The temperature and velocity fields in a round heated jet were investigated in detail. Both conventional measurements and conditional measurements (zone averages and point averages) were performed. The probability density functions of the lengths of turbulent and non-turbulent durations were also measured. Filtered correlation measurements show that large-scale turbulent motions were responsible for the bulk of momentum and heat transport, and also that small scales were more efficient in transporting heat than in transporting momentum. In no case was heat transported further or more than momentum, however. These results are discussed in detail, particularly with regard to the entrainment. Conservation equations for turbulent-zone variables and the intermittency factor are derived and a model for some of the resulting higher-order correlations is suggested. An exact equation for the intermittency function is presented.
Experimental studies are made of chaotic particle motion in a simple Stokes flow system. Surfaces-of-section that exhibit a generic mixture of regular and chaotic particle motions in good agreement with computer simulations are constructed experimentally. Deformations of line elements exhibit ‘ whorl ’ and ‘ tendril ’ structures of great complexity that can be correlated directly with the underlying particle dynamics and that agree well with numerical computations. In some cases, the laboratory studies are able to resolve dynamical features more accurately than the computer studies. Experiments demonstrating that the flows exhibit poor time reversal in régimes of chaotic particle motion are also performed.
An analysis of the response of an X-probe which takes into account the axial sensitivity k, the effect of the w component of velocity and the effective rectification by the hot wire is presented. Owing to rectification points in the measured u, v ‘phase plane’ are confined within a certain sector, thus leading to distortions in the measured joint probability density functions. Numerical computations show that high turbulence intensities lead to large errors in second-order moments measured by cross-wire probes; for instance, the error in the measured correlation (over and above that due to k) can be as high as 28% when the turbulence intensity is 35%.
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