Experimental Investigation of Turbulent Boundary Layer Dynamics Via Active Manipulation of Large-Scale Structures

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 periodic synthetic LSS. Planar PIV was used to measure the time-resolved two-dimensional velocity field downstream of the actuator at various streamwise locations. Detailed analysis of the PIV data, including phase-locked measurements of various Reynolds stresses at each streamwise location, was used to quantify the TBL response to the periodic spanwise-uniform actuation. The results are discussed and compared with previous experimental measurements.