Turbulent Friction Drag Reduction Using Electroactive Polymer Surfaces

Both experiments and numerical simulations have provided evidence that an initially fully developed two-dimensional boundary layer, subjected to a sudden spanwise forcing, exhibits a decrease of turbulent quantities such as the Reynolds shear stress, turbulent kinetic energy and turbulent friction drag. In past experiments and investigations, such forcing has traditionally been in the form of spanwise wall oscillations, spanwise travelling Lorentz forcing, superimposed spanwise pressure gradients and spanwise travelling waves of an inplane flexible wall. The aim of this work is to take the idea a step further and develop an active surface which locally executes the motions described above making such a system more readily deployable. Two surfaces were developed: both executing in-plane local oscillations with amplitude close to or larger than the mean streak spacing in a turbulent flow, but based on two different technologies, electroactive polymers in the dielectric form of actuation and electromagnetic motor forcing. The effect of these two surfaces was confined to wall-normal heights on the order of the linear sublayer of the turbulent boundary layer, and frequency and wavelength similar to those reported in literature. Extensive hot-wire measurements, some PIV measurements and direct measurement of friction drag using a bespoke drag balance are presented for the systematic variation of the relevant parameters for turbulent friction drag reduction. Electroactive polymers (EAP) are able to undergo relatively large deflections at high frequencies. Developments in the field of EAP such as static and dynamic characterisation of the EAP membranes in use in this work, development of robust electrodes and their characterisation, in-house manufacturing of thin silicone membranes and post-processing of pre-built silicone membranes are presented. Numerical studies of the optimum pre-strain values and of the optimum electrode to passive portions width ratios are presented. Actuator development techniques including EAP membrane pre-stretch in a bespoke jig, EAP membrane pre-conditioning to go past the Mullins' effect, electrode preparation procedure and deposition, and frame preparation are presented. Actuator characterisation results including analysis of multi-flash photographs and laser profilometer scans for in-plane and out-plane deflections at different frequencies are also presented

Structures Division

The NASA Lewis Research Center Structures Division is an international leader and pioneer in developing new structural analysis, life prediction, and failure analysis related to rotating machinery and more specifically to hot section components in air-breathing aircraft engines and spacecraft propulsion systems. The research consists of both deterministic and probabilistic methodology. Studies include, but are not limited to, high-cycle and low-cycle fatigue as well as material creep. Studies of structural failure are at both the micro- and macrolevels. Nondestructive evaluation methods related to structural reliability are developed, applied, and evaluated. Materials from which structural components are made, studied, and tested are monolithics and metal-matrix, polymer-matrix, and ceramic-matrix composites. Aeroelastic models are developed and used to determine the cyclic loading and life of fan and turbine blades. Life models are developed and tested for bearings, seals, and other mechanical components, such as magnetic suspensions. Results of these studies are published in NASA technical papers and reference publication as well as in technical society journal articles. The results of the work of the Structures Division and the bibliography of its publications for calendar year 1995 are presented

Index to 1985 NASA Tech Briefs, volume 10, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1985 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Aeronautical engineering: A continuing bibliography with indexes (supplement 119)

This bibliography lists 341 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1980. Abstracts on the engineering and theoretical aspects of design, construction, evaluation, testing, operation, and performance of aircraft (including aircraft engines) and associated components, equipment, and systems are presented. Research and development in aerodynamics, aeronautics, and ground support equipment for aeronautical vehicles are also presented

Evaluation of 3D Printed Soft Robots in Radiation Environments and Comparison With Molded Counterparts

Robots have an important role during inspection, clean-up, and sample collection in unstructured radiation environments inaccessible to humans. The advantages of soft robots, such as body morphing, high compliance, and energy absorption during impact, make them suitable for operating under extreme conditions. Despite their promise, the usefulness of soft robots under a radiation environment has yet to be assessed. In this work, we evaluate the effectiveness of soft robots fabricated from polydimethylsiloxane (PDMS), a common fabrication material, under radiation for the first time. We investigated gamma-induced mechanical damage in the PDMS materials' mechanical properties, including elongation, tensile strength, and stiffness. We selected three radiation environments from the nuclear industry to represent a wide range of radiation and then submerged a 3D printed hexapus robot into a radiation environment to estimate its operation time. Finally, to test the reliability of the 3D printed soft robots, we compared their performances with molded counterparts. To analyze performance results in detail, we also investigated dimensional errors and the effects of fabrication methods, nozzle size, and print direction on the stiffness of PDMS material. Results of this study show that with increasing exposure to gamma irradiation, the mechanical properties of PDMS decrease in functionality but are minimally impacted up to 20 kGy gamma radiation. Considering the fractional changes to the PDMS mechanical properties, it is safe to assume that soft robots could operate for 12 h in two of the three proposed radiation environments. We also verified that the 3D printed soft robots can perform better than or equal to their molded counterparts while being more reliable

Cumulative index to NASA Tech Briefs, 1970-1975

Tech briefs of technology derived from the research and development activities of the National Aeronautics and Space Administration are presented. Abstracts and indexes of subject, personal author, originating center, and tech brief number for the 1970-1975 tech briefs are presented

Research and technology, 1993. Salute to Skylab and Spacelab: Two decades of discovery

A summary description of Skylab and Spacelab is presented. The section on Advanced Studies includes projects in space science, space systems, commercial use of space, and transportation systems. Within the Research Programs area, programs are listed under earth systems science, space physics, astrophysics, and microgravity science and applications. Technology Programs include avionics, materials and manufacturing processes, mission operations, propellant and fluid management, structures and dynamics, and systems analysis and integration. Technology transfer opportunities and success are briefly described. A glossary of abbreviations and acronyms is appended as is a list of contract personnel within the program areas

Aeronautical engineering, a continuing bibliography with indexes

This bibliography lists 823 reports, articles, and other documents introduced into the NASA scientific and technical information system in November 1984

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

NASA Tech Briefs, September 1990

Topics covered include: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences