by the strengthened control.Finally the effectiveness of the control to the coherent structures at high Reynolds numbers is investigated by using a linear transient growth model.展开更多
Turbulent boundary layer control(TBLC) for skin-friction drag reduction is a relatively new technology made possible through the advances in computational-simulation capabilities,which have improved the understanding ...Turbulent boundary layer control(TBLC) for skin-friction drag reduction is a relatively new technology made possible through the advances in computational-simulation capabilities,which have improved the understanding of the flow structures of turbulence.Advances in micro-electronic technology have enabled the fabrication of active device systems able to manipulating these structures.The combination of simulation,understanding and micro-actuation technologies offers new opportunities to significantly decrease drag,and by doing so,to increase fuel efficiency of future aircraft.The literature review that follows shows that the application of active control turbulent skin-friction drag reduction is considered of prime importance by industry,even though it is still at a low technology readiness level(TRL).This review presents the state of the art of different technologies oriented to the active and passive control for turbulent skin-friction drag reduction and contributes to the improvement of these technologies.展开更多
Turbulent control and drag reduction in a channel flow via a bidirectional traveling wave induced by spanwise oscillating Lorentz force have been investigated in the paper.The results based on the direct numerical sim...Turbulent control and drag reduction in a channel flow via a bidirectional traveling wave induced by spanwise oscillating Lorentz force have been investigated in the paper.The results based on the direct numerical simulation(DNS)indicate that the bidirectional wavy Lorentz force with appropriate control parameters can result in a regular decline of near-wall streaks and vortex structures with respect to the flow direction,leading to the effective suppression of turbulence generation and significant reduction in skin-friction drag.In addition,experiments are carried out in a water tunnel via electro-magnetic(EM)actuators designed to produce the bidirectional traveling wave excitation as described in calculations.As a result,the actual substantial drag reduction is realized successfully in these experiments.展开更多
基金Tsupported by the National Natural Science Foundation of China (Grant Nos. 10925210 and 11132005)
文摘Herein is introduced the mechanism for active control influencing the generation of the near-wall streamwise vortices,which are closely related to the production of high skin friction in wall-bounded turbulent flows.A new opposition control scheme with adjusting control amplitude is proposed and evaluated in turbulent channel flow by direct numerical simulations.The maximum drag reduction rate can be greatly enhanced by the strengthened control.Finally the effectiveness of the control to the coherent structures at high Reynolds numbers is investigated by using a linear transient growth model.
基金supported by the European Commission though the Research and Innovation action DRAGY(Grant No.690623)the Ministry of Industry and Information Technology(MIIT)of the Chinese government
文摘Turbulent boundary layer control(TBLC) for skin-friction drag reduction is a relatively new technology made possible through the advances in computational-simulation capabilities,which have improved the understanding of the flow structures of turbulence.Advances in micro-electronic technology have enabled the fabrication of active device systems able to manipulating these structures.The combination of simulation,understanding and micro-actuation technologies offers new opportunities to significantly decrease drag,and by doing so,to increase fuel efficiency of future aircraft.The literature review that follows shows that the application of active control turbulent skin-friction drag reduction is considered of prime importance by industry,even though it is still at a low technology readiness level(TRL).This review presents the state of the art of different technologies oriented to the active and passive control for turbulent skin-friction drag reduction and contributes to the improvement of these technologies.
基金supported by the National Natural Science Foundation of China(Grant Nos.11172140 and 11202102)the Specialized Research Fund for Doctoral Program of Higher Education(Grant No.20123219120050)the EU FP6 Framework Program AVERT and the Faculty of Engineering,University of Nottingham
文摘Turbulent control and drag reduction in a channel flow via a bidirectional traveling wave induced by spanwise oscillating Lorentz force have been investigated in the paper.The results based on the direct numerical simulation(DNS)indicate that the bidirectional wavy Lorentz force with appropriate control parameters can result in a regular decline of near-wall streaks and vortex structures with respect to the flow direction,leading to the effective suppression of turbulence generation and significant reduction in skin-friction drag.In addition,experiments are carried out in a water tunnel via electro-magnetic(EM)actuators designed to produce the bidirectional traveling wave excitation as described in calculations.As a result,the actual substantial drag reduction is realized successfully in these experiments.
