Turbulence characteristics of flow in a full-scale spiral corrugated culvert fitted and sloped- and slotted-weir baffles

Ryan Richard Morrison

Baffles are often used to retrofit culverts to aid in the upstream passage of fish in spite of a lack of research regarding the effect baffles have on the turbulent structure of flow through culverts. The purpose of this experimental investigation was to examine the turbulent flow structure inside a full-scale spiral corrugated culvert fitted with sloped- and slotted-weir baffles. This purpose was accomplished through three objectives: - Objective 1: Compare the turbulence heterogeneity created by sloped-weir and slotted-weir baffles. - Objective 2: Compare turbulence parameters to available data for non-baffled culverts. - Objective 3: Compare turbulent kinetic energy values in a culvert fitted with sloped-weir and slotted-weir baffles to energy dissipation factor calculations suggested by various state fish passage design manuals. The objectives were completed through the collection of velocity measurements in a 1.83 m diameter, 12.2 m long corrugated metal culvert fitted with sloped- and slotted-weir baffles. Three baffles were spaced 4.57 m apart with the central baffle located 6.71 m from the culvert inlet. Measurements were collected at six cross sections using a Sontek Micro-acoustic Doppler velocimeter (MicroADV) for flow rates of 0.043, 0.085, 0.113, and 0.198 m3/s and culvert slopes of 1.14, 3.00, and 4.33%. The results show there are only minor differences in the turbulent flow structure created by each baffle type. The most significant differences included higher lateral turbulent intensity (TIl) values on the edges of the jet created by the slotted-weir baffles, and higher turbulent kinetic energy (TKE) values on the left side of the culvert (looking downstream) caused by the sloped-weir baffles. At 4.32 m downstream from a slotted-weir baffle, a reduced velocity zone (RVZ) was produced on the left side of the flow that contained streamwise velocities 36% of the velocities in the center of the culvert, similar to the RVZ produced in a bare culvert. Streamwise turbulent intensities also were reduced in this area. The sloped-weir baffles produced a less noticeable RVZ on the right side of the flow. This study was limited by the inability of the MicroADV to collect data in highly aerated flow conditions that exist downstream from baffles and near the culvert edge. The results also indicate that the use of the energy dissipation factor (EDF) equation does not adequately describe the energy contained in turbulent flow downstream from a baffle. The TKE produced by water plunging over a baffle was nearly 100 times greater than that predicted by the EDF equation. Furthermore, there were no correlations found between the measured TKE values and the predicted EDF values.

Turbulence characteristics of flow in a full-scale spiral corrugated culvert fitted and sloped- and slotted-weir baffles

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