LARGE EDDY STRUCTURE OF A TURBULENT WAKE.
PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF AEROSPACE ENGINEERING
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Lumleys objective definition of the intuitive concept of large eddy leads to an eigenvalue problem. In this report, the first few eigenfunctions are determined for velocity correlations measured in the turbulent wake of a circular cylinder these are interpreted in terms of the associated representation theorems. The eigenvalue problem was solved in Fourier space and the most energetic eigenfunction was transformed to real space. This mode is a vortex pair approximately normal to the plane of the wake its planes of circulation are normal to the direction of positive maximum mean strain rate. The structure is qualitatively similar to Grants intuitive model based on the same data. Lumleys interpretation of the most energetic modes as the large eddies is verified as correct. However, the strong non-linearity of the dynamics of these eddies suggested by the apparent dominance of vortex stretching combined with the slow decay of eigenvalues with increasing order, implies that analytic solution of the equations of motion for these eddies will be a formidable problem. Author
- Fluid Mechanics