Flow State Research Articles

Do traffic flow states follow Markov properties? A high-order spatiotemporal traffic state reconstruction approach for traffic prediction and imputation

Assessing traffic states accurately is challenging due to the complex, high-dimensional, and nonlinear nature of traffic systems. This study introduces the innovative High-Order Spatiotemporal Traffic State Reconstruction (HOSTSR) algorithm, designed to track and predict traffic flow dynamics effectively. It combines phase space reconstruction with time delays and high-order neighborhood concepts from graph theory to improve traffic state assessments' accuracy. The algorithm's effectiveness is validated using chi-square tests and the Chapman-Kolmogorov equation to confirm the Markovian properties of traffic flows. A lean autoencoder, informed by prior Markov knowledge of traffic states, is developed for mapping traffic states to real traffic data, proving highly effective for traffic data imputation due to the Markov model's memoryless property. Experimental results from the PeMSD04 and PeMSD08 datasets show that HOSTSR outperforms traditional state reconstruction methods based on delayed coordinate embedding in predicting future traffic flow state based on four key metrics. The autoencoder framework, guided by prior Markov knowledge, shows significant advantages in addressing traffic data gaps in different cases over six baseline models. Gradient sensitivity analysis further evaluates the impact of prior knowledge on improving the autoencoder's interpretability for interpolation efforts.

An asymmetric orifice-based active micromixer in the microfluidic chip with 3D microelectrode

The fluid mixing in microscale is central to the development of flow patterns in microfluidic chips for particles separation and biological analysis. Yet, as the size of the fluid decreases, the mixing becomes challenging to change this state of flow. In this work, a novel active micromixer for enhancing the mixing performance in the micromixer with asymmetric orifices is presented. To induce the electric-driven micromixing, an AC electric field is employed to the inserted 3D microelectrodes to produce the local electric field through the asymmetric orifices located on the opposite channel walls, which is perpendicular to the main microchannel. Then the mixing experiments were conducted in a microfluidic chip comprising microelectrode with asymmetric orifices, specifically exploiting the mixing efficiency varying with the asymmetric orifice pairs, applied electric potential and frequency of the AC electric field, and flow rate. The bending degree of the mixing interface was calculated and found increasing as a function of applied electric voltage at a given AC frequency, thus enabling effective mixing crossing the microelectrode's area. The predictions are confirmed by optical microscopy experiments and the micromixing can be significantly improved as they experience longer-exposed electrical forces. The integration of multiple asymmetric orifices leads a larger zone to increase mixing efficiency and makes it a promising method for rapid and stable fluid mixing in microscale.

Study on the smoke flow characteristics in inclined tunnel with an upstream shaft under natural ventilation

The rapid expansion of urban highway tunnels has led to a significant increase in the risk of fire incidents. Moreover, the urban highway tunnels often have inclinations, which further exacerbates the complexity of the smoke flow. In contrast to the extensive research on natural ventilation in horizontally tunnels, there is still a lack of studies on the natural ventilation of shaft in inclined tunnels. Therefore, this study employed numerical simulations and theoretical analysis to investigate the length of smoke back-layering and flow patterns in inclined tunnel fires with an upstream shaft. By comparing the induced air inflow velocity and smoke back-layering length in inclined tunnels, both with and without an upstream shaft, three types of smoke flow states were identified. State 1: smoke spreading to the upstream shaft, State 2: smoke being limited between the shaft and the fire source, State 3: no smoke backflow in the inclined tunnel. In State 1, the shaft discharges smoke outward. The downstream length and the distance between the shaft and the fire source determined smoke back-layering length. In States 2 and 3, the shaft fills the air inward. The shaft has no obvious effect on the smoke back-layering length. Furthermore, the effects of HRR, fire source position and shaft position on smoke flow characteristics are analyzed. As a result of the analysis, a segmented prediction model for smoke back-layering length and a quantitative method for predicting smoke flow state are proposed. By fine-tuning the tunnel slope, two critical values between the three smoke flow states are obtained. The research results can provide a useful reference for ventilation and evacuation design of inclined tunnels.

