Coupled CFD Research Articles

Two-Way Coupled CFD Approach for Predicting Gear Temperature of Oil Jet Lubricated Transmissions

Two-Way Coupled CFD Approach for Predicting Gear Temperature of Oil Jet Lubricated Transmissions

A multi-physics methodology for the simulation of reactive flow and elastoplastic structural response

We propose a numerical methodology for the numerical simulation of distinct, interacting physical processes described by a combination of compressible, inert and reactive forms of the Euler equations, multiphase equations and elastoplastic equations. These systems of equations are usually solved by coupling finite element and CFD models. Here we solve them simultaneously, by recasting all the equations in the same, hyperbolic form and solving them on the same grid with the same finite-volume numerical schemes. The proposed compressible, multiphase, hydrodynamic formulation can employ a hierarchy of five reactive and non-reactive flow models, which allows simple to more involved applications to be directly described by the appropriate selection. The communication between the hydrodynamic and elastoplastic systems is facilitated by means of mixed-material Riemann solvers at the boundaries of the systems, which represent physical material boundaries. To this end we derive approximate mixed Riemann solvers for each pair of the above models based on characteristic equations. The components for reactive flow and elastoplastic solid modelling are validated separately before presenting validation for the full, coupled systems. Multi-dimensional use cases demonstrate the suitability of the reactive flow-solid interaction methodology in the context of impact-driven initiation of reactive flow and structural response due to violent reaction in automotive (e.g. car crash) or defence (e.g. explosive reactive armour) applications. Several types of explosives (C4, Detasheet, nitromethane, gaseous fuel) in gaseous, liquid and solid state are considered.

Potential Energy as Metric for Understanding Stick–Slip Dynamics in Sheared Granular Fault Gouge: A Coupled CFD–DEM Study

We study the stick–slip behavior in a sheared granular fault gouge using a coupled discrete element method and computational fluid dynamics. We compare characteristics of slip events in dry and fluid-saturated granular fault gouge in drained conditions. The granular layer is confined under constant normal load and sheared with a velocity-controlled mechanism. Potential energy is stored through overlaps between particles. We show that the potential energy builds up during the stick phase and drops during slip instability. Our observations show that on average 8% of the drop in potential energy is converted into particle kinetic energy, while the rest dissipates. Our simulations show that drop in potential energy is a good measure of slip size showing a strong correlation with the drop in macroscopic friction coefficient. Our simulations show that in fluid-saturated granular fault gouge, the potential energy drop is higher leading to a higher drop in friction coefficient and in a higher kinetic energy of particles during slip event.

High-resolution simulation for rotorcraft aerodynamics in hovering and vertical descending flight using a hybrid method

A high-resolution simulation tool for rotorcraft aerodynamics is developed by coupling CFD with a Vorticity Transport Model (VTM). An Eulerian-based CFD module is used to model the blade near body flowfield, and a Lagrangian-based VTM module is employed for vortex tracking in the far wake. The coupling procedure is implemented by transmitting vortex sources to the VTM module and feeding boundary conditions back to the CFD module. The presented CFD/VTM hybrid solver is firstly validated by hover cases of three different rotor configurations. Simulation results, including the blade surface pressure distribution, rotor downwash, and hover figure of merit, exhibit favorable correlations with available experimental data. Then, a rotor operated in vertical descending flight with a fixed collective pitch is investigated. It is shown that the CFD/VTM coupling method is suitable for rotor wake simulation. Wake instabilities (far wake breakdown in hover and toroidal wake pattern in the vortex ring state) are successfully demonstrated with a moderate computational cost.

Extension and application on a pool-type test facility of a system thermal-hydraulic/CFD coupling method for transient flow analyses

The development of multi-scale modeling capabilities through the use of coupled system thermal-hydraulic and CFD codes is addressed in this paper, which presents the extension and application of a partitioned, domain decomposition computational method coupling the 1D code RELAP5-3D and the CFD code FLUENT. An implicit coupling scheme for the solution of the flow field, based on a Quasi-Newton algorithm, is developed and tested on a case with multiple coupling interfaces. Moreover, modeling capabilities of the tool are enhanced through the implementation of thermal coupling to compute conjugate heat transfer phenomena. In this work, a coupled model has been developed for the analysis of the pool-type test facility E-SCAPE, currently under commissioning at the Belgian Nuclear Research Centre SCK•CEN. The installation represents a thermal-hydraulic scaled model of the MYRRHA reactor, with an electrical core simulator, cooled by Lead-Bismuth Eutectic (LBE). The coupling tool is applied on the analysis of a total loss of flow (LOF) transient, involving the complex transition from forced to natural circulation flow in the primary system. The simulation results, compared against stand-alone system thermal-hydraulics (STH) simulation data, highlighted that the transient behavior of a pool-type system in natural circulation is characterized by complex multi-dimensional flow and temperature fields, difficult to predict by 1D STH codes. The study also confirmed the capability of the developed tool to predict the impact of such phenomena on the system behavior, and to capture the development of thermal stratification in a plenum at low flow condition. The planned experimental tests will be used for the validation of the tool, in the view of its use for design and licensing activities.

