LATERAL DYNAMICS, SHAPE OPTIMIZATION, AND NUMERICAL ANALYSIS OF CHINED FOREBODIES: IMPLICATIONS ON WING ROCK MOTION

Abstract

Wing rock is a highly nonlinear complex phenomenon in which an aircraft undergoes self-excited roll oscillations about its longitudinal axis at high angles of attack and low Mach number, also known as limit cycle oscillations (LCO). It is a significant phenomenon that requires evaluation during the design phase of any flight, particularly during takeoff and landing. The successful mitigation of this nonlinear complex phenomenon is crucial to ensure safe and stable flights. However, the modeling, simulation, and optimization of wing rock present formidable challenges due to its complex nature. The primary objective of this research aims to investigate the wing rock phenomenonon the chine forebody and develop an optimization strategy for its shape. To achieve this objective, a reference chine forebody, derived from an experimental study, is parametrized using a third-order Bezier equation. The Design of Experiment (DOE), a widely recognized technique, is employed to optimize the chine forebody shape. Four control variables are utilized to modify the chine forebody's geometry through the DOE process. Subsequently, the application of DOE yields a total of 31 distinct geometries. Computational Fluid Dynamics (CFD) has been used to solve the flow-field using Reynolds-Averaged Navier-Stokes (RANS) equations at low Mach numbers. The reference chine forebody obtained from the literature is validated using experimental data. Steady aerodynamic simulations are conducted at a subsonic Mach number of 0.179 and various angles of attack. The experimental data for the coefficient of the normal force is successfully validated up to an angle of attack of 45 degrees, exhibiting a maximum error of 10%. The dynamic stability derivatives are necessary for investigating wing-rock phenomena. This study's stability derivatives are computed using forced oscillation CFD simulations. To ensure the accuracy of the simulation setup, it is validated using the Stability and Control Configuration (SACCON) UCAV, a widely recognized test case for dynamic simulations involving vortex-dominated flows. xvii The research results demonstrate that shape optimization significantly delays the onset angle (α onset ). The baseline geometry has an α onset of 32 o , and the optimized geometry has an α onset 60 o . The response surface method predicted an α onset of 57 o compared to the actual 60 o through CFD. Hence, the accuracy of the DOE technique for this study is 95%. The flow physics is explained using velocity and vortex trace on the chine baseline and optimized geometry. It is concluded that the flow separation is delayed in optimized geometry compared to baseline geometry, resulting in delayed wing rock.