Dynamic Flow Behavior Research Articles

Identification of flow structures in a closed chamber in the presence of a needle plasma actuator

This study deals with the experimental characterization of the induced flow dynamics by a disk-needle-type plasma actuator driven by a sinusoidal generator and located in a rectangular cross-section burner. Flow characterization was performed using different plasma actuation conditions and standoff distances. Experiments were conducted under non-reactive flow conditions. Electrical characterization was carried out. Airflow behavior was also analyzed using smoke flow visualization. Smoke flow visualization showed the dynamic behavior of the plasma-induced flow. Post-processing of high-quality images was performed by using Proper Orthogonal Decomposition (POD) technique to recognize the dominant flow vortexes and coherent structures. This could support the design of plasma actuation devices in real combustors and be useful for the implementation of numerical models. Moreover, it has been concluded that flow dynamics can be controlled by a variation of the plasma power or the gap distance between two electrodes. Laser Droplet Velocimetry (LDV) was used to investigate the distribution of flow velocities and turbulent kinetic energy (TKE) at different plasma power values of the sinusoidal alternating current generator and standoff distances. From POD and LDV analyses, it has been observed that there is quite a linear relation between the POD energy of the first mode and the maximum TKE. The POD method could be used to identify motions in the flow field carrying the most TKE. TKE peaks are present in the area with the most energetic flow structures, as identified by the POD.

Shear transformation zones and serrated flow dynamics of metallic glasses revealed by nanoindentation

The relationship between shear transformation zones (STZs) and serrated flow dynamics of Co-, Fe-, Zr-, La- and Al-based metallic glasses (MGs) with different plasticity were analyzed by nanoindentation. The serrated flow dynamic behaviors were analyzed using statistical analysis of shear stress drops, Δτ. The STZ size was estimated via the nanoindentation creep method based on the cooperative shear model. Examination of two distinct types of serrated flow dynamics were performed. For MGs (e.g., Al- or Zr-based) where STZs could be easily activated or at low loading rates, shear stress exhibited a decreasing trend and followed a power-law distribution, which was an indicator of a self-organized critical (SOC) state in the dynamics. In contrast, a Gaussian law distribution was found for STZs in hard MGs (e.g., La-, Co-, and Fe-based) or at high loading rate. In the case of Gaussian distribution case, serrated flow dynamics were in a chaotic state, which indicated that STZ aggregation reduced the stresses required for plastic deformation.

Numerical analysis of the dynamic two-phase flow behaviour in the ionic liquid compressor for hydrogen refuelling stations

The ionic liquid compressor is a promising compression means for pressure elevation of hydrogen gas in refuelling stations. However, the two-phase flow behaviour of the ionic liquid compressor is unknown, which directly influences the thermodynamic performance of the compressor and therefore is critical for compressor design. Considering the significant effect of the liquid viscosity on the two-phase flow behaviour and the wide range of the viscosity of the ionic liquid, this paper proposed a design method for the ionic liquid compressor and investigated the dynamic flow behaviour during one compression cycle under varied liquid viscosities through numerical simulations. Results found that the number of droplets and the gas vortexes were influenced by the liquid viscosity. Both the highest discharge mass of the hydrogen gas and the lowest discharge mass of the ionic liquid were obtained in the case of 1 mPa∙s. The minimum peak value of the sum of turbulent kinetic energy was observed when the liquid viscosity was 100 mPa∙s. The viscosity of 100 mPa∙s was recommended for the ionic liquid selection under the design conditions considering the flow behaviour, discharged mass, and the sum of turbulent kinetic energy.

The Modification of the Dynamic Behaviour of the Cyclonic Flow in a Hydrocyclone under Surging Conditions

The aim in this study was to determine how surging modifies the dynamic behaviour of the cyclonic flow in a hydrocyclone using computational fluid and granular dynamics models. The Volume-of-Fluid model was used to model the air-core formation. Fluid–particle, particle–particle, and particle–wall interactions were modelled using an unsteady two-way coupled Discrete Element Method. Turbulence was modelled using both the Reynold’s Stress Model and the Large Eddy Simulation. The model predictions indicate that the phenomenon of surging modifies the dynamics of the cyclonic flow in hydrocyclones and subsequently impacts separation. The results reveal that the primary cyclonic separation mechanisms break down during surging and result in air-core suppression. The flow and primary separation mechanism in the core of the hydrocyclone is driven by the pressure drop and the flow and primary separation mechanism near the wall is primarily driven by the gravitational and centrifugal force-induced momentum. However, surging causes a breakdown in this mechanism by swapping this primary flow and separation behaviour, where the pressure drop becomes the primary driver of the flow near the walls and gravitational and centrifugal force-induced momentum primarily drives the flow in the core of the hydrocyclone.

