This work investigates the active control of a fully developed turbulent boundary layer by a submerged synthetic jet actuator.The impacts of the control are explored by measuring the streamwise velocities using partic...This work investigates the active control of a fully developed turbulent boundary layer by a submerged synthetic jet actuator.The impacts of the control are explored by measuring the streamwise velocities using particle image velocimetry,and reduction of the skin-friction drag is observed in a certain range downstream of the orifice.The coherent structure is defined and extracted using a spatial two-point correlation function,and it is found that the synthetic jet can efficiently reduce the streamwise scale of the coherent structure.Proper orthogonal decomposition analysis reveals that large-scale turbulent kinetic energy is significantly attenuated with the introduction of a synthetic jet.The conditional averaging results show that the induction effect of the prograde vortex on the low-speed fluid in a large-scale fluctuation velocity field is deadened,thereby suppressing the bursting process near the wall.展开更多
The turbulent boundary layer(TBL)is actively controlled by the synthetic jet generated from a circular hole.According to the datasets of velocity fields acquired by a time-resolved particle image velocimetry(TR-PIV)sy...The turbulent boundary layer(TBL)is actively controlled by the synthetic jet generated from a circular hole.According to the datasets of velocity fields acquired by a time-resolved particle image velocimetry(TR-PIV)system,the average drag reduction rate of 6.2%in the downstream direction of the hole is obtained with control.The results of phase averaging show that the synthetic jet generates one vortex pair each period and the consequent vortex evolves into hairpin vortex in the environment with free-stream,while the reverse vortex decays rapidly.From the statistical average,it can be found that a low-speed streak is generated downstream.Induced by the two vortex legs,the fluid under them converges to the middle.The drag reduction effect produced by the synthetic jet is local,and it reaches a maximum value at x^(+)=400,where the drag reduction rate reaches about 12.2%.After the extraction of coherent structure from the spatial two-point correlation analysis,it can be seen that the synthetic jet suppresses the streamwise scale and wall–normal scale of the large scale coherent structure,and slightly weakens the spanwise motion to achieve the effect of drag reduction.展开更多
The research focuses on the active control scheme of a fully-developed turbulent boundary layer(TBL)forced by the submerged synthetic jet,and the particle image velocimetry(PIV)system is used to capture the two compon...The research focuses on the active control scheme of a fully-developed turbulent boundary layer(TBL)forced by the submerged synthetic jet,and the particle image velocimetry(PIV)system is used to capture the two components velocity signals in the flow field.The mean velocity profiles near the wall obtained by the single-pixel ensemble correlation(SPEC)algorithm evidence the decline of streamwise velocity gradient,indicating the reduction of skin-friction drag.The deficit of streamwise velocity as well as turbulence attenuation in the cross flow attests that the perturbation effects are persistent in a certain range downstream of the synthetic jet injection section.The spatial topologies of the coherent structures detected by the improved quadrant splitting method(IQSM)reveal that the sweep events,responsible for the significant wall friction,are repressed under the action of synthetic jet.By employing the method of two-point correlation,destruction of the near-wall streaks is observed,and the control mechanism acts in a way to suppress the extension along the streamwise direction of the correlation coefficient.Based on the linear stochastic estimation,it is inferred that the influence of force is such the near-wall hairpin vortex detaches from the wall,and its ability to induce environmental fluid is vastly weakened.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11732010,11972251,11872272,11902218,and 11802195)the National Key Research and Development Program of China,on‘Green Buildings and Building Industrialization’(Grant No.2018YFC0705300)。
文摘This work investigates the active control of a fully developed turbulent boundary layer by a submerged synthetic jet actuator.The impacts of the control are explored by measuring the streamwise velocities using particle image velocimetry,and reduction of the skin-friction drag is observed in a certain range downstream of the orifice.The coherent structure is defined and extracted using a spatial two-point correlation function,and it is found that the synthetic jet can efficiently reduce the streamwise scale of the coherent structure.Proper orthogonal decomposition analysis reveals that large-scale turbulent kinetic energy is significantly attenuated with the introduction of a synthetic jet.The conditional averaging results show that the induction effect of the prograde vortex on the low-speed fluid in a large-scale fluctuation velocity field is deadened,thereby suppressing the bursting process near the wall.
基金the National Natural Science Foundation of China(Grant Nos.11732010,11972251,11872272,11902218,and 12172242)the National Key Research and Development Program of the Ministry of Science and Technology,China(Grant No.2018YFC0705300)。
文摘The turbulent boundary layer(TBL)is actively controlled by the synthetic jet generated from a circular hole.According to the datasets of velocity fields acquired by a time-resolved particle image velocimetry(TR-PIV)system,the average drag reduction rate of 6.2%in the downstream direction of the hole is obtained with control.The results of phase averaging show that the synthetic jet generates one vortex pair each period and the consequent vortex evolves into hairpin vortex in the environment with free-stream,while the reverse vortex decays rapidly.From the statistical average,it can be found that a low-speed streak is generated downstream.Induced by the two vortex legs,the fluid under them converges to the middle.The drag reduction effect produced by the synthetic jet is local,and it reaches a maximum value at x^(+)=400,where the drag reduction rate reaches about 12.2%.After the extraction of coherent structure from the spatial two-point correlation analysis,it can be seen that the synthetic jet suppresses the streamwise scale and wall–normal scale of the large scale coherent structure,and slightly weakens the spanwise motion to achieve the effect of drag reduction.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.11732010,11972251,11872272,11902218,and 12172242)the Ministry of Industry and Information Technology(Grant No.[2019]360).
文摘The research focuses on the active control scheme of a fully-developed turbulent boundary layer(TBL)forced by the submerged synthetic jet,and the particle image velocimetry(PIV)system is used to capture the two components velocity signals in the flow field.The mean velocity profiles near the wall obtained by the single-pixel ensemble correlation(SPEC)algorithm evidence the decline of streamwise velocity gradient,indicating the reduction of skin-friction drag.The deficit of streamwise velocity as well as turbulence attenuation in the cross flow attests that the perturbation effects are persistent in a certain range downstream of the synthetic jet injection section.The spatial topologies of the coherent structures detected by the improved quadrant splitting method(IQSM)reveal that the sweep events,responsible for the significant wall friction,are repressed under the action of synthetic jet.By employing the method of two-point correlation,destruction of the near-wall streaks is observed,and the control mechanism acts in a way to suppress the extension along the streamwise direction of the correlation coefficient.Based on the linear stochastic estimation,it is inferred that the influence of force is such the near-wall hairpin vortex detaches from the wall,and its ability to induce environmental fluid is vastly weakened.
