Aeronautical Engineering. A continuing bibliography, supplement 115

This bibliography lists 273 reports, articles, and other documents introduced into the NASA scientific and technical information system in October 1979

Wake-induced `slaloming' response explains exquisite sensitivity of seal whisker-like sensors

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of Fluid Mechanics 783 (2015): 306-322, doi:10.1017/jfm.2015.513.Blindfolded harbour seals are able to use their uniquely shaped whiskers to track vortex wakes left by moving animals and identify objects that passed by 30 s earlier, an impressive feat, as the flow features have velocities as low as 1 mm s−1. The seals sense while swimming, hence their whiskers are sensitive enough to detect small-scale changes in the flow, while rejecting self-generated flow noise. Here we identify and illustrate a novel flow mechanism, causing a large-amplitude ‘slaloming’ whisker response, which allows artificial whiskers with the identical unique undulatory geometry as those of the harbour seal to detect the features of minute flow fluctuations when placed within wakes. Whereas in open water the whisker responds with very low-amplitude vibration, once within a wake, it oscillates with large amplitude and, importantly, its response frequency coincides with the Strouhal frequency of the upstream cylinder, making the detection of an upstream wake and an estimation of the size and shape of the wake-generating body possible. This mechanism has some similarities with the flow mechanisms observed in actively controlled propulsive foils within upstream wakes and trout swimming behind bluff cylinders in a stream, but there are also differences caused by the unique whisker morphology, which enables it to respond passively and within a much wider parametric range.The authors acknowledge with gratitude support by ONR, monitored by Dr. Thomas Swean, Jr. under grant N00014-13-1-0059, the William I. Koch Chair in Marine Technology, the MIT Sea Grant Program, and the Singapore National Research Foundation through the Singapore-MIT Alliance for Research and Technology: Center for Environmental Sensing and Modeling (CENSAM).2016-04-1

Aeronautical Engineering: A continuing bibliography, supplement 120

This bibliography contains abstracts for 297 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1980

Aeronautical Engineering: A special bibliography with indexes, supplement 48

This special bibliography lists 291 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1974

Aeronautical engineering: A continuing bibliography, supplement 122

This bibliography lists 303 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1980

Aerodynamics of Wings in Tandem at Low Reynolds Numbers

The aerodynamic interactions between two wings of NACA0012 section arranged in tandem configuration were experimentally investigated at low Reynolds number of 20,000 and 100,000 in the wind tunnel and water tunnel. The force/moment measurements, wake surveys, and flow visualization results at pre and post-stall angles of attack ranging from -90 to +90 degrees were compared with the data of the isolated wing to determine the aerodynamic interactions. At Re = 20,000, a highly nonlinear lift response was observed without discrete stall and four distinct lift behavior regions. Flow visualization revealed laminar instability waves, vortex shedding, and complex interactions between surface vortices and trailing edge vortices in the wake. At Re = 100,000, conventional lift behavior was exhibited with a linear lift curve at pre-stall angles of attack, abrupt leading-edge stall, and static stall hysteresis. Surface flow visualization showed signatures of laminar separation bubble and progression with changing angle of attack. For the tandem configuration, three test cases consisted of: 1) changing the angle of attack of upstream wing while holding the downstream wing at fixed angles of attack; 2) holding the upstream wing at fixed angles while sweeping the downstream wing; and 3) simultaneously varying the angles of attack of both wings. Results highlighted complex aerodynamic couplings between the wings in tandem configurations in the form of upstream wing wake induced downwash on the downstream wing, modifying local velocity and turbulence intensity, altering the pressure distribution and wake trajectory depending on the relative geometric angle, stagger, and gap. The interactions manifest themselves as boundary layer transition, separation, and vortex shedding for each wing. The combined L/D ratio improved in the post-stall region and a novel “secondary stall” phenomenon was observed in the form of a sudden decrease in lift and drag of the upstream wing. Secondary stall showed dependence on wing spacing and angle of attack but was independent of Reynolds number and aspect ratio. Flow visualization indicated that the downstream wing suppressed vortex shedding from the upstream wing at a critical distance by preventing shear layer interaction that reduced lift and drag simultaneously. Spectral analysis of signals from hotwire and force sensor confirmed the aeroelastic coupling between the wake turbulence and wings for relative positions of the wings

Aeronautical Engineering: A special bibliography with indexes, supplement 74

This special bibliography lists 295 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1976

Development of cost-effective alternatives to conventionally-manufactured metal foam for industrial turbine combustors

The work presented here aims to provide design guidelines to create vortex-damping structures. A design of experiment was developed to investigate the individual and combined effects of the geometrical properties of planar regular grid structures, i.e., the wire diameter, the porosity, and the inter-grid spacing, on their vortex-breakdown performance. The simulations were carried out using a commercial unsteady RANS solver. The model relies on the Von Karman street effect to generate vortices in a pipe which are convected downstream, where they interact with an array of grids. The vortex-breakdown efficiency is characterized by the pressure drop, the residual turbulent kinetic energy, the flow homogeneity, and the size of the transmitted vortices. The wire diameter is shown to be an important design lever as it affects the level of distortion of the transmitted vortices. Increasing the number of grids augments the pressure loss, but their contribution to vortex breakdown is otherwise limited when the wire diameter is small. The influence of grid spacing strongly depends on the wire diameter and grid alignment. For instance, minimizing this gap reduces the pressure drop for the inline configurations, but increases the pressure drop for the offset configurations. Ultimately, the optimal design should be a graded structure, starting with a very porous grid made from a large wire diameter to breakdown the incoming vortices. Additional grids should be rotated and offset to increase the tortuosity, as it improves the velocity homogeneity. The wire diameter of the subsequent grids should be progressively smaller to reduce the TKE. The spacing between the grids should be as large as possible and their numbers must be kept to a minimum to avoid excessive pressure losses. The porosity should only be reduced when the desired velocity uniformity cannot be obtained by other means

Aeronautical Engineering: A continuing bibliography with indexes, supplement 163

The bibliography lists 387 reports, articles and other documents introduced into the NASA scientific and technical information system in June 1983