Linear stability of flow in a 90° bend

The paper considers a two-dimensional flow in channel, which consists of straight inlet and outlet branches circularly 90-degree curved bend. An incompressible viscous fluid flows through the elbow under action constant pressure gradient between outlet. Navier-Stokes equations were solved numerically using high-fidelity spectral/hp element method. In range Reynolds numbers, an adaptive selective frequency dumping method was used to get steady-state flow. It found that three separation bubbles vortex shedding can exist modal stability two- three-dimensional perturbations investigated. Critical number disturbances as extrapolation by lower results. is much greater than one, but could subcritically unstable with respect imposed small-amplitude white noise. For perturbations, dependence critical numbers on bending radius obtained. case moderate neutral curve provided eigenfunctions are studied detail: instability be caused periodic or monotonically growing mode, these modes regard recirculation occur after