The response of turbulent flow to time-modulated forcing is studied by direct numerical simulation of the Navier-Stokes equations. The forcing is modulated via periodic energy input variations at a frequency $\omega$. Such forcing of the large-scales is shown to yield a response maximum at frequencies in the range of the inverse of the large-eddy turnover time. Time-modulated broad-band forcing is also studied in which a wide spectrum of length-scales is forced simultaneously. If smaller length-scales are explicitly agitated by the forcing, the response maximum is found to occur at higher frequencies and to become less pronounced. In case the forced spectrum is sufficiently wide, a response maximum was not observed. At sufficiently high frequencies the amplitude of the kinetic energy response decreases as $1/ \omega$, consistent with theoretical predictions.
|Number of pages||4|
|Publication status||Published - 2006|