Evaluation of Transition Models in the Slipstream of Distributed Propulsion Systems

In this study, different transition prediction methods are evaluated in propeller-wing interaction simulations of a distributed propulsion configuration with a laminar wing. Both steady computations using an actuator disk method and unsteady computations using an actuator line method are conducted. In the steady computations, local variations in the angle of attack modify the pressure distribution, which is the primary effect influencing the transition location on the wing. The DLR-γ model shows good agreement with the eⁿ method, whereas the γ–Re_θt model predicts premature transition, particularly on the upper surface of the wing. In the unsteady computations, the propellers' effect on the pressure distribution is combined with the effect of the helical vortices impinging on the wing, changing the boundary layer characteristics. The transition criterion of the DLR-γ model indicates an upstream shift of transition in sync with the blade tip vortex impinging on the leading edge, followed by a downstream displacement—temporarily even farther downstream than that of the clean wing. However, both the γ–Re_θt and the DLR-γ models struggle to respond meaningfully to the unsteady flow. A simplified case, in which the propellers are deactivated after vortex impact, reveals that neither model recovers the clean-wing transition location. To assess the influence of the intermittency production formulation, the production term from the γ–Re_θt model is used within the DLR-γ framework, improving the model's responsiveness, though not fully recovering clean-wing behavior. Additional development is needed to ensure that transition models correctly follow changing inflow conditions in unsteady computations.