Strategy for Fast Decision on Material System Suitability for Continuous Crystallization Inside a Slug Flow Crystallizer.

There is an increasing focus on two-phase flow in micro- or mini-structured apparatuses for various manufacturing and measurement instrumentation applications, including the field of crystallization as a separation technique. The slug flow pattern offers salient features for producing high-quality products, since narrow residence time distribution of liquid and solid phases, intensified mixing and heat exchange, and an enhanced particle suspension are achieved despite laminar flow conditions. Due to its unique features, the slug flow crystallizer (SFC) represents a promising concept for small-scale continuous crystallization achieving high-quality active pharmaceutical ingredients (API). Therefore, a time-efficient strategy is presented in this study to enable crystallization of a desired solid product in the SFC as quickly as possible and without much experimental effort. This strategy includes pre-selection of the solvent/solvent mixture using heuristics, verifying the slug flow stability in the apparatus by considering the static contact angle and dynamic flow behavior, and modeling the temperature-dependent solubility in the supposed material system using perturbed-chain statistical associating fluid theory (PC-SAFT). This strategy was successfully verified for the amino acids l-alanine and l-arginine and the API paracetamol for binary and ternary systems and, thus, represents a general approach for using different material systems in the SFC.

Numerical Investigation of Bladeless Compressor on Different Disk Spaces and Diffuser Configurations

Abstract The cost-effectiveness of turbomachinery is a key aspect within the small-size compressor market. For this reason, Tesla turbomachinery, invented by Nikola Tesla in 1913, could be a good solution, particularly for low volumetric flow applications, where volumetric compressors are usually used. It consists of a bladeless rotor that stands out for its ease of construction and its ability to maintain almost the same performance as size decreases. One of its advantages is that it can run either as a turbine or as a compressor with minor modifications at the stator. The objective of this paper is to investigate a 3 kW Tesla compressor, which design was derived from an analogous Tesla expander prototype (58% isentropic efficiency from the numerical study), by conducting a computational fluid dynamic analysis for different disk gaps and diffuser configurations. The potential of the Tesla compressor is shown to be quite promising, with a peak isentropic efficiency estimated at 53%. Although bladeless compressor is a simple turbomachinery device, different parts, i.e., diffuser, tip clearance, and volute need to be optimized. Utilizing computational fluid dynamics algorithms, different disk gaps and different diffusers are simulated in order to increase the overall performance of the compressor and understand the flow dynamic behavior behind this technology. The dimensionless Ekman number is used to express the optimum disk space of the compressor rotor. Thus, the overall performance of the Tesla compressor is improved by 5–10% points compared to the initial model. Simultaneously, diffuser optimization strategies are applied and proved that there is a direct impact on the optimum design conditions, improving the pressure ratio at high mass flow rates.

The Flow Stress-Strain and Dynamic Recrystallization Kinetics Behavior of High-Grade Pipeline Steels.

The hot deformation behavior of high-grade pipeline steels was studied in the strain rate range of 0.001~0.1 s−1 and the temperature range of 1050~1200 °C by using hot compression tests on a Gleeble 3500 thermomechanical simulator. The flow stress increases with the increase in strain rate and the decrease in deformation temperature, and the deformation activation energy is about 358 kJ/mol. The flows stress–strain behavior of the work-hardening and dynamic recovery (DRV) was calculated using the Estrin–Mecking equation, and the kinetics model of the dynamic recrystallization (DRX) was established based on the Avrami equation through characteristic strains. Furthermore, the flow stress–strain behavior of high-grade pipeline steels was predicted by the established model based on the coupling effects of DRV and DRX. The corresponding predicted results are in good agreement with the experimental results according to standard statistical parameters analysis. Finally, the economic strain (ε3) is proposed by the third derivative of the given kinetic model. Based on these calculation results, when the economic strain (ε3) is reached, uniform and refined DRX grains can be obtained, the energy consumption reduced, and the production costs controlled, which is of great significance to actual factory production.

Bifurcation analysis of a new stochastic traffic flow model

Abstract The stochastic function describing the stochastic behavior of traffic flow in the process of acceleration or deceleration can better capture the stochastic characteristics of traffic flow. Based on this, we introduce the stochastic function into a high-order viscous continuous traffic flow model and propose a stochastic traffic flow model. Furthermore, we performed the bifurcation analysis of traffic flow system based on the model. Accordingly, the traffic flow problem is transformed into the stability analysis problem of the system, highlighting the unstable traffic characteristics such as congestion. The model can be used to study the nonlinear dynamic behavior of traffic flow. Based on this model, the existence of Hopf bifurcation and the saddle-node bifurcation is theoretically proved. And the type of the Hopf bifurcation is theoretically derived. The model can also be used to study the mutation behavior of system stability at bifurcation point. From the density space-time diagram of the system, we find that the system undergoes a stability mutation when it passes through the bifurcation point, which is consistent with the theoretical analysis results.

