Inhomogeneity and anisotropy in Eulerian-Eulerian near-wall modelling

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record This paper tackles the issue of image vorticity in turbulent Eulerian-Eulerian simulations. A pressure-velocity model to account for the no permeability constraint on the fluid- and particle-phase wall normal stress components is proposed. The pressure-velocity model is derived with in a Reynolds-Averaged Two-Fluid model (RA-TFM) framework and is implemented within the open-source CFD toolbox OpenFOAM. We demonstrate that this approach is capable of accounting for the strong near-wall inhomogeneity, a flow feature that hitherto has been neglected in Eulerian-Eulerian modelling. Simulation predictions are validated against benchmark Direct Numerical Simulation data and show a promising step forward in near-wall modelling in Eulerian-Eulerian simulations. The predictions reveal that the approach proposed herein can lead to a satisfactory agreement across all turbulence statistics paving the way for the correct prediction of more complex mechanisms. Finally, the source code of the recently developed solver ratfmFoam and supplementary material used in this work is made available online.University of Exete

Near-wall modelling in Eulerian–Eulerian simulations

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordThe near-wall region in turbulent Eulerian–Eulerian (E–E) simulations has hitherto received little to no attention. A standard approach to modelling this region is through the employment of single-phase wall-functions in the fluid-phase and it is unclear whether such an approach is capable of capturing the turbulent fluid-particle interaction in the near-wall region. In order to both investigate and alleviate E–E models reliance on single-phase wall-functions we propose an E–E elliptic relaxation model to account for the near-wall non-homogeneity which arises in wall-bounded flows. The proposed model is derived within an E–E framework and enables the full resolution of the boundary layer and arbitrary wall sensitivity. The model is then compared against the conventional kf−εf turbulence model with standard single-phase wall-functions. Additionally, the modelling is compared against a low-Re number turbulence model. The elliptic relaxation model is implemented within the open-source CFD toolbox OpenFOAM, applied to a vertical downward-facing channel and validated against the benchmark experimental data of Kulick et al. [1]. Model results show marked improvements over the conventional turbulence model across mean flow and turbulence statistics predictions. The use of conventional single-phase wall functions were shown to negatively impede on the prediction of the velocity covariance coupling term and as a result the particle fluctuation energy. Moreover, this also lead to an underestimation of the near-wall volume fraction accumulation. Finally, the elliptic relaxation model, E-E model and accompanying validation cases are made open-source.University of Exete

Reynolds-Averaged Two-Fluid Model prediction of moderately dilute fluid-particle flow over a backward-facing step

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record In this work a Reynolds-Averaged Two-Fluid fully coupled model (RA-TFM) for modelling of turbulent fluid-particle flow is implemented in OpenFOAM and applied to a vertically orientated backward-facing step. Three particle classes with varying mass loadings (10–40%) and different Stokes number are investigated. Details of the implementation and solution procedure are provided with special attention given to challenging terms. The prediction of mean flow statistics are in good agreement with the data from literature and show a distinct improvement over current model predictions. This improvement was due to the separation of the particle turbulent kinetic energy kp, and the granular temperature Θp, in which the large scale correlated motion and small scale uncorrelated motion are governed by separate transport equations. For each case simulated in this work, turbulence attenuation was accurately predicted, a finding that is attributed to separate coupling terms in both transport equations of kp and εp

Fully-coupled pressure-based two-fluid solver for the solution of turbulent fluid-particle systems

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordA fully-coupled pressure-based two-fluid solver for the solution of turbulent fluid-particle flows is presented. The numerical framework details several crucial aspects: implicit treatment of the phase-velocity-pressure coupling, the implicit treatment of inter-phase momentum transfer and finally the solution algorithm. The two-fluid solver is implemented within the open source tool-box foam-extend which is a community driven fork of OpenFOAM. The coupled solver is verified against a standard segregated implementation of the two-fluid solution algorithm and validated against benchmark experimental data. The coupled solver shows marked improvements in convergence, stability and solution time. The coupled implementation is capable of solving to a tolerance that is six orders of magnitude smaller in residual error and 1.7 times quicker than the segregated solver. Additionally, the sequentially solved system of phase-energies experienced performance improvements when solved in conjunction with the coupled solver

