円形ノズルからの乱流噴流の直接シミュレーション

抄録

A direct numerical simulation (DNS) of turbulent round jet was carried out in the cylindrical coordinate system to provide a tool for a numerical experiment for jet control. The spatial development from the formation of vortex rings to the transition to turbulence was accurately obtained by a finite difference method. The characteristics of simulated flow field, such as vortex rings and self-similar profile of mean flow in turbulent region, is in good agreement with experimental findings. Insufficiency of the computational domain in the radial direction leads the flow field to turbulence earlier. The influence of superposition of coherent disturbances to random perturbation at the nozzle exit, e.g. axial and helical ones, has also been investigated. The perturbation mode strongly affected the configuration, strength and location of vortices and their turbulence transition. The delay in turbulence transition, especially by axial excitation, was due to the maintenance of the strong vortices. Such a structure was clearly detected by the proper orthogonal decomposition (POD) method.