High-speed Flow Research Articles

A novel acid-free combined technology to achieve the full recovery of crystalline silicon photovoltaic waste

To achieve the global carbon neutrality commitment, photovoltaics, a clean and renewable source of energy, is increasingly deployed. Photovoltaic panels are core components of photovoltaic systems. As these panels reach the end of their life, recovering the photovoltaic waste becomes crucial. Currently, strong acid reagents are commonly used in the recovery of silver from crystalline silicon photovoltaic waste, posing environmental risks and restricting the industrialization of their recycling. In this study, a novel acid-free technology to achieve the full recovery of crystalline silicon photovoltaic waste was proposed. A pyrolysis process was first conducted for decapsulation, with carbon dioxide being the main gas component at 60.64 %. Next, bioleaching technology was employed to leach silver from waste crystalline silicon photovoltaic cells. The silver leaching rate in a single leaching cycle reached 44.7 %. Meanwhile, the mechanism of silver leaching was further analyzed. Finally, high-velocity fluid frictional separation, a technique that uses high-speed fluid flow to separate material, was chosen to obtain silicon wafers. The reclaimed silicon samples had a total thickness variation of 6.64 µm to11.62 µm, with average carrier lifetimes exceeding 4.9 µs, higher than that obtained by wet etching. This study is expected to advance the industrialization of the recovery of photovoltaic waste, which is also beneficial for the sustainable development of the photovoltaic supply chain.

Enhancing improved advection upstream splitting method on triangular grids: A hybrid approach for improved stability and accuracy in compressible flow simulations

This paper introduces NAUSM+M+AUFS (New Improved Advection Upstream Splitting Method Plus Artificially Upstream Flux Vector Splitting), a novel hybrid computational scheme for simulating compressible flows on triangular grids. The AUSM+M (Improved Advection Upstream Splitting Method) method is enhanced through two key modifications to boost numerical stability and robustness in high Mach number and hypersonic flows. The first modification redefines the interfacial numerical sound velocity, reducing shock anomalies and improving shock-capturing by integrating velocity and characteristic sound speed parameters. The second modification addresses the insufficiency of the pressure flux dissipation term at supersonic speeds by introducing a formulation that increases dissipation proportionally to the Mach number, thereby enhancing performance in high-speed flows. These enhancements constitute the NAUSM+M method. The NAUSM+M+AUFS scheme combines the strengths of NAUSM+M and AUFS (Artificially Upstream Flux Vector Splitting) methods, particularly in overcoming the limitations of NAUSM+M in handling shock instabilities and the carbuncle phenomenon on structure triangular grids. A dynamic switching function adjusts the weighting between NAUSM+M and AUFS, optimizing accuracy and stability based on local flow conditions. Numerical tests demonstrate that NAUSM+M+AUFS significantly outperforms AUSM+M, NAUSM+M, and AUFS, effectively eliminating the carbuncle phenomenon and providing smooth shock wave contours. In steady flow analysis, the new hybrid method achieves convergence speeds comparable to AUFS and shows 15% to 45% superior convergence accelerating than AUSM+M, depending on the convergence rate. In addition, in steady flow analysis, the accuracy of NAUSM+M+AUFS is 46% better than that of AUFS. This approach represents a significant advancement, offering a robust, accurate, and efficient solution for high-speed aerodynamic simulations, with broad applicability across various compressible flow challenges.

Motion process and failure mode of Pusa landslide, China based on dense optical flow method

ABSTRACT Unmanned aerial vehicle (UAV) is widely applied in geohazard monitoring with its high resolution and feasibility features, where UAV videos can record the whole landslide failure process. Previous studies can only provide the qualitative depiction of the landslide failure process, rather than the quantitative motion process, which makes it difficult to analyse the landslide dynamic characteristics and failure mode. In this letter, we take UAV video of Pusa landslide, China obtained on 28 August 2017 to retrieve the landslide motion process by using the dense optical flow method. Firstly, the landslide boundary can be clearly depicted by the cumulative landslide motion time series maps. Secondly, the maximum cumulative motion distance of the Pusa landslide was located in the middle of the slope body, with the maximum distance as 79 m, while the maximum instantaneous motion rate was around 42 m/s in the middle and lower part of the slope body. Finally, the failure mode of Pusa landslide can be characterized as ‘fissure zone in the middle, fissure extension to the top, rock bulges outward in the middle and landslide failure to high-speed runout debris flow’.

