![Sample our Built Environment journals, sign in here to start your access, Latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5926/TOC-Subject-Sample-2021-Built-Environment.jpg"})
ABSTRACT
Detailed velocity measurements beneath a modelled ice jam with both smooth and rough surfaces were conducted using acoustic Doppler velocimetry and particle image velocimetry. The experiments were conducted at Reynolds numbers based on hydraulic diameter of 28,400 and 72,000. The topography of the mean flow field revealed acceleration and deceleration of the flow within the upper and lower toe sections of the modelled jam, respectively. The introduction of surface roughness increased flow blockage, thereby increasing the maximum streamwise mean velocity within the upper toe section. The estimated bed shear stress attained a maximum within the toe section, with roughness significantly increasing the values. Large vortical structures dominated the flow over the rough surface compared to the smooth case. The present results suggest the possibility of enhanced sediment transport beneath the modelled jam when both bed and ice jam were roughened.
Acknowledgements
We thank Alexander Wall for his assistance in constructing the set-up.
| Notation | ||
| Cf | = | skin friction coefficient (–) |
| h | = | inlet channel height (mm) |
| htoe | = | toe height (mm) |
| Kv | = | acceleration and deceleration parameter (–) |
| Kp | = | pressure gradient parameter (–) |
| k | = | roughness height (mm) |
| ks | = | equivalent sand grain roughness height (mm) |
| = | dimensionless equivalent sand grain roughness (–) | |
| Ruu | = | streamwise correlation function (–) |
| Rvv | = | wall-normal correlation function (–) |
| U | = | streamwise mean velocity (m s−1) |
| Ub | = | bulk velocity (m s−1) |
| Ublocal | = | local bulk velocity (m s−1) |
| Um | = | local streamwise maximum mean velocity (m s−1) |
| Uτ | = | friction velocity (m s−1) |
| u | = | streamwise fluctuating velocity (m s−1) |
| u′ | = | streamwise turbulence intensity (m s−1) |
| V | = | wall-normal mean velocity (m s−1) |
| v | = | wall-normal fluctuating velocity (m s−1) |
| v′ | = | wall-normal turbulence intensity (m s−1) |
| ym | = | wall-normal location of Um (mm) |
| α, β | = | ice jam angles (°) |
| ΔB+ | = | roughness shift (–) |
| κ | = | von Kármán constant (–) |
| τbb | = | bed shear stress (Pa) |
| ν | = | kinematic viscosity (m2 s−1) |