Numerical investigation of mixed-phase turbulence in flow past a partially merged plate

Large-eddy simulation (LES) is conducted to study the statistical properties of mixed-phase turbulence induced by the breaking of bow waves in flow past a partially submerged plate. The simulation is performed using a finite difference method, with the air-water interface captured by a coupled level-set and volume-of-fluid method. Four cases are conducted to investigate the effects of Froude number on turbulent statistics, including the mean velocity, turbulence kinetic energy, and turbulence mass flux (TMF), which is an additional unclosed term in the Reynolds-averaged momentum equation. The TMF, especially its vertical component, shows a complex behaviour with respect to the Froude number. This property of the TMF imposes high demands on the robustness of the closure model of TMF. The present LES data is further used to examine a closure model of the TMF production term, which shows a high correlation with the data obtained from LES

Wind farm fluid mechanics for high-penetration wind energy

Advancements in aerodynamics during the early 20th century laid the foundation for modern wind energy. The increasing penetration of wind power presents novel challenges in fluid mechanics, which stem from an incomplete understanding of the dynamics of wind turbine wakes and their interactions with the atmospheric flow. This article provides a comprehensive review of the current understanding of the mechanisms of wind turbine wakes and wake-atmosphere interactions. It summarizes existing models for wind turbine wakes and explores control strategies for mitigating wake losses and tracking power reference signals. Finally, it delves into research trends in the field and summarizes the review

Physical and MPM modelling of sand column collapse with different moisture and density conditions

The sand column collapse test is a simple but useful experiment for investigating the dynamic behaviour of granular flow, which is an important topic in engineering geology and the validation of numerical models. Previous studies have not adequately considered the influence of soil moisture and density conditions. In this study, a series of sand column collapse tests were conducted, considering five water contents ranging from 0 to 10 % and two relative densities of 40 % and 58 %. Particle Image Velocimetry (PIV) was utilised to post-process the experimental results. A hydro-mechanical coupled Material Point Method (MPM), improved by incorporating a non-linear strain hardening/softening law, was employed to back-analyse the physical model tests. The measured and computed results show that as water content increases, the degree of collapse and post-collapse runout distance initially decrease, consistent with changes in Bishop's stress, affected by suction and interparticle water meniscus. As relative density increases, both the degree of collapse and the post-collapse runout distance decrease due to the greater shear strength and Bishop's stress. The MPM simulations closely matched experimental results, confirming the model's accuracy in simulating large deformations in both dry and unsaturated soils

Nonlinear dynamic responses of wing flexible sealing undergoing flapping effect

With the increasing demands of higher performance of advanced aircrafts, the flexible sealing have been used to seal the gap between main wing surface and its movable control surface so as to improve stealth performance and control effectiveness. However, during whole flight process undergoing various operation states and severe loadings, the flexible sealing could be separated from control surface and consequently strongly vibrate under the disturbances coming from ambient airflow. In that case, "flapping" motions between flexible sealing and other wing components may cause complicated nonlinear dynamic structural response due to discontinuous boundary conditions along with impact effect. In this study, the static structural responses in multiple states, including original state, installation state and lifting process, are firstly examined based on FEM numerical simulations. The displacements and contact preloads that can influence the dynamic characteristics and responses, changing with flight states and speeds, are given so as to analyze and model the discontinuous boundary conditions. Furthermore, the dynamic responses of the flexible sealing during its flapping motions under these particular discontinuous constraints, considering combination actions of periodic excitation and intermittent impact forces, are comprehensively studied. Our numerical results show that the dynamic displacement amplitude and root moment of flapping motion increase respectively by 86.3 % and 177.9 % than static values. And, a mixing of standing waves and traveling waves of the acceleration and shear stress responses is observed through spatiotemporal evolutions. Generally speaking, the flapping is a dynamic response with broadband spectrum rather than a simple forced vibration, which include superharmonic frequencies of excitation frequency, natural frequency and high frequencies due to impact. More interestingly, significant nonlinear phenomena such as superharmonic resonance and chaos are found due to combination actions of discontinuous constraints and intermittent impacts. To deeply explore the nonlinear behaviors of this flapping motion, an analytical model including stiffness jump and impact force is developed, and the Runge-Kutta algorithm is used to obtain the solutions of the nonlinear system. The phase diagram and Poincare section of the analytical solutions give similar qualitative results with our numerical simulations

Exceptional tensile properties induced by interlayer-compatible deformation in a gradient ultra-nanograined Cu

In this study, a gradient ultra-nanograined (GUNG) Cu was prepared by surface rolling and shearing processing at liquid nitrogen temperature. Microstructural analysis reveals a significant presence of ultrananograins (similar to 5-20 nm) within the topmost surface layer (SL), transitioning to coarser grains beneath, culminating in a gradient structure over 600 mu m deep. The GUNG Cu exhibits an exceptional strength-ductility synergy, achieving yield strengths of 250-330 MPa and uniform elongations of 17 %-30 %. The deformation mechanisms of GUNG Cu are elucidated through in-situ electron backscatter diffraction and microscopic digital image correlation, highlighting the interlayer-compatible deformation of GUNG Cu under tensile loading. It is noteworthy that the topmost ultra-nanograined SL (within depths of 0-2 mu m) in GUNG Cu maintains high mechanical stability with minimal change in grain size during tensile plastic deformation, whereas the subsurface layer (at a depth of similar to 15 mu m) displays a deformation-driven grain coarsening behavior, facilitating deformation compatibility across individual layers. The enhanced strength-ductility synergy exhibited in GUNG Cu can be attributed to the interplay between interlayer compatible deformation and hetero-deformation induced (HDI) hardening, in which softer and harder layers interact with each other, thus promoting the strain hardening throughout the GUNG structure. The present findings provide a more profound understanding of deformation compatibility and HDI hardening mechanisms in gradient structures, demonstrating how tailored microstructural heterogeneity can potentially circumvent the traditional strength-ductility trade-off in nanostructured materials. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology

