Momentum balance in flows over mobile granular beds: application of double-averaging methodology to DNS data

Vowinckel, Bernhard; Nikora, Vladimir; Kempe, Tobias; Fröhlich, Jochen

doi:10.1080/00221686.2016.1260656

Cited by 22 publications

(33 citation statements)

References 49 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…After an initialization period of 40T b (case HP) and 20T b (case LP) to reach steady-state conditions, the simulations were run for the total simulation time of 175 T b (case HP) and 134 T b (case LP), where T b = U b /H is the bulk time unit. Preliminary analysis showed that the generated data are sufficient for obtaining fairly converged first and second-order statistics in the major part of the simulation domain (Vowinckel, Nikora, et al, 2017). In the following, a summary of the key flow features of the two scenarios are given recapping the preliminary analyses presented in and .…”

Section: Key Parametersmentioning

confidence: 96%

“…Application of this methodology for mobile-bed conditions, however, remains challenging as it requires highresolution data in both space and time. In a companion paper (Vowinckel, Nikora, Kempe, & Fröhlich, 2017), the DAM was successfully applied to DNS data in the analysis of the momentum balance in a turbulent flow over a mobile granular bed. Vowinckel, Nikora, et al (2017) provide details on the spacetime sampling and averaging strategies and report a detailed assessment of the key terms of the double-averaged momentum balance.…”

Section: Introductionmentioning

confidence: 99%

“…In a companion paper (Vowinckel, Nikora, Kempe, & Fröhlich, 2017), the DAM was successfully applied to DNS data in the analysis of the momentum balance in a turbulent flow over a mobile granular bed. Vowinckel, Nikora, et al (2017) provide details on the spacetime sampling and averaging strategies and report a detailed assessment of the key terms of the double-averaged momentum balance. The goal of the present study is to assess governing physical mechanisms by means of spatially-averaged momentum fluxes and link them to the typical flow and bed surface patterns observed in the simulations to gain a deeper insight into the fluid-particle interactions.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Spatially-averaged momentum fluxes and stresses in flows over mobile granular beds: a DNS-based study

Vowinckel

Nikora

Kempe

et al. 2017

Journal of Hydraulic Research

Self Cite

View full text Add to dashboard Cite

Based on direct numerical simulations, the paper investigates momentum fluxes and hydrodynamic stresses within and above a mobile granular bed in a turbulent open-channel flow laden with monodisperse spherical particles. Two simulation scenarios are considered: one with partially mobilized particles ("heavy" particles) and another with all particles in motion ("light" particles). The momentum fluxes were computed as temporal and spatial averages following the double-averaging methodology for rough-bed flows. The analysis, hence, allows the DNS data to be convoluted in a rigorous way to provide detailed description and quantification of the physical mechanisms involved in momentum exchanges. In particular, it was found that heavy particles create streamwise bedforms causing heterogeneity in the spanwise direction. This yields significant form-induced momentum fluxes that cannot be neglected. For both scenarios, the mobile particles take up a substantial amount of the momentum supplied, which ultimately increases the hydraulic resistance of the channel. These effects enhance and stabilize secondary flows in the channel.

show abstract

Section: Key Parametersmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Spatially-averaged momentum fluxes and stresses in flows over mobile granular beds: a DNS-based study

Vowinckel

Nikora

Kempe

et al. 2017

Journal of Hydraulic Research

Self Cite

View full text Add to dashboard Cite

show abstract

“…For all of the simulations to be presented in the following, we have chosen e dry = 0.97 and µ = 0.15, which is a common parameterization for silicate materials (e.g. Biegert et al 2017a;Joseph et al 2001;Joseph & Hunt 2004;Vowinckel et al 2014Vowinckel et al , 2017a.…”

Section: Cohesionless Particle-particle Interactionmentioning

confidence: 99%

Settling of cohesive sediment: particle-resolved simulations

et al. 2018

View full text Add to dashboard Cite

We develop a physical and computational model for performing fully coupled, grainresolved Direct Numerical Simulations of cohesive sediment, based on the Immersed Boundary Method. The model distributes the cohesive forces over a thin shell surrounding each particle, thereby allowing for the spatial and temporal resolution of the cohesive forces during particle-particle interactions. The influence of the cohesive forces is captured by a single dimensionless parameter in the form of a cohesion number, which represents the ratio of cohesive and gravitational forces acting on a particle. We test and validate the cohesive force model for binary particle interactions in the Drafting-Kissing-Tumbling (DKT) configuration. Cohesive sediment grains can remain attached to each other during the tumbling phase following the initial collision, thereby giving rise to the formation of flocs. The DKT simulations demonstrate that cohesive particle pairs settle in a preferred orientation, with particles of very different sizes preferentially aligning themselves in the vertical direction, so that the smaller particle is drafted in the wake of the larger one. This preferred orientation of cohesive particle pairs is found to remain influential for systems of higher complexity. To this end, we perform large simulations of 1,261 polydisperse settling particles starting from rest. These simulations reproduce several earlier experimental observations by other authors, such as the accelerated settling of sand and silt particles due to particle bonding, the stratification of cohesive sediment deposits, and the consolidation process of the deposit. They identify three characteristic phases of the polydisperse settling process, viz. (i) initial stir-up phase with limited flocculation; (ii) enhanced settling phase characterized by increased flocculation; and (iii) consolidation phase. The simulations demonstrate that cohesive forces accelerate the overall settling process primarily because smaller grains attach to larger ones and settle in their wakes. For the present cohesion number values, we observe that settling can be accelerated by up to 29%. We propose physically based parametrization of classical hindered settling functions introduced by earlier authors, in order to account for cohesive forces. An investigation of the energy budget shows that, even though the work of the collision forces is much smaller than that of the hydrodynamic drag forces, it can substantially modify the relevant energy conversion processes.

show abstract

“…Since the Gibson theory was derived for pure muds in the first place, applying the model to sand-mud mixtures might be problematic [38]. At the same time, the larger sized particles render the physical configuration attractive for phase-resolved simulations that allow for a full description of the fluid and the particle motion [39][40][41][42][43][44].…”

Section: Introductionmentioning

confidence: 99%

Consolidation of freshly deposited cohesive and noncohesive sediment: Particle-resolved simulations

et al. 2019

Self Cite

View full text Add to dashboard Cite

We analyze the consolidation of freshly deposited cohesive and non-cohesive sediment by means of particle-resolved direct Navier-Stokes simulations based on the Immersed Boundary Method. The computational model is parameterized by material properties and does not involve any arbitrary calibrations. We obtain the stress balance of the fluid-particle mixture from first principles and link it to the classical effective stress concept. The detailed datasets obtained from our simulations allow us to evaluate all terms of the derived stress balance. We compare the settling of cohesive sediment to its non-cohesive counterpart, which corresponds to the settling of the individual primary particles. The simulation results yield a complete parameterization of the Gibson equation, which has been the method of choice to analyze self-weight consolidation. arXiv:1907.03700v1 [cond-mat.soft]

show abstract

Momentum balance in flows over mobile granular beds: application of double-averaging methodology to DNS data

Cited by 22 publications

References 49 publications

Spatially-averaged momentum fluxes and stresses in flows over mobile granular beds: a DNS-based study

Spatially-averaged momentum fluxes and stresses in flows over mobile granular beds: a DNS-based study

Settling of cohesive sediment: particle-resolved simulations

Consolidation of freshly deposited cohesive and noncohesive sediment: Particle-resolved simulations

Contact Info

Product

Resources

About