A numerical simulation method for predicting global and local hydroelastic response of a ship based on CFD and FEA coupling

In this paper, a simulation method for predicting global and local hydroelastic response of a ship which couples CFD and FEA is developed and validated. By comparing the prediction with linear/nonlinear strip method, 3D panel method and towing tank test results under various wave conditions in terms of rigid body motions and slamming impact pressure, the effectiveness of the CFD-FEA coupling method is confirmed. The hydroelastic behavior, so-called the whipping moment, evaluated from the CFD-FEA coupling method is further validated by comparing with nonlinear strip method, 3D panel method and tank test results. Finally, the proposed method is applied to a realistic large container ship structure in severe waves. The structural response of the double bottom structure subjected to global and local bending moments is investigated.

Automated two-way coupling of CFD fire simulations to thermomechanical FE analyses at the overall structural level

Coupled CFD fire simulations and thermomechanical FE analyses typically consist of fire simulations, heat transfer analyses and structural response analyses, mutually coupled by three coupling steps. There are two coupling approaches, one-way and two-way coupling, where two-way coupling includes the effects of the structural response on fire propagation. In the first part of this paper, one- and two-way coupling approaches including the coupling steps are proposed to include coupling at the structural level. Then a case study comprising an office space with a 12-plate thin-walled steel façade under fire conditions is introduced, as well as the related CFD and FE models. A newly developed automated coupling interface and subprograms are used to perform several one-way and two-way coupled analyses using a coarse and fine CFD mesh for the case study. Slight differences are found in the results of identical simulations due to random effects in the fire simulations. Nevertheless, it can be concluded that two-way coupling is feasible, and that significant differences in the façade failure progression illustrate its effectiveness. Future research includes additional developments of both the fire and structural models, as well as verification and parametric studies to further confirm the findings.

Effects of particle mass loading on the hydrodynamics and separation efficiency of a cyclone separator

Abstract The effect of the particle mass loading (1.6–115.3 g/m3) on the performances of a cyclone separator is studied by two-way coupling CFD simulation and experiments. The increasing of the particle mass loading enriches the particles at the wall region. At lower inlet air velocity, the separation efficiency increases with the increasing of the particle mass loading due to the larger particle sweeping effects and the aggregation of smaller particles. The full elastic particle–wall collision and the perfect dust box bottom collection assumptions cause CFD simulation overpredicting the separation efficiency of smaller particles. A partial elastic particle–wall collision assumption overcame the problem and reduced the calculated separation efficiency. Our CFD simulation can reasonably predict the separation efficiency at different particle mass loadings.

Coupling CFD-DEM and microkinetic modeling of surface chemistry for the simulation of catalytic fluidized systems.

In this work, we propose numerical methodologies to combine detailed microkinetic modeling and Eulerian-Lagrangian methods for the multiscale simulation of fluidized bed reactors. In particular, we couple the hydrodynamics description by computational fluid dynamics and the discrete element method (CFD-DEM) with the detailed surface chemistry by means of microkinetic modeling. The governing equations for the gas phase are solved through a segregated approach. The mass and energy balances for each catalytic particle, instead, are integrated adopting both the coupled and the operator-splitting approaches. To reduce the computational burden associated with the microkinetic description of the surface chemistry, in situ adaptive tabulation (ISAT) is employed together with operator-splitting. The catalytic partial oxidation of methane and steam reforming on Rh are presented as a showcase to assess the capability of the methods. An accurate description of the gas and site species is achieved along with up to 4 times speed-up of the simulation, thanks to the combined effect of operator-splitting and ISAT. The proposed approach represents an important step for the first-principles based multiscale analysis of fluidized reactive systems.

Bridging the gap across scales: Coupling CFD and MD/GCMC in polyurethane foam simulation

This work presents a multi-scale approach to reacting and expanding polyurethane (PU) foams modeling and simulation. The modeling strategy relies on two pillars: an atomistic model (molecular dynamics (MD)/Grand Canonical Monte Carlo (GCMC)) that provides liquid mixture density and reactant solubility and a continuum model (CFD) in which the expansion characteristics of the foam is modeled exploiting the results of the atomistic simulations. The resulting coupled model is validated for two different PU systems applied in four batches with chemical and physical blowing agents. The results demonstrate the efficacy and reliability of the developed model in the simulation of different PU foam properties such as apparent density and temperature evolutions.

