SOME MEASUREMENTS DOWNSTREAM OF A LOBED FORCED MIXER WITH DIFFERENT TRAILING-EDGE CONFIGURATIONS

Velocity and turbulence characteristics have been measured downstream of a lobed forced mixer with three different trailing edge configurations, using a two-component laser-Doppler anemometer at a Reynolds number of 2.27 x 10(4) (based on a reference velocity of 10m/s, and a nominal wavelength of the lobe of 33 mm). The three trailing edge configurations under investigation have the shape of a square wave, a semi-circular wave and a triangular wave. Measurements for a velocity ratio of 1:1 indicate that the strength of the secondary flow shed by a lobe is not the only parameter which determines the effectiveness of mixing, as previously suggested. The boundary layer thickness which grows along the side-walls of the lobe penetration and the subsequent shedding of the boundary layer to the wake region are of equal importance. High turbulence regions do not appear downstream of the mixers within six wavelengths downstrewn of the trailing edge. The normal and shear stresses in two cases (the semi-circular and triangular wave lobes) are shown to have a similar trend of decaying in magnitude.