CBET Award Achievements
Notable Accomplishments from CBET Awards

Advanced Turbulence Instrument Sheds Light
on the Microscopic Variations of Flow Near Walls

Roger Simpson  -  Virginia Polytechnic Institute and State University

Background:  Despite its occurrence in all practical macroscopic engineering flows, the available measurement tools have limitations which preclude full analysis of turbulent flows over bodies. The central problem is that many scales of flow phenomena within the turbulence are important for predicting the resulting flow field, but resolving all these scales is computationally impossible in many practical applications. To make engineering decisions, mathematical models for the flow effects due to ranges of flow scales are devised using laboratory data from similar flow situations. Unfortunately, complete datasets are rare due primarily to limitations in instrumentation available to researchers.

Results:  With the comprehensive laser Doppler velocimetry instrumentation (CompLDV) developed, research in wall-bounded flows such as those over an aircraft has been given a new tool. The third generation of this instrument currently being applied to practical test flows employs a novel use of the Doppler shift of light to obtain velocity and acceleration measurements of sub-micron particles following the turbulent shear flow due to a boundary with spatial resolution of about 3 microns. The laser beam probe volume may be placed within about 15 microns of a flow boundary to get details of the turbulent flow which changes very rapidly in the vicinity of the wall. With these data, new measurements of the microscopic structure of the flow adjacent to the boundary are being obtained and analyzed. Since this region directly results in the friction exerted by the fluid on the boundary, these results are of fundamental engineering importance for designing more efficient vehicles.

Roger Simpson Image 1
A Probe hardware in the Boundary Layer
Research Wind Tunnel for the CompLDV
measurement system.

Credit:  Roger L. Simpson, Virginia Tech

Roger Simpson Image 2
Laser beam configuration in the
Boundary Layer Research Wind Tunnel
for the CompLDV system..

Credit:  Roger L. Simpson, Virginia Tech

This work is notable because it is providing new information and capabilities not obtainable with previous instrumentation to improve the analysis tools available to engineers to make more efficient transportation systems.

This work involves multidisciplinary research in the fields of optics, electronics, signal processing and fluid dynamics.

Program Officer:   Michael Plesniak
NSF Award Number:   0233653
Award Title:   Direct Measurements of Dissipation Rate and Determination of the Velocity/pressure-gradient Correlation in Complex High Reynolds Number Turbulent Flows
PI Names:   Roger Simpson
Institution Name:   Virginia Polytechnic Institute and State University
Program Element:   1443
CBET Nugget:   FY 2006

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This Nugget was Updated on 24 September 2008.