Numerical simulation of catalytic upgrading of biomass pyrolysis vapours in a FCC riser

Catalytic upgrading of biomass pyrolysis vapours is a potential method for the production of hydrocarbon fuel intermediates. This work attempts to study the catalytic upgrading of pyrolysis vapours in a pilot scale FCC riser in terms of hydrodynamics, residence time distribution (RTD) and chemical reactions by CFD simulation. NREL's Davison Circulating Riser (DCR) reactor was used for this investigation. CFD simulation was performed using 2-D Eulerian–Eulerian method which is computationally less demanding than the alternative Euler-Lagrangian method. First, the hydrodynamic model of the riser reactor was validated with the experimental results. A single study of time-averaged solid volume fraction and pressure drop data was used for the validation. The validated hydrodynamic model was extended to simulate hydrodynamic behaviours and catalyst RTD in the Davison Circulating Riser (DCR) reactor. Furthermore, the effects on catalyst RTD were investigated for optimising catalyst performance by varying gas and catalyst flow rates. Finally, the catalytic upgrading of pyrolysis vapours in the DCR riser was attempted for the first time by coupling CFD model with kinetics. A kinetic model for pyrolysis vapours upgrading using a lumping kinetic approach was implemented to quantify the yields of products. Five lumping components, including aromatic hydrocarbons, coke, non–condensable gas, aqueous fraction, and non–volatile heavy compounds (residue) were considered. It was found that the yield of lumping components obtained from the present kinetic model is very low. Thus, the further research needs to be carried out in the area of the kinetic model development to improve the yield prediction.

Coupled flight dynamics and CFD – demonstration for helicopters in shipborne environment

ABSTRACTThe development of high-performance computing and computational fluid dynamics methods have evolved to the point where it is possible to simulate complete helicopter configurations with good accuracy. Computational fluid dynamics methods have also been applied to problems such as rotor/fuselage and main/tail rotor interactions, performance studies in hover and forward flight, rotor design, and so on. The GOAHEAD project is a good example of a coordinated effort to validate computational fluid dynamics for complex helicopter configurations. Nevertheless, current efforts are limited to steady flight and focus mainly on expanding the edges of the flight envelope. The present work tackles the problem of simulating manoeuvring flight in a computational fluid dynamics environment by integrating a moving grid method and the helicopter flight mechanics solver with computational fluid dynamics. After a discussion of previous works carried out on the subject and a description of the methods used, validation of the computational fluid dynamics for ship airwake flow and rotorcraft flight at low advance ratio are presented. Finally, the results obtained for manoeuvring flight cases are presented and discussed.

室内気流連成型動的空調システムシミュレーションに関する研究 : 第1報-冷却減湿コイルの潜熱処理動的特性と人工気候室を対象とした計算精度検証

室内気流連成型動的空調システムシミュレーションに関する研究 : 第1報-冷却減湿コイルの潜熱処理動的特性と人工気候室を対象とした計算精度検証

室内気流連成型動的空調システムシミュレーションに関する研究 : 第3報-非定常温度環境下での温冷感を利用した空調の冷房運転における送風温度リセット制御とデマンド抑制制御が与える影響

室内気流連成型動的空調システムシミュレーションに関する研究 : 第3報-非定常温度環境下での温冷感を利用した空調の冷房運転における送風温度リセット制御とデマンド抑制制御が与える影響

Coupled CFD and building energy simulations for studying the impacts of building height topology and buoyancy on local urban microclimates

The temperatures in cities are increased due to the urban heat island effect. Heat can be removed from urban areas by wind and buoyancy driven ventilation. Building geometries have a strong impact on the wind flow patterns and heat removal in urban areas. The microclimate is analysed for a generic urban area with 23 buildings. Six different urban topologies are studied, where only the building heights of the individual buildings are changed. The local air temperatures are studied with coupled CFD and building energy simulations. The results show that the building height topology has a minimal impact on the mean air temperatures, but influences local air temperatures and the size of local heat islands. An analysis based on a comparison of simulations with/without buoyancy, shows a strong impact of buoyancy on the mean and local air temperatures. Further, correlations are found showing that the normalized increase in local air temperature is linked to the local air volume flow rates and thermal diffusivities. With higher volume flow rates and thermal diffusivities more heat can be removed from the environment. Based on these correlations an approach to evaluate the local heat island formation risk using isothermal CFD simulations is proposed.

