Detailed Flow Information Research Articles

Intrinsic insight of energy-efficiency optimization for CO2 capture by amine-based solvent: effect of mass transfer and solvent regeneration

Here the energy-efficiency performance of CO2 capture is investigated based on the combination of bench-scale experiments and simulated calculation. A comprehensive evaluation is performed by L25(56) orthogonal tests to analyze the effect of crucial operating conditions on CO2 capture. Experiments reveal desorption temperature and flue gas flow play a major role for CO2 capture efficiency. Rising flue gas flow could promote interfacial area, but decreases contact time, overally, net CO2 flow approximately determines the linear relationship of capture efficiency and absorption rate. With combination of Eulerian-Eulerian method with the population balance model, we predict the dynamics evolution process of dispersed bubble, in order to provide the detailed information of interphase contact area and multiphase flow for modelling complete mass transfer parameters. Meanwhile, rigorous process simulation is developed to analyze the energy consumption of carbon capture. Higher desorption temperature provides much leaner solvent, which is beneficial to CO2 absorption, but consumes greater energy penalty.

Passive Probe: Mechanically-Modulated Field Sensing for Motion Tracking and Flow Estimation

The internal mechanical motions of a dynamic system can serve as the basis for developing “free” sensors that probe operating state and potentially diagnostic health. Specifically, the interaction of a moving mechanical structure with an applied, nonintrusive field, e.g., an electric or magnetic field, can produce a signal that creates a sensor with little additional hardware. In this paper, bellows-and-diaphragm natural gas (BDNG) meters provide an illustrative example for three different approaches for transforming a metering mechanism and its consumption totalizer into a high quality flow meter. Detailed flow information provides a data-stream for nonintrusively monitoring the real-time operation of loads – in this example case, loads that consume natural gas such as burners, heaters, and engines. The flow information can also be used for fault detection and diagnostics, e.g., for finding leaks or correlating faulted operation with respect to the operation of electrical actuators or other flows of consumables like water. This paper examines three BDNG meters and presents a methodology for inexpensively adding digital flow-rate measurement capabilities to each meter. The methods developed here can in principle be applied to any dynamic machine for consumption estimation or fault detection. They can also be used with other nonintrusive field stimuli including light and sound. Mechanical retrofit techniques are described, and exemplary signal processing and estimation chains including compensation, flow rate estimation, and post processing are presented.

Blood flow image by multi-angle composite ultrasonic Doppler vector

Precise measurement of blood flow is of vital importance in studying the formation of thrombus and atherosclerotic plaque. However, conventional color Doppler methods are limited to obtaining the velocity component along the ultrasound beam and have poor accuracy. Several Doppler flow imaging methods based on the plane wave emission can estimate the blood velocity vectors and visualize hemodynamic parameters, which provide more detailed blood flow information and effectively improve the capability of clinical diagnosis treatment. Considering the low accuracy of the Doppler flow methods for measuring velocity in complex flow fields, an optimization technique is used to improve the imaging quality and the accuracy of velocity estimation. In this study we propose a modified vector Doppler method through combining multi-angle compound technique, to reconstruct blood velocity vectors of carotid bifurcations obtained from 3D printing. Since the multi-angle compound technology can effectively improve the quality of imaging, this technology is applied to Doppler imaging to achieve high-accuracy velocity estimation. It can significantly reduce the velocity estimation errors. Comparing the velocity estimation accuracy of different angle compound numbers (<i>n</i> = 1, 3, 5, and 7) in the simulation, it is found that the accuracy of velocity estimation increases with angle compound increasing. Beside, the 5-angle compound method is more robust for velocity estimation and can obtain higher frames. The experiments were carried out using a programmable ultrasonic array system and a high-frequency linear array transducer L12-5c with a central frequency of 8.125 MHz. The sample rate is set to be 31.25 MHz. The imaging results of carotid bifurcation also show that the vector Doppler based on 5-angle compound can obtain a clear image of intravascular vector flow, which is beneficial to the identifying of complex flow state, and realize intravascular dynamic imaging. Especially, it can capture the vortex phenomenon in the blood stream. The quantitative results indicate that this method significantly reduces the error between the flow calculation results and the reference results, making the estimation results more accurate. In conclusion, the vector Doppler method based on multi-angle compound has the good performance of visualizing complex blood flow and calculating hemodynamic parameters. It also provides the reference for the diagnosis of cardiovascular disease and the research of flow imaging methods.

On the merging and splitting processes in the lobe-and-cleft structure at a gravity current head

