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Abstract: This paper presents the application of a comprehensive approach to the design of small scale sustainable distributed generation systems with special focus on energy recovery from paper production process sludge. The methodology integrates a detailed fluid-dynamic analysis tool with preliminary experimental analysis on a laboratory scale to guide the design of a prototype bubbling fluidized bed gasifier in the 85kW power range fitting with small and medium size paper production industries. Preliminary tests show stable operation even for this rather small power scale, and deviation from chemical equilibrium concentration in agreement with literature available data. Energy content in the sludge may be recovered along with a significant reduction of residual volume and mass. The concept may then be used to increase the overall sustainability of paper production. [Copyright &y& Elsevier]

Abstract: This paper seeks to develop a structure–performance relationship for gas diffusion layers (GDLs) of polymer electrolyte fuel cells (PEFCs), and hence to explain the performance differences between carbon paper (CP) and carbon cloth (CC). Three-dimensional simulations, based on a two-phase model with GDL structural information taken into account, are carried out to explore the fundamentals behind experimentally observed performance differences of the two carbon substrates, i.e. CC and CP, under low- and high-humidity operations. Validation against polarization data is made under both operating conditions, and the results indicate that the CC is the better choice as a GDL material at high-humidity operations due to its low tortuosity of the pore structure and its rough textural surface facilitating droplet detachment. However, under dry conditions, the CP shows better performance due to its more tortuous structure, which prevents the loss of product water to dry gas streams, thus increasing the membrane hydration level and reducing the ohmic loss. The present work is one step toward developing a science-based framework for selection of materials for next-generation, high-performance gas diffusion media. [Copyright &y& Elsevier]

Abstract: The impact dynamics of water drops on sized and unsized smooth cellulose films and paper surfaces with controlled roughness levels were studied. The objective was to better understand the effect of roughness on the liquid drop impact dynamics on paper surfaces, isolating from the effect chemical heterogeneity. Drop impact in the first few milliseconds were recorded using high-speed CCD camera and the three-phase contact line movement of the water drop was analyzed. Smooth cellulose film surface and rough paper surface showed similar impact dynamics, suggesting that the surface energy plays a more dominant role than surface roughness. Significantly different dynamic contact angles of water drop on the sized and unsized surfaces were observed during drop impact. The Laplace pressure of the curved spreading front pointing to the centre of a spreading drop on these sized cellulose and paper surfaces reduces the three-phase contact line movement, and leads to smaller maximum spreading diameter. Our results suggest that the water drop spreads on the rough surface is most likely via a “roll-over” action rather than “stick and jump” movements. [Copyright &y& Elsevier]

The future use of eddy resolving simulations (ERS) such as Large Eddy Simulation (LES), Direct Numerical Simulation (DNS) and related approaches in aerospace is explored. The turbulence modeling requirements with respect to aeroengines and aircraft is contrasted. For the latter, higher Reynolds numbers are more prevalent and this especially gives rise to the need for the hybridization of ERS methods with Reynolds Averaged Navier–Stokes (RANS) approaches. Zones where future use of pure ERS methods is now possible and those where hybridizations with RANS will be needed is outlined. The major focus is the aeroengine for which the component scales are much smaller. This gives rise to generally more benign Reynolds numbers. The use of eddy resolving methods in a wide range of zones in an aeroengine is discussed and the potential benefits and also cost drawbacks with such approaches noted. The tension when using such computationally intensive calculations in an area where the coupling of components and even the airframe and engine is becoming increasingly important is explored. Also, the numerical methods and meshing requirements are considered and the implications of ERS methods for future numerical algorithms. It is postulated that such simulations are ready now for niche uses in industry. However, to perform the scale of simulations that industry requires, to meet pressing environmental needs, challenges remain. For example, there is the need to develop optimal numerical methods that both map to the accuracy requirements for ERS and also future computer architectures. [ABSTRACT FROM AUTHOR]

Extensive computer simulations have been carried out to model imbibition of a coating fluid into a paper. The microstructure of the paper''s pore space is represented by a network of interconnected channels or pore throats that are formed between the paper''s fibers. The geometrical characteristics of the channels, such as their effective radius and length, as well as their connectivity, are selected from the experimental data presented in Part II of this series. The imbibition process that we simulate is the result of forcing the coating fluid into the pore space by applying a time-dependent flow-driven pressure distribution to the external surface of the paper, or is driven only by capillary forces. The dynamic pressure distribution is representative of a high-speed coating process. The simulations indicate that the connectivity of the pore throats, the anisotropic structure of the paper''s pore space, and the dynamic pressure distribution all have a strong influence on imbibition of a coating fluid into a paper''s pore space and, hence, on the quality of the coating. [Copyright &y& Elsevier]

Hydrodynamic flow characteristics of solid–liquid–gas slurry made by intimately mixing fibrous paper pulp with water and air were investigated in a short, vertical circular column. The pulp consistency (weight fraction of pulp in the pulp–water mixture) was varied in the low consistency range of 0.0–1.5%. The test section was 1.8 m long, with 5.08 cm inner diameter. Mixing of the slurry prior to entering the test section was done using a patented mixer with controlled cavitation that generated finely dispersed micro-bubbles.Flow structures, gas holdup, and the geometric and population characteristics of gas bubbles in the gas–pulp–liquid three-phase flow were experimentally investigated, using visual observation, Gamma-ray densitometry, and flash X-ray photography. Superficial velocities of the gas and liquid/pulp mixture covered the ranges 0–26 cm/s and 21–51 cm/s, respectively.Five distinct flow regimes could be visually identified. These included dispersed bubbly, characterized by isolated micro-bubbles entrapped in fiber networks; layered bubbly, characterized by bubbles rising in a low consistency annular zone near the channel wall; plug; churn-turbulent; and slug. The dispersed and layered bubbly regimes could be maintained only at very low gas superficial velocities or gas holdups. Flow regime maps were constructed using phasic superficial velocities as coordinates, and the regime transition lines were found to be sensitive to consistency.The cross section-average gas holdup data showed that both the dispersed and the layered bubbly regimes could best be represented by the homogeneous mixture model. The drift flux model could best be applied to the reminder of the data when the plug and churn-turbulent flow regimes were treated together, and the slug flow was treated separately. The drift flux parameters depended on the pulp consistency. [Copyright &y& Elsevier]

Abstract: We report on the results of investigations into the characteristics of an air–water isothermal two-phase flow in minichannels, that is, in capillary tubes with inner diameters of 1 mm, 2.4 mm, and 4.9 mm, also in capillary rectangular channels with an aspect ratio of 1 to 9. The directions of flow were vertical upward, horizontal and vertical downward. Based on the authors 15 years of fundamental research into the gas–liquid two-phase flows in circular tubes and rectangular channels, we summarized the characteristics of the flow phenomena in a minichannel with special attention on the flow patterns, the time varying holdup and the pressure loss. The effects of the tube diameters and aspect ratios of the channels on these flow parameters and the flow patterns were investigated. Also the correlations of the holdup and the frictional pressure drop were proposed. [Copyright &y& Elsevier]

