Alexander G. Kuzmin

St. Petersburg state university

At a supersonic velocity of the airflow incident on a channel/intake with curved walls, there is the formation of shock waves, across which flow parameters change abruptly. The location of shock waves can change crucially with small changes in flow conditions at the entrance or exit; moreover, the flow can exhibit non-unique regimes and hysteresis. Transitions between the regimes were studied in previous years for two-dimensional, axisymmetric and 3D convergent-divergent intakes, as well as for bent channels of rectangular cross-section at steady or unsteady changes in the supersonic flow parameters at the entrance. In this paper, we consider a two-dimensional 9%-bent channel with a sufficiently long part located downstream of the bend. The turbulent transonic flow is studied numerically under given pressure fluctuations in the exit section of the channel. Solutions of the system of Reynolds-averaged Navier-Stokes equations, which govern flow parameters and the structure, are obtained with the ANSYS-18.2 software based on the finite element method. The solutions show the occurrence of different regimes at the same steady or oscillatory pressure given at the exit. Conditions for the transition from the regime with multiple reflections of oblique shocks from the walls to the regime with a shock located at the entrance are established. It is shown that the inverse transition cannot be obtained with pressure variations in the exit section of the channel; in order to perform such a transition, one needs an increase in the inflow Mach number or pressure.

numerical simulation, transonic flow, oscillations, non-uniqueness