Numerical modeling investigation on turbulent oscillatory flow over a plane rough bed composed by randomly arrayed parti
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Numerical modeling investigation on turbulent oscillatory flow over a plane rough bed composed by randomly arrayed particles ZHOU Zhibo1, 2, ZHANG Jinfeng1*, ZHANG Qinghe1, LIU Run1 1 State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300072, China 2 Center for Ocean Hydrodynamics Research, Tianjin Research Institute for Water Transport Engineering, Ministry of
Transport, Tianjin 300456, China Received 26 August 2017; accepted 10 October 2017 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
A three-dimensional numerical model is established to simulate the turbulent oscillatory boundary layer over a fixed and rough bed composed by randomly arrayed solid spheres based on the lattice Boltzmann method and the large eddy simulation model. The equivalent roughness height, the location of the theoretical bed and the time variation of the friction velocity are investigated using the log-fit method. The time series of turbulent intensity and Reynolds stress are also investigated. The equivalent roughness height of cases with Reynolds numbers of 1×104–6×104 is approximately 2.81 d (grain size). The time variation of the friction velocity in an oscillatory cycle exhibits sinusoidal-like behavior. The friction factor depends on the relative roughness in the rough turbulent regime, and the pattern of solid particles arrayed as the rough bed in the numerical simulations has no obvious effect on the friction factor. Key words: turbulence, oscillatory boundary layer, lattice Boltzmann method, large eddy simulations, equivalent roughness height, friction factor Citation: Zhou Zhibo, Zhang Jinfeng, Zhang Qinghe, Liu Run. 2018. Numerical modeling investigation on turbulent oscillatory flow over a plane rough bed composed by randomly arrayed particles. Acta Oceanologica Sinica, 37(7): 62–68, doi: 10.1007/s13131-018-1244-y
1 Introduction One of the fundamental problems of coastal engineering is to estimate the oscillatory boundary layer near the seabed, and a better understanding of the wave boundary layer flow over rough beds, including the structure and dynamics of the turbulence and the corresponding bed friction characteristics, is essential to evaluating its effect on sediment transport. The turbulent oscillatory flow over the rough bed and the bed friction characteristics are the basic topics of sediment transport and wave dissipation (Jonsson, 1966; Swart, 1974; Nielsen, 1992; You and Yin, 2006; Camenen et al., 2009; Ding and Zhang, 2010). Baas et al. (2016) reviewed the bed form and stratification in the field and also examined the extended bed form phase diagram to summarize the bed forms generated in mixtures of sand and mud under rapidly decelerated flows. In addition to observation in the field, experiments on small-scale and large-scale wave flumes have also examined the wave boundary layers over a rough bed (Dixen et al., 2008; Corvaro et al., 2014; Miozzi et al., 2015). Dixen et al. (2008) carried out an experiment
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