Abstract: Three-dimensional numerical simulations of the laminar flow and heat transfer of water in silicon microchannels with non-circular cross-sections (trapezoidal and triangular) were performed. The finite volume method was used to discretize the governing equations. Numerical results were compared with experimental data available in the literature, and good agreements were achieved. The effects of the geometric parameters of the microchannels were investigated, and the variations of Nusselt number with Reynolds number were discussed from the field synergy principle. The simulation results indicate that when the Reynolds numbers are less than 100, the synergy between velocity and temperature gradient is much better than the case with Reynolds number larger than 100. There is an abrupt change in the intersection angle between velocity and temperature gradient around . In the low Reynolds number region the Nusselt number is almost proportional to the Reynolds number, while in the high Reynolds number region, the increasing trend of Nusselt number with Reynolds number is much more mildly, which showed the applicability of the field synergy principle. In addition, for the cases studied the fully developed Nusselt number for the microchannels simulated increases with the increasing Reynolds number, rather than a constant. [Copyright &y& Elsevier]

Abstract: Transient heat conduction in solid prismatic bars of constant cross-sectional area having uniform heat generation and unsteady momentum transport in infinitely long ducts of arbitrary but constant cross-sectional area are examined. In both cases the solutions are mathematically modeled using a transient Poisson equation. By means of scaling analysis a general asymptotic model is developed for an arbitrary non-circular cross-section. Further, by means of a novel characteristic length scale, the solutions for a number of fundamental shapes are shown to be weak functions of geometry. The proposed models can be used to predict the dimensionless mean flux at the wall and the area averaged temperature or velocity for the tube, annulus, channel and rectangle for which exact series solutions exist. Due to the asymptotic nature of the proposed models, it is shown that they are also applicable to other shapes at short and long times for which no solutions or data exist. The root mean square (RMS) error based on comparisons with exact results is between 2.2–7.6 percent for all data considered. [Copyright &y& Elsevier]

Abstract The present discussion concerns some doubtful results included in the above paper. [ABSTRACT FROM AUTHOR]

The present comment concerns some doubtful results included in the above papers. [ABSTRACT FROM AUTHOR]

Abstract: The squeeze force for a power law fluid with partial wall slip was first obtained by Laun [H.M. Laun, M. Rady, O. Hassager, Analytical solutions for squeeze flow with partial wall slip, J. Non-Newtonian Fluid Mech. 81 (1999) 1–15]. It is shown herein that a power law exponent n was missing in the relation between the radial stress and the axial stress (Laun''s equation 50), which has a great effect on the squeeze force for the power law fluid, especially in the full lubrication limit. [Copyright &y& Elsevier]

Abstract: A response to the “discussion paper” by Mr A. K. Majumder for the paper: “Characterisation method for population of mineral particles for flow processes and the assessment of its application potential” by Ireneusz Pyka and Krzysztof Wierzchowski, published in International Journal of Mineral Processing 110–111 (2012) 126–134. [Copyright &y& Elsevier]

A specific fluid dynamics related feature associated with application of corrugated sheet structured packings in distillation columns operated under deep vacuum conditions is that the vapour ascends through a sparsely irrigated packed bed under laminar flow conditions. In the present paper the well-known Delft Model (DM) and two ad-hoc arranged fully appropriate predictive models have been evaluated in this respect using experimental evidence obtained in total reflux vacuum distillation tests carried out with conventional and advanced geometries of a well-established wire-gauze corrugated sheet structured packing. Shortcomings and strong points of compared predictive models, which have exhibited large discrepancies with respect to relative magnitude of governing flow resistances, have been addressed, and upon a tedious elaboration the way paved for upgrading DM accordingly. As shown in present paper, a simple fundamentally sound correction of existing expressions for gas-gas interaction under laminar and turbulent flow conditions, and implementation of empirically founded expressions to account for previously unrecognized form drag related losses, occurring in case of conventional packing due to a rather sharp disrupted change in gas flow direction at transitions between packing layers, resulted in a remarkable advancement in performance of the upgraded Delft model (DM) in all cases. Yet, a further in-depth research effort is necessary to unravel true nature and scale of governing flow resistances. • In deep vacuum distillations vapour ascends under laminar flow conditions. • Preferred contactor is a corrugated sheet structured packing made of wire gauze. • Unrecognized sources of pressure loss identified and quantified. • Special modelling features related to laminar vapour flow conditions revealed. • Delft model upgraded accordingly reproduces experimental data amazingly well. [ABSTRACT FROM AUTHOR]

Abstract: Agitated pulp chests act as low-pass filters attenuating high-frequency variability and thus complimenting the action of control loops which attenuate slow disturbances. Dynamic tests made on industrial and scale-model chests show that non-ideal flows, including short-circuiting, recirculation, and dead zones, are common and significantly reduce the ability of the chest to attenuate fluctuations. In this paper, we explore the effect of suspension yield stress on the extent of non-ideal flow and upset attenuation by conducting dynamic tests using two different pulp suspensions: a long-fibred softwood pulp and a shorter-fibred hardwood pulp. Dynamic tests were also made as a function of the fibre mass concentration, with the yield stress used to characterize the dynamic behaviour observed in mixing. It was found that while the yield stress plays a significant role determining the mixing of pulp suspensions, the dynamic behaviour of pulp mixing could not be fully described by yield stress alone. Tests show that when the surface of the cavern created by the impeller approaches the pulp outlet, which was located on the impeller wall, the percentage of short-circuiting approached zero. [Copyright &y& Elsevier]

This paper addresses the numerical approximation of a compressible three-phase flow. The mixture is composed of a liquid, its vapour and an inert gas, with realistic equations of state. Since the liquid is immiscible and the gaseous phases are miscible, it yields constrictive volume and mass constraints. The fluid dynamics is depicted by a one-velocity hyperbolic system with relaxation terms toward the thermodynamical equilibrium of the mixture. The core of the paper is the comparison and the analysis of two possible choices of relaxation terms, accounting for a detailed analysis of mixture entropy and the associated thermodynamical equilibrium. As numerics are concerned, a fractional step approach is proposed, based on a finite volume approximation of the convective part. The complexity of the source term requires an implicit Broyden resolution. Numerical results allow to compare both the performance of the chosen numerical schemes and the impact of the source term choices. [ABSTRACT FROM AUTHOR]

• There are at least ten different methods to classify bloodstain patterns. • Most of the current methods are mechanistic and prone to contextual bias. • A lack of clearly defined, unambiguous classification criteria is a key limitation. • An unambiguous method for bloodstain classification resolves current limitations. • Further research in statistical descriptions and fluid dynamics is required. Classifying bloodstains is an essential part of Bloodstain Pattern Analysis. Various experts have developed methods. Each method considers the same basic bloodstain pattern types. These use either terminology based on the observable characteristics or the mechanistic cause of the bloodstain patterns as part of the classification process. This review paper considers ten classification methods from fourteen sources, which are used to classify bloodstain patterns. There are fundamental differences in how the patterns are classified, how differentiated the classification is, and whether the classification process uses clear, unambiguous criteria, and is susceptible to contextual bias. Experts have also reported issues with classifying bloodstains that have indistinguishable features. These differences expose key limitations with current classification methods: mechanistic terminology is too heavily relied on, and the classification process is susceptible to contextual bias. The development of an unambiguous classification method, based on directly observable characteristics within bloodstain patterns is recommended for future work. [ABSTRACT FROM AUTHOR]

