Finite Volume Model Research Articles

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Hydrodynamic analysis with the aid of numerical modeling tools is widely used in the design and modernization of hydraulic systems of aircraft, as well as in the analysis of the causes of depressurization, local destruction, and so on. This analysis includes both the operation of the hydraulic system in different modes, and the process of switching from one mode to another. However, in the scientific literature there is no information that would take account of high-frequency pressure pulsations from the hydraulic pump in the dead-end lines of hydraulic systems, and their possible impact on the pipelines and attachment points to the elements of the airframe. In the scope of this research, the possibility of low-frequency resonance in the dead-end lines of hydraulic systems is determined. A technique for setting and performing finite-volume modeling and hydro-gasdynamic analysis is described. The results of the analysis of the eigenfrequencies of oscillations in prefabricated structures of the hydraulic system pressure lines are presented. It is proven that the frequency of the resulting low-frequency resonance of the hydraulic fluid pulsations does not correspond to any of the eigenfrequencies of oscillations of the structural elements, and is, therefore, forced. The need for further assessment of the degree of influence of the described phenomenon on the operational life of the attachment points to the elements of the airframe is highlighted.

An extended finite volume model for implicit cohesive zone fracture propagation in a poroelastic medium

Models for fluid-driven fractures in a poroelastic medium involve the simultaneous simulation of multiple physical processes—diffusion of pore pressure, poroelastic stresses, fluid injection into a fractured porous medium, and fracture propagation. To simulate the above-mentioned physics, many algorithms and discretization techniques have been used in the past. The finite volume method has been gaining popularity for simulating solid mechanics problems. The discretization algorithms discussed in the past have used a segregated method for solving the poroelastic momentum balance, where iterations are necessary to obtain a converged solution for each component of the displacement vector. This segregated approach, when coupled with fluid-driven fracture propagation, can lead to excessive simulation times because of the coupled nature of the problem.In this study, an implicit formulation was designed to construct a linear system of equation for the components of the displacement vector to solve the poroelastic momentum balance equation (without iterating between components). Within this formulation, a fluid-driven fracture propagation model was implicitly incorporated using a cohesive zone approach. This methodology provided accurate solutions as shown by the validations in this paper where simulated results were compared with various well-known analytical solutions. The implicitness of the new model allowed significant improvements in computation speed when solving multi-physics problems. The simulation speed-ups were found to be 2 to 8 times when compared with the segregated method.

Hydraulic analysis of EU-DEMO divertor plasma facing components cooling circuit under nominal operating scenarios

Within the framework of the Work Package DIV 1 – “Divertor Cassette Design and Integration” of the EUROfusion action, a research campaign has been jointly carried out by University of Palermo and ENEA to investigate the steady state thermal-hydraulic behaviour of the DEMO divertor cassette cooling circuit, focussing the attention on its Plasma Facing Components (PFCs). The research campaign has been carried out following a theoretical-computational approach based on the Finite Volume Method and adopting the commercial Computational Fluid-Dynamic code ANSYS-CFX.A realistic model of the PFCs cooling circuit has been analysed, specifically embedding each Plasma Facing Unit (PFU) cooling channel with the foreseen swirl tape turbulence promoter, hence resulting in a finite volume model much more detailed than those assessed in previous analyses. Its thermal-hydraulic performances have been numerically evaluated under nominal steady state conditions, also comparing the obtained results with the corresponding outcomes of analogous analyses carried out for a simplified PFCs configuration, without swirl tapes. Moreover, the main thermal-hydraulic parameters have been evaluated in order to check whether the considered PFCs cooling circuit might fulfil the total pressure drop requirement (Δp <1.4 MPa), providing a uniform cooling of the Vertical Target PFU channels with a viable CHF margin (>1.4).The PFCs cooling circuit thermal-hydraulic behaviour has been additionally assessed at alternative operative conditions, issued to check the viability of a coolant velocity reduction, in order to minimize corrosion and vibrations inside the PFU channels.Models, loads and boundary conditions assumed for the analyses are herewith reported and critically discussed, together with the main results obtained.

