Global Stability Analysis of a Compressible Turbulent Flow Around a High-Lift Configuration

The stability of flow over a complex high-lift configuration with significant regions of separated flow is analyzed. Current state-of-the-art flow solvers encounter difficulties in predicting both the onset of flow separation over similar configurations and the progression of the separated region when the angle of attack is increased. The present analysis provides useful insights into the mechanisms responsible for limiting the maximum lift on multielement wing configurations by relating flow separation with the onset of flow instability. A steady solution based on a finite volume discretization is used as the basic state for the linear stability analysis. The resulting generalized eigenvalue problem has been solved using a Krylov subspace projection technique in the form of the Arnoldi iterative method. This methodology is first applied to a NACA0012 test case at subsonic and transonic conditions. Then, for the first time, the stability of flow over an industrial multicomponent geometry involving the A310 airfoil has been investigated in order to identify the low-frequency instabilities related to flow separation. One important conclusion is that, for both configurations, one unstable mode related to flow separation appears at an angle of attack greater than that corresponding to the maximum lift coefficient condition. Finally, the adjoint problem is solved in order to evaluate the receptivity characteristics and the structural sensitivity of both configurations, identifying the regions of flow that can be manipulated to yield the largest change in the flowfield.