This paper investigates the behavior of magnetohydrodynamic (MHD) peristaltic flow with electroosmosis. The Jeffrey fluid in microchannel under the influence of homogeneous-heterogeneous chemical reaction has been taken. The heat absorption and nonlinear radiation are also scrutinized here. This study contributes to the fundamental understanding of complex fluid dynamics in microscale systems and offer valuable insights for designing and optimizing microfluidic devices. In the framework of mathematical simulation, the relevant dimensional nonlinear equations are reduced into dimensionless equations by using linear transformations. Thus Debye-Hückel linearization has been employed. The streamline approach with mathematical modelling has been performed within the limits of δ ≪ 1 and Re → 0. The appropriate equations for temperature and concentration with boundary conditions are solved by using perturbation approach whereas, the exact solution is found for velocity equation. A graphical depiction of crucial physical characteristics on velocity, temperature, concentration and streamlines are reported in the last section. It is observed that the velocity distribution decreases for the higher value of M (0.5 ≤ M ≤ 2) however, it increases for the escalating values of U hs (− 0.5 ≤ U hs ≤ 1.5). When R n (0.1 ≤ R n ≤ 0.6) gets stronger then temperature profile decreases. It is noticed that the concentration profile decays owing to enhancement in Sc (− 0.5 ≤ Sc ≤ 1.5). As the M (0.5 ≤ M ≤ 2) increases, the size of trapped bolus decreases. Escalating values of temperature ratio parameter θ w (1.0 ≤ θ w ≤ 1.6) enhances the Nusselt number. The novelty of this study lies in the comprehensive analysis of multiple complex phenomena in a single framework. The interplay between MHD electroosmotic flow, homogeneous heterogeneous chemical reactions, peristalsis, nonlinear thermal radiation, heat absorption and no-slip condition has not been explored in previous research. [ABSTRACT FROM AUTHOR]

Fluid dynamics experimentation at scale provides an important means of investigation that is presently underpinned by dimensional analysis and computational fluid dynamics (CFD). Unfortunately, despite the obvious success of this twin approach, dimensional analysis provides no solution if scale effects are prevalent and CFD offers reduced practical advantage in the absence of a theory that links information across scaled experiments. This issue is addressed in this paper with the introduction of a new approach to scaled experimentation founded on the theory of finite similitude. Finite similitude is founded on the metaphysical concept of space scaling, where experimental apparatuses, facilities, prototypes, systems, wind tunnels etc., are scaled by the means of space contraction or expansion. There exists no practical means to contract or expand space but what is possible is a mathematical description of space scaling and its impact on governing physics, so providing a means for comparison with scaled systems and real-world experimental behaviours. This paper examines an adaptation of the finite-similitude theory, where two scaled experiments are involved but a second-order version of the theory is applied. All previous work has been limited to zeroth and first-order applications, but in the case of fluid dynamics, second order is shown necessary to capture more accurately convective terms. It is demonstrated in the paper by means of two scaled experiments (designed using second-order theory) that the approach is able to represent behaviours at the full scale that hitherto would have been deemed impossible with traditional dimensional analysis. Numerical and analytical case studies on gravity impacted flows are trialled to illustrate the benefits of the approach with percentage errors reduced from double to single digits. [ABSTRACT FROM AUTHOR]

Wall-modeled large eddy simulation (WMLES) is considered to be a powerful method in high Reynolds number wall-bounded fluid dynamics calculations. However, little research on aero-acoustic simulation by lattice Boltzmann method (LBM) combined with LES considering wall model has been found. Moreover, the discussion of the dominant geometric parameters of the wall model, which is dedicated to curved boundary modeling and based on a non-fitted Cartesian mesh, is rarely addressed. This paper proposes a WMLES algorithm based on a hierarchical Cartesian mesh and utilizing LBM, including the treatment of dominant geometric parameters. Firstly, based on the Green's formula, a strategy for obtaining detection point positions is developed using the mathematical formulas to solve the boundary free parameters, such as the normal direction of the curved surface and the distance from the lattice point to the solid-fluid boundary in the given direction. Secondly, a new wall model adapted to non-fitted Cartesian mesh is proposed to improve the precision of pressure fluctuation calculation. This model applies an interpolation bounce-back (IBB) scheme where slip velocity is estimated by an implicit wall function proposed by Spalart, and the eddy viscosity is reconstructed in the near-wall region. Finally, to enhance the accuracy of pressure fluctuation propagation, an appropriate transition zone treatment method of a multi-domain scheme with spatio-temporal second-order is applied and validated with a point source case. The aforementioned algorithms are implemented in a self-developed LBM code and validated through a three-element airfoil 30P30N benchmark, demonstrating their effectiveness and high accuracy in acoustic calculations. [ABSTRACT FROM AUTHOR]

Indirect evaporative cooling is a technology that can be used sustainably to replace traditional cooling systems using thermodynamic compression cycles, especially in tropical countries like Brazil, which have many regions with hot climates and low relative humidity. These meteorological aspects favor the simultaneous transfer of heat and mass, allowing the thermal cooling effect characteristic of evaporative cooling processes. Thus, this paper investigates the performance of a sustainable air cooling system by combining the psychrometric effects of warm, dry air with the flow features inside a cyclone covered by a layer of a fabric moistened with water. Fluid dynamic simulations previously indicated temperature decreases of up to 12.2 K between the feed and overflow streams of the cyclone. In addition, temperature contours showed that the fluid dynamics of the cyclone provide instantaneous thermal exchange between the walls and the internal fluid. These results directed the study to execute an experimental design using the response surface methodology to evaluate the influence of some variables in the process. The decrease in air stream temperature ranged from 3.9 to 13.1 K, with relative humidity and ambient temperature being the most significant variables. The results also indicated that water consumption to maintain the fabric wet is relatively low since 16·10-3 kg of liquid is required to cool 1 m³ of air flowing through the cyclone. [Display omitted] • High inlet temperature and low relative humidity provided maximum thermal gradients. • Within 0.75 s, in average, the system provided a thermal reduction of up to 13 K. • The thermal efficiency of the wet-bulb for the new system varied from 54.8 to 67.8 %. • Dimensionless numbers for psychrometric cooling system showed a linear behavior. [ABSTRACT FROM AUTHOR]

An accurate prediction of motion responses of a moored floating structure requires high-fidelity coupled analysis between the structure and its mooring system in waves, which involves both mooring line dynamics and fluid dynamics. In this paper, we develop a nonlinear finite element dynamic mooring analysis module that allows large axial stretching of mooring lines under the open source CFD framework OpenFOAM, and couple it with an Overset CFD solver to establish a fully coupled finite element mooring-CFD analysis model for floating structures. The coupled model is advantageous over existing models in that it is able to deal with large axial mooring stretching and complex mesh motions induced by significant structure responses under severe operating conditions. The developed dynamic mooring analysis method is firstly validated against publicly available data. In order to validate the coupled model, a series of experimental tests were carried out for a semi-submersible platform moored by eight catenary lines under different operating conditions, including free decay, regular and irregular wave tests. The dynamic responses of the floating structure and mooring tension are analyzed and compared with experimental data. Results show that numerically predicted structure responses and mooring tension are generally in good agreement with experimental measurements. Meanwhile, the strongly nonlinear large-amplitude resonant motions generated by the interaction of irregular waves with the moored floating structure are also investigated. Comparisons reveal that the coupled model can accurately predict the resonant spectral peaks of the structure responses, indicating that the it is capable of simulating large-amplitude motions of moored floating structures. The coupled model developed in this paper can be further applied to study the survivability of moored floating structures under harsh sea conditions. • A finite element mooring dynamics module was developed in OpenFOAM. • The developed mooring module was coupled with an Overset CFD solver in OpenFOAM. • The coupled model was validated against model tests of a moored platform. • The coupled model can accurately predict large-amplitude motion responses. [ABSTRACT FROM AUTHOR]

