PERTURBATION STRUCTURE AND SPECTRA IN TURBULENT CHANNEL FLOW

The strong mean shear in the vicinity of the boundaries in turbulent b oundary layer flows preferentially amplifies a particular class of per turbations resulting in the appearance of coherent structures and in c haracteristic associated spatial and temporal velocity spectra. This e nhanced response to certain perturbations can be traced to the nonnorm ality of the linearized dynamical operator through which transient gro wth arising in dynamical systems with asymptotically stable operators is expressed. This dynamical amplification process can be comprehensiv ely probed by forcing the Linearized operator associated with the boun dary layer flow stochastically to obtain the statistically stationary response. In this work the spatial wave-number/temporal frequency spec tra obtained by stochastically forcing the linearized model boundary l ayer operator associated with wall-bounded shear flow at large Reynold s number are compared with observations of boundary layer turbulence. The verisimilitude of the stochastically excited synthetic turbulence supports the identification of the underlying dynamics maintaining the turbulence with nonnormal perturbation growth.