The results of a numerical study of unsteady viscous fluid flow in the area of the branching of a circular cross-section channel at an angle of 60° are presented for four values of the inlet Re number that are less than or equal to 1475; in the upstream region, the channel flow is assumed to be unperturbed and fully-developed. The main results relate to the case of equality of the flow rates in two branches, with flow separation regions in both branches. It was shown, in particular, that at Re = 750, intense quasi-periodic oscillations develop in the computational domain due to the Kelvin-Helmholtz instability. At Re = 1475, a zone of locally turbulent motion is formed in the flow, the size of which depends on the proportion of the flow going into the side branch. The vortex pattern of the flow and the type of the velocity pulsation spectrum at various points in the region are analyzed.
E. M. Smirnov (2025) studied this question.