The literature is rich in fluid–structure interaction studies of a single rod in oscillating fluid (or the reciprocate), however, there is a dearth of experimental data for rod bundle oscillation, particularly if the bundle is in a confined environment. The presence of the fluid surrounding the moving solid is modeled with force coefficients such as inertial and drag. In case of small amplitudes oscillating flow, these force coefficients depend non-linearly on the Keulegan–Carpenter number K C. The dependence present different regimes, separated by threshold K C numbers. At different regimes correspond different fluid dynamics, hence different force coefficients. The aim of this paper is to experimentally investigate the fluid dynamic for a rod bundle oscillating in a stagnant fluid. The velocity fields have been measured with Particle Image Velocimetry (PIV). Both the rod bundle and the fluid have the same refractive index, which allow to measure the velocity fields within the rod bundle in an non intrusive manner. The bundle is hosted in a double tank, immersed in a refractive index matched solution and placed on an earthquake shake table. The shake table sets the bundle into motion along a single direction. Data enable the identification of a threshold effect in the fluid response to the oscillating assembly. This threshold effect is due to the formation of vortexes in the fluid. Data show a clear trend on how the development of turbulence occurs firstly inside the rod assembly and then in the bypass between the assembly and the tank wall. The experimental results indicate the presence of a viscous boundary layer developed along the rod, above the threshold K C. The results presented in this paper represent a step forward the comprehension of the damping effect induced by the fluid at different oscillating amplitudes and frequencies, due to different K C regimes. • PIV measurements with refraction index match conditions for an oscillating rod bundle in stagnant oil. • Determination of Keulegan Carpenter instability threshold. • Comparison fluid dynamics in different points of the rod bundle inner part. [ABSTRACT FROM AUTHOR]

Physics is a field of science that has traditionally used the scientific method to answer questions about why natural phenomena occur and to make testable models that explain the phenomena. Discovering equations, laws, and principles that are invariant, robust, and causal has been fundamental in physical sciences throughout the centuries. Discoveries emerge from observing the world and, when possible, performing interventions on the system under study. With the advent of big data and data-driven methods, the fields of causal and equation discovery have developed and accelerated progress in computer science, physics, statistics, philosophy, and many applied fields. This paper reviews the concepts, methods, and relevant works on causal and equation discovery in the broad field of physics and outlines the most important challenges and promising future lines of research. We also provide a taxonomy for data-driven causal and equation discovery, point out connections, and showcase comprehensive case studies in Earth and climate sciences, fluid dynamics and mechanics, and the neurosciences. This review demonstrates that discovering fundamental laws and causal relations by observing natural phenomena is revolutionised with the efficient exploitation of observational data and simulations, modern machine learning algorithms and the combination with domain knowledge. Exciting times are ahead with many challenges and opportunities to improve our understanding of complex systems. [ABSTRACT FROM AUTHOR]

This paper launches a thorough discussion on the locality of local neural operator (LNO), which is the core that enables LNO great flexibility on varied computational domains in solving transient partial differential equations (PDEs). We investigate the locality of LNO by looking into its receptive field and receptive range, carrying a main concern about how the locality acts in LNO training and applications. In a large group of LNO training experiments for learning fluid dynamics, it is found that an initial receptive range compatible with the learning task is crucial for LNO to perform well. On the one hand, an over-small receptive range is fatal and usually leads LNO to numerical oscillation; on the other hand, an over-large receptive range hinders LNO from achieving the best accuracy. We deem rules found in this paper general when applying LNO to learn and solve transient PDEs in diverse fields. Practical examples of applying the pre-trained LNOs in flow prediction are presented to confirm the findings further. Overall, with the architecture properly designed with a compatible receptive range, the pre-trained LNO shows commendable accuracy and efficiency in solving practical cases. [ABSTRACT FROM AUTHOR]

This paper presents a study on the influence of inlet radial angle in a multi-inlet cyclone separator using Eulerian-Lagrangian (EL) fluid dynamics approach. The investigation focuses on the behavior of air and solid particles within the cyclone. Air circulation was simulated at velocities ranging from 2 to 6 m/s, with inlet radial angles of 15°, 32°, 45°, 61°, and 72°. To model the turbulent flow, the Reynolds stress model (RSM) and renormalization group k-model (RNG) were employed, while the particle trajectories were simulated using the discrete phase model (DPM) in ANSYS Fluent. The purpose of this study was to determine how the inlet radial angle impacts various parameters: collection efficiency, pressure drop, cut-off diameter, axial velocity, and tangential velocity. The numerical data obtained from the simulations were validated and found to be consistent with the existing literature. The results revealed interesting findings. In the case of an inlet velocity of 6 m/s, the highest pressure drop of 84.5 Pa was observed for the 15° inlet radial angle, while the lowest pressure drop of 77.42 Pa was observed for the 32° inlet radial angle. It was found that the collection efficiency varied according to the radial angle of the inlet, with values of 89.00%, 91.70%, 92.50%, 94.77%, and 94.83% for 32°, 45°, 15°, 72°, and 61°, respectively. Additionally, at an inlet velocity of 2 m/s and a radial angle of 72°, 61°, 15°, 45°, and 32°, the corresponding cut-off sizes were determined to be 1.17 μm, 1.19 μm, 1.25 μm, 1.33 μm, and 1.38 μm, respectively. At an inlet velocity of 6 m/s, the peak tangential velocities were found to be approximately 1.48, 1.44, 1.44, 1.39, and 1.34 times the inlet velocity for the 15°, 72°, 61°, 45°, and 32° radial angles, respectively, within the axial location range of z = 1.5 D to z = 3.4 D. The peak axial velocity values for the 32°, 72°, 45°, 15°, and 61° radial angles, were reported as 0.85, 0.89, 0.92, 0.94, and 0.96 times the inlet velocity respectively. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the haemodynamics of a left atrium (LA) by proposing a computational model suitable to provide physically meaningful fluid dynamics indications and detailed blood flow characterization. In particular, we consider the incompressible Navier–Stokes equations in Arbitrary Lagrangian Eulerian (ALE) formulation to deal with the LA domain under prescribed motion. A Variational Multiscale (VMS) method is adopted to obtain a stable formulation of the Navier–Stokes equations discretized by means of the Finite Element method and to account for turbulence modelling based on Large Eddy Simulation (LES). The aim of this paper is twofold: on one hand to improve the general understanding of blood flow in the human LA in normal conditions; on the other, to analyse the effects of the turbulence VMS-LES method on a situation of blood flow which is neither laminar, nor fully turbulent, but rather transitional as in LA. Our results suggest that if relatively coarse meshes are adopted, the additional stabilization terms introduced by the VMS-LES method allow to better predict transitional effects and cycle-to-cycle blood flow variations than the standard SUPG stabilization method. [ABSTRACT FROM AUTHOR]

