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In this paper we use the Computational Fluid Dynamics (CFD) toolbox OpenFOAM to perform numerical simulations of multiple floating point absorber wave energy converters (WECs) arranged in a geometrical array configuration inside a numerical wave tank (NWT). The two-phase Navier-Stokes fluid solver is coupled with a motion solver to simulate the hydrodynamic flow field around the WECs and the wave-induced rigid body heave motion of each WEC within the array. In this study, the numerical simulations of a single WEC unit are extended to multiple WECs and the complexity of modelling individual floating objects close to each other in an array layout is tackled. The NWT is validated for fluid-structure interaction (FSI) simulations by using experimental measurements for an array of two, five and up to nine heaving WECs subjected to regular waves. The validation is achieved by using mathematical models to include frictional forces observed during the experimental tests. For all the simulations presented, a good agreement is found between the numerical and the experimental results for the WECs’ heave motions, the surge forces on the WECs and the perturbed wave field around the WECs. As a result, our coupled CFD–motion solver proves to be a suitable and accurate toolbox for the study of fluid-structure interaction problems of WEC arrays.

A CFD solver naoe-FOAM-SJTU (The abbreviation naoe stands for naval architecture and ocean engineering) is developed based on the open source platform OpenFOAM with the purpose of simulating various marine hydrodynamic problems. In the present paper, self-developed modules, i.e., wave generation and absorption, 6 degrees of freedom motion, mooring system, dynamic overset grid, fluid-structure interaction, unsteady actuator line model, implemented on the open source platform OpenFOAM are introduced to illustrate the development of the marine hydrodynamics CFD solver. Furthermore, extensive simulations of marine hydrodynamic problems using the developed modules are conducted and validated by available experimental data. It has been proved that the CFD solver naoe-FOAM-SJTU is suitable and reliable in predicting the complex viscous flow around ship and offshore structures. Efficiency and accuracy need to be focused in the future development of the present CFD solver.

In the present study, a topology optimization method of thermal-fluid-structural problems is researched to design the three-dimensional heat sink with load-carrying capability. The optimization is formulated as a mean temperature minimization problem controlled by Navier-Stokes (N-S) equations as well as energy balance and linear elasticity equations. In order to prevent an unrealistic and low load-carrying design, the power dissipation of the fluid device and the normal displacement on the load-carrying surface are taken as constraints. A parallel solver of multi-physics topology optimization problems is built-in Open Field Operation And Manipulation (OpenFOAM) software. The continuous adjoint method is adopted for the sensitivity analysis to make the best use of built-in solvers. With the developed tool, the three-dimensional (3D) thermal-fluid topology optimization is studied. It is found that the Darcy number, which is suitable for fluid design, may cause severe problems in thermal-fluid optimization. The structural features of 3D thermal-fluid-structural problems are also investigated. The “2D extruded designs” are helpful to improve the structural stiffness, and channels with a larger aspect ratio in high-temperature areas improve the cooling performance.

Bends and confluences are often observed in rivers, and one of the phenomena that characterize flows in open channel bends and confluences is secondary current. Instead of moving somewhat parallel to the channel axis, the movement of the fluid particles in curved and confluent channels takes a spiral path. In this paper, a 3D OpenFOAM numerical model is employed to simulate the effect of secondary currents on water velocity in channel bends and confluences. The behavior of these currents is simulated by using the finite volume method (FVM). The experimental data of a sharply curved channel and a confluent channel were used to compare the numerical results and to evaluate the validity of the model. To assess the performance of different models in predicting the behavior of these secondary flows, two turbulence models (i.e., standard k–ε and realizable k–ε) were applied in the current study, and the accuracy of the standard and realizable k–ε turbulence models was evaluated and discussed. The results of this study showed the better performance of the standard k–ε model in curved channels and the realizable k–ε model in confluent channels.

The thermal radiation of gaseous combustion products in an aero-engine combustion chamber has obvious non-ash-body characteristics. In this paper, based on the OpenFOAM platform, a numerical study on multi-field coupled turbulence-combustion-radiation radiative heat transfer was carried out for a certain type of aero-engine combustion chamber using the mean weighted sum of grey gas (WSGG) gas radiation model, which can accurately describe the non-ash characteristics of the gas. The results show that the radiation heat transfer characteristics are influenced by several factors such as equivalent ratio, combustion pressure and wall emissivity, among which the equivalent ratio is dominant. Increasing the equivalence ratio from 0.11 to 0.4 resulted in a 189% increase in average incident radiation at the combustion chamber wall and a 233% increase in average incident radiation at the exit. Increasing the equivalent ratio, combustion pressure or wall emissivity will increase the average radiation intensity in the combustion chamber and the inhomogeneity of radiation distribution at the exit of the combustion chamber. The radial radiation distribution factor (RRDF) also increases with the increase of equivalent ratio, combustion pressure and wall emissivity. 航空发动机燃烧室气态燃烧产物热辐射具有明显的非灰体特性。基于OpenFOAM平台, 采用能准确描述气体非灰体特性的灰气体均值加权和(WSGG)气体辐射模型, 针对某型航空发动机燃烧室开展了湍流-燃烧-辐射多场耦合辐射换热数值研究。结果表明, 辐射换热特性受到当量比、燃烧压力、壁面发射率等多个因素的影响, 其中当量比占主要地位, 当量比从0.11提升至0.4, 燃烧室壁面平均入射辐射增加189%, 出口处平均入射辐射增加233%。当量比、燃烧压力、壁面发射率增大会提高燃烧室内平均辐射强度及燃烧室出口处辐射分布的不均匀性。径向辐射分布系数(radial radiation distribution factor, RRDF)随着当量比、燃烧压力、壁面发射率的增加而增大。