Numerical investigation of mixed-phase turbulence in flow past a partially merged plate

Large-eddy simulation (LES) is conducted to study the statistical properties of mixed-phase turbulence induced by the breaking of bow waves in flow past a partially submerged plate. The simulation is performed using a finite difference method, with the air-water interface captured by a coupled level-set and volume-of-fluid method. Four cases are conducted to investigate the effects of Froude number on turbulent statistics, including the mean velocity, turbulence kinetic energy, and turbulence mass flux (TMF), which is an additional unclosed term in the Reynolds-averaged momentum equation. The TMF, especially its vertical component, shows a complex behaviour with respect to the Froude number. This property of the TMF imposes high demands on the robustness of the closure model of TMF. The present LES data is further used to examine a closure model of the TMF production term, which shows a high correlation with the data obtained from LES

A numerical toolkit for the ignition delay time and ignition probability density predictions based on instantaneous mixing fields in OpenFOAM

The OpenFOAM built-in chemistry solver, chemFoam, is extended as multiMeshChemFoam to simultaneously calculate the zero-dimensional (0D) ignition processes on the entire computational domain of practical simulations. The instantaneous temperature, pressure, and species mass fractions of a mixing field are input for the ignition calculation. A solver termed idtFoam is then developed to extract the Ignition Delay Time (IDT) on all cells from the 0D calculations. Several ignition criterions including the temperature exceeds a threshold value, the peaks in heat release rate (or equivalently, the time derivative of temperature) and species mass fractions are available. Another solver denoted as ipdFoam is finally compiled to construct the Ignition Probability Density (IPD) on the entire domain for a certain period. A time series of transient data from the mixing field are necessitated for the ignition calculation, IDT extraction, and IPD construction on individual cells. The numerical toolkit is verified with chemFoam for the 0D ignitions of ethylene. It is then applied to the mixing fields of an ethylene-fueled model supersonic combustor. It is computationally-efficient to evaluate the ignition performance of practical combustion systems in the design phase. Furthermore, assessment on the ignition properties can be made prior to any detailed and computationally-expensive simulations on the reactive flow, since only mixing field is required for calculating the IDT and IPD

Creep strain and stress state-dependent creep asymmetry during early-stage room-temperature creep in a titanium alloy

Room-temperature (RT) creep may happen below yield stress in titanium alloys, while the creep asymmetry remains pending under various stress states. The creep behavior and plastic damage were investigated during the early-stage RT-creep up to 60 h in a titanium alloy. The investigated TC4 ELI Ti-alloy is a high-purity ("Extra-Low-Interstitial") version of Ti-6Al-4V with a near- alpha type microstructure after thermomechanical treatment. Three kinds of creep testing were conducted, including axial tension, compression, and torsion, respectively. The microstructure and especially, dislocation behaviors were analyzed in detail by using electron backscattered diffraction, transmission electron microscopy, and X-ray diffraction after an interrupted and terminated creep testing. The creep strain differs, which is 5 %, 1 %, and 0.5 % under tension, compression, and torsion, respectively. It undoubtedly indicates the presence of creep asymmetry. To clarify the creep mechanism, the slip system was then analyzed. It is shown that the prismatic slip is dominant during tensile creep, while the pyramidal slip appears most during compressive creep. The limited slip transmission and immobile dislocations result in lower creep strain. The reason behind the creep asymmetry is attributed to the stress state, producing the activation of various slip systems, along with the evolution of true stress. Finally, the mechanistic origins are also discussed as to the distinctive creep rate under various stress states. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology

Physical and MPM modelling of sand column collapse with different moisture and density conditions

The sand column collapse test is a simple but useful experiment for investigating the dynamic behaviour of granular flow, which is an important topic in engineering geology and the validation of numerical models. Previous studies have not adequately considered the influence of soil moisture and density conditions. In this study, a series of sand column collapse tests were conducted, considering five water contents ranging from 0 to 10 % and two relative densities of 40 % and 58 %. Particle Image Velocimetry (PIV) was utilised to post-process the experimental results. A hydro-mechanical coupled Material Point Method (MPM), improved by incorporating a non-linear strain hardening/softening law, was employed to back-analyse the physical model tests. The measured and computed results show that as water content increases, the degree of collapse and post-collapse runout distance initially decrease, consistent with changes in Bishop's stress, affected by suction and interparticle water meniscus. As relative density increases, both the degree of collapse and the post-collapse runout distance decrease due to the greater shear strength and Bishop's stress. The MPM simulations closely matched experimental results, confirming the model's accuracy in simulating large deformations in both dry and unsaturated soils

An arc-melted eutectic medium-entropy alloy with superior strength-ductility synergies at room and cryogenic temperatures

The cryogenic compressive mechanical properties of eutectic multi-principal alloys have rarely been reported. In this work, the superior fracture strength-fracture strain synergies at room and liquid nitrogen temperatures (RT and LNT) of the arc-melted Cr50Co25Ni25 eutectic medium-entropy alloy were found. These values were 1917 MPa and 39.1 % at RT, along with 1990 MPa and 26.1 % at LNT. The reduction of ductility at LNT was primarily attributed to the inferior deformation capability of the BCC phase containing HCP phase. The fracture mechanisms were dominated by ductile fracture of the FCC phase and brittle fracture of the BCC phase at both temperatures, while dislocation pile-ups and stacking faults were responsible for the deformation mechanisms