Date of Award

June 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical and Aerospace Engineering

Advisor(s)

Melissa A. Green

Keywords

delta wing, dynamic stall, FTLE, surface pressure, unsteady aerodynamics, vortex dynamics

Subject Categories

Engineering

Abstract

Delta wings are triangular-shaped lifting surfaces, and in past decades, they have been found to have important applications in maneuvering combat aircraft and supersonic aircraft. Slender, or high swept, delta wings have been widely studied in early investigations since they suffer less wave drag in supersonic environments. Recently, however, with more and more low-aspect ratio wing applications on UCAVs (Unmanned Combat Aerial Vehicles) and MAVs (Micro Air Vehicles), non-slender delta wing configurations (low-sweep angle) begin to raise interest. The collaborative investigation of flow coherent structure, suction side surface pressure, and aerodynamic forces of non-slender delta wings presented here provides critical insight for effective flow-control development, especially for non-slender delta wings at high angles of attack, or encountering unsteady aerodynamic or atmospheric phenomena. As a baseline for studying non-slender delta wings under axial or vertical acceleration, experiments of steady translation with fixed wings under multiple angles of attack were conducted both in the Center of Excellence at Syracuse University at Re ≈ 20, 000, and in the OTTER lab at Queen’s University at Re ≈ 300, 000. According to the comparison of experimental results from both labs, 3D reconstruction of the flow field exhibits the tendency a ''conical" flow structure departing the wing surface at high angles of attack, and the flow fully stalling.

Force measurements confirmed the static stall angle for both tested Lambda = 45-deg non-slender delta wings in two groups. Similar lift and drag behavior is observed for two non-slender delta wings at Re of 20,000 and 300,000. For the collaborative project, table 3.1, table 4.1 and table 5.1 give detailed information of experimental datasets and corresponding sections in each chapter. Chapters based on collaborator’s experimental results comprise data analysis conducted in the Green Fluid Dynamics Lab.

Axial and vertical accelerated translation experiments were conducted at pre- and post-stall angles of attack in the OTTER lab by that research group. FTLE analysis of this data, and its comparison with surface pressure and aerodynamic forces, were conducted in the Green Fluid Dynamics Lab in the Syracuse University. Sufficiently strong axial accelerations are shown to enable reattachment at the post-stall angle of attack. Meanwhile, the surface pressure distribution reveals a high pressure region created by the axial acceleration, whose motion from leading edge to trailing edge can be indicated by the topology change of nFTLE ridges. This reveals a direct connection of the kinematics (FTLE scalar field) to the aerodynamic performance (surface pressure). The high pressure is followed by a strong leading edge suction, which further confirms the establishment of flow reattachment at the leading edge. The motion of the high pressure region also potentially causes the coefficient of pitching moment to fluctuate under certain circumstances. Hence, the axial acceleration also brings challenge for the flow control along with the increased lift. With a limited magnitude, the tested vertical acceleration does not contribute to a clear flow reattachment. However, it induces more rolled-up coherent structures in the leading edge shear layer. The surface pressure distribution on the suction side exhibits no obvious evolution through the tested vertical acceleration.

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