Research and Analysis of the Small Disturbance Equation in Subsonic, Transonic, and Supersonic Regimes

This paper explores the application of the Small Disturbance Equation (SDE) across subsonic, transonic, and supersonic flow regimes. Derived from the Euler and Navier-Stokes equations, the SDE offers an efficient framework for analyzing aerodynamic behaviors, particularly through the utilization of discretization techniques and iterative solving methods executed in Python. The study assesses the accuracy and limitations of the SDE in detailing essential flow characteristics, revealing that while the equation performs effectively in subsonic and transonic flows, it encounters challenges in supersonic regimes. Nonlinear effects such as shock waves significantly hinder its performance at high speeds. Compared with conventional computational fluid dynamics (CFD) methods, the SDE stands out in scenarios where computational efficiency is paramount. However, its limitations in handling high-speed flows must be carefully considered, highlighting the need for further refinement in its application to supersonic dynamics. This analysis suggests that while the SDE is beneficial for certain aerodynamic studies, its scope and utility are constrained by the inherent complexities of high-speed fluid dynamics.

The mechanical environment regulates the extent of aortic valve calcification and thickness: an ex vivo whole mouse heart study

Abstract Background Aortic stenosis (AS) is a narrowing of the aortic valve opening due to calcification and thickening of the leaflets. Calcifications are mostly located at regions with high mechanical stress and disturbed flow suggesting that mechanical environment is important in the regulation of calcification. However, direct evidence linking valve calcification and mechanical stress is still lacking. Recently, we established an ex vivo calcification model for whole mouse hearts (Miniature Tissue Culture System MTCS) which allows the study of the mechanical environment underlying aortic valve calcification. Purpose Aim of this study was to investigate the role of mechanical stress on aortic valve calcification and thickening using the MTCS. Methods Whole mouse hearts were cultured in the MTCS with 2 distinct configurations: 1) medium flowing from the aorta towards the aortic valve to create a continuous closed aortic valve (n=28) and 2) medium flowing from the left ventricle through the aortic valve towards the aorta to create a continuous open aortic valve (n=17) (Figure1). The hearts were subjected to low (300 ul/min) or high (3000 ul/min) flow speed in the presence of calcifying medium (3mM phosphate buffer). After culture for 1 week, the hearts were isolated and fixed overnight with 4% PFA/PBS. Alizarin red staining was performed to determine calcification presence. Quantifications were performed using Caseviewer software. Results Aortic valves in closed configuration exposed to a high flow speed, exhibited significant increase in calcification compared to aortic valves in the closed configuration exposed to low flow speed or aortic valve cultured in the open position (p<0.01, Figure2A). Of interest, the extent of calcification in the aortic valve in closed position exposed to high flow speed strongly correlated with the diameter of the aortic annulus (R²=0.86, p<0.0001, Figure2B). Conversely, leaflet thickness was significantly lower in the closed aortic valve configuration as compared with the open aortic valves configuration (p<0.05, p<0.001, Figure2C). Conclusion Our study demonstrates the influence of mechanical environment on aortic valve calcification and thickening. The presence of calcification in the closed but not the open aortic valve configuration exposed to high flow suggests that increased pressure promotes calcification. The correlation of the extent of aortic valve calcification with the diameter of the aortic annulus implies that configuration of the valve is an important determinator of calcification, with potential implications for the results of aortic valve repair. The presence of a minimal amount of mechanical stress as experienced by aortic valves in the open position, however, resulted in thicker aortic valves, indicating that the right balance of mechanical stresses is required to maintain normal valve morphology. These findings provide valuable insights into AS pathogenesis, guiding future therapeutic approaches.ex vivo cultured aortic valvesCalcification in ex vivo aortic valves

