Date of this Version
Zhang,C.(2023) Energy Dissipation Optimization For Circular Culverts [Unpublished master's thesis]. University of Nebraska - Lincoln.
The principal goal of the current research is to develop and improve weir-based energy dissipator designs at the outlets of circular culverts. In the present case, we are interested in full-length weirs and staggered weirs. A review of related literature was completed and reported; a test facility was carefully designed and constructed to collect flow information in a basin downstream of a model broken-back circular culvert; instrumentation was installed to measure discharges, streamwise depths, and velocities. Both full-length and staggered weirs were tested over a range of discharges and tailwaters. The two types of weirs were subjected to two types of tests: (1) tailwater-independent tests and (2) tailwater-influenced tests. The tested weir heights ranged from D/8 to 4D/8, in which D is the culvert diameter. Data was processed to assess energy dissipation and hydraulic jump position associated with each dissipator configuration.
Dissipation basin outlet depths predicted with a simple weir equation, some general assumptions about the flow upstream of the weir, and the energy equation with no head losses were reasonably close to measured outlet depths for the tallest full weirs (weirs with heights of 3D/8 and 4D/8). For the shorter weirs (weirs with heights of D/8 and 2D/8), the flow appeared to skim the weir and the weir equation was invalid, especially for high discharges.
Within the range of testing conditions, the optimal weir heights for full weir and staggered weir are 4D/8 and 3D/8. Once the optimal dissipation is achieved for full weir, increasing the height of the weir will only reduce the total energy dissipation of the weir/expansion/culvert system; the same is not necessarily true for the staggered weir, for which some flow does not pass over the weir. The geometry of the staggered weir can be altered to optimize its design.
Forcing the toe of the jump to approach the culvert break for all tested discharges required the outlet of the culvert to be submerged to about 1.1D by the tailwater. This result was independent of the weirs that were tested because at this submergence the weirs had little influence on energy dissipation. The result was not independent of discharge, and higher discharges than those tested may require greater submergence. However, raising the weir to achieve full submergence is not advisable based on the present observations since taller weirs will lead to higher basin outlet velocities. Forcing a jump to form within the runout section does not appear to be optimal for energy dissipation purposes. Testing taller weirs would help corroborate this observation.
Advisor: David M. Admiraal