Experimental and numerical validation of a Francis turbine draft tube designed for mitigation of pressure fluctuations

This paper presents an experimental and numerical investigation of the internal flow in a Francis turbine draft tube previously designed for minimizing pressure fluctuations and energy losses in off-design conditions. The design of the draft tube geometry is based on an original approach combining Design of Experiments and steady/unsteady Computational Fluid Dynamics (CFD) simulations of the draft tube internal flow. The proposed method provides new insight on the influence of the draft tube geometry on the flow dynamic behaviour on one hand and enables the determination of a geometry promoting flow stability and hydraulic performance on another hand. CFD simulations of the internal flow in the final geometry showed promising results in terms of flow stability compared with the initial geometry designed by conventional CFD-aided methods. A reduced-scale model of the prototype machine featuring the final draft tube geometry is finally installed and tested in laboratory. Tests include performance and pressure fluctuations measurements over the complete operating range. The analysis of the results shows that the draft tube flow remains globally stable over the complete part-load range with pressure fluctuations amplitude lower than 1% of the net head. It is also shown that the dominant pressure component at the runner outlet in the draft tube cone is of synchronous nature. The physical mechanisms of excitation are finally highlighted by analysis of unsteady CFD simulation results.

Numerical Study of Structural Performance and Wind Flow Dynamic Behavior for PPVC Steel Modular Construction (MSC) under Various Extreme Wind Loads

PPVC modular construction building has become one of the most recent construction technologies in the civil engineering sector and has piqued researchers’ interest. Few published studies consider the overall structural response to extreme wind load. As a result, there is a lack of appropriate design for PPVC modular systems under extreme wind standards. However, the existing literature has not yet studied the wind flow dynamic behaviors of PPVC modular steel construction (MSC) systems subjected to extreme wind loads. This paper, therefore, presents a numerical investigation into the structural performance and wind flow dynamic behavior of innovative PPVC modular steel construction (MSC) systems under extreme wind loads. The numerical technique varied in comparison with previous studies. The results showed that the suggested novel (MSC1) modular system is applicable to prevention of extreme wind action up to cyclone 2nd degree, the high story drift resistance compared with previous research, high stiffness performance, and overall strain energy. Additionally, the actual wind velocity surrounding (MSC2) was 31.5% higher compared to the Saffir–Simpson wind speed scale, and the 1.5 wind speed safety factor was suggested.

A study on debris flow dynamic behavior in a drainage channel with step-pool configuration

A study on debris flow dynamic behavior in a drainage channel with step-pool configuration

Modelling Dynamic Recrystallization of A356 Aluminum Alloy during Hot Deformation

The flow stress and dynamic recrystallization behavior of A356 aluminum alloy was studied, with a strain rate ranging from 0.001 s−1 to 1 s−1 and temperature ranging from 300 to 500 °C. Both the true stress–strain curves and microstructure examination of A356 aluminum alloy indicated that dynamic recrystallization occurred during the isothermal compression. A physical dynamic recrystallization model based on the Arrhenius equation was developed, and this model can accurately predict the dynamic recrystallization fraction of A356 aluminum alloy during the isothermal compression. Finally, this model was implemented in FEM software Forge, and the microstructure evolution was simulated well.

Numerical Simulations on Dynamic Behavior of Multiphase Flow and Heat Transfer in a Round Mold with a Swirling Flow Tundish Design

Numerical Simulations on Dynamic Behavior of Multiphase Flow and Heat Transfer in a Round Mold with a Swirling Flow Tundish Design

Analysis of airborne sputum droplets flow dynamic behaviors under different ambient conditions and aerosol size effects

The coronavirus (COVID-19) is becoming more threatening with the emergence of new mutations. New virus transmission and infection processes remain challenging and re-examinations of proper protection methods are urgently needed. From fluid dynamic viewpoint, the transmission of virus-carrying droplets and aerosols is one key to understanding the virus-transmission mechanisms. This study shows virus transmission by incorporating flow-evaporation model into the Navier-Stokes equation to describe the group of airborne sputum droplets exhaled under Rosin-Rammler distribution. Solid components and humidity field evolution are incorporated in describing droplet and ambient conditions. The numerical model is solved by an inhouse code using advection-diffusion equation for the temperature field and the humidity field, discretized by applying the total-variation diminishing Runge-Kutta method. The results of this study are presented in detail to show the different trends under various ambient conditions and to reveal the major viral-transmission routes as a function of droplet size.