In the development of tidal energy, in order to extract more energy in the limited tidal farm, large-scale deployment of tidal current turbine is needed. In this paper, based on the PimpleDyMFoam solver in Open Source Fluid Dynamics Software (OpenFOAM), an effective numerical method is proposed for the two-dimensional VATCT (Vertical Axis Tidal Current Turbine). Secondly, the symmetrical simplified model is introduced to simulate the multi-rotor VATCT array. The interaction and wake characteristics of each turbine in different array layout schemes are studied in order to enhance the understanding of the interaction between multiple turbines. It is well known that the interaction between multiple turbines improves the overall power conversion efficiency, so it is of great significance to conduct in-depth research. The CFD numerical simulation results of the multi-rotor turbine array are compared in three aspects: blade force, wake flow field and power conversion efficiency. The results show that the power conversion efficiency of multi-rotor turbine array is higher than that of the stand-alone turbine. The smaller the spacing of each turbine in the multi-rotor turbine, the larger the overall output power. The single-row multi-rotor array in the form of opposite-rotation is more advantageous for energy acquisition. The analysis of the multi-rotor array from the aspect of the wake flow field can provide some insights into the reasons for the increased power conversion in the array. In this paper, force characteristics, wake characteristics and the energy efficiency of multi-rotor VATCT under different array layouts are considered comprehensively. The array optimization scheme proposed from the point of view of hydrodynamics will provide technical insights for the industrialization of large-scale VATCT array farm. • A hydrodynamic analysis model of multi-rotor turbine array is established. • The power of the array farm increases with the decrease of the lateral spacing. • The single-row array farm in the form of opposite-rotation is more advantageous. • The interaction between turbines changes the velocity in the rotor disk region. • In the multi-rotor array, the power conversion efficiency can be increased by 36.5%. [ABSTRACT FROM AUTHOR]

The subsea jumper, a crucial pipeline connector facilitating liquid transport between underwater structures, experiences dynamic alterations in flow direction, rate, and phase volumes owing to its distinctive design. These complex flow characteristics can trigger flow-induced vibrations, potentially causing fatigue damage to the jumper. This paper explores the multiphase flow patterns (oil, gas, and water) in a rigid M-shaped subsea jumper under varied mixing velocities (2–4 m/s) and different volume fractions of each phase (0.1–0.7). It analyzes the factors influencing structural vibration response. The findings reveal diverse flow patterns within the jumper, each exhibiting distinct characteristics based on flow parameters. Concurrently, spatiotemporal oscillations from fluid dynamics impact each bend. Pressure on jumper walls gradually diminishes with changing flow direction. Furthermore, the study performs structural modal and frequency domain analyses of pulsating pressure to evaluate potential resonance conditions. The results of this paper contribute to a deeper understanding of the multiphase flow characteristics in jumpers, offering valuable insights to enhance the reliability of underwater oil and gas production. • The three-phase flow pattern evolution of oil, gas, and water in the M-shaped jumper was studied through simulation. • The flow characteristics of slug flow induced by multiphase flow in the jumper were investigated. • Explored the pressure drop characteristics of oil, gas, and water flow in the jumper at different flow rates. • Through one-way fluid-structure interaction, the jumper's vibration under multiphase flow was obtained. [ABSTRACT FROM AUTHOR]

Findings on PEMFC designs grew tremendously in the past decade. Commercially, PEMFCs are usually configured in a stack to achieve higher electrochemical output. However, the two-phase fluid transport in a multiple-cell stack raises the complexity of reactant diffusion towards the porous electrodes than a single-cell stack as the higher current generation naturally increases water and heat production. Ensuring optimum hydration with even thermal distribution is critical in maintaining the MEA durability and overall electrochemical performance. Therefore, this review paper provides a comprehensive discussion of how the inconsistencies in water and thermal distribution impact the electrochemical reactiveness within the cell and electrode layers of a multiple-cell PEMFC stack. Targeting the bipolar plate design is not only essential for uniform fluid distribution but it can also be used to maximise the contact surface area to achieve a greater reactant consumption rate. Hence, the effect of varying manifold, flow field and distribution zone designs towardthe fluid and reaction dynamics per cell of a multiple-cell stack were discussed based on available literature. Although the difference in water and heat saturation between single- and multiple-cell stacks could be highlighted clearly in this paper, more research is needed particularly for novel bipolar plate designs. This would be essential knowledge in generating an optimal bipolar plate design that can enhance the durability and performance of PEMFC stacks. • Water and temperature dispersal in multiple-cell PEMFC stacks differ from single-cell units. • Cell dehydration causes higher performance loss in fuel cells compared to flooding. • The fluid dynamics and electrochemical responses across a single-cell stack differ from a multiple-cell stack. [ABSTRACT FROM AUTHOR]

• A comprehensive numeric model of a condensation-driven dilution refrigerator is established. • Systematical simulations are carried out to analyze the system performances. • T-S and P-T figures of the cold cycle at typical operating conditions are given. • The influence of the key operating parameters such as 3He flowrate are investigated. The dilution refrigerator is the most popular subkelvin refrigerator and important for research fields such as condensed matter physics, astronomical observation, and quantum computing. For applications requiring small cooling powers as well as small footprints, the cold-cycle dilution refrigerators without ambient mechanical pumps and complex connecting gas circuits have become a new research frontier. In this paper, a condensation-driven dilution refrigerator, as a kind of cold-cycle dilution refrigerator, is studied numerically. A comprehensive model covering the thermodynamics, heat transfer and fluid dynamics is established and systematical simulations are carried out to analyze the system performance and the influence of key operating parameters. Through simulations, the T - S and P - T figures of the cold cycle at typical operating conditions are given, and the thermodynamic processes and irreversibility are analyzed. Typically, a COP of 0.025 with the corresponding thermodynamic second-law efficiency of 7.5% can be obtained at 100 mK with the still temperature being 450 mK and the condensation pump temperature being 400 mK. The results reveal the mechanism of the condensation-driven dilution refrigerators and provide useful guidance to the design and operation of experimental setup. [ABSTRACT FROM AUTHOR]

Future advanced aero-engine features highly complex internal flow mechanisms, such as small gap blade row interactions and coupled fluid-structure interactions. Simulating these is challenging for convectional body-fitted computation fluid dynamics methods. As a first step towards this ultimate goal, this paper presents applications of an immersed boundary (IB) method for internal-flow problems at high Reynolds numbers. A hybrid mesh strategy, with a single-block and structured mesh to fit the physical domain and an IB method to model the internal walls, is adopted to the internal-flow problems. To achieve this, an adaptive forcing distance (AFD) technique is proposed for determining the forcing point locations when large-aspect-ratio cells are involved near the walls. This extends the IB method to curvilinear grids so that the domain boundaries can be resolved by a body-fitted mesh, which significantly reduces the total cell number needed to resolve the boundaries compared to the usage of a Cartesian grid, and thus improve the computational efficiency. The present methodologies are firstly validated on a Cartesian grid through a 2D NACA0012 test case. Subsequently, the methods are tested for two internal flow problems with increasing complexity: a 3D subsonic compressor cascade and a well-known transonic rotor, NASA Rotor 37. These case studies prove that the present method can achieve the same overall accuracy for the pressure distribution with the traditional body-fitted simulations at the attached-flow regions, and further studies are still necessary to improve the accuracy of predicting the friction coefficient and separated flows. [ABSTRACT FROM AUTHOR]

