Flow and mixing characteristics of a forward-inclined stack-issued jet in crossflow

Abstract

The flow and mixing characteristics of a forward-inclined stack-issued jet at various inclination angles (θ) and jet-to-crossflow momentum flux ratios (R) were experimentally studied in an open-loop wind tunnel. Flow behaviors were examined using the laser-assisted smoke flow visualization technique. The instantaneous velocities of the upwind-side shear-layer were digitized by a hot-wire anemometer using a high-speed data acquisition system. The instability frequencies in the upwind-side shear-layer vortices were obtained by the fast Fourier transform method. Long-exposure flow images were processed using the binary edge-detection technique to obtain the jet spread width. Transverse dispersion of jet fluids was determined using tracer gas concentration detection. The upwind-side shear-layer vortices revealed four characteristic flow modes: the High impingement-crossflow dominated mode (about θ < 15° and low R), the High impingement-jet flow dominated mode (about θ < 25° and high R), the Low impingement-crossflow dominated mode (about θ > 15° and low R), and the Low impingement-jet flow dominated mode (about θ > 25° and high R). Increasing θ in the crossflow dominated regimes eliminated the upwind-side shear-layer vortices, while increasing θ in the jet flow dominated regimes emphasized the upwind-side shear-layer vortices. Increasing θ at a fixed value of R increased jet spread width in the far field in all modes. In the near field, at x/d < 5 in the High impingement-crossflow dominated regime, the jet spread width was greater than in the Low impingement-crossflow dominated regime. In the jet flow dominated regimes, higher θ values led to greater jet spread width. Transverse dispersion of the jet fluids approached the jet spread width results. In the Low impingement-jet flow dominated regime, transverse dispersion of the jet fluids was significantly increased compared to the other regimes. In addition, the maximum tracer gas concentration was severely reduced at all axial stages, which implied better dispersion of the jet fluids in this regime.