A novel notion of turbulent structure the local cascade structure-is introduced to study the convection phenomenon in a turbulent channel flow. A space-time cross-correlation method is used to calculate the convection...A novel notion of turbulent structure the local cascade structure-is introduced to study the convection phenomenon in a turbulent channel flow. A space-time cross-correlation method is used to calculate the convection velocity. It is found that there are two characteristic convection speeds near the wall, one associated with small-scale streaks of a lower speed and another with streamwise vortices and hairpin vortices of a higher speed. The new concept of turbulent structure is powerful to illustrate the dominant role of coherent structures in the near-wall convection, and to reveal also the nature of the convection-the propagation of patterns of velocity fluctuations-which is scale-dependent.展开更多
Optimizing the ventilation design of packaging system is of crucial importance for improving the efficiency of the forced-air precooling process to maintain the quality of horticultural produce and extend the shelf li...Optimizing the ventilation design of packaging system is of crucial importance for improving the efficiency of the forced-air precooling process to maintain the quality of horticultural produce and extend the shelf life in food cold chain.Many efforts had been devoted to the study about the impact of ventilation design on airflow and temperature distribution inside ventilated packages.This paper reviews relevant research methods,commonly used quantities for the measurement of precooling effectiveness,attractive design parameters,and their impact on precooling effectiveness.These allow us to know exactly the characteristic and deficiency of each research method,identify dominant design parameters,and seek a promising way for the future improvement of the ventilated packaging system.展开更多
基金the National Natural Science Foundation of China(10572004 and 90716008)
文摘A novel notion of turbulent structure the local cascade structure-is introduced to study the convection phenomenon in a turbulent channel flow. A space-time cross-correlation method is used to calculate the convection velocity. It is found that there are two characteristic convection speeds near the wall, one associated with small-scale streaks of a lower speed and another with streamwise vortices and hairpin vortices of a higher speed. The new concept of turbulent structure is powerful to illustrate the dominant role of coherent structures in the near-wall convection, and to reveal also the nature of the convection-the propagation of patterns of velocity fluctuations-which is scale-dependent.
基金This work is supported by the National Key R&D Program of China(Grant No.2016YFD0400100).
文摘Optimizing the ventilation design of packaging system is of crucial importance for improving the efficiency of the forced-air precooling process to maintain the quality of horticultural produce and extend the shelf life in food cold chain.Many efforts had been devoted to the study about the impact of ventilation design on airflow and temperature distribution inside ventilated packages.This paper reviews relevant research methods,commonly used quantities for the measurement of precooling effectiveness,attractive design parameters,and their impact on precooling effectiveness.These allow us to know exactly the characteristic and deficiency of each research method,identify dominant design parameters,and seek a promising way for the future improvement of the ventilated packaging system.
