Turbulent flow through a plane sudden expansion

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 with R greater than 1.5 produce asymmetric flows and this was again seen in this study. The literature for the asymmetric situation (R>1.5) is surprisingly limited and only axial velocity and axial turbulence intensity results have been reported previously. A laser Doppler anemometer was used to measure mean and r.m.s axial velocities, U and u', as well as the transverse r.m.s velocities, v', and the Reynolds shear stress, v u . Not only was the mean flow found to be asymmetric, but integration of the mean axial velocity profiles revealed significant departures from two dimensionality along the centreplane 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. A two-dimensional calculation method using the standard k – ε turbulence model has been utilised to calculate the flow along the centreplane of the expansion. Despite the acknowledged deficiencies of the k– ε model and the considerable deviation from two-dimensionality of the experimental flow, remarkably good agreement is found between the calculations and the measured centreplane flow structure.