Effect and mechanism of solution flow rate during interfacial polymerization on morphology and performance of hollow fiber membranes

Interfacial polymerization (IP) using m-phenylenediamine and trimesoyl chloride (TMC) is an essential method for producing thin-film composite (TFC) membranes. Nevertheless, IP is highly sensitive to changes in process parameters, especially the TMC solutions flow rate during inside-out TFC hollow fibers (HF) production. Research on the impact of flow conditions (i.e., laminar vs. turbulent flows) of these organic solutions on the final membrane characteristics and corresponding mechanism is still lacking. This research tested different TMC flow rates (0.1–2 mL/min) to produce inside-out TFC HF. With a TMC flow rate increase, (i) the leaf-like structures of the polyamide (PA) layer decreased in size, (ii) the thickness of the PA layer slightly increased, and (iii) the pure water permeability decreased. However, the elemental composition, chemical bonds, and NaCl rejection remained stable. Different fluid regimes are considered to affect the performance of HF membranes by affecting the heat dissipation process during IP reaction. A TMC flow rate in the laminar flow state (i.e., low flow rates) is recommended for synthesizing HFs. The current research provides new insights into the IP reaction mechanism of HF membrane, thus offering valuable guidance to optimize and produce membrane products with better performance.

Coherent structures of elastoinertial instabilities in Taylor–Couette flows

We combine flow visualisation techniques and particle image velocimetry to experimentally investigate the higher-order transition to elastoinertial turbulence of Boger fluids ( $El = 0.11\unicode{x2013}0.34$ ) in Taylor–Couette flows. The observed route to turbulence is associated with the appearance of chaotic inflow jets, termed flame patterns, for increasing inertia, and stable structures of solitons, known as diwhirls, for decreasing inertia. We also report for the first time spatially and temporally resolved flow fields in the meridional plane for the three characteristic viscoelastic flow regimes (diwhirls, flame patterns and elastoinertial turbulence). We observe in all cases coherent structures of dynamically independent solitary vortex pairs. The stability of these coherent structures is jet-dominated and can be mainly ascribed to the high extension of the polymer chains in the inflow boundaries in the $r$ – $z$ plane. Solitary pairs are self-sustained when created through random events and do not split; instead, they merge when moving sufficiently close and annihilate when hoop stresses are not sufficient to sustain them. The highly localised and random events result in highly fluctuating, chaotic flow states. We estimate the decay exponent of spatial power spectral density, illustrating a universal scaling of $-2.5$ for elastoinertial turbulence. Based on our observations and in an effort to unify and combine precedent theories with our results, we suggest a mechanism for the origins of elastoinertial instabilities, accounting for both the effect of elasticity on the vortex formation and the effect of increasing/decreasing inertia on the flow dynamics.

Dynamic detection of saturated distribution of activated carbon adsorbed volatile organic compounds based on electrical impedance tomography

The electrical impedance tomography (EIT) has been achieved for the dynamic detection of the adsorption saturation distribution in activated carbon. Volatile organic compounds (VOCs) emitted by industries pose a serious threat to human health and environmental quality. Therefore, adsorption method is widely used to treat such organic compounds. Activated carbon, as a commonly used adsorbent material, plays a crucial role in the efficient utilization and management of the adsorption process. Traditional adsorption detection methods suffer from information loss and discontinuity. We can obtain the conductivity distribution information during the current passing through the material by measuring the potential changes on the boundary of interest field, and analyze the saturation distribution information of VOCs adsorbed on activated carbon based on the conductivity distribution image. The feasibility of the technology in monitoring the saturation distribution of the adsorption process in activated carbon was verified by principle and simulation. For experimental verification, fixed bed and fluidized bed experiments were carried out, taking into account the special case of impedance change factors of activated carbon particles in the static and flow states. The experimental results confirm that in fixed-bed adsorption, the adsorption impedance change response can be effectively obtained at an excitation frequency of 1.0 MHz, while in a fluidized bed, a good adsorption impedance change response can be achieved at an excitation frequency of 4 kHz. By selecting the appropriate excitation frequency according to the change in the adsorbent’s state, stable imaging of the saturation distribution can be achieved. This study introduces a new method for visualizing the monitoring process of activated carbon adsorption.

Determinants of consumer adoption of multilingual self-service ordering systems in fast food restaurants

Due to the increasing number of international exchanges, foreign users have gradually become a significant consumer segment. Many of them are not proficient in the local language. Providing them with native language services will be an important trend, both from a business and a humanistic perspective. The purpose of this study is to investigate the fast-food restaurant ordering system that can provide multilingual services for foreigners, and to investigate factors that influence fast food restaurant consumers to adopt multilingual self-service ordering systems. Based on the characteristics of foreign users, we have proposed experience factors such as convenience, translation quality, social anxiety, and the Flow. According to research, the convenience of the service has a strong direct impact on consumers' intention to use, social anxiety has a weak direct impact on consumers' intention to use, and translation quality has a weak direct impact on consumers' intention to use through the intermediate variable of social anxiety. Particularly, Flow experience is not associated with intention to use. The Flow state is one in which users are completely immersed and do not notice time or the surroundings when the perceived difficulty of a task matches their abilities. The purpose of this study is to improve our understanding of the customer evaluation criteria for multilingual self-service systems, as well as to establish the MSSS model for future research on multilingual self-service systems.

