BROADCAST: A high-order compressible CFD toolbox for stability and sensitivity using Algorithmic Differentiation

The evolution of any complex dynamical system is described by its state derivative operators. However, the extraction of the exact N-order state derivative operators is often inaccurate and requires approximations. The open-source CFD (Computational Fluid Dynamics) code called BROADCAST discretises the compressible Navier-Stokes equations and then extracts the linearised N-derivative operators through Algorithmic Differentiation (AD) providing a toolbox for laminar flow dynamics. Furthermore, the gradients through adjoint derivation are extracted either by transposition of the linearised operator or through the backward mode of the AD tool. The software includes base-flow computation and linear global stability analysis via eigen-decomposition of the linearised operator or via singular value decomposition of the resolvent operator. Sensitivity tools as well as weakly nonlinear analysis complete the package. The numerical method for the spatial discretisation of the equations consists of a finite-difference high-order shock-capturing scheme applied within a finite volume framework on 2D curvilinear structured grids. The stability and sensitivity tools are demonstrated on two cases: a cylinder flow at low Mach number and a hypersonic boundary layer.