Flow characteristics in median plane of a backward-inclined elevated transverse jet

Abstract

The time-averaged flow patterns and instantaneous upwind-side shear-layer vortex flow modes of a backward-inclined elevated transverse jet were studied in an open-loop wind tunnel by laser-assisted smoke flow visualization method and hot-wire anemometry. The characteristic flow modes at various backward inclination angles θ and jet-to-crossflow momentum flux ratios R were identified from long- and short-exposure pictures of flow visualization. The jet width, which may denote the transverse dispersion characteristics of the jet, in the near and far fields were determined from the long-exposure picture by using a binary edge-detection method. The frequency and Strouhal number of the upwind-side shear-layer vortices were measured by the hot-wire anemometer. At θ<25°, large downwash recirculation bubble always appeared at small R’s. Increasing θ would quickly decrease the size of the downwash recirculation bubble. At θ>25°, no downwash recirculation bubble was observed in the near wake of the tube tip region. The jet width decreased with increasing θ. The Strouhal number of the upwind-side vortices increased with increasing θ. At a fixed θ, the Strouhal number of the upwind-side vortices decreased with increasing R at R<1. At R>1, the decrease rate became small. The ultimate Strouhal numbers at large R at different backward inclination angles θ did not converge to a single value—the larger the θ, the larger the Strouhal number.