Estimating local instabilities for irregular flows in the differentially heated rotating annulus

摘要

In stable flows, transient growth of 'non-normal' modes can lead to turbulence. Usu-ally, non-normal modes are computed from linearized model equations [1]. However, for some problems the proper set of equations is unknown, or unhandy for the pur-pose of finding non-normal modes. Therefore it is proposed to estimate non-normal modes from data alone, without using the model equations. Crucial for such an esti-mation is a good guess of the linear system matrix for the flow under consideration. Such a guess can be obtained following the approach by [2] discussed in the context of climate analysis.