Dynamic two-phase flow behaviors in permeable network integrated with microchannel

• Permeable network integrated with microchannel is developed. • Two-phase flow characteristics in such a structure are visually studied. • Liquid saturation increases with increasing gas flow rate. • Position for bubble generation increases with increasing gas flow rate. • Two-phase flow exhibits strong periodicity at low gas flow rates. The performance of a direct methanol fuel cell greatly depends on the two-phase flow behaviors in the anode gas diffusion layer and flow channel. However, complex and opaque nature of gas diffusion layer poses a grand challenge for deep insight into the two-phase flow behaviors. Therefore, a homogeneous permeable network integrated with a microchannel was put forward to simulate the anode gas diffusion layer and microchannel in the present study, by which the dynamic two-phase flow behaviors were visually studied with the help of adaptive image enhancement method. The influence of the position and number of the gas inlet, and the gas and liquid flow rates on the two-phase flow behavior were analyzed. The results showed that the liquid saturation decreased and the number of the position for bubble generation increased with increasing the gas flow rate in case the gas was suppled from only one gas supply orifice. When two gas supply orifices simultaneously supplied the gas, the liquid saturation was between the cases using a single one gas supply orifice. For given liquid and gas flow rates of 0.1 mL/min and 0.5 mL/min, the liquid saturation was about 84%, which was between 83% and 92% for the single-one cases. Besides, the two-phase flow exhibited strong periodicity at low gas flow rates. The obtained results provide a deep understanding of the two-phase flow behaviors in such a simulated structure, helping better design and operation of direct methanol fuel cells.

Adhesive dynamic behavior in the clinch-bonding process of aluminum alloy A5052-H34 and advanced high-strength steel JSC780

Mechanical clinching is a commonly used method for joining dissimilar materials in the automotive industry. The clinch-bonding process was developed based on the clinching process to ensure the fixation of the adhesively bonded parts up to the curing process, where the adhesive gains its maximum strength. However, the fluid flow of the adhesive during clinch-bonding interferes with the interlock formation, thereby causing quality issues. The lack of a systematic understanding of the dynamic behavior of adhesives during the process poses optimization obstacles. This study aims to clarify, using numerical simulation, the dynamic flow behavior of the adhesive and its influence on clinch-bonding joint formation. Simulation models of the clinching and clinch-bonding processes of high-strength steel JSC780 and aluminum alloy A5052-H34 under different process conditions were established and validated experimentally. The modeling clarified the critical role of blank holding force on the adhesive flow direction and local hydraulic pressure evolution that led to adhesive pockets. The Cockcroft–Latham damage criterion was introduced to evaluate the local damage to the steel, based on which the root cause of neck cracking generated under insufficient adhesive outflow condition was revealed. The knowledge obtained from the modeling was subsequently experimentally proven.

Understanding Morphology, Bulk Properties, and Binding of Silk Particles for 3D Printing

Silk fibroin has emerged as a leading biomaterial for biomedical applications. 3D printing has been successfully used for printing with silk fibroin, albeit in the form of a bioink, in direct-write 3D printers. However, in the form of bioinks, stability and mechanical attributes of silk are lost. An innovative alternative to producing 3D printed solid silk constructs is silk milled into powder for printing in a binder jetting printer. In this work, we focus on characteristics of silk powder to determine suitability for use in 3D printing. Two different silk powders are compared with hydroxyapatite powder, a known biomaterial for biomedical constructs. We have investigated powder size and shape by Camsizer X2 and Scanning Electron Microscope and bulk behaviour, dynamic flow behaviour, and shear behaviour by FT4 powder rheometer. Preliminary printing tests were conducted in an in-house custom-built printer designed for silk powder. It was found that silk powder has low flowability and stability. Therefore, to print solely out of silk powder, a 3D printer design will need sophisticated techniques to produce flow to ensure even distribution and consistent thickness of powder layers during the printing process. It was also found that high concentrations of formic acid (>75 to 99 wt.%) can fuse particles and therefore be used as a binder ink for 3D printing. The printer design challenges for silk powder are discussed.

