Current Projects
Experimentally analyzing and quantifying flow structures remains at the forefront of fluid mechanics research. The inability of simple particle image velocimetry (PIV) to fully capture phenomena in a flow field is directly related to its 2D nature. Attempts to remedy this and produce 3D flow fields have been generally successful through methods such as multi-plane stereo PIV and tomographic PIV. However, these methods require many cameras and complicated setups. Instead, a plenoptic camera can capture a 3D flow field instantaneously with only one camera.
In high speed rotorcraft applications, a large section of the retreating blade undergoes reverse flow due to a high advance ratio. Flow separation at the sharp aerodynamic leading edge during reverse flow (geometric trailing edge) leads to negative lift, pitching moment, and drag penalties. The kinematics of a rotor blade leads to a dynamic stall in reverse flow, which further accentuates the problem by causing unsteady loading. These problems have restricted the maximum forward speed of rotorcrafts to ~250 kts.
Wake surfing is a method of extracting energy from the trailing wing tip vortices of another airplane [1]. The energy is extracted by placing the wing tip of the trailing airplane in the upwash portion of the vortex. The vortex upwash reduces the lift-induced drag of the wing. The trailing aircraft must be flown within a very narrow section of the flow field where the upwind velocity leads to the best aerodynamic performance, which translates to fuel savings, increased range and endurance.
Fifth-Generation fighters such as the F-22 and F-35 favor chine-shaped forebodies which help reduce their Radar Cross-Section. The chine produces strong forebody vortices, which interact with the wing vortices. However, in certain conditions the interaction can produce asymmetric vortex breakdown, non-linear moments and roll departure. Future fighter aircraft will have this issue compounded as, to further reduce their RCS, future-generation fighter aircraft are projected to be tailless, sacrificing lateral control authority.
Separation is an adverse aerodynamic phenomenon resulting in loss of aerodynamic performance. Previous studies on separation have mainly dealt with a two-dimensional analysis due to the assumption that the third dimension was negligible or that it was too complicated to analyze, leading to an incomplete analysis. Literature has indicated however, that this is insufficient in understanding separation and needs to be studied as such as spanwise instabilities have been shown to play a major role in the flow field and physics.
This project is an experimental investigation of separated flows over cantilevered wings with a cross-section NACA 0015. The goal of this research is to link changes in the separated flow field to variations in aspect ratio, angle of attack, Reynolds number, sweep angle, and taper ratio. The results include qualitative surface topology from oil flow visualization, quantitative flowfield measurements using Stereo Particle Image Velocimetry (SPIV) and Time-Resolved Stereo Particle Image Velocimetry.