Optimal disturbances above and upstream of a flat plate with an elliptic-type leading edge
2014 (English)In: Theoretical and Computational Fluid Dynamics, ISSN 0935-4964, E-ISSN 1432-2250, Vol. 28, no 2, 147-157 p.Article in journal (Refereed) Published
Adjoint-based iterative methods are employed to compute linear optimal disturbances in a spatially growing boundary layer around an elliptic leading edge. The Lagrangian approach is used where an objective function is chosen and constraints are assigned. The optimisation problem is solved using power iterations combined with a matrix-free formulation, where the state is marched forward in time with a standard direct numerical simulation solver and backward with the adjoint solver until a chosen convergence criterion is fulfilled. We consider the global and, more relevant to receptivity studies, the upstream localised optimal initial condition leading to the largest possible energy amplification at time T. We find that the two-dimensional initial condition with the largest potential for growth is a Tollmien-Schlichting-like wave packet that includes the Orr mechanism and is located inside the boundary layer downstream of the leading edge. Three-dimensional optimal disturbances induce streaks by the lift-up mechanism. Requiring the optimal initial condition to be localised upstream of the plate enables us to better study the effects of the leading edge on the boundary layer receptivity mechanisms. Two-dimensional upstream disturbances are inefficient at triggering unstable eigenmodes, whereas three-dimensional disturbances induce streamwise streaks with significant growth.
Place, publisher, year, edition, pages
2014. Vol. 28, no 2, 147-157 p.
Boundary layer instabilities, Receptivity, Adjoint-based optimisation, Nonmodal growth
Engineering and Technology
IdentifiersURN: urn:nbn:se:kth:diva-144533DOI: 10.1007/s00162-013-0309-yISI: 000333108300002ScopusID: 2-s2.0-84961242002OAI: oai:DiVA.org:kth-144533DiVA: diva2:714470
FunderSwedish Research CouncilSwedish e‐Science Research Center
QC 201404282014-04-282014-04-242014-04-28Bibliographically approved