Some flow characteristics of lobed forced mixers at higher velocity ratios

The flow characteristics of two types of lobed forced mixers, the unscalloped and the scalloped mixers, have been examined at velocity ratios higher than unity, in relation to the variation of mass flux uniformity, the decay of the streamwise vorticity, the variation of turbulent kinetic energy and the growth of the shear layer with distance from the trailing edge. Three trailing edge configurations have also been considered for each type of mixer, namely a square wave, a semi-circular wave and a triangular wave. The analysis showed that the strength of the streamwise vorticity shed at the trailing edge and the subsequent decaying rate with downstream distance are found to be very important in studying the mixing effectiveness of the lobed mixers.List of Symbols C _I normalized streamwise circulation, _s/U _r h tan - _s streamwise circulation - k turbulent kinetic energy = 1/2(u²+v²+w²) - Re Reynolds number, U _r /=2.27×10⁴ - h (=) Lobe height, 33 mm - U ₁, U ₂ mean velocity of the slow and fast streams - U _r reference mean velocity, (U ₁ + U ₂)/2 = 10 m/s - U, u streamwise mean and the corresponding rms velocities - V, v horizontal mean and the corresponding rms velocities - W, w vertical mean and the corresponding rms velocities - x,y, z streamwise, horizontal and vertical directions - A _wake cross-sectional area bounded by the wake region. The wake region boundary is defined at the region bounded by one half of a lobe along the y/ direction and at the locations along the z/ direction where U ₂/U _r2 and U ₁/U _r1<0.95. - nominal lobe wavelength, 33 mm - half of the included divergent angle of the penetration region, 22° - U uniformity factor - momentum thickness Financial supports from the Applied Research Grant is gratefully acknowledged. The contribution of Mr. J. K. L. Teh, Dr. J. H. Yeo and Mr. T. H. Yip to the work presented here are sincerely appreciated.