Statistical Description of the Turbulent Round Jet Developing Region Along Its Centerline

Turbulent round jet is mapped in terms of statistical moments along the centerline throughout and beyond the developing region. The measurements are carried out using laser Doppler anemometry, which accurately measures high turbulence intensity flows with high spatial and temporal resolution and dynamic range.

The static moments, including mean velocity and variance, follow the expected trends. About 25‐ 30 jet exit diameters downstream, turbulence begins to approach the fully developed state where the mean velocity and variance develop in parallel in a seeming equilibrium. Turbulence intensity is consequently observed to initially increase before levelling out when approaching the fully developed state.

The downstream development of the measured spatial energy spectra and second‐order structure functions further support these observations in that they begin to develop the Kolmogorov characteristic ‐5/3 and 2/3 slopes in the inertial subrange within the downstream distance of 25‐30 jet exit diameters.

The validated convection record method is implemented to obtain the spatial dynamic statistics. The dissipation can be to a reasonable approximation extracted from the third‐order structure functions from about 20 jet exit diameters and further downstream. The results, acquired with an improved high‐accuracy laser Doppler anemometer, should be useful for development of analytic and numerical turbulence models.