Evacuated glazing with tempered glass

The application of tempered glass has made it possible to significantly reduce the support pillar number within evacuated glazing (EG) since tempered glass (T-glass) is four to ten times mechanically stronger than annealed glass (A-glass). The thermal transmittance (U-value) of 0.4 m by 0.4 m double evacuated glazing (DEG) with 4 mm thick T-glass and A-glass panes with emittance of 0.03 were determined to be 0.3 Wm−2K−1 and 0.57 Wm−2K−1, respectively (47.4% improvement) using previously experimentally validated finite volume model. The thermal transmittance (U-value) of 0.4 m by 0.4 m triple evacuated glazing (TEG) with 4 mm thick T-glass and A-glass panes with emittance of 0.03 were determined to be 0.11 Wm−2K−1 and 0.28 Wm−2K−1, respectively (60.7% improvement). The improvement in the U-value of EG with T-glass is due to a reduction in support pillar number, leading to reduction in heat conduction through pillar array. The impact of tempered glass on the thermal transmittance for TEG is greater than that of DEG since radiative heat transfer in TEG is much lower than that in DEG, thus the reduction in heat conduction resulted from the reduction of support pillar number in TEG is much larger than that in DEG.

Modelling laser-induced heat transfer phenomena of thin-films using OpenFOAM

• A Finite Volume (FV) Model for simulating laser annealing of thin-film based structure. • Experimental validation of the OpenFOAM-based conjugate heat transfer model. • Detailed understanding of the diode laser-induced thermal and optical phenomena of the multilayer structures. • A guideline for optimising and designing of thin-film based architecture. This paper presents a numerical simulation model for analysing diode laser-induced thermal phenomena on high absorbing thin-films. Continuous wave (CW) diode laser, in the form of millisecond annealing, is a promising tool for processing of the high absorbing thin-film based solar cells. The localised nature of laser processing, in one hand, gives an opportunity to heat the film to a higher temperature over a much shorter time than the conventional methods, while, on the other hand, allowing the substrate to remain at low temperature with a low ramp-up rate. Also, unlike the laser processing in pulse mode, the CW diode laser can heat the high absorbing thin-films over a longer period without initiating melting and dwetting. Since the CW diode laser-induced thermal treatment is entirely characterised by its parameters, the inappropriate setting of its parameters may lead to a negative effect on the absorber layer . In view of these, being highly a thermal process, the basic understating of the CW diode laser annealing of high absorbing thin-film is necessary, which arguably may not be possible using the experimental techniques. Numerical simulations, in this case, offer the possibility to acquire knowledge of the process; hence, in this contribution, a numerical model has been developed in an open-source based computational fluid dynamics (CFD) platform, known as OpenFOAM. Upon development of the model, its prediction has been compared with the experimental results of the CW diode laser annealing of silicon thin-film on the glass substrate , in which an excellent agreement with the experimental results has been observed. In the second part of this study, the developed numerical model has been implemented to reveal the CW diode laser-induced thermal phenomena of the high absorbing CZTS thin-films, which is considered as deposited on Molybdenum (Mo) coated glass substrate, a typical structure used for designing of CZTS thin-film based solar cells. Although CZTS thin-film is considered as the ideal material for using as an absorber in the next generation thin-film based solar cells, its behaviour in the case of CW diode laser-induced thermal treatment has not been understood yet. Hence, the present study may likely to contribute to the processing and optimising of the CZTS thin-film based structure.

Investigation of continuous carbothermal reduction of magnesia by magnesium vapor condensation onto a moving bed of solid particles

Magnesium metal production by carbothermic reduction (CTR) can reduce process emissions and energy requirements relative to silicothermic or electrolytic production, if high magnesium metal yields are achieved. A novel process was investigated where product magnesium gas condensed onto a moving bed of solid particles at high temperatures (≥300 °C) and in vacuum to minimize reversion and promote crystal growth. Using a half-system in which CTR product gases were artificially generated, magnesium continuously condensed onto steel, oxide, or carbide particles at yields >85% for PMg = 0.5 kPa. Steel particles exhibited the greatest bed retention and ease of separation, so this medium was used for scale-up to a full-system in which MgO CTR in a fixed bed gasifier at 1400 °C–1550 °C produced Mg(g) and CO. The initial reduction resulted in high Mg yield (>80%), but yield decreased as the reaction proceeded. The accumulation of Mg(s) and reversion product in the condenser promoted further reversion. The process yield could likely be improved by using high surface area particles to promote heat and mass transfer, allowing for shorter solid and gas residence times in the condenser. A finite volume model on the reactor tube and pellet bed described the kinetics, heat transfer, and mass transfer phenomena in the reduction reactor. The model predicted that the center of the bed was >50 °C cooler than the furnace, and the product gas pressures were near equilibrium. A wide and directly heated reactor could overcome these heat and mass transfer limitations.

