Modal Analysis of Instabilities in the BoLT-2 Flowfield

Boundary layer disturbances in the Boundary Layer Turbulence (BoLT-2) flowfield are investigated using a combination of low-dissipation numerics and a novel shock capturing scheme. This allows us to investigate the later stages of the transition process governed by nonlinear evolution of the boundary layer state. Unsteady simulations using US3D are performed with broadband stochastic forcing to mimic quiet wind tunnel noise. Disturbances are introduced at an interpolated inflow plane located downstream of the leading edge to allow disturbances to grow which are induced by boundary layer instability mechanisms. Two-dimensional time series snapshots are collected at streamwise locations along the geometry to compute spatio-temporal information from extracted boundary layer modes. Modal analysis is performed with a streaming version of total dynamic mode decomposition (STDMD) with a compressible energy norm weighting to identify modes associated with distinct transition processes. Frequencies computed from STDMD modes show excellent agreement with power spectral density peaks measured from experiments and simulation.