A new deep neural network framework with multivariate time series for two-phase flow pattern identification

Uncovering flow dynamic behavior of different flow patterns is an important foundation of multiphase flow research. But the traditional classifier is still adopted in the flow pattern identification based on statistical features of experimental measurements, and the utility of data is not sufficient in previous works. Therefore, a novel deep neural network framework is proposed to leverage abundant details of signals. The data was input into the new model after two innovative slicing operations, which combines BiLSTM and CNN to extract the deep characteristic information of different flow patterns. In addition, attention mechanism and residual connection are introduced to improve the network performance. Meanwhile, the dynamic experiment of vertical gas-water two-phase flow is carried out, four-channel conductance signals under five typical flow patterns, namely bubble flow (BF), slug flow (SF), bubble-slug transitional flow (BSF), churn flow (CF) and slug-churn transitional flow (SCF), are collected to feed the network. Finally, in order to verify the effectiveness of the proposed model, some comparative experiments are designed and implemented. The results demonstrate that our proposed model outputs more precise flow pattern identification, which opens up a new way for investigating industrial multiphase flow.

Effect of salt and particles on the hydrodynamics of foam flows in relation to foam static characteristics

• Investigated the effect of salt and particles on dynamic behaviour of foam flow. • Characterised regimes of three-phase foam flow using signal analysis of pressure data. • Demonstrated the effect of salt and particle on the frictional pressure of foam flow. Foam flows containing particles are present in many applications including mining, wastewater treatment, environmental remediation of contaminants such as PFAS using foam fractionation, dewatering of gas wells and particle cleanout in pipelines. These applications usually involve dissolved salts and solid particulates, which may have a positive or adverse impact on the foam flow and its performance depending on the application, the system’s constituents (e.g., type and concentration of salt/particles) and the operating condition (e.g., gas and liquid flowrates). This work aims to investigate the effect of salts (primarily NaCl) up to 0.2 M salt and solid particulates (mainly clay) up to 25 g/L particles on the dynamic behaviour of 200 ppm sodium dodecylbenzene sulfonate (SDBS) foam flows, frictional and hydrostatic pressure gradient, foam holdup and flow regimes in a vertical column. Flow regimes are analysed through power spectral density (PSD) and the probability density function of differential pressure data. The results show that salt and particles affect the foaming performance of SDBS solutions, thus influencing the transition of flow regimes. Our static tests show a 1.2-to-2.2-fold increase in the effect of salts and particles on the foamability of the SDBS solutions, whereas the foam flow dynamic data show a strong dependence on the hydrodynamics of the system. For example, the pressure gradient of the foam flow experienced a 16% reduction with the addition of salt and particles at low gas superficial velocity ( V sg of 0.48–2.4 m/s and fixed V sl of 0.02 m/s) due to the domination of gravitational dP/dz while it increased up to 22% at high V sg of up to 11.2 m/s due to the domination of frictional forces. Our results demonstrate that the foam static properties such as foamability, foam stability and wetness are useful to understand the stabilising mechanisms of foams. However, they cannot represent and explain the foam behaviour in dynamic systems.

Tailoring microstructure and texture of Mg–3Al–1Zn alloy sheets through curve extrusion process for achieving low planar anisotropy

• Symmetric curve extrusion (SCE) and asymmetric curve extrusion (ACE) processes were firstly proposed to fabricate AZ31 Mg alloy sheets. • The SCE and ACE sheets exhibited unique textures which were ascribed to the introduction of additional flow velocity difference along transverse direction during extrusion. • The ACE sheet exhibited the lowest basal pole intensity because of the introduction of extra asymmetric shear deformation during ACE process. Curve extrusion processes, including symmetric curve extrusion (SCE) and asymmetric curve extrusion (ACE) processes, were proposed to fabricate Mg–3Al–1Zn (AZ31) alloy sheets with the aim of improving planar anisotropy. For comparison, traditional extrusion (TE) was conducted on producing AZ31 sheets. The dynamic recrystallization and flow behavior of AZ31 Mg alloy during extrusion were examined and analyzed, and the final microstructures and mechanical properties of AZ31 sheets were investigated. In comparison with the TE sheet, finer grain size, more uniform microstructure and weaker tilted basal texture were achieved in the SCE and ACE sheets. Both the SCE and ACE sheets exhibited unique textures which basal poles tilted to extrusion direction (ED) and new transverse direction (TD)-tilted texture component was developed. The reasons were mainly ascribed to the introduction of additional flow velocity difference along TD during extrusion. Furthermore, the ACE sheet exhibited the lowest basal pole intensity, which was attributed to the introduction of extra asymmetric shear deformation during extrusion process. As a result, the ACE sheet showed the lowest yield strength and r -value, but highest elongation and n -value. Improving the planar anisotropy of AZ31 sheet was achieved by the ACE process.