For missions that involve launching satellites into sun-synchronous orbits, the load-carrying capacity can be improved by regulating the time distribution of different flight phases if a transfer orbit is planned. However, this will shorten the last burn time of the engines. This paper introduces the technologies to ensure a reliable engine restart after coasting when only a reduced level of propellants is left. The influence mechanism of different flight profiles on the carrying capacity is analyzed first. Then a joint simulation method integrating the attitude control and fluid dynamics is proposed that can accurately analyze the sloshing features of the cryogenic propellants and their influences under microgravity conditions. Finally, a guidance method is studied that eliminates the attitude deviations at the shutdown time of the first burn to suppress additional propellant sloshing during the follow-up coasting phase. The high-fidelity simulation system reveals the feasibility of a low level scenario, and with the action of the updated guidance method, the pressure drop can be controlled as needed and the sloshing can be well restrained, matching the existing pressurization ability and requirements for re-ignitions of engines. These technologies are applied in the successful launch of the LM-8/Y2 mission, in which the performance improvement is verified. • The performance improving mechanism by allocating times of flight phases is revealed. • A complete solution to a shallow startup under microgravity conditions is sorted out. • A high-fidelity joint simulation system with control/fluid dynamics is well modeled. • Innovative powered flight guidance is proposed to meet terminal attitude constraints. [ABSTRACT FROM AUTHOR]

• Optimize incompressible turbulent flow at bidimensional and tridimensional domains employing the continuous adjoint approach • Analyze the influence of integer design variables in topology optimization of incompressible turbulent fluids • Develop the adjoint near wall distance calculation to treat the adjoint spalart allmaras turbulence model Turbulent fluid flow is a challenging physical problem to be addressed with topology optimization due to the vortex generation and the near wall distance calculation that difficult the calibration of topology optimization parameters when continuous design variables based-optimizers are used. The intrinsic nature of topology optimization inverse permeability interpolation clashes with the accuracy requirements from turbulent fluid flow dynamics. To solve the mentioned challenge, the present paper investigates the influence of an integer continuous variable-based-optimizer, i.e. a [0, 1] binary behaviour, that avoids grey regions during the optimization process. Its influence on the near wall distance calculation is analyzed as it affects the permeability of the fluid domain. The turbulence phenomenon is treated via the Spalart-Allmaras model and its near wall distance calculation is approached by the Hamilton-Jacobi formulation. Permeability independence on the topology optimization formulation constraints is proposed firstly at the continuous adjoint approach to avoid miscalculations in the fluid cells. The finite volume method is employed to solve the Reynolds Averaged Navier-Stokes governing equations and 2D and 3D tests are developed, where discussions on the solid-fluid boundaries definition, the material penalization dependence, objective function comparisons and accuracy of the CFD analysis and the wall distance calculation are presented. [ABSTRACT FROM AUTHOR]

Under control action, wave energy devices typically display nonlinear hydrodynamic behaviour, making the design of energy maximising control somewhat onerous. One solution to approach the optimal performance for nonlinear control problem under model mismatches is to employ a linear control strategy, which can be robust to linear model mismatches. However, accurate characterisation of the uncertainty in the linear model is vital, if the controller is to adequately capture the full extent of the uncertainty, while not being overly conservative due to overestimation of the uncertainty. This paper describes a procedure, employing CFD-based numerical tank experiments, to accurately produce a nominal linear empirical transfer function model, along with an accurate estimate of the uncertainty bounds in that linear model, due to hydrodynamic uncertainty. A robust control case study is provided, illustrating the nominal model estimation process, and its corresponding uncertainty set, including the complete procedure, required to generate the robust controller. Robust control results, on the fully nonlinear CFD model, are provided to demonstrate the efficacy of the modelling and control philosophy. • Input signal synthesis and post-processing in numerical wave tank experiments. • Reducing conservatism in robust control of wave energy devices. • High-fidelity nominal and uncertainty model from computation fluid dynamics setup. • Quantifying hydrodynamic uncertainty description of the wave energy converters. • Empirical transfer function refinement based on physics of wave energy converters. [ABSTRACT FROM AUTHOR]

Feed-water valves are widely used in nuclear power plants to regulate the flow rate of the water supplying to steam generators, and thus holding the water level in steam generators at desired values. The flow rate characteristics of feed-water valves have important effects on the management quality of the water level in steam generators and therefore influence the safety and the efficiency of nuclear power plants. In this paper, the effects of throttling window shapes on the flow rate characteristics through feed-water valves are investigated in two aspects, the overall performances and the fluid dynamics. First of all, a dimensionless parameter defining throttling window shapes is proposed for the quantitative assessment. Then, for the analysis of overall performances, the rated flow coefficient, the loss coefficient, and the inherent valve characteristics are investigated. A revised fitting function is obtained to predict the inherent valve characteristics with different throttling window shapes for engineering applications. Finally, for the observation of the fluid dynamics, the velocity characteristics and the pressure characteristics are both discussed. The wear conditions are predicted at different relative travels and throttling window shapes. This paper provides a reference for researchers dealing with the design work of feed-water valves and is beneficial for the improvement of the whole water level control system. [ABSTRACT FROM AUTHOR]

• It is shown that the turbulent flow is a heterogeneous mixture of two fluids. • Based on the dynamics of two fluids, a closed system of equations of turbulent flow was obtained. • It is shown that the new model describes well the turbulence near the wall, free jet and rotating flow. The paper presents an elaboration of a well-known two-fluid model for the description of turbulence. The idea that a turbulent flow can be modeled by considering a heterogeneous mixture of two fluids that make a relative motion is proven mathematically in the paper. It is shown that the fluctuating nature of the turbulent flow is due to relative motion of these fluids. Therefore, the proposed mathematical model is based on the theory of the dynamics of two fluids. For each fluid its own equation of motion is written, that leads to a closed system of equations. To calibrate the unknown constants of a new model, a problem of turbulent flow around a flat plate is considered. It is shown that the model is a low-Reynolds-number model. To verify the calibrated model, numerical studies of round and plane turbulent jets for various flow sections are conducted. It is shown that the model is not affected by the well-known problem of "round jet anomaly". Another problem is investigated - an abrupt expansion of a strongly swirling flow - to study the possibility of the proposed model to describe anisotropic turbulent flows. The derived model is validated by comparing the results of numerical calculations with existing experimental data. [ABSTRACT FROM AUTHOR]

Predicting the outcome of jet-milling based on the knowledge of process parameters and starting material properties is a task still far from being accomplished. Given the technical difficulties in measuring thermodynamics, flow properties and particle statistics directly in the mills, modelling and simulations constitute alternative tools to gain insight in the process physics and many papers have been recently published on the subject. An ideal predictive simulation tool should combine the correct description of non-isothermal, compressible, high Mach number fluid flow, the correct particle-fluid and particle-particle interactions and the correct fracture mechanics of particle upon collisions but it is not currently available. In this paper we present our coupled CFD-DEM simulation results; while comparing them with the recent modelling and experimental works we will review the current understating of the jet-mill physics and particle classification. Subsequently we analyze the missing elements and the bottlenecks currently limiting the simulation technique as well as the possible ways to circumvent them towards a quantitative, predictive simulation of jet-milling. Unlabelled Image • CFD study of milling fluid dynamics as a function of geometry and process parameters. • DEM study of particle classification by the mill in agreement with cut-size model. • Analysis of the cut-size dependence on classifier geometry and milling conditions. • Study of particle collision energy and statistics for different milling conditions. • Analysis of bottlenecks and further step towards realistic simulation of jet milling. [ABSTRACT FROM AUTHOR]