The spear valve is one of the most eroded hydro-mechanical components of the Pelton turbine operating in sediment-laden conditions. The spear valve is used to regulate or control the flow. In a multi-nozzle system, though having the same design, the spear valves show varying erosion patterns and intensities. The only difference was found to be the openings of the nozzle/spear valve. This demonstrates that there is some sort of connection between the nozzle opening and the erosion of the spear valve. The difference in erosion intensity in different spear valves can be seen on the site but the underlying phenomenon behind the erosion needed to be studied numerically. In this research, erosion patterns were numerically investigated using an open-source CFD tool, OpenFOAM. For this simulation, the sediment particles and their properties were incorporated into the flow using the built-in Lagrangian library of the OpenFOAM. To investigate the erosion in real time, a transient simulation was undertaken for various nozzle openings. This study only focuses on the erosion at the tip of the spear valve neglecting other parts of the nozzle. This study demonstrates that the erosion in the tip of the spear valve increases with the restriction in flow.

The present numerical investigation identifies quantitative effects of fundamental controlling parameters on the detachment characteristics of isolated bubbles in cases of pool boiling in the nucleate boiling regime. For this purpose, an improved Volume of Fluid (VOF) approach, developed previously in the general framework of OpenFOAM Computational Fluid Dynamics (CFD) Toolbox, is further coupled with heat transfer and phase change. The predictions of the model are quantitatively verified against an existing analytical solution and experimental data in the literature. Following the model validation, four different series of parametric numerical experiments are performed, exploring the effect of the initial thermal boundary layer (ITBL) thickness for the case of saturated pool boiling of R113 as well as the effects of the surface wettability, wall superheat and gravity level for the cases of R113, R22 and R134a refrigerants. It is confirmed that the ITBL is a very important parameter in the bubble growth and detachment process. Furthermore, for all of the examined working fluids the bubble detachment characteristics seem to be significantly affected by the triple-line contact angle (i.e., the wettability of the heated plate) for equilibrium contact angles higher than 45°. As expected, the simulations revealed that the heated wall superheat is very influential on the bubble growth and detachment process. Finally, besides the novelty of the numerical approach, a last finding is the fact that the effect of the gravity level variation in the bubble detachment time and the volume diminishes with the increase of the ambient pressure.

This study focuses on the numerical analysis of the interaction between the exit flows of two supersonic nozzles, using the distance between their longitudinal axes as a parameter. The analysis is conducted in OpenFOAM, assuming two-dimensional, inviscid flow. The methodology employed to simulate flow in a nozzle is validated against experimental data and is subsequently used to investigate the interaction with a second nozzle. The numerical results indicate that discharge flows interfere, even from distant nozzles.

In the present study, the simulation of the three-dimensional (3D) non-isothermal, non-Newtonian fluid flow of polymer melts is investigated. In particular, the filling stage of thermoplastic injection molding is numerically studied with a solver implemented in the open-source computational library O p e n F O A M ® . The numerical method is based on a compressible two-phase flow model, developed following a cell-centered unstructured finite volume discretization scheme, combined with a volume-of-fluid (VOF) technique for the interface capturing. Additionally, the Cross-WLF (Williams–Landel–Ferry) model is used to characterize the rheological behavior of the polymer melts, and the modified Tait equation is used as the equation of state. To verify the numerical implementation, the code predictions are first compared with analytical solutions, for a Newtonian fluid flowing through a cylindrical channel. Subsequently, the melt filling process of a non-Newtonian fluid (Cross-WLF) in a rectangular cavity with a cylindrical insert and in a tensile test specimen are studied. The predicted melt flow front interface and fields (pressure, velocity, and temperature) contours are found to be in good agreement with the reference solutions, obtained with the proprietary software M o l d e x 3 D ® . Additionally, the computational effort, measured by the elapsed wall-time of the simulations, is analyzed for both the open-source and proprietary software, and both are found to be similar for the same level of accuracy, when the parallelization capabilities of O p e n F O A M ® are employed.

We investigate the aerodynamics of low-Reynolds-number contrarotating propellers (CRPs) through numerical simulations. This field has gained increasing relevance owing to advancements in unmanned aerial vehicle technologies. The primary objective of this study was to evaluate the effect of interpropeller distance on the aerodynamic performance of CRPs, measured using the thrust coefficient (CT ), power coefficient (Cp) , and efficiency (η). Transient three-dimensional computational fluid dynamics simulations employing the unsteady Reynolds-averaged Navier–Stokes equations coupled with the k–ε turbulence model were conducted on an isolated propeller at various advance ratios. The results were then compared with the experimental data from a similarly shaped propeller. Simulations of different CRP interpropeller distances were performed with OpenFOAM software. The results indicated that increasing the interpropeller distance significantly enhances thrust, with a corresponding slight increase in efficiency.