| The objective of this experimental study was to assess the ability to actively ‘control’ a particle-laden jet exiting a fully-developed turbulent channel flow using a moving wall attached to a piezoelectric actuator. The jet Reynolds number was 4240. The maximum velocity of the moving wall was 9.5 cm/s, and the maximum displacement was 120 μm. The actuator frequency and amplitude were tuned independently to generate different effects on the particle-laden flow. Two particle sizes were investigated at a particle-to-air mass-loading ratio of 3.5%. The Kolmogorov-based Stokes numbers (Skkol ) at the center plane were 1.9 and 7.4, and the Stokes number associated with the vortices in the forced flow (Skf) varied from 0.45 to 10.6. The flow behavior was documented by flow visualization, number density measurements, and particle and gas velocity measurements.; In terms of the gas flow, hot-wire measurements showed that actuation affected both the mean and rms velocity profiles downstream of the channel exit. In all cases, forcing yielded mean profiles that were symmetric with respect to the centerline. Forcing at low frequencies (St ≤ 0.30) caused faster decay of the centerline velocity, higher spreading rates in the far field, and asymmetric rms profiles compared with unforced flow. Forcing from St = 0.39 through 1.46 led to altered but symmetric rms profiles and spectra compared with unforced flow. Forcing in the range St < 0.50 yielded centerline rms values that initially were larger than, but further downstream smaller than in the unforced flow.; The experiments showed that actuation affected particle velocity and distribution both directly and indirectly; directly, by altering the boundary conditions seen by the particles, and indirectly, by controlling the spacing and the size of the induced vortices. The direct effects, useful for reducing the high particle concentration layers evolving near the channel sidewalls, required both a significant impact velocity and significant displacement of the activated wall. Larger impact velocities were associated with larger Strouhal numbers. The indirect effects were strongest for the lowest Stokes number tested (Skf = 0.45). This Stokes number was associated with the lowest Strouhal number (hence largest vortices) and smallest particles. |
