The non normality of several linear temporal stability operators has been taken into account during the last decade and appears to be an important matter in stability analysis [1]. This paper reports some results obtained following a similar approach applied to the centrifugal instability of Gortler, generally tackled as a spatial stability problem. It is now a well known feature that the nonorthogonality of the eigenfunctions can give rise to a large transient growth of some perturbations despite a damping of every single mode. Therefore the classical single value problem appears inadequate and we rather consider a global analysis of the spectrum and the associated set of eigenfunctions. It is found that even in the case of a parallel basic flow, a lot of eigenfunctions do not vanish at infinity, and may even grow infinitely in the non parallel case. The structure of these solutions suggests that the operator captures modes which conflict with the basic assumptions of the Gortler model.
展开▼
