The article discusses different metrological problems connected with the use of a hot-wire technique in the measurement of turbulence energy dissipation. In particular a short review of the experimental evidence for and against the local isotropy hypothesis is presented and its consequence for the design of hot-wire systems and data processing is discussed. Finally, the finite spatial resolution of a hot-wire technique is analysed with special emphasis on measurement of the dissipation rate and the correction of experimental results.

Slightly heated swirling jets have been investigated experimentally in order to determine the effect of swirl degree on the mean and turbulent flow pattern. In particular, it has been shown that the swirl action strongly intensifies the turbulent momentum and heat transport processes in the close vicinity of the jet outlet and tends to quench them further downstream.

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The paper deals with the effect of finite hot-wire resolution which reveals itself when both the one-dimensional energy spectrum in a high wavenumber range and turbulence energy dissipation are measured with a hot sensor of a finite wire length. The proposed correction functions derived for isotropic and homogeneous turbulence structures are based on the assumption that the hot-wire sensitivity to velocity fluctuations follows the local excess of the hot-wire temperature Ow(&) over the ambient temperature Q. of the flowing medium. The theoretical predictions compared with experimental data show that the measured quantities may effectively be corrected by means of the correction functions proposed.

The paper formulates the concept of a semi-preserving developing of a free nonisothermal swirling jet. On the basis of experimental data it may be estimated that the semi-preserving conditions are established at the distance x − x0 ≈ (15−20) D. Also, it has been pointed out that self-preservation, which requires the turbulence structure to be similar during decay, may be considered as an asymptotic state of the semi-preserving development achieved in practice at a distance where $\overline{u_r u_{\phi}/ \overline(u_x u_r) \ll 1\cdot 0$.