Nonisocyanate based polyurethane/silica nanocomposites and their coating performance

A series of silica nano-particles with different size were prepared by sol–gel technique, then surface modification by using cyclic carbonate functional organoalkoxysilane (CPS) was performed. Various amounts of carbonated silica particles directly added into carbonated soybean oil (CSBO) and carbonated polypropylene glycol (CPPG) resin mixture to prepare polyurethane–silica nanocomposite coating compositions by nonisocyanate route using an aliphatic diamine as a curing agent. Cupping, gloss, impact, and taber abrasion tests were performed on aluminum panels coated with those nano-composite formulations and tensile tests, thermogravimetric and SEM analyses were conducted on the free films prepared from the same coating formulations. An increase in abrasion resistance of CSBO-CPPG resin combination with the addition of silica was observed. In addition, the maximum weight loss of CSBO-CPPG resin combination was shifted to higher temperatures with incorporation of silica nano-particles The positive effect of modified silica particles on thermal stability of CSBO-CPPG system could be explained in such a way that PPG chains are able to disperse particles in the medium throughout the interactions between ether linkages and silanol groups

Mapping of QTLs for leaf area and the association with winter hardiness in fall-sown lentil

Variations in plant architecture are often associated with the ability of plants to survive cold stress during winter. In studies of winter hardiness in lentil, it appeared that small leaf area was associated with improved winter survival. Based on this observation, the inheritance of leaf area and the relationship with winter hardiness using an F6 - derived recombinant inbred line (RIL) population from the cross of WA8649090 x Precoz was investigated. The WA8649090 parent was winter hardy and had small leaves, while the Precoz parent was non-winter hardy and had large leaves. The 106 RILs and the parents were planted in a field in a randomized complete block design with three replications. Leaf area(cm2) of leaves from the fourth node was measured using a flatbed scanner and WinRHIZO software. Average leaf area for WA8649090 was 0.46 cm2, while leaf area for Precoz was 0.89 cm2. Average leaf area of the RILs was 0.63 cm2, and the frequency distribution was continuous, indicating the effects of more than one gene. Quantitative trait locus (QTL) analysis using a 130-point linkage map revealed one major QTL on linkage group 6 which explained 20.45% of the phenotypic variation for leaf area. The location of QTL for leaf area mapped the same region where one of the QTL for winter hardiness was mapped and significant association (r2 = 0.750, P< 0.01) was found between leaf area and winter hardiness. These results indicated an association between winter hardiness and leaf area that provides information applicable to lentil breeding.Keywords: Leaf area, lentil, recombinant inbred line (RIL), QTL mapping, winter hardines

Prediction of flow around a sharp-nosed bridge pier: Influence of the Froude number and free surface variation on the flow field (article)

This is the final version. Available on open access from Taylor & Francis via the DOI in this recordThe dataset associated with this article is located in ORE at: https://doi.org/10.24378/exe.1503Author accepted manuscript replaced with published version by Caroline Huxtable on 2019-10-11This study investigates the influence of free surface variation on the velocity field using numerical simulations of flow around a sharp-nosed pier that is representative of a typical masonry bridge pier. This study evaluates the assumption that free surface effects are negligible at small Froude numbers by comparing the change in flow field predictions due to the use of a free surface model (i.e. multi-phase simulation with a Volume of Fluid (VOF) model in place of a rigid-lid approximation (i.e. single phase simulation). Results show that simulations using the VOF model are in better agreement with experimental data than those using the rigid-lid approximation. Importantly, results show that even though the change in free surface height near the pier is small comparative to the approach flow, it still has a significant effect on velocities in front of the pier and in the wake region, and that too at low Froude numbers.Engineering and Physical Sciences Research Council (EPSRC