• The non-Newtonian general Cross model, the rheological parameters of which are determined by the Bingham model and the Mohr–Coulomb yield criterion, is introduced into the three-dimensional BSMPM for simulating granular flow and impact problems. • The proposed method well reproduces the overall process of granular flow and impact behavior, including its various stages of formation, acceleration, deceleration, and deposition, as well as the impact pressure. • The effectiveness of the proposed method has been demonstrated as the simulated results agree very well with the existing experimental results. Therefore, this paper provides an effective and promising method for solving soil landslides, debris flows, and other complex geotechnical engineering problems. Granular flow and impact, such as landslides and debris flows, are typical problems involving large deformations of non-Newtonian free surfaces, which are of great interest in geological engineering and also pose challenges for traditional mesh-based numerical methods. As an enhancement of the traditional Material Point Method (MPM), the B-Spline Material Point Method (BSMPM) can not only effectively reduce mesh-crossing and quadrature errors, but also facilitate the tracking and capturing of free surfaces and contact interfaces. In this paper, the non-Newtonian general Cross model, the rheological parameters of which are determined by the Bingham model and the Mohr-Coulomb yield criterion, is introduced into the three-dimensional BSMPM (3D BSMPM) for simulating granular flow and impact problems. Interparticle effects of granular materials are represented by artificial damping forces. Dynamic simulations are carried out on the collapse of sand column and glass beads, the flow of bentonite suspensions, and the impact between granular mass and elastic obstacles. The overall evolution of granular flow and impact behavior are presented and compared with existing experimental and/or original MPM results. It is found that the proposed method well reproduces the overall process of granular flow and impact behavior, including its various stages of formation, acceleration, deceleration, and deposition, as well as the impact pressure. The results show that the granular flow and impact behavior can be well represented by the proposed 3D BSMPM with the Cross rheological model, demonstrating the effectiveness of the proposed method in simulating complicated environmental fluid dynamics. [ABSTRACT FROM AUTHOR]

This paper addresses several control problems for a prototypical microfluidic process designed for the separation operations of a fluid containing particles. The device is composed of one or several cascaded bifurcations that are traveled by the fluid. The volume fraction of particles in the flow is modified at each bifurcation. Fractionation is caused by the Zweifach–Fung effect, which governs the fluid dynamics in this device. It is a nonlinear effect that solely depends on the ratio of the flow rates in the branches. Propagation through the dead- volumes of the device and its capillary tubings generate input-varying delays of hydraulic type. These hydraulic delays strongly contribute to the complexity of the input–output dynamics to be controlled. The paper presents a model of the device and formulates some concise control problem statements for future research, along with illustrative simulation results. The case of single and dual bifurcation are presented. [ABSTRACT FROM AUTHOR]

At the core of redox flow reactors, the design of the flow field geometry –which distributes the liquid electrolyte through the porous electrodes– and the porous electrode microstructure –which provides surfaces for electrochemical reactions– determines the performance of the system. To date, these two components have been engineered in isolation and their interdependence, although critical, is largely overlooked. Here, we systematically investigate the interaction between state-of-the-art electrode microstructures (a paper and a cloth) and prevailing flow field geometries (flow through, serpentine and four variations of interdigitated). We employ a suite of microscopic, fluid dynamics, and electrochemical diagnostics to elucidate structure-property-performance relationships. We find that interdigitated flow fields in combination with paper electrodes –which features a uniform microstructure with unimodal pore size distribution– and flow-through configurations combined with cloth electrodes –which have a hierarchical microstructure with bimodal pore size distribution– provide the most favorable trade-off between hydraulic and electrochemical performance. Our analysis evidences the importance of carrying out the co-design of flow fields and electrode microstructures in tandem. [Display omitted] • Coupled influence of electrodes and flow field geometries on reactor performance. • Woven electrodes perform best with flow through geometries. • Non-woven electrodes perform best with interdigitated designs. • Flow fields and electrodes must be designed in tandem. [ABSTRACT FROM AUTHOR]

This paper reports a theory investigation focusing on liquid penetration of diesel spray. A onedimensional model on liquid length is developed for the prediction of liquid length, based on the momentum flux and fuel mass flux conservation along the sprays' axis, and energy conservation on the control volume. The heterogeneous distribution of velocity and fuel concentration over the cross-section of spray is taken into consideration. A Gaussian radial profile is assumed for the velocity and fuel volume fraction distribution, and a distribution factor (β) is introduced to describe the distribution profile of axial velocity and fuel volume fraction. The model derived in this research was validated by the measured data from Siebers' experiment over a wide ambient gas temperature and density. This comparison indicates that the velocity and fuel concentration profiles are critical and cannot be neglected in the derivation of liquid length. The distribution factor is confirmed from the best fit of the calculated liquid lengths to the measured data, and should be set as 1.8 for the best fit. The model is further validated by the measured data over a wide orifice pressure drop, orifice diameter, and fuel temperature range. Based on the validated model, liquid length of diesel spray under different gas composition is calculated, and effect of ambient gas composition on liquid length is discussed. [ABSTRACT FROM AUTHOR]

The asymmetrical impact of hull-shaped bodies is quite common when a ship sails in oblique waves. In this paper, the impact hydrodynamics of a typical hull obliquely entering water are studied via drop tests. The influence of the bottom bulbous bow and inclination angle on the fluid flow and pressure characteristics are the main concerns. Some special fluid characteristics (jet flows and air cavities) are observed, and the mechanism of load characteristics (i.e., multiple peaks, negative pressure and high oscillations) is explored by combining the free surface characteristics. The existence of the bulbous bow causes obvious fluid separation and jet impact, and the separation degree and jet impact position are affected by the inclination angle. The influence of drop height on impact fluid dynamics is explored. Higher impact velocities result in more intense fluid flow and bubble breaking. The dimensionless pressure coefficient at different entry velocities is different because the affected air cavity flows near the bottom bulbous bow. These findings reveal the law of load and fluid characteristics of hull bodies under asymmetrical impact. • A series of oblique drop tests of a hull-shaped body is carried out to clarify the hydrodynamic impact characteristics. • Mechanism of fluid dynamic behaviors including flow separation, jet flow impact and air cavity is clarified. • Complete dataset (free surface and impact pressure) is provided to fill the gap of oblique water entry of hull-shaped bodies. • Influence of inclination angle and bottom appendage on the fluid dynamic behaviors and load characteristics is clarified. [ABSTRACT FROM AUTHOR]

