Spatial linear disturbances in a plane wall jet
2012 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 24, no 5, 054104- p.Article in journal (Refereed) Published
A two-dimensional direct numerical simulation study of the linear instability in a laminar plane wall jet is presented. The evolution of the wall jet disturbances is in reasonable agreement with predictions by spatial linear stability theory only with regard to the wavelength and the amplitude shape of the disturbance, whereas significant differences in the linear growth rate are noticed. As a consequence, the "stable island" on the instability map based on linear stability theory turns out to be connected with the outer stable region in the simulations, thus taking the form of a "stable peninsula". The failure of the theory is attributed to the rapid streamwise spread and decay of the wall jet, which is incompatible with the assumption of parallel flow. We also assess the maximum possible transient linear amplification of two-dimensional disturbances in the plane wall jet, using the concept of optimal initial disturbances. The transient energy growth relies on the Orr mechanism, and the upper bound of the disturbance energy increases linearly in time for the present flow configuration. The optimal disturbances exhibit local maxima near the edge of the jet and close to the wall, where sites of effective receptivity are hence expected. We find that the outer region of the plane wall jet is more receptive to time periodic forcing than the inner region.
Place, publisher, year, edition, pages
2012. Vol. 24, no 5, 054104- p.
Flow, Transition, Stability
IdentifiersURN: urn:nbn:se:kth:diva-98952DOI: 10.1063/1.4717954ISI: 000304826100023ScopusID: 2-s2.0-84861963708OAI: oai:DiVA.org:kth-98952DiVA: diva2:540532
FunderSwedish e‐Science Research Center
QC 201207102012-07-102012-07-052013-04-08Bibliographically approved