A numerical investigation has been carried out to examine turbulent flow and heat transfer characteristics in a three-dimensional ribbed square channels. Fluent 6.3 CFD code has been used. The governing equations are ...A numerical investigation has been carried out to examine turbulent flow and heat transfer characteristics in a three-dimensional ribbed square channels. Fluent 6.3 CFD code has been used. The governing equations are discretized by the second order upwind differencing scheme, decoupling with the SIMPLE (semi-implicit method for pressure linked equations) algorithm and are solved using a finite volume approach. The fluid flow and heat transfer characteristics are presented for the Reynolds numbers based on the channel hydraulic diameter ranging from 104 to 4 ′ 104. The effects of rib shape and orientation on heat transfer and pressure drop in the channel are investigated for six different rib configurations. Rib arrays of 45° inclined and 45° V-shaped are mounted in inline and staggered arrangements on the lower and upper walls of the channel. In addition, the performance of these ribs is also compared with the 90° transverse ribs.展开更多
Time sequence signals of instantaneous longitudinal and normal velocity components at different longitudinal and normal positions in a turbulent boundary layer have been finely measured simultaneously by IFA300 consta...Time sequence signals of instantaneous longitudinal and normal velocity components at different longitudinal and normal positions in a turbulent boundary layer have been finely measured simultaneously by IFA300 constant temperature anemometer and double-sensor hot-wire probe with sampling resolution higher than the frequency that corresponds to the smallest time scale of Kolmogorov dissipation scale before/after introducing artificial periodic blow/suction perturbation. The period-phase-average technique is applied to extract the periodic waveforms of artificial perturbation from instantaneous time sequence signals of longitudinal and normal turbulence background. Experimental investigation is carried out on the attenuation characteristics of periodic perturbation wave with different frequency along longitudinal direction and normal direction in a turbulent boundary layer. The amplitude distributions of longitudinal and normal disturbing velocity component for different perturbation frequencies are measured at different downstream and normal positions in turbulent boundary layer. The amplitude growth rate of artificial periodic perturbation wave is calculated according to flow instability theory. The experimental results are compared and in consistent with the theoretical and numerical results.展开更多
The world is undergoing profound changes unseen in a century.As the changes are accelerating,their impact is intensifying.International politics is experiencing a return to realism,and the rise of hegemonic power is a...The world is undergoing profound changes unseen in a century.As the changes are accelerating,their impact is intensifying.International politics is experiencing a return to realism,and the rise of hegemonic power is antagonizing global relations.Globalization has encountered setbacks,and world economic growth is contracting.The international order is tumbling and is facing reconstruction.Nontraditional security threats have become more diverse.Great power conflicts are looming large.The 20th National Congress of the Communist Party of China has drawn a magnificent blueprint for constructing Chinese-style modernization.China,a responsible power in its historic rise,will be a stabilizing force in a turbulent world and a constructive force for global transformation.China provides stability,positive energy,great global peace,and development opportunities.展开更多
文摘A numerical investigation has been carried out to examine turbulent flow and heat transfer characteristics in a three-dimensional ribbed square channels. Fluent 6.3 CFD code has been used. The governing equations are discretized by the second order upwind differencing scheme, decoupling with the SIMPLE (semi-implicit method for pressure linked equations) algorithm and are solved using a finite volume approach. The fluid flow and heat transfer characteristics are presented for the Reynolds numbers based on the channel hydraulic diameter ranging from 104 to 4 ′ 104. The effects of rib shape and orientation on heat transfer and pressure drop in the channel are investigated for six different rib configurations. Rib arrays of 45° inclined and 45° V-shaped are mounted in inline and staggered arrangements on the lower and upper walls of the channel. In addition, the performance of these ribs is also compared with the 90° transverse ribs.
文摘Time sequence signals of instantaneous longitudinal and normal velocity components at different longitudinal and normal positions in a turbulent boundary layer have been finely measured simultaneously by IFA300 constant temperature anemometer and double-sensor hot-wire probe with sampling resolution higher than the frequency that corresponds to the smallest time scale of Kolmogorov dissipation scale before/after introducing artificial periodic blow/suction perturbation. The period-phase-average technique is applied to extract the periodic waveforms of artificial perturbation from instantaneous time sequence signals of longitudinal and normal turbulence background. Experimental investigation is carried out on the attenuation characteristics of periodic perturbation wave with different frequency along longitudinal direction and normal direction in a turbulent boundary layer. The amplitude distributions of longitudinal and normal disturbing velocity component for different perturbation frequencies are measured at different downstream and normal positions in turbulent boundary layer. The amplitude growth rate of artificial periodic perturbation wave is calculated according to flow instability theory. The experimental results are compared and in consistent with the theoretical and numerical results.
文摘The world is undergoing profound changes unseen in a century.As the changes are accelerating,their impact is intensifying.International politics is experiencing a return to realism,and the rise of hegemonic power is antagonizing global relations.Globalization has encountered setbacks,and world economic growth is contracting.The international order is tumbling and is facing reconstruction.Nontraditional security threats have become more diverse.Great power conflicts are looming large.The 20th National Congress of the Communist Party of China has drawn a magnificent blueprint for constructing Chinese-style modernization.China,a responsible power in its historic rise,will be a stabilizing force in a turbulent world and a constructive force for global transformation.China provides stability,positive energy,great global peace,and development opportunities.
