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  • 1.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Experimental study and 3D numerical simulations for a free-overflow spillway2006In: Journal of Hydraulic Engineering, ISSN 0733-9429, E-ISSN 1943-7900, Vol. 132, no 9, p. 899-907Article in journal (Refereed)
    Abstract [en]

    The main objectives of the present work were to investigate the flow field over a spillway and to simulate the flow by means of a three-dimensional (3D) numerical model. Depending on the wall curvature, the boundary layer parameters decreased or increased with increasing distance along the spillway. The growth of the boundary layer along the spillway is better described as a function of Reynolds number than the normalized streamwise length. A simplified form of the 3D momentum equation can be used to obtain a rough estimate of the skin friction. The velocity profile in the boundary layer along the spillway is described by a velocity-defect relationship. Numerical models provide a cost-effective means of simulating spillway flows. In this study, the water surface profiles and the discharge coefficients for a laboratory spillway were predicted within an accuracy range of 1.5-2.9%. The simulations were sensitive to the choice of the wall function, grid spacing, and Reynolds number. A nonequilibrium wall function with a grid spacing equal to a distance of 30 wall units gave good results.

  • 2.
    Teng, Penghua
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Modeling and Prototype Testing of Flows over Flip-Bucket Aerators2018In: Journal of Hydraulic Engineering, ISSN 0733-9429, E-ISSN 1943-7900, Vol. 144, no 12, article id 04018069Article in journal (Refereed)
    Abstract [en]

    The paper deals with a unique spillway which incorporates an aerator in each flip bucket with the intention to aerate the flow and avoid subatmospheric air cavities enclosed by the jets. In terms of jet breakup and stability, the physical models and the prototype lead to contradicting conclusions. With sealed aerators, the models exhibit intact air cavities featuring negative air pressure, suggesting the aeration need. Computational fluid dynamics (CFD) is performed to determine the reason for the discrepancy. Both the prototype observations and CFD indicate that the jets break up as a result of air entrainment; the resulting cavity air-pressure drops are insignificantly small. The discrepancy is due to the small model scale, in which the threshold flow velocity for air entrainment is not met and the prerequisite for jet breakup does not exist. To correctly reproduce similar water-air flow phenomena, the model should be large enough to meet the air-entrainment criterion. When questioning a small-scale model with air-cavity formation, CFD simulations should be performed to check the model results and make corrections, if needed.

  • 3.
    Teng, Penghua
    et al.
    KTH, School of Architecture and the Built Environment (ABE).
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Modeling and Prototype Testing of Flowsover Flip-Bucket Aerators2018In: Journal of Hydraulic Engineering, ISSN 0733-9429, E-ISSN 1943-7900, Vol. 144, no 12Article in journal (Refereed)
    Abstract [en]

    The paper deals with a unique spillway which incorporates an aerator in each flip bucket with the intention to aerate the flow andavoid subatmospheric air cavities enclosed by the jets. In terms of jet breakup and stability, the physical models and the prototype lead tocontradicting conclusions. With sealed aerators, the models exhibit intact air cavities featuring negative air pressure, suggesting the aerationneed. Computational fluid dynamics (CFD) is performed to determine the reason for the discrepancy. Both the prototype observations andCFD indicate that the jets break up as a result of air entrainment; the resulting cavity air-pressure drops are insignificantly small. The discrepancyis due to the small model scale, in which the threshold flow velocity for air entrainment is not met and the prerequisite for jet breakupdoes not exist. To correctly reproduce similar water–air flow phenomena, the model should be large enough to meet the air-entrainmentcriterion. When questioning a small-scale model with air-cavity formation, CFD simulations should be performed to check the model resultsand make corrections, if needed.

  • 4. Wörman, Anders
    et al.
    Xu, S. L.
    Stochastic analysis of internal erosion in soil structures - Implications for risk assessments2001In: Journal of Hydraulic Engineering, ISSN 0733-9429, E-ISSN 1943-7900, Vol. 127, no 5, p. 419-428Article in journal (Refereed)
    Abstract [en]

    A new modeling framework for internal erosion in heterogeneous stratified soils is developed by combining existing methods used to study sediment transport in canals, filtration phenomena, and stochastic processes. The framework is used to study the erosion process in sediments caused by a flow of water through a covering filter layer that deviates from geometrical filter rules. By the use of spectral analysis and Laplace transforms, mean value solutions to the transport rate and the variance about the mean are derived for a transport constraint at the upstream boundary and a constant initial transport. Increasing the heterogeneity of a defective filter layer in a canal retards the propagation of the expected bed degradation. An implication is that the heterogeneity of the riprap, in this respect prolongs the expected degradation process and the expected lifespan of the structure. The increased variance and decreased correlation length of the riprap reduces the confidence of the mean value solution. The stochastic analysis is therefore suitable as part of risk analyses of extreme events such as failure of embankment dams, for which empirical observations are rare.

  • 5.
    Yang, James
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Kung, C. S.
    Nonlinear stability of differential surge chambers1992In: Journal of Hydraulic Engineering, ISSN 0733-9429, E-ISSN 1943-7900, Vol. 118, no 11Article in journal (Refereed)
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