Large-scale structures in a plane turbulent mixing layer are studied through the use of
the proper orthogonal decomposition (POD). Extensive experimental measurements
are obtained in a turbulent plane mixing layer by means of two cross-wire rakes
aligned normal to the direction of the mean shear and perpendicular to the mean
flow direction. The measurements are acquired well into the asymptotic region. From
the measured velocities the two-point spectral tensor is calculated as a function of
separation in the cross-stream direction and spanwise and streamwise wavenumbers.
The continuity equation is then used for the calculation of the non-measured components
of the tensor. The POD is applied using the cross-spectral tensor as its kernel.
This decomposition yields an optimal basis set in the mean square sense. The energy
contained in the POD modes converges rapidly with the first mode being dominant
(49% of the turbulent kinetic energy). Examination of these modes shows that the
first mode contains evidence of both known flow organizations in the mixing layer, i.e.
quasi-two-dimensional spanwise structures and streamwise aligned vortices. Using the
shot-noise theory the dominant mode of the POD is transformed back into physical
space. This structure is also indicative of the known flow organizations.
Three-dimensional numerical simulations and proper orthogonal decomposition analysis of flow over different bottom-mounted ribs
