Oscillating flows over periodic ripples are numerically investigated by solving the two dimensional time dependent incompressible Navier Stokes equations in curvilinear coordinates for a wider range of the paramete...Oscillating flows over periodic ripples are numerically investigated by solving the two dimensional time dependent incompressible Navier Stokes equations in curvilinear coordinates for a wider range of the parameters of KC, Re and ε, in particular for the oscillatory flow over propagating ripples. In the oscillating flows over periodic ripples, circulation cells due to the streaming effect are formed, which can help redistribute suspended sediments. In the present study, the circulation patterns for both stationary rigid ripples and propagating ripples are investigated. The energy dissipation in the flow field is also discussed.展开更多
Oscillatory flow facilitates gas exchange in human respiration system. In the present study, both numerical calculation and PIV (Particle Image Velocimetry) measurement indicate that, under the application of HFOV (Hi...Oscillatory flow facilitates gas exchange in human respiration system. In the present study, both numerical calculation and PIV (Particle Image Velocimetry) measurement indicate that, under the application of HFOV (High Frequency Oscillatory Ventilation), apparent steady streaming is caused and augmented in distal airways by the continuous oscillation, i.e., the core air moves downwards and the peripheral air evacuates upwards within bronchioles. The net flow of steady streaming serves to overcome the lack of tidal volume in HFOV and delivers fresh air into deeper lung region. Also, numerical calculations reveal that the intensity of steady streaming is mainly influenced by the geometry of airways with provided oscillatory frequency and tidal volume, and it rises with Re and Wo up to a Re of about 124 and Wo of about 5. Steady streaming is considered as an important factor for the ventilation efficiency of HFOV.展开更多
A perturbation analysis based on equations of motion in Lagrangian form is presented for the oscillatory and time-mean viscous flows induced by a propagating wave of small amplitude in an annulus with a viscoelastic o...A perturbation analysis based on equations of motion in Lagrangian form is presented for the oscillatory and time-mean viscous flows induced by a propagating wave of small amplitude in an annulus with a viscoelastic outer wall. Owing to the steady streaming effect, the existence of a catheter in a blood vessel brings in an additional steady pressure gradient, a correction to that predicted by the linear theory, and an additional steady shear stress, which may increase the possibility of hemolysis of red blood cells.展开更多
文摘Oscillating flows over periodic ripples are numerically investigated by solving the two dimensional time dependent incompressible Navier Stokes equations in curvilinear coordinates for a wider range of the parameters of KC, Re and ε, in particular for the oscillatory flow over propagating ripples. In the oscillating flows over periodic ripples, circulation cells due to the streaming effect are formed, which can help redistribute suspended sediments. In the present study, the circulation patterns for both stationary rigid ripples and propagating ripples are investigated. The energy dissipation in the flow field is also discussed.
文摘Oscillatory flow facilitates gas exchange in human respiration system. In the present study, both numerical calculation and PIV (Particle Image Velocimetry) measurement indicate that, under the application of HFOV (High Frequency Oscillatory Ventilation), apparent steady streaming is caused and augmented in distal airways by the continuous oscillation, i.e., the core air moves downwards and the peripheral air evacuates upwards within bronchioles. The net flow of steady streaming serves to overcome the lack of tidal volume in HFOV and delivers fresh air into deeper lung region. Also, numerical calculations reveal that the intensity of steady streaming is mainly influenced by the geometry of airways with provided oscillatory frequency and tidal volume, and it rises with Re and Wo up to a Re of about 124 and Wo of about 5. Steady streaming is considered as an important factor for the ventilation efficiency of HFOV.
基金Project supported by the Research Grants Council of the Hong Kong Special Administrative Region, China (Grant No. HKU 715609E)
文摘A perturbation analysis based on equations of motion in Lagrangian form is presented for the oscillatory and time-mean viscous flows induced by a propagating wave of small amplitude in an annulus with a viscoelastic outer wall. Owing to the steady streaming effect, the existence of a catheter in a blood vessel brings in an additional steady pressure gradient, a correction to that predicted by the linear theory, and an additional steady shear stress, which may increase the possibility of hemolysis of red blood cells.
