1,721,522 research outputs found
Introduction to Part 1: Introduction to Open Channel Flows
Full text linkIntroduction to Open Channel Flows (Chapter 1). This introduction chapter briefly reviews the fluid properties and some result for static fluids. Then open channel flows are defined
Hydraulic modelling of pipe culverts and low-velocity zones at less-than-design flows
No full textThe impact of waterway crossings and culverts on fish populations have often been underestimated despite their major impact on fish. Recent research in box culverts has shown that they can be more effective in terms of upstream fish passage, but circular pipe culverts are most common. In the current study, the hydrodynamics of smooth pipe culverts operating at less-than-design flows was characterised, including a quantitative estimate of the low-velocity zone relevant to upstream fish passage in a near-full-scale smooth pipe culvert (D = 0.50 m) operating with d/D < 0.5. The flow was sub-critical for all investigated flow conditions. Visual observations and detailed velocity measurements showed high velocities through the entire cross-section, with no obvious low-velocity region in the smooth circular channel. The flow resistance was slightly larger than that in a rectangular channel, for identical boundary roughness and flow conditions. The increased flow resistance was caused by the secondary motion resulting from the circular channel shape, while the skin friction boundary shear stress was less than the total boundary shear stress. The present physical results may serve as a validation data set for future computational fluid dynamics (CFD) modelling to assist with the development of more efficient designs
Full-height sidewall baffles in box culvert to assist upstream fish passage: physical modelling
No full textRiver crossings and culverts are important for delivering a range of socio-economic services, including transportation and hydrological control, but have negative impacts on freshwater river ecology, including small-body-mass native fish species and juvenile of larger fish. In relation to upstream fish passage, the excessive barrel velocities have a major negative impact on weak-swimming fish. Recently, full-height sidewall baffles have been proposed to assist upstream passage of small fish across a wide range of discharges, although the impact on the culvert hydraulics is not well understood. Physical modelling was conducted under controlled flow conditions in a 0.5 m wide rectangular channel, equipped with full-height sidewall baffles. Detailed free-surface and velocity measurements were performed at several locations along and across the channel for a broad range of discharges and baffle geometries. The findings demonstrated a drastic reduction in discharge capacity of the box culverts with the installation of full-height sidewall baffles, with increasing adverse impact as the flow rate increases for a given structure. In many cases when the discharge capacity cannot be compromised, alternative designs may be considered to assist upstream fish passage, e.g. small corner baffles, asymmetrical roughness
Step cavity and gabion aeration on a gabion stepped spillway
Full text linkRecent advances in gabion construction techniques have increased the interest for gabion stepped spillways. The present study investigates the air entrainment process in the stepped cavity of a gabion stepped spillway through physical modelling. The microscopic air-water flow characteristics were investigated using a phase-detection probe, complemented by some video observations. The visual observations indicated a high level of interactions between stepped cavity flow and gabion seepage, including some bubbly flow motion in the gabions. The measurements showed relatively lower aeration, velocity and turbulence levels than that in the mainstream flow. The air-water measurements demonstrated some self-similarity of main flow properties above the pseudo-bottom formed by the step edges at all measured locations
Turbulent mixing induced by rapid gate opening in a canal
Full text linkIn an open channel, the operation of a gate is associated with a lowering of the water level on one side and the generation of a negative surge. Herein some physical modelling of rapid gate opening was studied under controlled flow conditions in a relatively large size facility. The gate opening induced a negative surge travelling upstream into the canal. Detailed free-surface and velocity measurements were performed with three types of roughness. The experiments were repeated 25 times and the results were ensemble-averaged. The propagation of negative surges was gentle and barely perceptible, but very close to the gate. Large free-surface fluctuations and turbulent velocity fluctuations were recorded beneath the negative surge, as well as turbulent Reynolds stresses. For all bed configurations, the data of surge leading edge celerity showed a characteristic trend with an asymptotical value: (U+Vo)/(g×do)1/2 = 1 independently of the bed roughness. The results implied that the bed roughness had little effect within the experimental flow conditions
Major advance for minimum energy loss culverts
No full textHubert Chanson traces the history of culverts, explaining how the development of the minimum energy loss (MEL) culvert in culvert design is a testament to hydraulic engineering expertise. The design of the minimum energy loss culvert, developed by late Professor Gordon McKay, is based upon the concept of minimum head loss and nearly constant total head along the waterway. The first MEL culvert designs were developed for zero afflux, and some solid physical modeling was conducted. The culvert models were typically some 1:12 to 1:36 undistorted geometric scale models with fixed bed. In practice, the MEL culverts must be equipped with adequate drainage to prevent water ponding in the barrel invert. Drainage channels are preferred to drainage pipes. A key feature of the MEL culvert design is the small afflux. While many structures were designed with zero afflux, the optimum design could yield a small, non-zero afflux
“Vegan” culvert: application of hybrid modelling in modern hydraulic structures
No full textA culvert is a covered road structure constructed to pass flood and drainage. Modern society with a raise in environmental awareness demands modification in culvert design to incorporate a fish-friendly perspective. The migration of fish upriver is important for their breeding and feeding activities, contributing to a stable population and species diversity, and culverts have negative impacts on freshwater river system morphology and ecology, including blockage of upstream fish passage. Herein, a review is presented, highlighting the use of hybrid modelling in developing a fish-friendly culvert design solution. The hybrid modelling involves using both physical and numerical Computational Fluid Dynamics (CFD) modelling to test a range of design alternatives. Among the proposed design alternatives, a widening of the smooth culvert barrel proved to be best suited for the primary purpose of a culvert, i.e. flood passage, as well as fish passage. Field test is still needed to verify the effectiveness in practice. Full-height rectangular baffles and longitudinal beams both provided sizable and continuous low velocity zones for fish to traverse. However, relatively high turbulence can be induced by full-height baffles and the impact on fish behavior is unknown. The installation and maintenance of these two types of intrusive structures can also be difficult, while both reduce the flood capacity of the culvert by 30 to 50%
Hydraulic structures and society - Engineering challenges and extremes in perspective
Full text linkA hydraulic structure is an artificial system which interacts with the flow of water. A number of engineering challenges are closely linked to the hydrodynamics and fluid flow motion. Two key issues during the design and operation of hydraulic structures are conveyance and energy dissipation. The energy dissipation at a hydraulic structure can be enormous and its estimate is far from trivial. The re-evaluation of spillway discharge capacity, including the spillway re-design, is a further challenge, especially in the regions with extreme hydrology and limited records. Our community needs to broaden the knowledge base in hydraulic structures, through the development of independent learning skills, further education in hydraulic engineering and innovative research and development (R&D). It is believed that the proceedings of the 5th IAHR International Symposium on Hydraulic Structures (ISHS2014) provide the engineering profession with real-world state-of-the-art expertise in hydraulic structure design
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