Coupling CFD with a one-dimensional model to predict the performance of reverse electrodialysis stacks

Different computer-based simulation models, able to predict the performance of Reverse ElectroDialysis (RED) systems, are currently used to investigate the potentials of alternative designs, to orient experimental activities and to design/optimize prototypes. The simulation approach described here combines a one-dimensional modelling of a RED stack with a fully three-dimensional finite volume modelling of the electrolyte channels, either planar or equipped with different spacers or profiled membranes. An advanced three-dimensional code was used to provide correlations for the friction coefficient (based on 3-D solutions of the continuity and Navier-Stokes equations) and the Sherwood numbers (based on 3-D solutions of a scalar transport equation), as well as to test simple models for the Ohmic resistances (based on 3-D solutions of a Laplace equation for the electrical potential). These results were integrated with empirical correlations for the transport properties of electrolytes and membranes, and were used as the input for the higher scale model. The overall model was validated by comparison with experimental data obtained in laboratory-scale RED stacks under controlled conditions. This combined approach constitutes a fully predictive, potentially very accurate, and still extremely fast-running, tool for the approximate simulation of all the main variables, suitable for performance prediction and optimization studies.

Modelling heat transfer and physiological responses of unclothed human body in hot environment by coupling CFD simulation with thermal model

A coupling system was developed in the present study to simulate the heat transfer and physiological responses of the unclothed human body in hot environment. This system included a computational thermal manikin controlled by a mutli-node thermal model, which could dynamically respond to the environmental conditions. The computational thermal manikin was employed to determine the heat transfer between the human body and ambient environment as well as heat transfer coefficients at each body segment. The CFD simulation was then coupled with a multi-node thermal model to predict the heat transfer and human physiological responses in real time. The performance of coupling system was examined by comparing the simulated skin temperatures with the published measurements from human trials in hot environment. The CFD simulation results indicated that the calculated values of heat flux and heat transfer coefficients agreed well with test data and simulated results in literature. The coupling system reasonably predicted the skin temperatures at local body segments with the maximum discrepancies between the observed values and simulated ones no more than 1.0 °C, except for arm. The results suggested that the developed system was capable of simulating the heat flux and physiological responses in hot environment, which provided an effective tool to better predict thermal comfort, heat stress, and skin burn.

Coupled optical and CFD parametric analysis of an open volumetric air receiver of honeycomb type for central tower CSP plants

The performance of an open volumetric solar air receiver of honeycomb type (multiple parallel channels) for central tower CSP plants is evaluated numerically. A parametric study is conducted at the single channel level in order to investigate the influence of the main geometrical variables and of the air mass flow rate on the receiver performance. The adopted methodology consists of two steps: the first one is the optical analysis that is conducted using Tonatiuh, an open-source Monte-Carlo based ray-tracing software, providing the distribution of the absorbed heat flux on the channel inner surfaces, to be finally exploited as input data in the second step, i.e. the numerical evaluation of the thermal fluid dynamic performance of the channel. Using the commercial CFD software ANSYS Fluent, the convective heat transfer between the air flow and the absorber and the radiative heat transfer among the absorber inner walls and the channel aperture are simulated, computing the heat losses to the ambient. Different channel configurations are simulated, identifying the influence of the three key-parameters (the tilt angle with respect to the horizontal, the channel size and the air mass flow rate) on the receiver performance, in terms of solar-to-electricity efficiency.

Sensitivity analysis of feedback factors by neutronics and thermal-hydraulics coupling code based on FLUENT software

With the great improvement of computer performance, analyzing the complex flow and heat transfer phenomena under transient condition by coupling CFD and neutronics has attracted lots of attention nowadays. We developed a neutronics-thermal hydraulics coupled code for transient analysis of pool type lead cooled fast reactors based on FLUENT UDF. The coupled code FLUENT/PK was validated by critical and sub-critical reactor under unprotected transient condition. The validation results show the correctness and feasibility of CFD method in safety analysis of reactors. The coupled code was used to analyze the lead cooled fast reactor SNCLFR-100 (which had been proposed by USTC) under different transient conditions. The calculated results show that there exists great difference if the introducing time of reactivity is different. The sensitivities of the feedback factors were analysed for the reason that these factors will be quite different at different operation time of the reactor core, and the result shows that Doppler constant has the most important effect on reactor safety compared with coolant temperature coefficient, fuel rod axial expansion coefficient and cladding expansion coefficient.

Coupled flow network model and CFD analysis for a combined impingement and film cooled gas turbine nozzle guide vane

Coupled flow network model and CFD analysis for a combined impingement and film cooled gas turbine nozzle guide vane