Laplace transform finite volume modeling of water hammer along fluid–structure interaction

Water hammer or propagation of pressure waves generates profound forces through pipelines of industrial high pressure processes which causes structural vibration of the pipe in both radial and axial directions. To model the sudden rupture of a pipeline system the fluid–structure interaction, FSI, is taken into account by coupling the structural vibration equations to the fluid dynamic equation. In this paper, Laplace transform finite volume, LTFV, which is a new technique along the finite element method is developed to treat fluid transient and the structural vibration equations respectively.To evaluate the numerical results, a Thermal Hydraulic Test Loop (THTL facility) which has been designed and constructed for experimental research on the physical phenomena, characteristics and performance of the safety systems involved in plants is used. To conduct tests for representing a sudden break condition in the loop, the THTL facility has been equipped by devices and sensors to record pressure and vibration signals during simulated accidents. Under steady condition, by an electrical signal an electric valve, Break valve, is opened and simultaneously pressure along pipe vibration signals close to valve is recorded. Comparing the experimental data to results from numerical modeling validated the implemented method.

Modeling and control of a waste heat recovery system for integrated powertrain design optimization

Abstract The growing demand for increased vehicle efficiency has led to the introduction of waste heat recovery techniques in vehicle powertrains, with the organic Rankine cycle as the most interesting technique for automotive applications. In order to integrate the design of the waste heat recovery system into the design optimization of the full powertain, a novel modeling approach is suggested for capturing the key dynamics of a waste heat recovery system with low computational effort and number of design parameters, and which is scalable with the individual components of the cycle. The model is compared with a detailed finite volume model for a given organic Rankine cycle. Secondly, the organic Rankine cycle is integrated into a parallel hybrid vehicle model, and an optimization routine is proposed for obtaining the optimal control trajectories for the powertrain over a drive cycle. The main purpose of the waste heat recovery model designed in this paper in combination with the proposed optimization algorithm is to be used for powertrain design optimization studies.

3D Multiphysics Simulation of Jet Electrochemical Machining of Intersecting Line Removals

Jet electrochemical machining (Jet-ECM) is a non-conventional machining technology based on anodic metal dissolution. Jet-ECM utilizes a free-surface electrolyte jet to localize material removal. In this study Jet-ECM of intersecting line removals is investigated by help of experiments and simulation. The machining process is simulated with a 3D Finite Volume model considering the stratified two-phase flow of electrolyte and air. Furthermore, electrodynamics is modeled in terms of primary current distribution, and material removal is regarded transiently via geometry deformation according to Faraday’s law. The results reveal why an asymmetrical current profile occurs in Jet-ECM of intersecting line removals.

Energy performance of a low-cost PhotoVoltaic/Thermal (PVT) collector with and without thermal insulation

In this paper the performance analysis of a low cost/tech PhotoVoltaic/Thermal (PVT) solar collector is presented. The unit under investigation consists of a commercially available flat-plate hybrid unit, based on the use of a polycrystalline PV module and a roll-bond aluminium absorber. The unit is not equipped with any back/frame insulation and glass cover/air layer. A one-dimensional finite-volume model is developed in order to analyse the collector performance. The computational domain is discretized along the longitudinal flow direction of the collector, and mass and energy balance equations are used. This paper is based on a previous work, where the standard PVT collector configuration, without any back insulation, is experimentally and numerically analysed. Here, a possible integration of back insulation layer is analysed numerically considering different insulation materials and thicknesses. In particular, the available experimental data is used in order to simulate the operation of the collector with different back insulation configurations. A comparison between standard and insulated configurations is performed. The performance is also analysed along the discretization direction for all considered configurations. Finally, a sensitivity analysis is performed in order to compare the performance of the several collector configurations as a function of the main design/operation parameters.

Numerical investigation of the three-dimensional velocity fields induced by wave-structure interaction

Submerged shore-parallel breakwaters for coastal defence are a good compromise between the need to mitigate the effects of waves on the coast and the ambition to ensure the preservation of the landscape and water quality. In this work we simulate, in a fully three-dimensional form, the hydrodynamic effects induced by submerged breakwaters on incident wave trains with different wave height. The proposed three-dimensional non-hydrostatic finite-volume model is based on an integral form of the Navier-Stokes equations in σ-coordinates and is able to simulate the shocks in the numerical solution related to the wave breaking. The obtained numerical results show that the hydrodynamic phenomena produced by wave-structure interaction have features of three-dimensionality (undertow), that are locally important, and emphasize the need to use a non-hydrostatic fully-three-dimensional approach.

