Experimental Investigation of the Response of the Turbulent Boundary Layer to Synthetic Outer Layer Large-Scale Structure using PIV

It has been established that the dynamics of large-scale structures (LSS) in the outer region of turbulent boundary layers (TBL) and the near-wall small-scale turbulence are correlated. In previous experiments using a single hot-wire; it was shown that a synthetic LSS introduced by a plasma-based actuator in the outer region of TBL had a strong modulating effect on the near-wall turbulence. Results showed that for streamwise locations close to the actuator, an actuation frequency comparable to the burst/sweep frequency of the near-wall structure created the strongest modulation effect. Farther downstream, an actuation frequency related to the streamwise wavelength of the naturally occurring LSS resulted in the strongest modulation effect. In the study reported here, an improved plasma-based active flow control device was placed in a similar region of the TBL to introduce a periodic synthetic LSS. Planar PIV was used to measure the time-resolved two-dimensional velocity field downstream of the actuator at various streamwise locations. Using PIV, the streamwise evolution of the synthetic LSS and its modulating effect on the near-wall turbulence are described in more detail. The results are discussed and compared with previous hot-wire measurements.