Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session R1: Geophysical: General III - Open Channels and Sedimentation |
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Chair: Jorge Abad, University of Pittsburgh Room: 323 |
Tuesday, November 26, 2013 1:05PM - 1:18PM |
R1.00001: Vortex dynamics of rectangular lateral cavities in open channel flows: Effects of the aspect ratio on mass transport and residence times Cristian Escauriaza, Karina Soto, Christian Gonzalez, Cai Wei, Emmanuel Mignot, Nicolas Riviere Turbulent flows past lateral cavities in rivers and open channels play an important role in many environmental and geophysical applications. Large-scale coherent structures produced in the cavity are the most important mechanisms that control the dispersion and transport of contaminants in streams with transient storage zones. In this work we study the recirculating flow in lateral rectangular cavities with aspect ratios 1.0 and 3.0. We focus on the topology of the flow within the cavity and the dynamics of the shear-layer that forms in the main channel in shallow subcritical flows, using time-resolved Particle Image Velocimetry (PIV) and numerical simulations with coherent-structure resolving turbulent models (DES-LR). Through this investigation we provide new insights on the mechanisms of dispersion and transport of contaminants for each aspect ratio, and analyze the statistics of the mass exchange and residence times in the cavity for both configurations. [Preview Abstract] |
Tuesday, November 26, 2013 1:18PM - 1:31PM |
R1.00002: Hydraulic jumps with upstream shear Kelly Ogden, Karl Helfrich Hydraulic jumps in flows with background shear are investigated, motivated by applications such as the flow over sills in Knight Inlet and the Pre-Bosphorus Channel. The full solution space and allowable solutions to several two-layer theories for hydraulic jumps with upstream shear are identified. The two-layer theories considered, including a recent theory by Borden et al. (JFM, 2012), are distinguished by how dissipation is partitioned between the layers. It is found that upstream shear with a faster and thinner lower layer causes an increase in bore speed, for a given jump height. Further, these two-layer solutions only exist for a limited range of upstream shear. 2D numerical simulations are conducted, guided by the two-layer theory solution space, and the results are compared to the theories. The simulations show the qualitative types of hydraulic transitions that occur, including undular bores, fully turbulent jumps, and conjugate state-like solutions; the type depends on the jump height and upstream shear for fixed upstream layer depths. Numerical simulations are used to investigate the mixing. Finally, a few 3D numerical simulations were made and are found to be consistent with the 2D results. [Preview Abstract] |
Tuesday, November 26, 2013 1:31PM - 1:44PM |
R1.00003: Large-eddy simulation of density currents on inclined beds Saurabh Chawdhary, Ali Khosronejad, George Christodoulou, Fotis Sotiropoulos Density currents are stratified flow in presence of density differential and gravity field. We carry out Large-Eddy Simulation (LES) to simulate the flow of a density current formed over sloped bed due to an incoming jet of heavy density salty water for two different cases of bed slope: (a) 5 degrees and (b) 15 degrees. The Reynolds and Richardson numbers based on inlet height and inlet velocity were (a) 1100 and 0.471, and (b) 2000 and 0.0355, respectively. The Schmidt number is set equal to 620, which corresponds to the value for salt-water. The computed results are compared with laboratory experiments in terms of overall shape of the heavy-density plume and its spreading rate and are shown to be in reasonable agreement. The instantaneous LES flow fields are further analyzed to gain novel insights into the rich dynamics of coherent vortical structures in the flow. The half-width of the plume is plotted as a function of downstream length and found to exhibit three different regions on a log scale, in agreement with previous experimental findings. [Preview Abstract] |
Tuesday, November 26, 2013 1:44PM - 1:57PM |
R1.00004: Large-eddy simulation of coupled turbulence, free surface, and sand wave evolution in an open channel Ali Khosronejad, Fotis Sotiropoulos We develop and validate a coupled 3D numerical model for carrying out three-phase large-eddy simulations of turbulence, free-surface, and sand waves-bed morphodynamics under live bed conditions. We employ the Fluid-Structure Interaction Curvilinear Immersed Boundary (CURVIB) method of Khosronejad et al. (Adv. in Wat. Res.,2011). The LES is implemented in the context of the CURVIB method using wall modeling (Kang and Sotiropoulos, Adv. in Wat. Res.,2011). Free-surface motion is simulated by coupling the CURVIB method with a two-phase level set approach as in Kang and Sotiropoulos (Adv. in Wat. Res.,2012). Transport of bed load and suspended load sediments are combined in the non-equilibrium form of the Exner for the bed surface elevation, which evolves due to the spatio-temporally varying bed shear stress field induced by the turbulent flow. Simulations are carried out for the experiments of Venditti et al. (2005). It is shown that the model can accurately capture sand-wave initiation, growth, and migration processes observed in the experiment. The effects of free-surface on bed-form dynamics is also quantified by comparing the three-phase simulation results with two-phase simulations using a fixed rigid-lid as the free surface. This work is supported by NSF Grants EAR-0120914 and EAR-0738726, and National Cooperative Highway Research Program Grant NCHRP-HR 24-33. [Preview Abstract] |
