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Open channel flow
Published in Amithirigala Widhanelage Jayawardena, Fluid Mechanics, Hydraulics, Hydrology and Water Resources for Civil Engineers, 2021
Amithirigala Widhanelage Jayawardena
Open channel flow refers to flows in which the surface of flow is at atmospheric pressure. They may be natural or artificial by origin, prismatic or non-prismatic by geometry (prismatic channels have uniform cross section and constant slope). Examples include rivers, canals, flumes, sewers running partly full, etc. Forces acting are the gravity (driving force) where the Froude number is important and the viscous shear at the boundary (retarding force) where the Reynolds number is important. Therefore, both Re1 and Fr are important in open-channel flows.
Intakes and outlets
Published in Willi H. Hager, Anton J. Schleiss, Robert M. Boes, Michael Pfister, Hydraulic Engineering of Dams, 2020
Willi H. Hager, Anton J. Schleiss, Robert M. Boes, Michael Pfister
The presentation of data is improved as compared with Montes (1997), because flows with a scale effect are excluded. Note that Hp(0) = 0.618 is close to the critical depth of open-channel flow. The transition from subcritical upstream to supercritical downstream gate flow is thus forced by gate presence. Note also the steep pressure head gradient close to X = 0. Figure 8.28b shows the underflow of a standard gate, with a typical stagnation vortex at the upstream surface. The effect of non-hydrostatic pressure is confined to −2 < X < +2, as for the velocity field.
Open Channel Flow
Published in Ahlam I. Shalaby, Fluid Mechanics for Civil and Environmental Engineers, 2018
Given that the flow in the open channel is uniform (there are no channel or flow transitions), the occurrence of a particular flow regime is dictated by the classification of the channel bottom slope, So (mild, steep, or critical). The classification of the slope will depend on the channel roughness, the actual magnitude of the slope, and the discharge. Thus, if the channel bottom slope is mild, then the uniform open channel flow is a deep slow moving flow, known as subcritical flow (most common flow regime in open channel flow), and F = v/vc < 1. If the channel bottom slope is steep, then the uniform open channel flow is a shallow fast-moving flow, known as supercritical flow, and F = v/vc > 1. However, if the channel bottom slope is in between mild and steep, and at a critical slope, then the uniform open channel flow is at a critical depth and at a critical velocity, known as critical flow, and F = v/vc = 1.
Storm sewer pipe renewal planning considering deterioration, climate change, and urbanization: a dynamic Bayesian network and GIS framework
Published in Sustainable and Resilient Infrastructure, 2023
Yekenalem Abebe, Solomon Tesfamariam
Storm sewer system hydraulic capacity analysis requires runoff generation modeling, overland flow routing (1D or 2D simulation) and sewer flow modeling (1D simulation). Flow routing in a storm sewer network can be a dynamic model resolving continuity and momentum water equations or conceptual models that satisfy only the continuity equation (Ochoa-Rodríguez, 2013). Dynamic hydraulic models are computationally and time-intensive and require extensive data. In this paper, the likelihood of capacity failure is estimated based on the residual capacity of a pipe, by comparing the intended design capacity with the estimated current flow (Figure 2). Since, the initial design considerations and detail design document may not be available, it is proposed to use Manning’s equation to quantify the design capacity of pipes. The Manning’s equation provides an empirical approximation for rough turbulent open channel flow based on three parameters: channel slope, flow rate, and area (Dingman & Sharma, 1997). The parameter data can be collected from the city’s asset inventory record. If original design documents are available, they can be verified by comparing calculated capacities with those provided in the studies.
Numerical study of a symmetric submerged spatial hydraulic jump
Published in Journal of Hydraulic Research, 2020
Vimaldoss Jesudhas, Ram Balachandar, Tirupati Bolisetti
The hydraulic jump is an open-channel flow phenomenon which occurs when the flow evolves from a supercritical state to a subcritical flow state. This evolution is characterized by strong turbulence, free-surface fluctuations, flow separation, reattachment, air entrainment and energy dissipation. Over the years, several researchers (Chanson & Brattberg, 2000; Ohtsu, Koike, Yasuda, Awazu, & Yamanaka, 1990; Rajaratnam, 1967; Vischer & Hager, 1995) have experimentally studied the internal structure of a classical hydraulic jump (CHJ), i.e. the jump occurring in a regular rectangular prismatic, frictionless, horizontal channel. While these studies have generated improved empirical relationships for calculating the design parameters of hydraulic jumps, their internal structure has not been fully explored. This is due to the inherent limitations of the presently available measuring devices in air–water multiphase flow (Boyer, Duquenne, & Wild, 2002). Conductivity probes (Chachereau & Chanson, 2011; Chanson, 2002, 2007; Zhang, Wang, & Chanson, 2013) and optical probes (Mouaze, Murzyn, & Chaplin, 2005; Murzyn, Mouaze, & Chaplin, 2007) have been used to study the air–water flow characteristics of the classical hydraulic jump. However, these devices are intrusive and are often sensitive to sampling parameters (Felder & Chanson, 2015; Felder & Pfister, 2017). Following the recent advance in computing power, researchers have been successful in simulating the three-dimensional (3D) flow field of the classical hydraulic jump (Witt, Gulliver, & Shen, 2015; Jesudhas, Balachandar, Roussinova, & Barron, 2018). Jesudhas et al. (2018) demonstrated the capabilities of the improved delayed detached eddy simulation (IDDES) in conjunction with volume of fluid (VOF) with high resolution interface capturing (HRIC) in evaluating the internal turbulent structure of a high Froude number CHJ.