Evaluation of convective velocity in the Sommerfeld radiation condition for two-dimensional parallel jets

In numerical simulations of spatially developing incompressible flows, truncating the computational domain is necessary due to limited computational resources. Improper treatment of the outflow boundary can cause artificial vortex reflection and distortion. The Sommerfeld Radiation Condition (SRC), which incorporates a convective velocity Uc, is widely used to mitigate such effects. However, the optimal specification of Uc remains unclear, especially for vortex-dominated flows. This study investigates four methods for determining Uc in the SRC framework, applied to a two-dimensional parallel jet with complex vortex structures at a moderate Reynolds number of 3000. The methods include: (SRC1) fixed values, (SRC2) locally computed values with threshold-based corrections, and (SRC3) globally constrained values based on the maximum Courant number in the domain. Each method modifies Uc to suppress spurious reflections while maintaining physical accuracy at the outflow boundary. The performance of each method is evaluated using flow field visualization and the distribution of convective velocity on the outflow boundary. The objective is to clarify the effectiveness of SRC in handling complex vortex-dominated flows under different convective velocity conditions.