New Analysis Tools for Turbulent Flows

With the widespread use of techniques such as particle image velocimetry (PIV) and direct numerical simulation (DNS), wholefield velocity information of a flow in the region of interest is readily available. With this spatially resolved velocity data, it should be possible to examine flows in greater detail and explore features that are not accessible with the earlier point-wise measurement techniques. Further, the data are quantitative in nature, unlike flow visualization techniques which provide only qualitative information. With this as the basic philosophy, we have developed a number of novel approaches and algorithms for plotting the turbulent/non-turbulent interface [1], turbulence spectrum [2], vortices in turbulent flows [3-5], and low-speed streaks in turbulent boundary layer [6]. We have also obtained analytical solution for vorticity distribution in turbulent vortex cores [7], and performed similarity analysis of turbulent jets, plumes and wakes [8].

Interface separating the turbulent and non-turbulent regions of a turbulent jet(left), Experimentally determined variation of vorticity within a turbulent vortex core.(right)

In Ref. [1], we explored the possibility of detecting an important characteristic of turbulent flows, the turbulent/ non-turbulent interface, which has not received much attention primarily because of its irregular and time-varying shape and position, making it difficult to study. We have developed a novel method which uses information that is generally available from wholefield velocity data (velocity and out-of-plane vorticity) and without taking recourse to any other input (see figure).

References

  1. Anand, R.K., Boersma, B.J., and Agrawal, A., "Detection of turbulent/non-turbulent interface for an axisymmetric turbulent jet: Evaluation of known criteria and proposal of a new criterion," Experiments in Fluids, Vol. 47, pp. 995-1007, 2009.

  2. Agrawal, A., "Measurement of spectrum with particle image velocimetry," Experiments in Fluids, Vol. 39, No. 5, pp. 836-840, 2005.

  3. Agrawal, A., and Prasad, A.K., "Measurements within vortex cores in a turbulent jet," Journal of Fluids Engineering, Vol. 125, No. 3, pp. 561-568, 2003.

  4. Agrawal, A., and Prasad, A.K., "Organizational modes of large-scale vortices in an axisymmetric turbulent jet," Flow, Turbulence and Combustion, Vol. 68, No. 4, pp. 359-377, 2002.

  5. Agrawal, A., and Prasad, A.K., "Properties of vortices in the self-similar turbulent jet," Experiments in Fluids, Vol. 33, No. 4, pp. 565-577, 2002.

  6. Agrawal, A., Djenidi, L., and Antonia, R.A., "LIF based detection of low-speed streaks," Experiments in Fluids, Vol. 36, No. 4, pp. 600-603, 2004.

  7. Agrawal, A., "Analysis of vortex cores in turbulent flows," Journal of Turbulence, Vol. 11, pp. 1-9, 2010.

  8. Agrawal, A., and Prasad, A.K., "Integral solution for the mean flow profiles of turbulent jets, plumes and wakes," Journal of Fluids Engineering, Vol. 125, No. 5, pp. 813-822, 2003