Effects of freestream on piezoelectric fan performance.

Unsteady flow simulations were conducted to analyze the effects of the freestream on the 3D flow around a piezoelectric fan. Considering computational cost, eight different inlet velocities from 0 to 7 m/s were tested using 2D simulations for the symmetry plane at the plate center, and five velocities of 0, 1, 3, 5 and 7 m/s were then selected for 3D simulations. The counter-rotating vortices from the fan tip are more significantly affected by the freestream than the vortices from the fan side. The axial velocity on the symmetry plane decreases monotonically as the freestream velocity increases, but the axial velocity near the endwall increases at a low freestream velocity. This implies that only a low speed freestream could be helpful to improve the performance of the piezoelectric fan. Based on the vorticity distribution, pressure difference across the fan edge and isosurface of λ 2 , an attempt was made to understand the interaction between the vortices from the fan and the freestream. Finally, two critical values of Strouhal number were found in this study for determining the performance of a vibrating plate within the freestream. [ABSTRACT FROM AUTHOR]