ReCoVor

Abstract: Understanding the physics of flow-structure interactions (FSI) is crucial to developing next-level passive, adaptive flow control strategies for unmanned aerial vehicles operating in vortex-dominated, low Reynolds number regimes. High-fidelity simulation tools that compute the nonlinearly coupled flow-surface interplay are key to enabling this understanding. Developing a robust, high-fidelity simulation framework for FSI presents several challenges that remain an area of active research. An important challenge revolves around the treatment of the body within the flow grid, potentially involving complex modifications to the underlying flow solver, such as altering stencils or embedding costly linear solves that can significantly increase the cost compared with body-less solvers. To overcome these challenges, we present a new immersed method, Interface-manifold aware projection (IMAP). This technique provides a fast, novel, non-intrusive simulation framework for complex flow-structure interactions. IMAP's approach is rooted in viewing the no-slip constraint as a manifold within which the flow evolves. The method centers on constructing projections to constrain the dynamics to this manifold before time advancement. These projection steps leverage standard immersed-boundary operators and are built from small, surface-local operators that do not involve large-dimensional linear systems. IMAP eliminates the need for costly embedded solves inherent to many projection-based immersed boundary methods, as well as stencil modifications associated with other immersed boundary methods. In this talk, we introduce the methodology behind the approach and demonstrate results for two-dimensional channel flow past a cylinder.

Abstract: Flow reattachment is the final stage of the dynamic stall cycle, where the lift coefficient recovers to its quasi-static value after being lost due to flow separation. In this study, we analyze the reattachment process of a sinusoidally pitching airfoil using pressure and flow field data to identify the dynamics of the unsteady reattachment process. In unsteady conditions, decreasing angle of attack below critical stall angle is insufficient to trigger recovery. We identify a necessary condition for recovery onset by analyzing the leading-edge suction parameter. The recovery consistently begins after the leading edge suction parameter exceeds a critical threshold independent of the pitch rate. Once the critical leading edge suction parameter is reached, the shear layer reattaches to the airfoil in a wave-like motion from the leading to the trailing edge. Shear layer reattachment ends when the wave reaches the trailing edge, followed by boundary layer reattachment. The boundary layer reattachment concludes the recovery process, and the lift coefficient recovers to its quasi-static value. The wave propagation onset is delayed relative to when the angle of attack falls below the critical stall angle. The onset delay depends on the pitch rate, but the durations of wave propagation and boundary layer reattachment states are independent of the pitch rate. Understanding the characteristic timescales of the recovery process can lead to more accurate reattachment predictions and better control strategies for dynamic stall.