• Investigated thermal characteristics of tandem cylinders with different grooves and rotational speeds. • Analyzed impact of three groove types (rectangle, triangle, dimple) on wake dynamics and thermal performance. • Found triangular and dimpled grooves exhibit similar anti-phase trends in lift coefficient at θ = 90° and Ω = 1. • Observed significant variation in Strouhal number and vortex energy based on groove type, especially at θ = 45°. • Identified dimpled grooves enhance negative vortex activity, leading to distinct flow separation patterns. • Noted rectangular grooves reduce time-averaged surface Nusselt number by approximately 6.7%. • Achieved best drag reduction with tandem triangular grooves at low speed (Ω = 1) and θ = 0°. • Determined optimal thermal performance for triangular grooves at high speeds (Ω ≥ 5) and θ = 45°. • Confirmed all groove types positively influence thermal behavior despite slight TPI decrease at θ = 90°. This paper numerically analyses the thermal characteristics of tandem cylinders, considering different grooves and non-dimensional rotation speeds (Ω). Two cylinders have the same diameter, D , with a spacing of 4 D. The upstream cylinder features grooves on its leading surface, whereas the downstream smooth cylinder is subjected to different rotational speeds. Investigations are conducted at a constant Reynolds number (Re = 200) for three different types of grooves (rectangle, triangle and dimple) at various angular positions (θ = 0°, 45° and 90°) and six dimensionless rotational speeds (Ω = 0–5). This study focuses on how the Ω , groove type and angular position affect the wake dynamics and thermal characteristics. The results indicate that triangular and dimpled grooves demonstrate a similar anti-phase trend in lift coefficient under static conditions with Ω = 1 once θ is set to 90°. The variation in the Strouhal number is closely associated with groove type, significantly altering the energy of the dominant vortices. This effect is particularly remarkable at θ = 45°, where different groove types substantially impact vortex energy. On the other hand, dimpled grooves notably strengthen the activity of negative vortices in the wake. Moreover, groove patterns alter flow separation, resulting in a pea-shaped wake vortex on one side at θ = 90°. Subsequently, at the highest speed of Ω = 5, the thermal boundary layer tilts and distributes evenly, forming two asymmetric independent thermal plumes. Further investigation revealed that the groove's shape significantly impacts the time-averaged surface Nusselt number (< N ¯ u 1 >) value; notably, a rectangular groove decreases the < N ¯ u 1 > value by approximately 6.7 %. Besides, at low speed (Ω = 1) and θ = 0°, the tandem triangular groove configuration provides the best drag reduction. When θ increases to 90°, the pressure drop remains below 1 in all cases except when Ω = 5. However, at Ω = 5, the TPI of triangular grooves surpasses other cases, indicating optimal thermal performance at high speeds (Ω ≥ 5) and θ = 45°. Although the TPI for triangular and dimpled grooves slightly decreases at θ = 90° compared to θ = 45° (0 ≤ Ω ≤ 2), all groove types still positively impact thermal behavior. [ABSTRACT FROM AUTHOR]

The accurate and efficient simulation for violent free surface flow with intense splashing is import in engineering. The purpose of this paper was to extend and validate the capabilities of Sunway Lattice Boltzmann Method code (SWLBM, our in-house developed CFD framework) in simulating large-scale three-dimensional violent free surface flow. The lattice Boltzmann method was employed to solve the fluid dynamics. The interface was captured by the single-phase free surface model. For parallel computing, the computational domain was divided into parallel blocks and overlap layers were designed for inter-block communications. Several typical dam-break problems were selected for validating the ability of reproducing splashing details, where finest spatial resolution was up to about 0.6 billion cells. The numerical results were in good agreement with experimental results. The present results revealed more plentiful splashing details than various published results with relatively coarser spatial resolution. The efficiency of SWLBM was over 100 times higher than that of OpenFOAM in the testing example. It was demonstrated that SWLBM is capable of simulating large-scale violent free surface flow and reproducing splashing details with sufficient accuracy and efficiency. SWLBM has the potential to be applied in real engineering problems including simulating wave impact on decks. • The capabilities of free surface simulation have been extended for the LBM-based framework SWLBM. • The accuracy and robustness of SWLBM were validated through various dam-break cases. • Large-scale simulations for free surface flow with up to 0.6 billion lattice cells were achieved. • Much more plentiful splashing details are reproduced compared with existing relevant literature. • The efficiency of SWLBM was over 100 times higher than that of OpenFOAM in the testing example. [ABSTRACT FROM AUTHOR]

Acquisition of an instantaneous pressure field in a flow field is essential for experimental fluid dynamics research because pressure is associated with various flow phenomena. Machine learning has performed well in various fluid mechanics studies in recent years due to its nonlinearity. In this paper, we use the machine learning method to predict the pressure fields from incomplete velocity fields while reconstructing the missing velocity information, as exemplified by the stationary circular cylinder flow and circular cylinder undergoing forced oscillating problems, in which the incompleteness of the velocity field is caused by the optical path occlusion in experiments. We propose a network model based on convolutional neural networks. The experimental results show that the error of machine learning methods is around 4%, and even if the resolution of the training set is reduced, it does not affect the prediction accuracy of the network. For statistical averaging of prediction results, the network has high accuracy in predicting first-order quantities, but its ability to predict second-order quantities is limited. We also explore the effects of the amount of noise on the performance of networks. When applying the model to the forced oscillating cylinder problem, we use transfer learning to train the network given the similarity of the two problems, and the training error yields faster convergence and more minor convergence results. In addition to this, we use flow field data with a single vibration frequency to construct a single dataset, and flow field data with multiple vibration frequencies to construct a mixed dataset, and study the effect of different datasets on the prediction accuracy, which shows that it is difficult for neural networks to achieve both accuracy and generalization. • A deep neural network was constructed to predict the pressure field directly from the velocity field. • The model can reconstruct the missing velocity information while predicting the pressure field. • The model can be transferred from a circular cylinder flow to a forced oscillating circular cylinder flow. [ABSTRACT FROM AUTHOR]

This paper introduces an efficient numerical solver for simulating 2D turbulent cavitating flows. The solver builds upon the VIScous Vorticity Equation (VISVE) framework, which previously focused on simulating turbulent wetted flows. This work expands the capabilities of VISVE by incorporating an explicit pressure-solving scheme specifically designed for turbulent cavitating flows. A cavitation model and a mixture model are also integrated, extending VISVE's applicability to complex flows with both turbulence and cavitation. The effectiveness of this solver is demonstrated through validations across turbulent wetted flows and turbulent cavitating flows past NACA66 hydrofoils. The solver exhibits mesh independence and successfully handles variations in hydrofoil geometry. Comparisons with established commercial software and experimental data showcase good agreement. Remarkably, the solver achieves a computational speed exceeding that of traditional Reynolds-Averaged Navier–Stokes (RANS) solvers by at least one order of magnitude. This work represents an advancement in the VISVE solver's capabilities, enabling the efficient simulation of complex fluid dynamics involving turbulence and cavitation. • Software Development: Develops efficient software VISVE for 2D turbulent cavitating flow. • Applications: Model works on various hydrofoils and cavitation numbers. • Validation: Results validated by experiments and compared with commercial RANS solvers. • Efficiency: VISVE is faster by one order of magnitude when compared with RANS. [ABSTRACT FROM AUTHOR]

In the field of wave energy extraction, employing active control strategies amplifies the Wave Energy Converter's (WEC) response to wave motion. In this regard, a numerical simulation study was conducted on the interaction between Duck WEC and waves under discrete latching control, proposing an optimized latching duration strategy based on Deep Reinforcement Learning (DRL). The study utilized an improved Edinburgh Duck model to establish a numerical wave flume (NWF), verifying the motion of waves and the device. A DRL and Computational Fluid Dynamics (CFD) coupled framework was developed to implement the latching control strategy. In the limited trichromatic wave testing conditions provided in this paper, the latching control time is optimized using a DRL agent, and its capture efficiency is compared with two non-predictive latching control strategies. The DRL agent control showed a 13.4% improvement relative to reference threshold control, with less than 6.3% differences compared to optimal threshold latching results. Improvement of approximately 5.6% was observed compared to optimal constant latching control. For the first time in nonlinear fluid dynamics numerical simulation, this study demonstrates the efficacy of model-free reinforcement learning with discrete latching actions, establishing an environment-driven control strategy, and having the potential to become a general strategy for WEC latching control. • Established a coupled framework integrating with DRL and a numerical wave flume of CFD simulation. • Compared latching control based on DRL with two non-predictive latching control methods. • The trained agent demonstrates generalizability across trichromatic wave groups and regular wave tests. [ABSTRACT FROM AUTHOR]