Tuesday, November 26, 2013 1:57PM - 2:10PM |
R1.00005: A generalized shallow-water analysis of gravity currents in various cross-area channels for Boussinesq and non-Boussinesq systems Marius Ungarish The propagation of a high-Reynolds-number gravity current in a horizontal channel along the horizontal coordinate $x$ is considered. The bottom and top of the channel are at $z=0,H$, and the cross-section is given by the quite general $-f_1(z)\le y \le f_2(z)$ for $0 \le z \le H$. A shallow-water formulation is presented and used for the solution of the dam-break problem. The dependent variables are the position of the interface, $h(x,t)$, and the speed (averaged over the area of the current), $u(x,t)$. The non-rectangular cross-section enters the formulation via $f(h)$ and integrals of $f(z)$ and $z f(z)$, where $f(z) = f_1(z) + f_2(z)$ is the width of the channel. For a given geometry $f(z)$, the input parameters in the lock-release problem are the ratios of height $H/h_0$ and density $\rho_a/\rho_c$, of ambient to lock fluids. The dam-break problem can be solved by the method of characteristics, but complications (jumps, critical restrictions) appear when the return flow in the ambient is significant; these features are not captured by a one-layer model, and hence a two-layer model solution is introduced. A strong generalization is achieved: the standard classical solutions for a rectangular or unbounded channel are particular cases of the present theory. [Preview Abstract] |
Tuesday, November 26, 2013 2:10PM - 2:23PM |
R1.00006: Flow over interacting barchan dunes studied in a refractive-index-matched environment Z. Tang, N. Jiang, G. Blois, J.M. Barros, J.L. Best, K.T. Christensen Barchan dunes are three-dimensional topographic features characterized by a crescentic shape. Very common on Earth's surface, barchans are produced by unidirectional flows in regions of sediment starvation and are characterized by migration rates that are a function of their volume. This results in complex dune-to-dune interaction mechanisms that are poorly understood. In order to quantify the flow structure produced by interacting barchans, PIV measurements were made wherein the dune models were immersed in a flowing fluid that was refractive-index-matched to the dune material. Doing so provided full optical access to the obstructed regions of flow and eliminated reflections from the liquid-solid boundaries, allowing near-wall data to be collected. Clear barchan models with different volumetric ratios were arranged in tandem, and flow-field measurements were made in multiple streamwise--wall-normal and streamwise--spanwise planes. Ensemble-averaged flow fields and Reynolds stresses were obtained for different barchan spacings and compared to the reference case of an isolated barchan. Proper orthogonal decomposition analysis was employed to study the spatial characteristics of the energy distribution both between and downstream of the aligned dunes. [Preview Abstract] |
Tuesday, November 26, 2013 2:23PM - 2:36PM |
R1.00007: Bedforms migration and interactions: a PIV investigation G. Blois, J.L. Best, J.M. Barros, K.T. Christensen Bedforms, such as ripples and dunes, are ubiquitous in natural environments in which solid particles are immersed in a moving fluid that is above the critical bed shear stress for sediment movement. The mutual interactions between flow and bed topography result in processes in which both flow and bed morphology are unsteady and dynamic. Bedforms with different sizes, shapes and migration rates produce bedform superimposition and amalgamation whose marks are left in the rock record as a specific stratigraphic signature. We investigate the flow associated with amalgamating mobile bedforms using a narrow (5 mm width) flume coupled with PIV, which allows the behavior of quasi two-dimensional bedforms to be observed and quantified. Simultaneous measurements of both the morphology and flow during amalgamation provide a tool to assess validity of current theory and shed new light on the physics of this fundamental problem. Shear layer interactions between adjacent bedforms, leeside erosion and downstream bedform stalling due to the sheltering effect of an upstream bedform are found to be the key aspects of the amalgamation process. The implications of these processes with respect to flow resistance and transition between bedform states are discussed. [Preview Abstract] |
Tuesday, November 26, 2013 2:36PM - 2:49PM |
