Control the asymmetric instability in a 2D plane diffuser

The laminar flow in two-dimensional diffusers may produce either symmetric or non-symmetric steady solutions, depending on the value of the Reynolds number as compared with some critical value.

Transition to the asymmetric solution at Re=100 and re-symmetrization after the introduction of the control cylinder
Control the asymmetric instability in  a 2D plane diffuser

The stability properties of the flow have been studied in the context of linear theory. In this context, a sensitivity analysis of the flow instability is carried out with respect to perturbations that may be produced by a realistic passive control, thus providing qualitative hints and quantitative information for the control design. 

Following the so-obtained information, a passive control is built by introducing a small cylinder in the flow with the aim of stabilizing the unstable symmetric flow configuration in the diffuser.

The introduction of the cylinder, placed following the indications of the linear sensitivity analysis in the stable asymmetric flow configuration, allows a steady completely symmetric or less asymmetric flow to be recovered.

 Related publications:

Andrea Fani, Simone Camarri, Maria Vittoria Salvetti: Stability analysis and control of the flow in a symmetric channel with a sudden expansion. In: Physics of Fluids, 24 (8), pp. 084102, 2012, ISSN: 10706631.