Investigation of swirler effect on combustion and exergy efficiency of hydrogen/chlorine combustor based on entropy generation analysis

Inefficient reagent reaction limits the development of compact combustion-based HCl synthesis production. To address this issue, a non-premixed HCl synthesis combustor that combines a swirler at the hydrogen channel with a porous nozzle at the chlorine channel is proposed. A three-dimensional non-premixed combustion model is used to investigate the effects of this combustor structure on the combustion efficiency, exergy efficiency, and pressure loss coefficient. The entropy generation analysis is employed to evaluate multiple irreversible losses for different structures and flow states. Through experimental validation and numerical simulation analysis, the effects of the swirler installation, inlet flow rate, and H2/Cl2 equivalence ratio on the combustion and heat transfer characteristics are investigated. The results demonstrate that the combustor with the swirler and porous nozzle improves exergy efficiency, leading to higher HCl purity and a reduced flame height for faster reactions under low-flow states. Chemical reactions contribute to over 96% of entropy generation during combustion, with the swirler reducing total entropy by approximately 5%. Optimal heat transfer effects and minimized entropy generation are achieved when the swirler is installed below the combustor spray hole. The installation of the swirler can increase the exergy efficiency of the H2/Cl2 combustor to approximately 43.73%.

Flow instabilities driven by Prandtl number effect and rotation-depth coupling effect in the cylinder with a top disk

We employed linear stability analysis to investigate the Prandtl number (Pr) effect and rotation-depth coupling effect on the complex flow instability in a cylinder with a top disk. The dependence of the critical Rayleigh number on the Pr number, as well as the relationship between the critical disk rotation rate and the aspect ratio at Pr = 6.7, were obtained. Results reveal that the flow stability increases with increasing Pr number, and the convection instability stems from the inertial mechanism for 0.011 ≤ Pr ≤ 0.0258 and thermal buoyancy mechanism for 1.4 ≤ Pr ≤ 28.01. Regarding the rotation-depth coupling effect for the melt with Pr = 6.7, a decreasing melt level leads to a general increase in the critical disk rotation rate. Furthermore, within the interval of aspect ratio (ratio of depth to cylinder radius) 0.7 ≤ Γ ≤ 1.62, multiple transitions of the flow state from stable to unstable and then back to stable were observed with increasing disk rotation rate before finally becoming unstable. Energy analysis reveals that multiple transitions in the flow state are attributed to the competition between thermal buoyancy and inertial mechanisms.

Research on optimization method for traffic signal control at intersections in smart cities based on adaptive artificial fish swarm algorithm

The transportation environment of smart cities is complex and ever-changing, and traffic flow is influenced by various factors. With the increase of traffic flow in smart cities, optimizing traffic intersection signal control has become an important method to improve traffic efficiency and reduce congestion. To this end, a smart city traffic intersection(SCTI) signal control optimization method based on adaptive artificial fish swarm algorithm was studied. Establish the Equation of state of traffic flow at SCTIs to understand the actual traffic flow at SCTIs. On this basis, design SCTI signal control parameters, with the minimum average delay and average number of stops as objective functions, and construct an optimization model for SCTI signal control. By combining chaotic search theory and adaptively improving the artificial fish swarm algorithm, based on the adaptive artificial fish swarm algorithm, the intelligent city traffic intersection signal control optimization model is solved to achieve intelligent city traffic intersection signal control optimization. The experimental results show that the average delay of this method is 7.8 ms, the average number of stops is 2, and the travel time is 68.4 s s. Thus, it is proved that the method in this paper has a good optimization effect of traffic signal control at smart city intersections, which can improve the optimization efficiency of traffic signal control at smart city intersections and reduce traffic congestion at smart city intersections.

Effect of Chute on Gas Flow and Temperature of the Top of Blast Furnace

The top gas temperature is an apparent indicator of the distribution state of gas flow, and it is an important parameter to judge the furnace condition. It is related to the top equipment in addition to the charge characteristics and bottom-up generation and distribution. Therefore, the fluid-solid heat transfer model from burden surface -chute-rising ducts is established in this paper. The finite element method is used to calculate the flow and heat transfer of the gas at the top of the blast furnace, and the influence of the chute on the top gas temperature is analyzed. The accuracy of the model is verified by the actual blast furnace top temperature. The results show that the chute has a guiding effect on the gas flow. As the chute rotates, the top gas temperature fluctuates. This research is helpful for actual blast furnace operators to understand the top temperature and make the condition judgment more accurate.

