Leading-edge flow criticality as a governing factor in leading-edge-vortex initiation in unsteady airfoil flows

A leading-edge suction parameter (LESP) that is derived from potential flow theory as a measure of suction at the airfoil leading edge is used to study initiation of leading-edge vortex (LEV) formation in this article. The LESP hypothesis is presented, which states that LEV formation in unsteady flows for specified airfoil shape and Reynolds number occurs at a critical constant value of LESP, regardless of motion kinematics. This hypothesis is tested and validated against a large set of data from CFD and experimental studies of flows with LEV formation. The hypothesis is seen to hold except in cases with slow-rate kinematics which evince significant trailing-edge separation (which refers here to separation leading to reversed flow on the aft portion of the upper surface), thereby establishing the envelope of validity. The implication is that the critical LESP value for an airfoil–Reynolds number combination may be calibrated using CFD or experiment for just one motion and then employed to predict LEV initiation for any other (fast-rate) motion. It is also shown that the LESP concept may be used in an inverse mode to generate motion kinematics that would either prevent LEV formation or trigger the same as per aerodynamic requirements

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

Theoretical Analysis of Quality of Conventional Beamforming for Phased Microphone Arrays

A theoretical study is performed to analyze the directional response of different types of microphone array designs. 1-D (linear) and 2-D (planar) microphone array types are considered, and the delay and sum beamforming and conventional beamforming techniques are employed to localize the sound source. A non-dimensional parameter, G, is characterized to simplify and standardize the rejection performance of both 1-D and 2-D microphone arrays as a function of array geometry and sound source parameters. This parameter G is then used to determine an improved design of a 2-D microphone array for far-field sound localization. One such design, termed the Equi-area array is introduced and analyzed in detail. The design is shown to have an advantageous rejection performance compared to other conventionally used 2-D planar microphone arrays

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

Duncan Macrae. Legible Religion: Books, Gods, and Rituals in Roman Culture. Cambridge, Mass. and London: Harvard University Press, 2016. Pp. 272. [Book review]

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90737/1/AIAA-2011-6527-603.pd

Experiments on Free-to-Pivot Hover Motions of Flat Plates

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83602/1/AIAA-2010-4456-518.pd

Experiments and Computations on Abstractions of Perching

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