Predicting the High-Angle-of-Attack Characteristics of a Delta Wing at Low Speed

Abstract

Ensuring the safe operation of new supersonic transport aircraft requires understanding their stability during takeoff and landing. These phases involve flying at subsonic speeds and high angles of attack, where the aerodynamics are characterized by unsteady vortical flow. This work assesses the accuracy of Reynolds-averaged Navier–Stokes (RANS) and delayed detached eddy simulations (DDES) at predicting the vortex-dominated flow over a delta wing for angles of attack up to and past stall. The delta wing has an aspect ratio of 2 and is a simplified representation of a supersonic transport wing. The predicted aerodynamic coefficients are compared with experimental data, focusing on the shape of the pitching moment curve. In addition, a steadiness metric is formulated to distinguish between steady and unsteady angles of attack. It is found that RANS accurately predicts vortex effects in the steady regime but is inaccurate at high angles of attack where the flow is unsteady. DDES is more reliable in the unsteady regime, but the computational cost is at least 100 times that of RANS. Predicting the pitching moment at the highest angles of attack is difficult even with DDES on a 69-million-cell mesh. These results provide guidelines for choosing the appropriate fidelity depending on the flow characteristics, the required accuracy, and the computational budget.