ABSTRAKT

In this paper, the effects of the Taylor Reynolds number, mean shear rate and intermittency are considered on the spectral scaling exponents in a round, free, turbulent jet. Hot wire measurements were taken over a range of exit Reynolds numbers 10000 < Re_D < 50000. The energy spectra in the inertial sub-range demonstrate considerable departure from the k^−5/3 power law so that the inertial sub-range wave number exponent along the jet centreline is in the range −1.55 ≤ m ≤ −1.43, which confirms earlier findings for grid generated turbulence that this change is Re dependent. However, farther away from the centreline, the inertial sub-range spectral scaling exponents show a considerable decrease and the exponent reaches the lower values of m (e.g., m = −5/3 can be found at a radial position across the jet where the local mean velocity is around one third of the jet centreline mean velocity). It is argued that the effect of the large-scale (external) intermittency and mean shear rate are also important for determining the magnitude of the scaling-range power-law exponents in a turbulent jet.