A DMD-based automatic transition prediction methodfor flows over airfoils

The efficient and accurate prediction of transition from laminar to turbulent flow is essential to the prediction of aerodynamic characteristics of an aircraft based on computational simulations. This paper presents a “DMD/e^N” method for predicting flow transition location over airfoils. The “DMD/e^N” method is used to find the transition location, which is then used to switch from a laminar to turbulent regime in RANS calculations. This approach combines a spatial dynamic mode decomposition (DMD) technique and an e^N method. The DMD is used for stability analysis, and the e^N method is employed to integrate the disturbance growth. Transition is assumed to take place when the amplified mode’s N-factor at a given location reaches a prescribed threshold (e.g. typically N=9). Transition prediction of flows around a transonic natural-laminar-flow (NLF) LSC72613 airfoil and a low-speed laminar NLF0416 airfoil are performed to validate and demonstrate the methodology. The results show that, for flows at different angles of attack, the predicted transition locations agree well with experimental data and compare favorably to other numerical methods. Furthermore, the growth rate curve for the disturbances matches well with that from e^N envelope method, which indicates that the method has the ability to predict transition of flows over airfoils and the potential to become a useful transition prediction tool in the future.