Flowfield Evolution vs. Lift Coefficient History for Rapidly-Pitching Low Aspect Ratio Plates

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90678/1/AIAA-2011-3118-471.pd

Free-to-Pivot Flat Plates in Hover for Reynolds Numbers 14 to 21,200

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140682/1/1.j053169.pd

Trends in Early Vortex Formation on a Wall-to-wall Plate in Pure Plunge

Discernible trends in early vortex formation have been in inter vortex-plate distance, circulation, and vortex maximum azimuthal velocity when plunging a wall-to-wall flat plate at fixed angles of attack ranging from 15o to 90o with two different accelerative profiles. Vortex formation and shedding continues to play an important role in unsteady aerodynamics with applications ranging from flapping wings to maneuvering flight to helicopter rotors. Above a relatively low angle of attack when a flat plate is plunged in a fluid a leading edge vortex (LEV) is formed close to the leading edge and a trailing edge vortex (TEV) is formed close to the trailing edge. The formation, growth and convection of the LEV and TEV strongly influence the pressure field surrounding the flat plate and ultimately the forces experienced by the plate. Experiments were performed at the United States Air Force Research Labs Horizontal Free Surface Water Tunnel (AFRL/HFWT) with linear and sinusoidal acceleration profiles. The formation of the LEV was investigated for both acceleration profiles using Particle Image Velocimetry (PIV). Trends were identified in both the LEV distance to the plate as a function of convective distance and with angle of attack. Similarly, trends were identified in maximum vortex azimuthal velocity. The LEV normalized azimuthal velocity profiles were compared with several vortex models in the literature. The existing models were unable to reproduce the asymmetric azimuthal velocity distributions resulting from vortex proximity to the plate. A new model based on experimental results is proposed for the LEV core azimuthal velocity distribution inclusive of plate proximity effects

Experiments and Computations on Abstractions of Perching

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83613/1/AIAA-2010-4943-835.pd

Thoretical, computational and experimental studies of a flat plate undergoing high-amplitude pitching motion

A pitch-up, hold, pitch-down motion for a flat plate is studied using theoretical, computational (immersed boundary method), and experimental (water-tunnel) methods. This motion is one of several canonical pitch motions introduced by the AIAA Fluid Dynamics Technical Committee's Low Reynolds Number Discussion Group. An inviscid theoretical method that is applicable to non-periodic motions and that accounts for large amplitudes and nonplanar wakes is employed. Results from theory are compared against those from computation and experiment which are also compared with each other. The variation of circulatory and apparent-mass loads as a function of pivot location for this motion is examined. The flow phenomena leading up to leading edge vortex shedding and the limit of validity of the inviscid theory in the face of vortex dominated flows is investigated. Also, the effect on pitch amplitude on leading edge vortex shedding is examined and two distinctly different vortex dominated flows are studied using dye flow visualizations from experiment and vorticity plots from computation

An unsteady airfoil theory applied to pitching motions validated against experiment and computation

An inviscid theoretical method that is applicable to non-periodic motions and that accounts for large amplitudes and non-planar wakes (large-angle unsteady thin airfoil theory) is developed. A pitch-up, hold, pitch-down motion for a flat plate at Reynolds number 10,000 is studied using this theoretical method and also using computational (immersed boundary method) and experimental (water tunnel) methods. Results from theory are compared against those from computation and experiment which are also compared with each other. The variation of circulatory and apparent-mass loads as a function of pivot location for this motion is examined. The flow phenomena leading up to leading-edge vortex shedding and the limit of validity of the inviscid theory in the face of vortex-dominated flows are investigated. Also, the effect of pitch amplitude on leading-edge vortex shedding is examined, and two distinctly different vortex-dominated flows are studied using dye flow visualizations from experiment and vorticity plots from computation