This study aims at investigating the effect of flow condition at the inlet for flow in an axisymmetric sudden expansion flows with an expansion ratio (ER) of 2.0 and study its flow characteristics. A series of large eddy simulations (LES) with WALE model proposed by Nicoud and Ducros1 were conducted for different inlet Reynolds numbers and turbulence intensities (u0 rms=Um), and the reattachment lengths were calculated for each case. The reattachment length is defined as the length measured downstream of the expansion joint where the flow direction is reversed adjacent to the wall (Lr). For widely studied inlet turbulence intensity values, the simulation results are in good agreement with the experimental and numerical results reported in the literature2–4. Parametric studies revealed that turbulence intensity affects the value of the critical Reynolds number which divides the flow into laminar and transition regions and the reattachment length. Critical Reynolds number was found to decrease with increase in turbulence intensity, a correlation expression is proposed. The Proper Orthogonal Decomposition (POD) analysis was performed to gain enhanced understanding of complex flow structure downstream of the expansion. Finally, overall correlation expression for the reattachment length was obtained for 500 Re 15,000 and 0.2 TI [%] 20. For a given turbulence intensity, the reattachment length can be expressed for laminar and turbulent regions with a relation function of Reynolds number. The reattachment length in the transition region can be expressed as a fractional average of reattachment lengths for laminar and turbulent flows.
