Date of Award
Doctor of Philosophy (PhD)
The accurate predictions of 3D high lift flows have proven to be a significant challenge for Computational Fluid Dynamics (CFD) using the Reynolds-Averaged Navier-Stokes (RANS) equations with a turbulence model. While RANS methods typically require less computational resources than Scale Resolving Simulation (SRS) methods, they generally struggle to accurately predict flow separation and the complex interactions that occur between the fuselage, different elements of the wing, the engine nacelle, and the accompanying support hardware. As a result, significant effort has been put in improving the accurate prediction of these flows with the goal of developing better computational methodologies and turbulence models as well as to obtain a better understanding of the limitations of current CFD methods in predicting high lift flows.Both two- and three-dimensional high-lift configurations are considered in this dissertation using the Spalart-Allmaras (SA), SST k-ω and recently developed one-equation Wray-Agarwal (WA) turbulence models. The capability of employing the non-linear Quadratic Constitutive Relation (QCR) for eddy viscosity in conjunction with these models is also investigated. Each high-lift configuration is chosen due to the availability of excellent experimental data. The configurations considered are 2D MDA 30P30N three element airfoil and 3D JAXA (Japanese Aerospace Exploration Agency) Standard Model and NASA Common Research Model, both in a modified high-lift configuration (JSM-HL and CRM-HL). The two latter geometries represent the conventional transport aircraft in a landing configuration and have been developed as part of the AIAA 3rd and 4th High Lift Prediction Workshops (HLPW). The simulations are performed using the commercial CFD software ANSYS Fluent. The SA model is shown to give better agreement with experimental results in most cases; however, at high angles of attack, each turbulence model struggles to accurately predict separation patterns along the wing resulting in poor prediction of the lift and drag. The use of QCR results in local improvements in accuracy for certain flow quantities but is not found to have a significant change on the overall flow field. Finally, both passive and active flow control techniques are employed to reduce drag as well as separation. The passive flow control is used to investigate the effect of sinusoidal leading-edge protuberances. It is observed that while the sharp drop-off in lift that typically occurs above stall is diminished, this occurs at the cost of decreased CLmax and critical angle of attack. An active flow control (AFC) system is applied on a simplified form of the CRM-HL (CRM-SHL-AFC) model. A simplified hinge flap has the potential to significantly decrease the necessary fuel burn of conventional transport aircraft; however, in order for this to be feasible, a method must be developed to recover the lift “lost” as a result of this simplification. It is shown that the use of steady jets for AFC results in an increase in the lift, but not to a suitable level. Because unsteady blowing has been shown to generate better performance for the same mass flow, the steady jets are replaced by sweeping jet actuators. The naturally bi-stable nature of sweeping jets takes advantage to create an unsteady AFC system without any moving parts or substantially adding more complexity compared to steady jets. It is shown that by utilizing unsteady blowing, significant improvements can be achieved in augmentation of the lift on the CRM-SHL-AFC.
Richard Axelbaum, Swami Karunamoorthy, Mark Meacham, David Peters,
Available for download on Wednesday, May 15, 2024