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Dong-hyuk Shin
School of Engineering University of Edinburgh King's Buildings, Edinburgh, EH9 3DW, UK

A. J. Aspden
School of Mechanical & Systems Engineering Newcastle University Stephenson Building, Newcastle upon Tyne, NE1 7RU, UK

Edward S. Richardson
Faculty of Engineering and Environment, University of Southampton, Southampton, UK


Scalar mixing is investigated in a decelerating turbulent round jet using direct numerical simulation. The mass fraction of jet fluid and the fluid residence time, measured by the mass-weighted age of the jet fluid, both exhibit self-similar radial profiles in statisticallystationary turbulent jets. Upon stopping the inflow, a deceleration wave passes through the jet, behind which a new self-similar state is observed for the two scalar variables. The self-similar state during the jet deceleration is different from that in the statisticallystationary jet. Opposite to its behaviour in the steady-state jet, the jet fluid mass fraction exhibits a linear increase with downstream distance in the decelerating jet, whereas the centreline massweighted age of jet fluid remains proportional to downstream distance. The dynamics of the scalar mixing in the transient selfsimilar state are discussed through analysis of the scalar transport budgets.