Flows through plane sudden-expansions

A calculation method has been developed and used to represent flows downstream of plane symmetric expansions with dimensions and velocities encompassing laminar and turbulent flows. Except for very low Reynolds numbers, the flows are time-dependent and asymmetric and the calculated results are appraised first in relation to published measurements of laminar flows and then to new measurements obtained at a Reynolds number of 26 500. The time-dependent laminar simulations indicate that the critical Reynolds numbers are predicted with excellent accuracy for different expansion ratios and the details of the asymmetric velocity profiles are in good agreement with experimental measurements. The laminar flow calculations also show that increasing the thickness of the separating boundary layer leads to longer regions of separation and no dominant frequency for Reynolds numbers up to those at which the third separation region was observed. The turbulent flow simulations made use of the k–ε turbulence model and provided a satisfactory representation of measurements, except in regions close to the wall and within the recirculation regions. Also, the longer reattachment length was underestimated. Limitations are discussed in relation to these and higher-order assumptions.