Analytical solution of inertia effect in high-speed flows through disordered porous media

Analytical solution of inertia effect in high-speed flows through disordered porous media

Physics-based modeling of debris flows and assessing the performance of effective mitigation measures

BackgroundClimate change-induced geohazards are increasingly posing a critical threat to the sustained functionality and resilience of constructed infrastructures. Among these hazards, debris flows represent significant natural disasters, particularly in mountainous terrains, causing widespread property damage and loss of life globally. These phenomena involve complex interactions between solid and fluid forces, resulting in long run-out distances and high-speed flows. Predicting and monitoring debris flows is challenging due to the intricate interplay of these forces.ObjectiveThe objective of this study is to evaluate the structural damage caused by debris flows and assess the efficacy of rigid barrier structures with passages/apertures.MethodEmploying Smoothed Particle Hydrodynamics, a Lagrange-based mesh-free computational technique, the researchers simulated the impact of debris on a stiff structure. The focus was on the Rishiganga river valley in the Indian state of Uttarakhand, a region recently devastated by a debris flow that severely compromised essential infrastructure, including a hydroelectric power station. The research entailed modeling the debris flow in this specific locale and analyzing its effects on an assumed downstream rigid structure. Additionally, the study explored the outcomes of introducing a rigid barrier upstream.Results and ConclusionResults indicated a substantial reduction in the impact on the downstream structure with the presence of an upstream rigid structure. Moreover, as the number of apertures in the upstream barrier was increased, the impact of flow on the downstream structure further diminished, because of a more streamlined flow pattern.

Probing double-distribution-function models in discrete-velocity Boltzmann methods for highly compressible flows: Particles-on-demand realization

The double distribution function approach is an efficient route toward an extension of kinetic solvers to compressible flows. With a number of realizations available, an overview and comparative study in the context of high-speed compressible flows is presented. We discuss the different variants of the energy partition, analyses of hydrodynamic limits, and a numerical study of accuracy and performance with the particles on demand realization. Out of three considered energy partition strategies, it is shown that the nontranslational energy split requires a higher-order quadrature for proper recovery of the Navier-Stokes-Fourier equations. The internal energy split, on the other hand, while recovering the correct hydrodynamic limit with fourth-order quadrature, comes with a nonlocal—both in space and time—source term that contributes to higher computational cost and memory overhead. Based on our analysis, the total energy split demonstrates the optimal overall performance. Published by the American Physical Society 2024

Investigation of Water Film Dynamics on the Surface of an Airfoil in a High-Speed Flow and Subsequent Ligament Formation and Breakup from the Trailing Edge

Abstract In this work, the dynamics of a liquid film on the surface of NACA 0012 airfoil placed in a high-speed air flow is investigated. Experimental studies were carried out to assess the film thickness, droplet shedding, and the dynamics of the sheet. In the present work, air velocities up to 175 m/s were used with water films flowing between 1.4 and 2.6 cm2/s. The water was introduced on the airfoil via 26 holes each measuring of 0.5 mm holes separated by 1mm at 35 mm downstream of the leading edge of the vane. The results were obtained using four experimental tools. The first is a point measurement of the time-resolved film thickness using a confocal laser induced fluorescence method. Second is time averaged images of the film thickness on the entire vane surface. Third, high speed videos are obtained to study the accumulation and breakup of the liquid at the trailing edge of vane. Finally, laser diffraction and Phase Doppler interferometry were used to document the spray dynamics. The results illustrate that the average film thickness decreases with air velocity and increases with the water flow rate. Also, the dominant frequency of liquid film wave, ligament breakup length, drop size and spray concentration increase with the air velocity and is modestly affected by water flow rate. Finally, design tools are provided to predict the average film thickness and dominant frequencies of the film thickness, ligament breakup, spray concentration and droplet average size.