Real-world black carbon emissions of gasoline vehicles at urban intersections

To gain insight into the real-world black carbon (BC) emission patterns at urban intersections, we employed a portable emission measurement system (PEMS) to assess the BC emissions from three light-duty gasoline vehicles along a designated urban route. The BC emission factors were evaluated, and the contributions of vehicle operating conditions at the intersections to the total BC emissions were quantified. The results show that the BC emission factors in an intersection area range from 0.045 to 0.291 mg/km, higher than those at an intersection's connecting sections. The average BC emission factor at signalized intersections is 17.07% higher than at roundabouts. Emission contribution analysis of driving conditions showed that in a state of non-free traffic flow, acceleration and deceleration conditions are responsible for 39% ∼ 56% and 24% ∼ 33% of BC emissions at intersections, respectively. We also found that vehicle specific power (VSP) and delay time are almost equally crucial for BC emissions from vehicles at intersections in the multiple linear regression. Our research reveals the significant impact of vehicle delay time and acceleration conditions on black carbon emissions at urban intersections, further emphasizing the importance of smooth (congestion-free) intersection operation and steady driving in reducing urban black carbon emissions.

Structural evolution and rheology of continuous shear-induced dense granular flow in unsteady state

The structural properties of particulate matter can significantly affect the rheology of the system. We report the structural evolution and flow properties of dense granular flows induced by Couette shear and try to reveal the relationship between them. In unidirectional shear, monodisperse particles undergo a transformation from disorder to order. Throughout this continuous process, both the velocity and shear strain rate of the particles experience alterations. By filling with particles of varying polydispersity, the structural potential of the system can be controlled, thereby influencing the extent of structural transformations. The results indicate that the transition in flow characteristics is suppressed as the initial filling in the system approaches from high to low structural potential. The results based on the local volume fraction and relative positions of particles suggest that it is due to the weakening of the structural thinning effect caused by order. We found that both fixed shear paths and more rotatable local structures caused a significant reduction in the contact force to transfer energy. Inertia number and apparent viscosity vary with volume fraction, indicating a transition in dense granular flow after volume fraction φ≳ 0.62, with the onset of significant structural thinning effects. We have revealed the physical mechanisms influencing fluidity from a local structural perspective and established the relationship between fluidity g and φ in the continuous process of unsteady flow.

Numerical Simulation of Flowslide Considering Transient Seepage Flow and Progressive State Transition

Numerical Simulation of Flowslide Considering Transient Seepage Flow and Progressive State Transition

Interstage transmission and differential analysis of pressure fluctuations in multistage centrifugal pump-as-turbine

Pumps as turbines (PATs) are used in petroleum and chemical industries to recover high-pressure residual energy. Multistage PATs allow for a wider energy recovery interval and wider range of applications. However, because multistage centrifugal pumps were not originally designed for turbine conditions, complex pressure fluctuations occur, impacting the stable operation and performance of multistage PAT. Pressure fluctuation is essentially a wave, and by analogy with the wave intensity definition, pressure fluctuations were quantified using the pressure wave energy flow density, and the pressure fluctuation patterns at different stages were investigated. The findings reveal significant differences in the intensity of pressure fluctuations at different locations within the multistage PAT. Specifically, the pressure fluctuation intensity is significantly higher from the second to the final stage, compared to the first stage. The difference in inlet flow conditions is the main reason for this difference in pressure fluctuations between stages. The inlet inflow from the second to the final stage is subject to rotational effects that exacerbate the difference in pressure fluctuation intensity between stages. Pressure fluctuations are found to be negatively related to the distance from the source of fluctuations and positively related to the flow state. Different flow conditions and interaction regions of the impeller affect the distribution of pressure fluctuation intensity and the distribution of pressure fluctuation energy across different frequency domains within the guide vanes. The main source of fluctuations in the shaft frequency and four times the shaft frequency is the impeller inlet interaction region, whereas the fluctuations in the blade passing frequency originate from the impeller outlet interaction region. This paper provides a reference for improving the stable operation of multistage PATs.

A Simplified Approach for Calculating Heat Transfer Coefficients for Fluid Guiding Elements with Alternating Redirections of Flow

AbstractFluid guiding elements (FGEs), additive manufactured inserts that enhance heat transfer, have shown the potential to reduce the size of pipe‐in‐pipe heat exchangers up to a factor of 20. Due to their unique design, the calculation of the geometrical parameters for a specific application remains challenging and was initially solved by computationally expensive computational fluid dynamics simulations. This work presents a simplified approach, which treats the fluid and the FGE as pseudo‐homogeneous to enable the fast calculation of effective heat transfer coefficients. The approach is developed based on water in laminar flow state and subsequently tested with different fluids.

