Measurements of the full instantaneous dissipation rate & dissipation transport in a high-Reynolds number turbulent round jet

An experimental facility capable of measuring and resolving the dissipation rate of the turbulent kinetic energy as well as the dissipation transport balance (i.e., the ε-equation) using particle tracking velocimetry is presented. A detailed discussion and comparison of the resolution requirements to the system resolution capabilities is presented. The long-term objective of the measurements is to study turbulence at different degrees of non-equilibrium to test the range of validity of the classical theories as well as to form the basis for developing new, improved models. Measurements have been carried out in a round turbulent jet, which is the ideal and in fact the only viable test-bed for these investigations, since the jet is the only flow that has all the necessary properties altogether; The stationary jet is very near equilibrium and can thus in a practical, arbitrary and calibrated manner be pushed out of equilibrium by modulating the jet exit velocity in time. Furthermore, the smallest relevant scales in the jet are large and slow enough that they can be resolved, while the flow also evolves over distances that are practical on a laboratory scale. In the present study, the Reynolds number (Re_D = 10^4 – 10^5) as well as the degree of mean shear, in the form of radial distance from the jet centreline (r / D = {0, 1.1, 2.2}, where D is the jet exit diameter), have been varied at a downstream distance of 30 jet exit diameters from the jet nozzle exit. Initial results of the dissipation rate, displaying expected intermittency behaviour, are presented and discussed. The results are preliminary, as noise plays a key role in the measurements, not least for spatial velocity gradient based estimates. This will be dedicatedly targeted in future efforts.