The primary purposes of the Federal Highway Administration’s (FHWA’s) aerodynamics research are to evaluate new designs; investigate performance problems of inservice structures; develop effective retrofit solutions; establish the aerodynamic properties of structures and structural components; support the development of new design guides and specifications; develop more effective experimental procedures and simulation methods; and explore fundamental wind engineering problems.
FHWA operated an Aerodynamics Laboratory at the Turner-Fairbank Highway Research Center from the 1950s through 2018. That laboratory is now closed. Current aerodynamics research is focused on completing data analysis and documentation of the experiments conducted in the laboratory.
The Aerodynamics Laboratory was used to study the complex interactions between wind and bridges or other highway structures, including design, stability, safety, and performance of highway structures under all combinations of geographical and meteorological wind conditions.
Figure 1. Bridge deck model mounted in front of large wind tunnel.
The Aerodynamics Laboratory was the only wind tunnel facility in the United States dedicated solely to the study of wind effects on transportation structures. It has the longest continuous history of exploring bridge aerodynamics to ensure the performance and safety of long-span bridges in strong winds and to advance our understanding of wind effects on transportation structures.
The laboratory was federally-owned and staffed by a team of experienced scientists and engineers in the areas of structural engineering, aerodynamics, experimental methods, computational fluid dynamics, and wind engineering.
Figure 2. Setting up test to evaluate pressure-sensitive paint in the small-scale, closed-circuit wind tunnel.
Recent Accomplishments and Contributions:
- Monitored the site wind conditions and aerodynamic performance of several major structures to validate the effectiveness of wind tunnel simulations and aerodynamic mitigation measures.
- Compiled a comprehensive database of wind tunnel results from tests conducted on long span bridges located in North America.
- Completed unique wind tunnel tests on a full-scale section model of a bridge stay cable to assess the influence of helical fillets, high-density polyethylene (HDPE) pipe roundness, damping, and wind turbulence on aerodynamic stability.
- Developed and implemented a unique robotic device to climb bridge stay cables and survey the roundness of in situ HDPE pipe.
- Completed survey of HDPE pipe shape properties from dozens of in situ stay cables at seven bridge sites for use in compiling a catalog of representative pipe properties.
- Completed unique wind tunnel force measurements on rigidly mounted section models of assumed and actual out-of-round bridge stay cable shapes.
- Initiated unique wind tunnel response measurements on elastically suspended section models of assumed and actual out-of-round bridge stay cable shapes in conjunction with analytical studies to better define design requirements for improved aerodynamic performance of cables.
- Developed a computational fluid dynamics (CFD) model to simulate and evaluate the effects of natural wind and truck-induced gust loading on large variable message sign (VMS) structures.
- Developed a CFD model to simulate and evaluate the effects of bridge tower and deck wakes on the safety of high-sided vehicles (trucks) and to aid in studying the effective design of wind screens.
- Updated and extended a comprehensive, searchable bibliography of publications regarding the subject of bridge stay cable aerodynamics.
- Conducted an extensive series of static wind tunnel tests on uniform (as well as tapered) circular and multisided cylinders (representative of those used in highway support structures) to establish a catalog of aerodynamic properties for improved design.
- Completed a series of full scale vibration tests on the stay cables of three bridges under construction to establish the in situ dynamic properties of representative cables and cable networks for use in study of cable aerodynamics and evaluating the effectiveness of mitigation measures.
- Developed a CFD model to simulate and evaluate the aerodynamic interference effects of twin deck bridges.
- Instrument design.
- High-performance computation for bridge aerodynamics simulation and analysis.
- Structural analysis.
- Full-scale testing and analysis.
- Wind tunnel experiments (especially fit for bridge applications).
- Long-term monitoring of structural and wind conditions.
To advance the state of the art in wind engineering, bridge engineering, and the complex interaction of wind and highway structures while contributing to the continuous development of a modern, technically advanced, and structurally safe transportation system.
The dramatic collapse of the Tacoma Narrows Bridge in 1940 sparked a major investigation into the effects of wind on suspension bridges. To coordinate the many activities that were to be undertaken, the Advisory Board on the Investigation of Suspension Bridges was formed. The Board was broadly representative of engineers responsible for specific suspension bridges, research engineers having competence in aerodynamics and suspension bridge theory, and representatives of industry with demonstrated ability and leadership in the fabrication and erection of suspension bridges.
The Bureau of Public Roads (later the Federal Highway Administration), embarked upon a broad research program that involved coordinating national and international wind investigations, sponsoring contract research, conducting laboratory and field studies in-house, and providing technical guidance through committees, panels, or research councils.
The Bureau made a careful survey of existing wind tunnel facilities in the United States to determine if one might be adapted to study the effects of wind forces on suspension bridges. The results of the study determined that it would be more cost effective and expeditious to build a specialized facility. During the 1950s, the Aerodynamics Laboratory and wind tunnel were designed, constructed, and placed into service at the Turner-Fairbank Highway Research Center (TFHRC) in McLean, VA. The facilities, which evolved from this research program, are unique in the Nation. The Aerodynamics Laboratory had the only wind tunnel specifically designed for and dedicated to ensuring the aerodynamic stability of transportation structures, especially long-span bridges. The main wind tunnel, with its relatively large cross section, produces laminar flow and is very stable at low velocities. Its size and velocity range enable both static and dynamic investigations of large-scale section models of structures and structural components. The significance of structural details can be evaluated as well. A computer-driven turbulence simulation system is available to introduce properly scaled gusting into the air flow during testing. This system was the first of its kind in the world. To measure wind forces on sectional models, a high-frequency, dual force-balance system is available. Although other wind tunnels use high-frequency balances, the wind tunnel at TFHRC is unique because it is actually two matched balances in one system and can be used to directly measure unbalanced loads on the structural model.
To complement the research and development activities associated with wind tunnel experiments, the activities of the laboratory were expanded. Over the years, laboratory activity grew to include more full-scale studies, with many bridges across the United States instrumented and analyzed. Staff also worked to develop numerical and computational modeling of fluid and structural behavior interaction, particularly for long-span bridges.