Turbulent flow through a plane sudden expansion of modest aspect ratio

The results are reported of an experimental investigation of turbulent flow through a plane sudden expansion of expansion ratio R=D/d=4 and aspect ratio A=w/h=5.33. It is well known that plane sudden expansions of high aspect ratio (A>10) with R greater than 1.5 produce asymmetric flows and this was again seen in this study. The literature for the asymmetric flow situation is surprisingly limited and only axial velocity and axial turbulence intensity results have been reported previously. A laser Doppler anemometer was used here to measure mean and rms axial velocities, U and u('), as well as the transverse mean and rms velocities, V and v('), and the Reynolds shear stress, u'/uv. Not only was the mean flow found to be strongly asymmetric, but integration of the mean axial velocity profiles revealed significant departures from two dimensionality along the centerplane of the expansion duct. Results are reported at three spanwise locations to highlight this three dimensionality and qualitative arguments are made to relate this to the influence on corner vortices of the modest aspect ratio. (C) 2002 American Institute of Physics.