The phenomenon of laminar-turbulent transition exists universally in nature and various engineering practice. The prediction of transition position is one of crucial theories and practical problems in fluid mechanics ...The phenomenon of laminar-turbulent transition exists universally in nature and various engineering practice. The prediction of transition position is one of crucial theories and practical problems in fluid mechanics due to the different characteristics of laminar flow and turbulent flow. Two types of disturbances are imposed at the entrance, i.e., identical amplitude and wavepacket disturbances, along the spanwise direction in the incompressible boundary layers. The disturbances of identical amplitude are consisted of one two-dimensional （2D） wave and two three-dimensional （3D） waves. The parabolized stability equation （PSE） is used to research the evolution of disturbances and to predict the transition position. The results are compared with those obtained by the numerical simulation. The results show that the PSE method can investigate the evolution of disturbances and predict the transition position. At the same time, the calculation speed is much faster than that of the numerical simulation.展开更多
Direct numerical simulation(DNS)of incompressible flows in a zeropressure gradient turbulent boundary layer(TBL)is conducted by a finite difference method in which a fourth order upwind scheme is applied to discretize...Direct numerical simulation(DNS)of incompressible flows in a zeropressure gradient turbulent boundary layer(TBL)is conducted by a finite difference method in which a fourth order upwind scheme is applied to discretize the convective terms while a re-scaling approach is used to set inlet flow conditions.The Reynolds numbers based on free flow velocity and momentum thickness at the recycle section are respectively 687,1074,and 1430.The DNS has obtained favorable results indicating that the turbulence statistics is quite satisfactory as compared with the existing numerical and experimental results.The three dimensional turbulent structures at the momentum thickness Reynolds number of 1430 in several different instants are illustrated by the iso-surface of swirl strength square(the square of imaginary part of the complex eigenvalue of velocity gradient tensor)together with velocity vectors in three different cross sections.It is found that there are three kinds of vortical structures:quasi-symmetrical and asymmetrical hairpin vortices,and worm-like vortices.The DNS based on the numerical method can certainly reveal the main characteristics of the TBL flows at the given Reynolds numbers.展开更多
基金Project supported by the National Basic Research Program of China (No.2009CB724103)
文摘The phenomenon of laminar-turbulent transition exists universally in nature and various engineering practice. The prediction of transition position is one of crucial theories and practical problems in fluid mechanics due to the different characteristics of laminar flow and turbulent flow. Two types of disturbances are imposed at the entrance, i.e., identical amplitude and wavepacket disturbances, along the spanwise direction in the incompressible boundary layers. The disturbances of identical amplitude are consisted of one two-dimensional （2D） wave and two three-dimensional （3D） waves. The parabolized stability equation （PSE） is used to research the evolution of disturbances and to predict the transition position. The results are compared with those obtained by the numerical simulation. The results show that the PSE method can investigate the evolution of disturbances and predict the transition position. At the same time, the calculation speed is much faster than that of the numerical simulation.
文摘Direct numerical simulation(DNS)of incompressible flows in a zeropressure gradient turbulent boundary layer(TBL)is conducted by a finite difference method in which a fourth order upwind scheme is applied to discretize the convective terms while a re-scaling approach is used to set inlet flow conditions.The Reynolds numbers based on free flow velocity and momentum thickness at the recycle section are respectively 687,1074,and 1430.The DNS has obtained favorable results indicating that the turbulence statistics is quite satisfactory as compared with the existing numerical and experimental results.The three dimensional turbulent structures at the momentum thickness Reynolds number of 1430 in several different instants are illustrated by the iso-surface of swirl strength square(the square of imaginary part of the complex eigenvalue of velocity gradient tensor)together with velocity vectors in three different cross sections.It is found that there are three kinds of vortical structures:quasi-symmetrical and asymmetrical hairpin vortices,and worm-like vortices.The DNS based on the numerical method can certainly reveal the main characteristics of the TBL flows at the given Reynolds numbers.