Thermal and economic evaluation of new insulation materials for building envelope based on textile waste

New thermal insulation materials made from textile waste based on acrylic and wool were developed using needle punching method. The aim of this work is to investigate the thermal performance of an external building wall outfitted with the developed insulation materials and submitted to the real climatic conditions of Casablanca, Morocco. A numerical finite volume model is developed and validated against the experimental results of a thermally controlled cavity at reduced scale. The numerical model is used to study the thermal performance of the considered wall in winter and summer season and to compute the annual heating and cooling loads. The thermal and energetic performances of the developed insulation materials are compared to the ones of some classical thermal insulation materials (i.e. Rock wool and Expanded polystyrene). Furthermore, a Life Cycle Cost (LCC) analysis is conducted with the local market cost in order to investigate the competitiveness of the new insulation materials and to seek the optimal insulation thicknesses. The results show that the developed thermal insulation materials are a competitive solution in terms of annual loads compared to the conventional thermal insulations. The optimum insulation thicknesses of the new materials and of the considered classical thermal insulations materials are determined using the LCC analysis. The effect of the specific cost of the developed insulation materials is studied and findings show that, the developed insulation can be a competitive solution if their initial cost don’t exceed 590 MAD/m3.

Temperature dependent dynamic growth of thermally grown oxide in thermal barrier coatings

Failures in thermal barrier coatings (TBCs) are often associated with a thermally grown oxide (TGO) due to thermal mismatch and the growth stress associated with growth of TGO. Unjustifiably, existing models assume constant growth profile of the TGO and diffusivity of oxygen in both the TGO and the bond coat (BC). The objective of this paper is to overcome this deficiency by using an integrated finite volume (FV) – finite element (FE) model to account for the change in material properties during oxidation. Three aspects of the work were accordingly examined. The first is concerned with the use of a dedicated FV model to describe the diffusion of oxygen and oxidation of BC. The second is the use of coupled FE simulations to determine the induced stress state due to oxidation using the results from the FV model. The third is to examine the combined effect of thermal load and oxidation. The results reveal that the undulating interface results in an uneven oxidation profile. Conclusively, uneven oxidation leads to higher stresses at the BC-TGO interface compared with existing models. Additionally, the change in the coefficient of thermal expansion during oxidation reduces the amplitude of the undulation and out of plane stresses.

The influence of low-temperature surface induction on evacuation, pump-out hole sealing and thermal performance of composite edge-sealed vacuum insulated glazing

Hermeticity of vacuum edge-sealing materials are one of the paramount requirements, specifically, to the evolution of energy-efficient smart windows and solar thermal evacuated flat plate collectors. This study reports the design, construction and performance of high-vacuum glazing fabrication system and vacuum insulated glazing (VIG). Experimental and theoretical investigations for the development of vacuum edgeseal made of Sn-Pb-Zn-Sb-AlTiSiCu composite in the proportion ratio of 56:39:3:1:1 by % (CS-186) are presented. Experimental investigations of the seven constructed VIG samples, each of size 300 mm·300 mm·4 mm, showed that increasing the hot-plate surface temperatures improved the cavity vacuum pressure whilst expediting the pump-out hole sealing process but also increases temperature induced stresses. Successful pump-out hole sealing process of VIG attained at the hot-plate set point temperature of 50 °C and the approximate cavity pressure of 0.042 Pa was achieved. An experimentally and theoretically validated finite volume model (FVM) was utilised. The centre-of-pane and total thermal transmittance values are calculated to be 0.91 Wm−2K−1 and 1.05 Wm−2K−1, respectively for the VIG. FVM results predicted that by reducing the width of vacuum edge seal and emissivity of coatings the thermal performance of the VIG is improved.

A Surface Flux Scheme Based on the Monin‐Obukhov Similarity for Finite Volume Models

AbstractWe proposed a surface flux scheme based on the Monin‐Obukhov similarity for finite volume models. The scheme solves a negative bias existing in conventional surface flux schemes. In the conventional schemes, the model prognostic variables are used as the center point value in the model grid to estimate the surface fluxes even though the variables are volume‐averaged values in finite volume models. The substitutional use of the volume‐averaged model variables for the point value results in underestimation of friction velocity and temperature scale and consequent surface fluxes. The underestimation is more remarkable for a thinner layer, namely, higher resolution, and larger roughness length. In the proposed scheme, the model variables are used as volume‐averaged quantities. Large‐eddy simulation and single‐column model experiments on a planetary boundary layer show that the surface fluxes calculated with the conventional scheme are, in fact, smaller compared to those with the proposed scheme. The proposed scheme allows better estimation of not only surface fluxes but also surface atmospheric diagnostics. Improved estimation of the surface flux with this scheme will contribute to improving the reliability of several kinds of simulations (e.g., those related to the atmosphere, ocean, ice sheet, and sea ice). Importantly, its impact becomes even more significant for higher‐resolution simulations, which are likely to be more sought after in the future.

