This study investigates scalar (smoke) dispersion in the turbulent near-wake of an Ahmed body. The effects of rear slant angles ($\varphi ={15}^{\circ }, {25}^{\circ }, {35}^{\circ }$, and ${40}^{\circ }$) on the flow structures, scalar concentration, and dispersion are investigated. Smoke was essentially a passive scalar, with a typical Stokes number of $3.62\times {10}^{-5}$. Smoke particle concentration fields were measured (at ${\text{Re}}_l=1.9\times {10}^5$) using a nonintrusive technique, quantitative smoke visualization, based on laser Mie-scattering. Smoke dispersion was quantified using nondimensional dispersion ($\mathcal{D}$) and dispersion length scales (${\mathcal{L}}_y, {\mathcal{L}}_z$). The predominant turbulent wake structures were obtained by particle image velocimetry. The connection between wake structures and the dispersion phenomenon was explored. It is found that the existence, strength, and size of wake structures (spanwise and trailing vortices) depend on $\varphi$, and these structures play a key role in the dispersion phenomenon. Two distinct flow regimes and their implications on dispersion are explored. For $\varphi ={15}^{\circ },{25}^{\circ }$, there is no separation over the rear slant, and the trailing vortices are generated, which dominate and determine the dispersion scales beyond the recirculation region ($x^{*}>1$). The entrainment of flow due to trailing vortices increases the lateral dispersion (${\mathcal{L}}_z$) of smoke rapidly. For $\varphi ={35}^{\circ }, {40}^{\circ }$, a massive separation on the rear slant is observed, and the trailing vortices do not exist. The spanwise vortices dominate the dispersion phenomenon in the recirculation region ($x^{*}⩽1$) and determine the vertical dispersion (${\mathcal{L}}_y$) of the smoke. Based on the observed smoke dispersion for both the flow regimes, the characteristics of the near-wake are proposed.

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• Turbulence
• Turbulent mixing