An investigation of forced structures in turbulent jet flows

In many cases, turbulence is superimposed on an unsteady organized motion o f a mean flow. In the past, these turbulent flows have been studied by time or ensemble averaging methods and some decomposition techniques such as pr oper orthogonal decomposition (POD). In this study, a new decomposition tec hnique called the turbulence filter will be used to decompose the forced tu rbulent jet flows. By using the turbulence filtering technique, the fluctua ting (turbulent) part and the more organized (forced) part of the velocity field are analyzed. Within this context several experiments on organized tu rbulent jet flow have been carried out. In the experiments, variable freque ncy and amplitude oscillation are imposed on a 1D jet. An elliptical plate was used in order to obtain sinusoidal forcing. The axial distance, Reynold s number and the forcing frequency of the signal were varied. The multiple hot wires (six probes) were used to investigate the evolution of the signal along the radial distance. The obtained results of the turbulence filter a re compared with those of phase-averaging and POD techniques. The eigenmode s of the data are also evaluated by using the POD method.