Abstract This paper analyses the downstream developments of the mean and the turbulent velocity fields of a plane jet. Based on the conservation of mass and the conservation of momentum, the mean-velocity half width (reflecting the jet spread rate) and the relative mass flow rate (jet entrainment) are related to the decay rate of the centreline mean velocity. These relations are not subject to self-preservation. Both analytical and experimental results suggest that the jet spread rate (K1) and the entrainment rate (K3) (and thus the decay rate K2) can be well estimated from the centreline velocity, i.e., K1 ≈ 0.6K2 and K3 ∝ K2. The effect of initial mean velocity and RMS velocity profiles on the downstream mean velocity field appears to be embodied in the constants K1K2 and K3. The analytical relationship for the self-preserving Reynolds shear stress, obtained for the first time, works well.
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