Journal of Fluid Mechanics

Characteristic-eddy decomposition of turbulence in a channel

Parviz  Moin a1 and Robert D.  Moser a2
a1 Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA and NASA Ames Research Center, Moffett Field, CA 94035, USA
a2 NASA Ames Research Center, Moffett Field, CA 94035, USA

Article author query
moin p   [Google Scholar] 
moser rd   [Google Scholar] 


The proper orthogonal decomposition technique (Lumley's decomposition) is applied to the turbulent flow in a channel, to extract coherent structures by decomposing the velocity field into characteristic eddies with random coefficients. In the homogeneous spatial directions a generalization of the shot-noise expansion is used to determine the characteristic eddies. In this expansion the Fourier coefficients of the characteristic eddy cannot be obtained from second-order statistics. Three different techniques are used to determine the phases of these coefficients: (i) a technique based on the bispectrum, (ii) a spatial compactness requirement, and (iii) a functional continuity argument. Results from these three techniques are found to be very similar. The implications of these techniques and the shot-noise expansion are discussed in the Appendix. The dominant eddy is found to contribute as much as 76% to the turbulent kinetic energy. In two and three dimensions, the characteristic eddies consist of an ejection region straddled by streamwise vortices which leave the wall in a very short streamwise distance of approximately 100 wall units.

(Published Online April 26 2006)
(Received January 11 1988)
(Revised September 5 1988)