A communication method of integrated DNC(direct numerical control) system is introduced and a new system based on wireless technology is presented. Advantages of wireless communication are described. The scheme of act...A communication method of integrated DNC(direct numerical control) system is introduced and a new system based on wireless technology is presented. Advantages of wireless communication are described. The scheme of actual communication system is designed,and the integrated system and its function are introduced.展开更多
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
Direct numerical simulations are carried out to assess the potential drag reduction of compressible turbulent flow between isothermal walls.For the sake of achieving drag reduction,the flow is actively controlled by d...Direct numerical simulations are carried out to assess the potential drag reduction of compressible turbulent flow between isothermal walls.For the sake of achieving drag reduction,the flow is actively controlled by deformable dimples lying on the bottom wall of the channel.The first stage of the procedure consists in assessing the optimum geometry of the dimples.In this regard,the lower wall is allowed to freely deform itself according to the loop of control.This method is called the smart wall approach in this paper.By an analysis of the typical shape of the wall deformation thus obtained,it is found that dimples should be thinner than or comparable to the width of streaky structures in the spanwise direction and elongated in the streamwise direction.With active dimples as the wall-deformation actuators,a 15% drag reduction is obtained for the flow at Mam = 0.35 while the drag reduction rate is about 12% for the flow at Mam = 1.5.The fundamental mechanism of the drag reduction is then discussed in this paper.The drag reduction is believed to result from two aspects:the reduction of the mean streamwise velocity gradient near the deformable wall and the suppression of the turbulent fluctuations.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
文摘A communication method of integrated DNC(direct numerical control) system is introduced and a new system based on wireless technology is presented. Advantages of wireless communication are described. The scheme of actual communication system is designed,and the integrated system and its function are introduced.
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 National Natural Science Foundation of China (Grant Nos.10932005 and 50910222)
文摘Direct numerical simulations are carried out to assess the potential drag reduction of compressible turbulent flow between isothermal walls.For the sake of achieving drag reduction,the flow is actively controlled by deformable dimples lying on the bottom wall of the channel.The first stage of the procedure consists in assessing the optimum geometry of the dimples.In this regard,the lower wall is allowed to freely deform itself according to the loop of control.This method is called the smart wall approach in this paper.By an analysis of the typical shape of the wall deformation thus obtained,it is found that dimples should be thinner than or comparable to the width of streaky structures in the spanwise direction and elongated in the streamwise direction.With active dimples as the wall-deformation actuators,a 15% drag reduction is obtained for the flow at Mam = 0.35 while the drag reduction rate is about 12% for the flow at Mam = 1.5.The fundamental mechanism of the drag reduction is then discussed in this paper.The drag reduction is believed to result from two aspects:the reduction of the mean streamwise velocity gradient near the deformable wall and the suppression of the turbulent fluctuations.
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.