Mixed-Mesh Finite-Volume Model for Shallow Water Flow with Drying and Wetting

The Godunov-type finite-volume model is able to accurately simulate complex fluid flows without numerical oscillation. In particular, the mesh-based finite-volume model can capture the feature geometry with precision at the nodes of the grid, and thus has a benefit in flood modeling. However, the mesh-based model may cause partial drying and wetting, which are challenges to solve in the 2D numerical model. Begnudelli and Sanders (2006) proposed a triangular mesh-based volume/free surface relationship (VFR) for resolving partial drying and wetting, and Kim et al. (2014) extended the method to mixed mesh. In this study the accuracy and applicability of VFRs extended by Kim et al. (2014) were examined by applying three mesh types, namely triangular, quadrilateral and mixed mesh, with various resolutions. Model errors and run times were acceptable and VFRs applied in this study performed well regardless of mesh type and resolution. Keywords: Mixed Mesh, VFRs, Drying and Wetting, Dam-break, Mesh Type

Reducing the thermal influence of a bleed pipe near a composite fuel tank wall

PurposeThe purpose of this paper is to determine thermal behaviour of wing fuel tank wall via heating by external heat sources.Design/methodology/approachA 3D finite element model of the structure has been created that takes into account convection, conduction and radiation effects. In addition, a 3D finite volume model of the air inside the leading edge is created. Through a computational fluid dynamics approach, the flow of air and thermal behaviour of the air is modelled. The structure and fluid model are coupled via a co-simulation engine to exchange heat flux and temperature. Different ventilation cases of the leading edge and their impact on the thermal behaviour of the tank wall (corresponding to the front spar) are investigated.FindingsResults of 3D analysis illustrate good insight into the thermal behaviour of the tank wall. Furthermore, if regions exist in the leading edge that differs significantly from the overall thermal picture of the leading edge, these are visible in a 3D analysis. Finally, the models can be used to support a flammability analysis assessment.Practical implicationsProvided that the bleed pipe is located far enough from the spar and covered with sufficient thermal heat isolation, the composite leading edge structure will not reach extremely high temperatures.Originality/valueThese detailed simulations provide accurate results which can be used as reliable input for the fuel tank flammability analysis.

Coupled CFD-Response Surface Method (RSM) Methodology for Optimizing Jettability Operating Conditions

A volume-of-fluid (VOF) finite volume model under the ANSYS® Fluent framework was coupled with the response surface method (RSM) to find the best operating conditions within a jettability window for two selected responses in a drop-on-demand inkjet printing process. Twenty-five runs were generated using a face centred design and numerical simulations were carried out using viscosity, surface tension, nozzle diameter, and inlet velocity as input factors. A mesh study was first conducted to establish the necessary number of cells to best combine accuracy and expended time. Selected runs were discussed, identifying the underpinning mechanisms behind the droplet generation at different time periods. Each one of the responses was evaluated under different input factors and their effects were identified. Finally, the desirability function concept was advantageously used to proceed with a multiple optimization where all the responses were targeted under usual jettability/printability conditions.

Development of 1D finite volume model for discontinues flow simulation (K-River)

Development of 1D finite volume model for discontinues flow simulation (K-River)

Thermal analysis of Stirling thermocompressor and its prospect to drive refrigerator by using natural working fluid

The Stirling thermocompressor (STCP), usually working at low frequency (<5 Hz), is a novel Stirling-type external-combustion machine. It utilizes the temperature difference between the heating temperature and ambient temperature to generate the thermoacoustic power and pressure wave for refrigerators. In order to explore the characteristics of STCP, a detailed thermal analysis based on the third order 1-D finite volume model considering the real gas effect and variable physical properties was proceeded. Three natural fluids, helium, nitrogen and hydrogen are chosen as the working fluids and compared with each other. The parameter effects of pressure fluctuation under no-load operation were studied. To understand the output capacities for refrigerator with using different working fluids, the RC load method is adopt to analysis the STCP’s capacity and efficiency of the conversion from heat energy to acoustic energy, also the loss characteristics under different working gas. When the working pressure, frequency and heating temperature are 4 MPa, 4 Hz and 800 K respectively, the STCP using helium as the working fluid could output about 380 W acoustic power for the RC load and relative Carnot efficiency is about 33%.