Sustainable drag reduction in Taylor-Couette flow using riblet superhydrophobic surfaces

Superhydrophobic surfaces (SHSs) have been proven effective in reducing frictional drag force in various flow conditions. However, at high flow speeds, the air plastron on these surfaces collapses, leading to a decline in their effectiveness. In this study, we investigated the frictional drag forces of various SHSs and their combination with surface patterns across a wide range of flow conditions (5.00×102 < Re < 1.12×105) by using an facile coating method. Our experiments involved incorporating a superhydrophobic coating on the inner cylinder of a custom-made Taylor-Couette apparatus, integrated with a rheometer to measure torque applied on the inner rotor as a function of rotational speed. As part of our research, we calculate the effective slip length to assess the drag reduction performance of coatings, revealing an effective slip length of around 63 µm on a flat SHS. Furthermore, we explore the combined effect of superhydrophobic coatings and triangular-shaped riblets on drag reduction in Taylor-Couette flow, comparing the performance of these surfaces based on the riblet’s sharpness and the Reynolds number. Our experimental results show a reduction in measured torque of up to 24 % and 48 % on a V-grooved SHS in laminar and turbulent flow, respectively. Longevity tests confirm that the designed surfaces maintain their superhydrophobicity and drag reduction performance under turbulent flow conditions. Overall, this work introduces a passive drag reduction strategy through surface design, which substantially mitigates the frictional drag force and demonstrating considerable potential for enhanced performance and increased efficiency of Taylor-Couette systems.

An evaluation of the hybrid Fokker–Planck-DSMC approach for high-speed rarefied gas flows

The Direct Simulation Monte Carlo (DSMC) method has been widely used for simulations of rarefied gas flows. It has been proven that the numerical solution of the DSMC method converges to the Boltzmann equation, providing a solid physical foundation for high Knudsen numbers. However, many aerospace engineering problems include both low and high-density regions in a single domain, making the DSMC method computationally expensive. Over the past decade, the particle Fokker–Planck (FP) method has been studied as a means to reduce computational costs near the continuum regime. While enhancing efficiency, the FP method loses physical accuracy at high Knudsen numbers. Aiming for universal accuracy and efficiency across the whole range of Knudsen numbers, the hybrid FP-DSMC method has been studied. Nevertheless, consistent comparisons among the DSMC, FP, and hybrid FP-DSMC methods have received limited attention so far. This paper presents a consistent comparative study of the DSMC, FP, and hybrid FP-DSMC methods to assess the accuracy and efficiency of the hybrid FP-DSMC method. The hybrid FP-DSMC solver is developed based on the open-source SPARTA framework. The benchmark problems include supersonic flow in a planar nozzle, hypersonic flow around a cylinder, and hypersonic flow around a THAAD-like missile. The results demonstrate that the hybrid FP-DSMC method can be more efficient than the DSMC method while being more accurate than the FP method. The speed-up achieved by the FP-DSMC method ranged from 1.5 to 14 times compared to the converged DSMC simulation.

Surface Transformation Of Ultrahigh-Temperature Ceramics HfB2-SiC-C(graphene) Under The Influence Of High-Speed Disossociated Nitrogen Jets

In order to study the promising potential of HfB2–30 vol % SiC ultrahigh-temperature ceramic materials modified with low amounts of reduced graphene oxide for the creation of aerospace equipment intended for use in N2-based atmospheres, the effect of high-speed dissociated nitrogen flow on it has been investigated. It has been established that under the chosen conditions of exposure during the stepwise increase of the anode power supply of plasma torch and, accordingly, the influencing heat flux, at certain parameters there is a sharp increase in the surface temperature from ~1750 to 2000-2100°C. At the same time, further increase of the heat flux has no obvious and proportional effect on the temperature of the sample surface, which may indicate its high catalyticity with respect to the reactions of surface recombination of atomic nitrogen. It is shown that the surface layers of the material undergo chemical transformation (removal of silicon-containing substances, formation of a new phase based on HfN), which is accompanied by a significant change in the microstructure (formation of dendrite-like structures), which affects the optical and catalytic characteristics of the surface.

