Numerical Investigation of the Dynamical Behavior of a Row of Square Jets in Crossflow Over a Surface

Abstract

Results of a three dimensional unsteady computational study of a row of jets injected normal to a cross-flow are presented with the aim of understanding the dynamics of the large scale structures in the region near the jet. The jet hole is square in cross-section, and the jet to cross-flow velocity ratio is 0.5. The calculations are based on higher-order finite differences, and are performed on extremely refined spatial and temporal meshes so that all the important energy-carrying scales are resolved. Results obtained indicate that the near field large scale structures include the shear layer vortices, the counter rotating vortex pair (CVP), the horseshoe vortex system, and wake and wall vortices. The dynamics of these structures appear to be significantly influenced by a time-periodic interaction between the jet hole boundary layer and the approaching crossflow. This periodic behavior involves the approaching crossflow periodically ingressing into the jet hole region and pushing the injected jet back toward the trailing edge at a Strouhal number of 0.44 based on the jet velocity and diameter. A new mechanism for the formation of shear layer vortices is identified and consists of alternate shedding of positive vorticity from the hole leading edge boundary layer and negative vorticity from the leading horseshoe vortex. Comparison of the predicted turbulent statistics with experimental measurements are made and reasonable agreement is observed.