We introduce an open-source and unified framework for transition analysis for laminar boundary layer natural transition at transonic conditions and over complex geometries, where surface irregularities may be present. Different computational tools are integrated in the framework, and therefore overcomes the difficulties of two separate and usually quite disparate processes when using 𝑒 𝑁 method for transition analysis. To generate a baseflow with desired pressure distribution, appropriate pressure compatible inflow boundary condition needs to be developed and enforced. We first derive the system for 1D numerical stability analysis for boundary conditions, and construct three types of pressure compatible inflow. We demonstrate that the entropy-pressure compatible inflow is stable unlike other choices. Compared with the steady baseflow computation, the unsteady simulation for the disturbance field is more challenging for compressible flows because of complex wave reflections, which can easily contaminate the results. We therefore introduce the two main sources of wave decontamination and corresponding methods to obtain clean signal. The workflow within the framework is then verified by computing the disturbance development in 2D flat plate boundary layer flows at Mach 0.8. The 𝑁-factors over a clean flat plate and a flat plate with a forward-facing step are generated, and agree well with the results from the reference. Following the verified workflow, We then analyze the disturbance growth on a wing section of the CRM-NLF model. The 𝑁-factor on a 2D simulation is generated and studied.

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Laminar boundary layer natural transition for external flows is of particular interest in both the aeronautical industry and academia. The transitional process is dominated by the linear growth of disturbances, e.g., Tollmien–Schlichting waves and crossflow waves, and therefore a correct prediction on the development of the disturbances is necessary for a successful transitional analysis. Most conventional studies focused on the disturbances developing based on incompressible boundary layer flows over ideal, clean geometries. However, the physical settings for wider real applications are different for the flow compressibility and geometrical complexity. The compressibility stems from the transonic operational conditions, and for the real geometries the main source of the complexity is the existence of surface imperfections, which typically take the form of steps and gaps whose sizes are comparable with the boundary layer thickness. In the current study we therefore further extend the physical settings to transonic laminar boundary layer at realistic Reynolds numbers, and over wing sections with surface imperfections.

One approach to reducing the computational cost of simulating transitional compressible boundary layer flow is to adopt a near body reduced domain with boundary conditions enforced to be compatible with a computationally cheaper three-dimensional RANS simulation. In such an approach it is desirable to enforce a consistent pressure distribution which is not typically the case when using the standard Riemann inflow boundary conditions. We therefore revisit

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