The Wall Pressure Field Of High Reynolds Number Rough-Wall Turbulent Boundary Layers

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

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.