R1.00008: Suspension and transport of sediment under a plunging wave breaker Xinhua Lu, Xin Guo, Yi Liu, Lian Shen To understand the mechanism of suspension and transport of sediment under breaking water waves, we perform large-eddy simulations of a plunging breaker over seabed. The breaking water surface is captured by a coupled level-set and volume-of-fluid method. The mass exchange of sediment between the water region and the bottom is computed through the local upward erosion and downward deposition fluxes. The erosion flux is modeled based on the local shear stress at the bottom, and the deposition flux is estimated based on the sediment concentration near the bottom. We analyze in detail the instantaneous velocity and sediment concentration fields, the erosion and deposition fluxes near the bottom, as well as the bottom deformation under breaking waves. It is found that the sediment is mainly picked up from the bottom at the early stage of wave breaking, brought upwards, mixed by the turbulent motion, and then transported in the wave propagation direction by the current generated by the breaker. The wave breaking significantly enhances the horizontal transport of the sediment. It is also found that the air pocket entrained by the breaking wave plays an important role in the suspension, transport, and redistribution of sediment. [Preview Abstract] |
Tuesday, November 26, 2013 2:49PM - 3:02PM |
R1.00009: Investigation of the mechanism of contaminant release through the sediment-overlying water interface Jia-Hong Guo, Shu-Jun Zheng, Dao-Zeng Wang After the external pollutant discharge has been reduced, the release of the contaminant from the sediment to the overlying water may cause the river and lake be contaminated again. On the condition that the overlying water flow does not lead to sediment suspension, numerical and experimental researches are carried out for the contaminant release mechanism through the sediment-overlying water interface. In the numerical simulation, the overlying water flow is calculated as turbulent flow. The sediment is regarded as isotropic homogeneous porous medium, therefore the seepage field in the porous sediment layer is obtained by solving Darcy's equations. Several coupled two dimensional steady and unsteady flows of the overlying water and the pore water in the sediment are calculated. Based on the flow fields obtained, the unsteady contaminant solute transportation process in the sediment and the overlying water is numerically simulated, as the shapes of the sediment-overlying water interface are flat or periodic triangular respectively. The numerical results agree with the experimental results quite well. The results show that the exchange of the pore water and the overlying water is an important factor which decides the release flux of the contaminant from the sediment to the overlying water. [Preview Abstract] |
Tuesday, November 26, 2013 3:02PM - 3:15PM |
R1.00010: Modeling of matrix acidizing process under reservoir conditions Karlygash Turegeldieva, Bakhytzhan Assilbekov, Uzak Zhapbasbayev, Anatoly Zolotukhin, Timur Bekibaev, Nurlan Kenzhebekov Effectiveness of the process depends on the parameters: well choice, geological structure of the reservoir, definition of physical and chemical properties of rocks and fluids, agent choice. There are different mathematical models of the matrix acidizing, including the two scale model. These models describe the process in the core scale and Darcy scale, i.e. in an area with dimensions of several centimeters. It leads to the main problem -- how to use these models to the near wellbore scale under reservoir conditions. Some authors have increased the dimensions of the cores in numerical simulations and investigated the influence of the core dimensions to acidizing process. In this paper effort to indirectly solve this problem made. It based on boundary conditions alteration and simultaneous solution of matrix acidizing in damaged zone and reservoir fluid flow models. Furthermore in this work the criterion of the acid injection shut down for optimal breakthrough volume calculation was modified. Influence of boundary conditions on near well-bore zone treatment process was investigated. [Preview Abstract] |
Tuesday, November 26, 2013 3:15PM - 3:28PM |
R1.00011: Turbulent flow structure during the amalgamation process of river bed forms Christian Frias, Jorge Abad Most of the fluvial channels present bedforms such as dunes and ripples which are product of the interaction between hydrodynamics and sediment transport. Although, the effect of this bedforms has been studied by several researchers, very little has been done to study the ripple-dune transition. The purpose of the present study is to extend the observations made by previous experimental results on the bedforms amalgamation process. To this end, three LES cases were carried out to replicate an amalgamation process, a train of ripples (RUN I), a superimposed bed forms (RUN II) and a complete amalgamated bed forms stage(RUN III). Although the experimental base case involved two dimensional bedforms, a three dimensional simulation was developed to analyze the effects of superimposition in transversal and streamwise directions. Some important conclusions from this study are: the region of high shear stresses was related to turbulence production, in which the streamwise velocity fluctuations were associated to the modification of the bed morphology. The turbulence Horseshoes Vortices (THV) were more frequent in RUN I than in the other two cases. Finally, the frequency of the bursting events increased from RUN I to RUN II and decreased from RUN II to RUN III. [Preview Abstract] |
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