Designing Culvert Outlet Diffusers to Increase Culvert Capacity and Decrease Outlet Velocity

The objective of this project is to investigate the design of flared outlets (diffusers) as a method of increasing culvert capacity in this time where an aging, yet hard to replace drainage system is being stressed by land use changes and other factors. Inlet and outlet modifications can significantly increase the capacity of existing or slip- lined culverts. Diffusers are used in numerous applications, and the concept was demonstrated in a laboratory setting by Yarnell 1926, Venegas 1950, and Smith 1951. The few field trials in California were apparently inconclusive due to a poor understanding of how the inlet and the outlet diffuser work together to increase flow through the culvert, which has prevented the adoption of this innovation. Since Computational Fluid Dynamics (CFD) modeling can now be easily be done on the Transportation Research and Analysis Computing Center (TRACC) computer, diffusers and associated inlet improvements can now be understood and utilized. This project will continue CFD diffuser research begun in 2011 and presented at the 2012 National Hydraulic Engineering Conference. Continued research will identify a promising subset of designs for physical model testing and demonstration project construction (to be funded by future research grants).