Re-entry rocket basic flow characteristics and thermal environment of different retro-propulsion modes

During the supersonic re-entry of multi-nozzle heavy rockets into the atmosphere, the basic flow state becomes increasingly complex due to the coupling effect between the retro-propulsion plumes and the freestream. A numerical method using the hybrid Reynolds-Averaged Navier-Stokes and Large Eddy Simulation (RES) method and discrete coordinate method is developed to accurately estimate the thermal environment. In addition, finite rate chemical kinetics is used to calculate the afterburning reactions. The numerical results agree well with wind tunnel data, which confirms the validity and accuracy of the numerical method. Computations are conducted for the heavy carrier rocket re-entry from 53.1 km to 39.5 km altitude with 180° angle of attack by using three different Supersonic Retro-Propulsion (SRP) modes. The numerical results reveal that these three SRP flow fields are all Short Penetration Models (SPM). As the re-entry altitudes decrease, both the plume-plume interaction and the plume-freestream interaction become weaker. The highest temperatures in the plume shear layers of the three SRP modes increase by 8.36%, 7.33% and 6.92% respectively after considering afterburning reactions, and all occur at a re-entry altitude of 39.5 km. As the rocket re-enters the atmosphere, the maximum heat flux on the rocket base plate of three SRP modes stabilizes at 290, 170 and 200 kW/m2 respectively, but the maximum heat flux on the side wall increases significantly. When the altitude declines to 39.5 km, the extreme heat flux of the three modes increase by 84.16%, 49.45% and 62.97% respectively compared to that at 53.1 km.

A stabilized state-based peridynamic heat conduction model for interface thermal resistance problems

A stabilized state-based peridynamic heat conduction model for interface thermal resistance problems

Microscopic investigation and local standard deviation analysis of liquid propane jets in supercritical environment

To improve the thermal efficiency of engines, the temperature and pressure in the combustion chamber are continually increased, potentially reaching the critical points of the fuels. Additionally, light fuels such as liquid ammonia and propane are utilized to reduce carbon emissions. The relatively low critical temperature of light fuels facilitates their transition into a supercritical state, which greatly change the jet characteristics. To gain a deeper understanding of the supercritical transition of fuels, jets of liquid propane are investigated through high-speed microscopic imaging technology, covering subcritical to supercritical environmental conditions. Liquid propane is injected through a transparent flat nozzle to observe the internal flow states within the nozzle. For image and data processing, local standard deviation (LSD) analysis and a Residual Network (ResNet-50) model are employed to identify the structures within the mixing region. Droplets counting and frequency domain analysis are also performed to reveal the features of supercritical transition. The findings highlight the importance of mask size in the jet feature extraction. Large mask highlights large scale structures including jet surface and mixing region structures, while small mask brings about full-scale feature including droplets and all other features. A criterion for mixing regime classification based on reduced temperature (Tr) and reduced pressure (Pr) is established directly from image data using the ResNet-50 model, where a condition of Tr1.6Pr0.4 ≥ 1.067 indicates a transcritical mixing regime. Both droplet counting and frequency domain analysis corroborate this mixing regime criterion. These insights enhance our understanding of supercritical transitions and are useful for simulation verifications.

Numerical study of structural optimization for improving gas-liquid flow and microalgae carbon fixation rate in air-lift photobioreactors

In this paper, the gas-liquid flow pattern and CO2 dissolution transport process of microalgae solution in an air-lift photobioreactor (PBR) are investigated by numerical simulations. In order to promote the gas-liquid mass transfer efficiency to enhance the carbon fixation, we propose different optimization schemes for the structure. Firstly, a two-phase flow model and a mass transfer model are employed to investigate the fluid flow characteristics. The flow state is evaluated by velocity in light direction, turbulent kinetic energy (TKE), gas hold-up and CO2 mass transfer coefficient. The results show that the gas flow rate of 0.2 V/V/min is the optimum value for the inlet. Secondly, CO2 mass transfer and carbon fixation rates are analyzed for different inlet CO2 volume fractions. With the increase of CO2 volume fraction, the carbon fixation rate first increases and then decreases, the highest fixation rate reaching 2.21 × 10−4 mol m−3 s−1 at 6 %. Finally, based on numerical simulations, three optimized structures with different spacing of baffles are proposed and evaluated the performance in comparison with the original. The results show that the gas distribution and CO2 mass transfer are significantly improved, with the one-sided baffle structure is the best. In summary, this study provides a new and useful reference to evaluate the gas-liquid mixing and improve the microalgae carbon fixation rate.