Nonlinear aerothermoelastic analysis of deployable control fin with actuator stiffness subjected to high-speed compressible flows

Nonlinear aerothermoelastic analysis of deployable control fin with actuator stiffness subjected to high-speed compressible flows

Two-phase flow properties for air sheets injected from rectangular slots in high-velocity crossflow

This work presents an experimental contribution towards the understanding of the two-phase jet dynamics in high-speed transverse flows, a field that is essential to many industrial applications. Four slot injectors are the subject of this investigation, which examines air flows as high as 0.05 m3/s and cross flows as high as 6 m/s. Using an invasive optical probe, the study reveals the presence of an air cavity surrounded by a two-phase mixing zone. Analysis of the spatial void fraction reveals counter-rotating vortices that direct bubbles towards their centers while larger bubbles rise to the top of the vein and form an upper zone with a maximum void fraction. The study also looks at the dynamic evolution of air sheet characteristics, which reveals an increasing trend in average void fraction along the flow. The comparison of bubble characteristics of different slots and conditions provides valuable insights into the impact of environment pressure and slot geometry on void fraction and bubble size in two-phase flows. Finally, correlations based on dimensionless numbers generalize the information on bubble characteristics for a wide range of conditions, assisting in estimation and validation in numerical simulations.

Compositional simulation of coupled transport mechanisms in fractured-vuggy underground gas storage: A case study of LWC in the Sichuan Basin

Compositional models were built to simulate the underground gas storage (UGS) operation, which is characterized by multiple cycles of rapid injection and production. Based on the validated model of the fractured-vuggy underground gas storage Lao Weng-Chang (LWC), this study evaluated the individual and coupling effects of stress sensitivity, relative permeability hysteresis, and high-speed non-Darcy flow on UGS operation. It was found that stress sensitivity is the main controlling factor behind the reduced working gas volume, and it led to a 6.07% decline in working gas volume. Relative permeability hysteresis is the determining factor for the storage capacity, and it led to a 9.05% decline in storage capacity. The high-speed non-Darcy flow only led to a 0.16% reduction in storage capacity but led to a 4.19% decline in working gas volume. A higher stress sensitivity coefficient and increased residual gas saturation both lead to greater losses in both storage capacity and working gas volume. Coupling stress sensitivity and relative permeability hysteresis would have a more pronounced effect on working gas volume than when considered individually. Considering the high-speed non-Darcy flow further decreases working gas volume. The gas production per unit pressure drop will also decrease with the increasing Reynolds number, and there exists a critical value of Re where the decrease significantly accelerates.

Evaluation navigation controlled gate of aging spillway on cavitation damage.

High-speed flow of clean water or water with sediment released from aging spillways may cause abrasion and cavitation on the concrete surface gradually. The occurrence of irregularities on the concrete surface can exacerbate the erosion problem. Which might jeopardize the safety of dams constantly, hence the rehabilitation efforts become urgent tasks in dam safety projects. This study employs a 3D Computational Fluid Dynamics (CFD) model to quantitatively analyze the cavitation risk on the aging concrete surface of the Chay 5 spillway in Ha Giang, Vietnam, under various operation scenarios. There are two standards used to measure cavitation: the cavitation index (σ) which indicates the danger due to the drop of pressure in rapid flow, and the new gasification index (β) which takes into consideration the formation and collapse of bubbles behind asperities. Three extreme flood cases may not result in potential cavitation because both σ and β exceed critical thresholds. Regarding the six controlled gate scenarios with normal water level, the σ profiles are approximated 1,0 showing a low likelihood of cavitation damage while the β values are smaller than 0.8, indicating a considerable risk of cavitation. Besides, the opening height of 100 cm poses the greatest risk of creating severe cavitation erosion in the concave area and slope portion. The flip bucket experienced the most vulnerable cavitation when the opening height is 400 cm. In addition, an approach to spillway surface rehabilitation involving specialized mortars has been presented. For aging conveyance structure, gasification index (β) takes into account irregularities surface, providing a more comprehensive assessment of the likelihood of cavitation damage than cavitation index (σ). After rehabilitation with anti-shrinkage high abrasion resistance mortar, the entire spillway surface is smooth. This allows for reducing the cavitation risk and improvement of life service thereof.

