Characterization of entrainment through turbulent diffusion in a self-similar jet

摘要: A large-scale experimental Lagrangian study based on particle tracking velocimetry has been completed in an incompressible self-similar water jet. The jet is seeded with tracers only through the nozzle: inhomogeneous seeding called nozzle seeding. The Lagrangian flow of tracers therefore does not contain any contribution from particles entrained into the jet from the surrounding fluid. The mean velocity field based on tracer trajectories «U ϕ» is essentially indistinguishable from the mean velocity field of the jet «U» for the axial velocity while important discrepancies are experimentally found for the radial velocity. Even if▽.«U»= 0, we have▽.«U ϕ»≠ 0 due to the absence of entrained particles. By considering the mean tracer concentration field «ϕ», a new mass conservation equation is proposed:▽.(«ϕ»«U ϕ»)= 0, which leads to a correct description of the experimental radial velocity field and gives new …