William J. Devenport - US grants

Under a Small Grant for Exploratory Research, a pilot model of a novel non-intrusive laser velocimeter system will be built and tested. The system tracks laser illuminated particles across an array of very small photodiodes and times them with an electronic clock. Multi-dimensional velocity capability is achievable with a single beam and suitable arrangements of diode arrays. The system is in principle much more simple than conventional LDV flow diagnostic systems. If a workable system based on this idea can be developed, it would offer a rugged, portable, and inexpensive alternative for LDV systems.

The objective of this proposal is the development of a series of novel computer-based instructional units in key areas of engineering mechanics that serve as a national model for the development of similar materials throughout engineering and science. The units are centered on instructional programs written in the universally compatible Java programming language, and are made available to all engineering students and educators over the World Wide Web. They are focused, self-contained and independent so that they can be easily integrated into a broad range of engineering courses and curricula. The units are designed to have a significant impact on engineering students, providing them additional materials that promote their understanding of central concepts over a medium that allows independent learning at an individual pace from anywhere in the world. A broadly advertised site on the World Wide Web will contain these peer-reviewed instructional units and similar reviewed materials developed by others. Stimulating the development of similar materials by other instructors is a crucial goal to be accomplished by direct contact with educators at Virginia Tech and its many sister institutions as well as by providing supplementary information over the Web and through scholarly publications and meetings. Evaluation of the educational effectiveness of the units is an integral part of the project. Formative evaluation are used to improve and modify the units based on the responses of users. Both quantitative and qualitative evaluations are performed to assess the effectiveness of the units in terms of the cognitive gains of students who use them.

CBET -0853674
Devenport, William J.

This research program aims to reveal and better understand the fluctuating surface pressure field produced by high Reynolds number rough-wall boundary layers. This pressure field is a source of vibration and noise in many applications. It also provides a measure of the turbulence structure of the boundary layer weighted in favor of the near-wall dynamics. However, there have been remarkably few prior studies of rough-wall boundary-layer pressure fluctuations. Studies have included only a limited set of rough surfaces and there has been little systematic examination of the effects of roughness type or sparseness. Most importantly, there have been almost no measurements of boundary layers with Reynolds number and boundary-layer-to-roughness scale ratios large enough to be free of transitional effects, where universal scalings and behaviors are likely to be observed and are of the most practical and scientific value. The objectives of this study are as follows: to extend the existing database of fluctuating pressure measurements for rough wall boundary layers into the high Reynolds number regime; to extend the database to include stochastic and deterministic surfaces with fully defined geometry and a significant range of sizes and sparseness values; to use these data to establish the low and high-frequency scaling of the rough wall pressure spectrum and the behavior of the convection velocities and the spatial pressure coherence functions; and to provide a cutting-edge research education to a diverse group of students including graduate, undergraduate and high-school students. The PI's experimental approach centers on the new aeroacoustic capabilities provided by the Virginia Tech Stability Wind Tunnel. This facility is both large and acoustically quiet and thus is uniquely suited to pressure fluctuation measurements and the growth of thick, fully developed, high-Reynolds number turbulent boundary layers with smooth or rough walls. A complete program of experiments on high Reynolds number flows over stochastic and deterministic rough surfaces will be performed to directly address the deficiencies in current knowledge. In many situations, such as with wind turbines or aircraft, the noise and vibration are a direct consequence of the fluctuating pressure field of a rough wall turbulent boundary layer. The improved understanding generated by this research will have a direct impact on the accuracy of noise source predictions. This is critical to advancing the environmental acceptability and economic viability of these devices. The Virginia Tech Stability Tunnel is a multi-user facility that draws a wide variety of users including research groups, commercial testing and a range of undergraduate classes. The planned work includes two specific sub-projects to be conducted by groups of undergraduate and high school students. These groups will be mentored by the graduate students involved in the project under the guidance of the PI. This continues a long history of undergraduate involvement in the PI's research group. High school students will be recruited through existing programs with the Southwest Virginia Governor?s School for Science, Mathematics and Technology.

PI: Devenport, William J
Proposal Number: 1436088


The goal of the proposed research is to investigate experimentally and theoretically the scaling of pressure fluctuations in high Reynolds number boundary layers over rough walls. The focus of the work will be on practically and scientifically-relevant conditions at which most vehicles operate and at which universal behaviors are most likely to be observed. Results from the proposed research could have a strong impact on engineering for prediction of sound and vibration produced by boundary layers, and on scientific understanding of pressure effects with the development of a predictive function for rough-wall boundary layer pressure spectra.