Modification of temperature jump condition for modified Navier-Stokes equations included molecular diffusivity in high-speed rarefied gas flows

Modification of temperature jump condition for modified Navier-Stokes equations included molecular diffusivity in high-speed rarefied gas flows

Event-Based Measurement of Aeroelastic Structure in High-Speed Flow

In high-speed aerodynamics research, point sensors are ideal for embedding in test models but lack spatial resolution, whereas high-speed cameras offer spatiotemporally resolved measurement but involve significant footprint, cost, and data size. To address these tradeoffs, this study explores the application of nascent event-based cameras for high-speed tests. Event-based cameras support continuous, data-sparse kilohertz-equivalent imaging at 720p resolution, on form factors as small as 36 mm and 40 grams in mass, combining the benefits of point sensors and high-speed cameras. However, these attributes come from asynchronous pixels that necessitate unique operating and postprocessing approaches. Here, the authors adapted event-based cameras for two-/three-dimensional photogrammetric tracking of aeroelastic structures, demonstrating an event-based workflow and two tracking algorithms (mean-shift filtering and circle fit). Bench-top validations achieved three-dimensional precision of 0.35 mm/s on 20 mm/s motion across a 259 mm field of view, while two-dimensional measurements of an aeroelastic titanium panel in Mach 0.76 transonic flow successfully identified millimeter-scale vibrations at 43.7, 120, and 270 Hz, validated against a laser displacement and high-speed camera. The transonic test’s raw data were 145.8 MB on the event-based camera, compared to 88.5 GB on the high-speed camera. The presented results demonstrated the viability of event-based techniques in high-speed aerodynamic testing, while highlighting challenges such as polarity switching and pixel latency.

High-speed flows in the plasma accelerator channel for the regime of electron current-transport on coaxial electrodes

High-speed flows in the plasma accelerator channel for the regime of electron current-transport on coaxial electrodes

Mixing enhancement assisted by dual plate cavity in supersonic flow

Fast and efficient mixing of high-speed shear flow formed by fuel and oxidizer is of great importance for the improvement of rocket-based combined cycle engine performance. Nevertheless, the existence of compressibility effects of high-speed flow significantly inhibits the growth process of a mixing layer. Moreover, a finite-length combustor of the engine calls for more effective enhanced-mixing strategies to complete mixing in a shorter streamwise distance. To this end, in present paper, the strategy called dual plate cavity (DPC) is proposed to promote mixing. Three cases including the benchmark, front-DPC and back-DPC cases are selected to perform the comparative study. By means of high-order direct numerical simulations, the structure evolution characteristics and turbulence intensity distributions are researched. The index of velocity thickness is utilized to assess the mixing layer growth. The results indicate that with the introduction of DPC, the mixing process is dramatically promoted. The penetration behavior of newly found T-shaped structures into the upper main stream can engulf more fluid into the mixing region. Specifically, in the back-DPC case, the coexistence of both large-scale and small-scale structures in the far flow field can improve the turbulence intensity. The spatial correlation analysis results show that with the influence of DPC, the structure sizes are much larger than that of the benchmark case in the same streamwise position. Meanwhile, the contour line equal to 0.5 possesses property of distortion for the back-DPC case. The drastic pulsation of a mixing layer edge can obviously promote the mixing process. Through exploration of the enhanced-mixing mechanisms, this work indicates that the proposed DPC strategy is a good candidate for efficient mixing, and in the future, more detailed work including three-dimensional simulations concerning the strategy optimization is suggested to be performed.