Start Date
4-30-2025 1:30 PM
Description
Existing physically based methods for estimating stepped chute friction factors or energy dissipation rates consider relative step height and relative step-tip spacing to be key factors, but do not fully account for chute slope and associated step orientation. For slopes steeper than 45° each step acts as an offset into the flow, while for flatter slopes each step presents an offset away from the flow, but methods that consider only the step-tip spacing do not account for this difference. Furthermore, most experimental studies have been performed in open channel spillway models, where two-phase air-water flow and variable flow depths make it difficult to isolate the effects of geometric factors, and relations developed in studies restricted to narrow slope ranges (either steep or mild) do not extrapolate accurately into other slope ranges. To address these limitations, this study reports physical tests and complementary computational fluid dynamics simulations that isolate the geometric factors influencing flow resistance in stepped chutes. A water tunnel facility that prevents aeration and stabilizes flow properties over multiple steps was used to determine the effects of relative step height and chute slope (i.e., step orientation). Preliminary results suggest stepped chute flow resistance can be related to the Moody diagram or Colebrook-White equation, providing a robust physical framework for determining friction factors. A key finding is that the effective roughness height of steps is directly related to the tangent of the chute slope over the full range of practical slopes.
Included in
Physically Based Assessment of Flow Resistance in Stepped Chutes
Existing physically based methods for estimating stepped chute friction factors or energy dissipation rates consider relative step height and relative step-tip spacing to be key factors, but do not fully account for chute slope and associated step orientation. For slopes steeper than 45° each step acts as an offset into the flow, while for flatter slopes each step presents an offset away from the flow, but methods that consider only the step-tip spacing do not account for this difference. Furthermore, most experimental studies have been performed in open channel spillway models, where two-phase air-water flow and variable flow depths make it difficult to isolate the effects of geometric factors, and relations developed in studies restricted to narrow slope ranges (either steep or mild) do not extrapolate accurately into other slope ranges. To address these limitations, this study reports physical tests and complementary computational fluid dynamics simulations that isolate the geometric factors influencing flow resistance in stepped chutes. A water tunnel facility that prevents aeration and stabilizes flow properties over multiple steps was used to determine the effects of relative step height and chute slope (i.e., step orientation). Preliminary results suggest stepped chute flow resistance can be related to the Moody diagram or Colebrook-White equation, providing a robust physical framework for determining friction factors. A key finding is that the effective roughness height of steps is directly related to the tangent of the chute slope over the full range of practical slopes.