Massively Parallel Solution of the BiGlobal Eigenvalue Problem Using Dense Linear Algebra

Abstract

Linear instability of complex flows may be analyzed by numerical solutions of partial-derivative-based eigenvalue problems; the concepts are, respectively, referred to as BiGlobal or TriGlobal instability, depending on whether two or three spatial directions are resolved simultaneously. Numerical solutions of the BiGlobal eigenvalue problems in flows of engineering significance, such as the laminar separation bubble in which global eigenmodes have been identified, reveal that recovery of (two-dimensional) amplitude functions of globally stable but convectively unstable flows (i.e., flows which sustain spatially amplifying disturbances in a local instability analysis context) requires resolutions well beyond the capabilities of serial, in-core solutions of the BiGlobal eigenvalue problems. The present contribution presents a methodology capable of overcoming this bottleneck via massive parallel solution of the problem at hand; the approach discussed is especially useful when a large window of the eigenspectrum is sought. Two separated flow applications, one in the boundary-layer on a flat plate and one in the wake of a stalled airfoil, are briefly discussed as demonstrators of the class of problems in which the present enabling technology permits the study of global instability in an accurate manner.