The proposed work is based on recent findings that pressure fluctuations within turbulent boundary layers over rough surfaces behave differently that velocity fluctuations, and this different behavior is important. The PI proposes to conduct experiments in a rather unique facility at Virginia Tech to explore the wall-pressure spectrum and the turbulence scales that it reveals. Prior results indicate that there are three different scaling regions (low, medium and high frequency), and the proposed experiments aim to establish the persistence of these scalings, and the physical processes they imply, as the geometry and density of the roughness elements is varied. Proposed are also experiments on a two-scale surface that could lead to the development of an interpolation function for rough-wall boundary layer pressure spectra. The proposed work would be important for the theory of boundary layer turbulence with engineering applications where noise is a concern, such as vehicle design (cars, planes, helicopters) and wind turbines. The proposal also offers a plan to integrate research with education. High school, undergraduate and graduate students will be involved in designing and building parts of the wind tunnel as well as manufacturing of the new rough surfaces, providing a complete hands-on, engineering experience.

This catalytic project development visit led by principal investigator, Kevin Todd Lowe, will initiate new collaboration between researchers at the Center for Renewable Energy and Aerodynamic Testing (CREATe) at Virginia Polytechnic Institute and State University (Virginia Tech) and counterparts in the Department of Wind Energy at the Technical University of Denmark (DTU). Scientists at both institutions have well-established expertise and share common interests in basic and applied research on wind energy systems. Their ongoing activities and existing facilities are fully complementary for addressing component scale wind energy testing (Virginia Tech) with full scale wind turbine research (DTU). A balanced, mutually beneficial match of strengths would position this U.S.-Danish team to make significant future contributions in renewable energy. For broader impact, four U.S. graduate students will participate in the Virginia Tech planning visit to gain valuable early career experience through exposure to the full-scale testing capabilities at DTU. To fully realize plans for follow-on cooperation and proposal preparation, the U.S. and Danish researchers and students will anchor their visit, during September 26-October 4, 2015, with a core planning meeting at the DTU Risø campus where the Department of Wind Energy facilities are located. The primary goal is to jointly outline the next steps for addressing critical needs for research, including education as well as technological development, for wind energy advancement in areas such as noise reduction on wind tunnel blades.

These U.S. and Danish partners have significant and complementary capabilities in wind energy engineering research and education. The DTU team offers world class facilities such as full-scale wind turbine testing up to the 10 megawatt scale and an extensive catalog of courses geared specifically toward the details of wind energy science and technology. Virginia Tech hosts a leading U.S. academic facility for research on wind turbine blade aerodynamics and aeroacoustics, the Stability Wind Tunnel, while offering courses on several fundamental topics in aerodynamics, aeroacoustics, computational fluid dynamics and instrumentation. The partners envision extensive opportunities for research cooperation and collaboration using the unique strengths of both sides. Initial success is expected to produce the data required for validating planned hybrid resolved/modeled turbulence simulations from wind tunnel developments to turbine-scale and farm-scale. Furthermore, integrated graduate student research visits in both directions are to be organized to provide the broad perspective needed by the next generation of scientists and engineers who must tackle important problems in renewable energy. For broader impact, the partners envision incorporating a course exchange and possibly research semesters abroad to more fully build the intended long-term U.S.-Danish collaboration in research and education.

Wind tunnels are a fundamental part of the engineering and scientific process used to develop quieter and more efficient aircraft, wind turbines, and other systems. The hybrid anechoic wind tunnel, introduced some 13 years ago, provides a way to substantially increase the accuracy and scope of wind tunnel tests concerned with flow generated noise. This configuration, which has already been adopted by a number of research facilities across the world relies on ?acoustic windows? ? large panels of tensioned fabric that are transparent to sound but largely impervious to flow. Such windows have been made from commercially available Kevlar fabric which has many desirable characteristics for this purpose, but the fabric was designed for composites manufacture. A Kevlar fabric explicitly designed for wind tunnel applications promises additional benefits ? an even quieter test environment and embedded instrumentation that can monitor the flow. Under this project, an interdisciplinary team of textiles, acoustics, and aerodynamics researchers will conduct a short-term research program to develop these materials. This innovative, potentially high payoff effort, promises to bring the advantages of hybrid anechoic testing to national scale facilities and greatly enhance the development quieter and more efficient vehicles and systems. This project will also be dedicated to research education at the postdoc, graduate and undergraduate levels.

This research is based upon the observation that Kevlar fabric used as acoustic windows generates noise at high frequencies (>10kHz) that potentially limits the application of this technology in the context of national scale wind tunnel facilities that perform applied model scale testing for vehicle development by industry and government. The hypothesis is that the noise is made by pores in the fabric that serve no useful aeroacoustic function. Adjusting the weave to eliminate the pores requires the multi-disciplinary collaboration needed to perform a systematic study of the optimum fabric design for aeroacoustic applications. The work is being performed by a team of researchers from Virginia Tech, Florida Atlantic University, and NC State. The NC State group will use a research loom fabricate the needed modified fabrics and also investigate the feasibility of embedding sensors. Wind tunnel experiments directed at documenting and understanding the aeroacoustic performance of the fabrics will be performed at Virginia Tech, which will also provide input on sensor choices and requirements. Theoretical modeling and understanding of the nature of the acoustic source will be performed at Florida Atlantic University. Together this effort is expected to generate robust recommendations for optimal acoustic window design and embedded sensors that can be adopted by current and planned hybrid anechoic wind tunnels.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.