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22 results on '"Stretch, Derek D."'

12. Automated pattern eduction from turbulent flow diagnostics

Author

Stretch, Derek D

Subjects
Fluid Mechanics And Heat Transfer
Abstract

The development of an automated technique for the eduction of 3-D spatial patterns in vector or scalar diagnostics was completed. The method is based on an iterative convolution between a trial pattern and the data field. It was applied to the analysis of low Reynolds number turbulent channel flow and homogeneous shear flow. The results yielded new information on the dominant flow structures in these flows, particularly with respect to the spatial relationships between various forms of organized motion. A particular application of the pattern eduction method, which is tentatively referred to as an 'adaptive wavelet transformation', is proposed with the objective of investigating the way turbulence structure changes with scale. Preliminary results using data from homogeneous turbulent shear flow simulations are presented. At the low Reynolds numbers of the simulations, there is no evidence of scale similarity. The small scales appear to be associated with the edges of the larger scale vortical structures.

Published
1991

15. Estuary and lake hydrodynamics

Author

Stretch, Derek D., primary, Chrystal, Clinton P., additional, Chrystal, Robynne A., additional, Maine, Christopher M., additional, and Pringle, Justin J., additional

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21. Defining the Zonal Structure of Turbulence Using the Pressure and Invariants of the Deformation Tensor

Author

Fung, Jimmy Chi Hung, Hunt, Julian Charles Roland, Perkins, R.J., Wray, Alan A., Stretch, Derek D., Fung, Jimmy Chi Hung, Hunt, Julian Charles Roland, Perkins, R.J., Wray, Alan A., and Stretch, Derek D.

Abstract

A set of objective criteria based on the local strain rate, vorticity and pressure have been found to describe regions in which the streamlines circulate, converge or diverge, and form streams of high velocity flow. The homogeneous and sheared turbulent flow fields are made up of characteristic flow zones — eddy, shear, convergence and streaming zones. These are studied in turbulent velocity fields produced by different methods of simulation, including the novel method of Kinematic Simulation of homogeneous isotropic turbulence are summarised. We derive and explain the zonal algorithm to classify structures and then use this classification to compare the results of two different numerical simulations (DNS, KS) both qualitatively (turbulence structure, physical processes) and quantitatively (turbulence statistics) for homogeneous isotropic turbulence and then we apply the zonal algorithm to a turbulent shear flow. New conclusions are reached about the significant regions in turbulent flows for dynamical and kinematical processes.

Published
1991

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