High-resolution simulations are performed for gravity currents propagating on a no-slip boundary to study the merging and splitting processes in the lobe-and-cleft structure at a gravity current head. The simulations reproduce the morphological features observed in the laboratory and provide more detailed flow information to elucidate the merging and splitting processes. Our mean lobe width$\tilde {b}$and mean maximum lobe width$\tilde {b}_{max}$satisfy the empirical relationships$\tilde {b}/\tilde {d}=7.4 Re^{-0.39}_f$and$\tilde {b}_{max}/\tilde {d}=12.6 Re^{-0.38}_f$, respectively, over the front Reynolds number in the range$383 \le Re_f \le 3267$, where the front Reynolds number is defined as$Re_f= \tilde {u}_f \tilde {d} / \tilde {\nu }, \tilde {u}_f$is the front velocity,$\tilde {d}$is the height of the gravity current head and$\tilde {\nu }$is the fluid kinematic viscosity. When measured in terms of the viscous length scale$\tilde {\delta }_\nu = \tilde {\nu }/\tilde {u}^*$, where$\tilde {u}^*$is the shear velocity at the gravity current head, the mean lobe width and the mean maximum lobe width increase with increasing front Reynolds number and asymptotically approach$126 \tilde {\delta }_\nu$and$230 \tilde {\delta }_\nu$at$Re_f=3267$, respectively. The vortical structure inside a lobe has an elongated tooth-like shape and a pair of counter-rotating streamwise vortices are positioned on the left- and right-hand sides of each cleft. For the merging process, it requires the interaction of three tooth-like vortices and the middle tooth-like vortex breaks up and reconnects with the two neighbouring tooth-like vortices. Therefore, a cleft may continually merge with another neighbouring cleft but may never disappear. For the splitting process, even before the new cleft appears, a new born streamwise vortex is created by the parent vortex of opposite orientation and the parent vortex can be either the left part or the right part of the existing tooth-like vortex inside the splitting lobe. The new born streamwise vortex then induces the other counter-rotating streamwise vortex as the new cleft develops. The initiation of the splitting process can be attributed to the Brooke–Hanratty mechanism reinforced by the baroclinic production of vorticity. Depending on the orientation of the parent vortex, the resulting new cleft after the splitting process can shift laterally in the positive or negative spanwise direction along the leading edge of the gravity currents as the lobe-and-cleft structure moves forward in the streamwise direction. For gravity currents propagating on a no-slip boundary, the lobe-and-cleft structure is self-sustaining and the manifestations of the merging and splitting processes are in accord with reported laboratory observations.

Coupling of pyrolysis and heat transfer of supercritical hydrocarbon fuel in rectangular minichannels

The coupling of pyrolysis and heat transfer of endothermic hydrocarbon fuels (EHFs) plays an important role in the design of cooling channels for advanced aircrafts. In this work, the convective heat transfer of EHFs with pyrolysis was experimentally investigated in horizontal rectangular channels under supercritical conditions (3.5 MPa, 700 °C) with different aspect ratios (λ = 1 ~ 5) by electrically heated tube test. CFD simulations with an updated kinetics were conducted and extensively validated to get detailed information of local flow, pyrolysis and heat transfer. The heat transfer is non-uniform in the cross-section with obvious temperature difference due to non-uniformity of boundary layer. Increasing λ is beneficial for heat transfer at topwall because of a relative lower heat flux and higher chemical heat absorption in bulk fluid. In addition, significant distribution of boundary layer along topwall and sidewall results in M-shape velocity distribution and subsequent high-degreed pyrolysis near sidewall region. This leads to dramatical variations of thermophysical properties and considerable decrease of chemical heat absorption, thus increasing the near-wall thermal resistances. Therefore, the local heat transfer is deteriorated at sidewall and corner, ascribed to a thicker boundary layer at the corner for increased fluid viscosity with secondary reactions, as well as the increased thermal resistances attributed to huge property gradient for pyrolysis distribution near sidewall.

3D CFD simulation of the liquid flow in a rotating packed bed with structured wire mesh packing

An in-depth understanding of the liquid flow characteristics in rotating packed beds (RPBs) is very important for the optimization and modelling of RPB reactors. However, the complex and dense packing makes it very difficult to accurately obtain the dynamic and detailed characteristics of liquid flow in RPBs through experimental methods. Therefore, this paper carried out a 3D gas–liquid flow CFD simulation of an RPB with structured wire mesh packing to obtain detailed liquid flow information. Detailed macro and micro characteristics of the liquid flow in the packing region of the RPB are obtained. The dynamic evolution processes of droplets are observed and analysed. A new flow pattern of “branch flow” is observed in the packing region. In addition, two typical liquid disintegration modes of liquid ligament-droplet disintegration and liquid bridge-droplet disintegration are observed, and the disintegration mechanisms are analysed. Finally, the effects of contact angle and rotational speed on the characteristic parameters are investigated, and the interfacial areas between different phases in the RPB are analysed. In both hydrophilic and hydrophobic packings, the wetted packing surface area is always less than the gas–liquid interfacial area, and their ratio decreases with the increases of contact angle and/or rotational speed, but increases with the increase of the liquid viscosity.

Virtual Real-Time for High PRF Multiline Vector Doppler on ULA-OP 256.

The recent development of high-frame-rate (HFR) imaging/Doppler methods based on the transmission of plane or diverging waves has proposed new challenges to echographic data management and display. Due to the huge amount of data that need to be processed at very high speed, the pulse repetition frequency (PRF) is typically limited to hundreds hertz or few kilohertz. In Doppler applications, a PRF limitation may result unacceptable since it inherently translates to a corresponding limitation in the maximum detectable velocity. In this article, the ULA-OP 256 implementation of a novel ultrasound modality, called virtual real-time (VRT), is described. First, for a given HFR RT modality, the scanner displays the processed results while saving channel data into an internal buffer. Then, ULA-OP 256 switches to VRT mode, according to which the raw data stored in the buffer are immediately reprocessed by the same hardware used in RT. In the two phases, the ULA-OP 256 calculation power can be differently distributed to increase the acquisition frame rate or the quality of processing results. VRT was here used to extend the PRF limit in a multiline vector Doppler (MLVD) application. In RT, the PRF was maximized at the expense of the display quality; in VRT, data were reprocessed at a lower rate in a high-quality display format, which provides more detailed flow information. Experiments are reported in which the MLVD technique is shown capable of working at 16-kHz PRF, so that flow jet velocities higher up to 3 m/s can be detected.

Depiction of detailed surgical anatomy and CSF flow information using a single MRI technique

We describe a novel MRI sequence (T2 SPACE) capable of demonstrating detailed structural anatomy and functional CSF flow information simultaneously. While traditionally, a variety of sequences are utilised for this purpose, we have highlighted the advantages of this technique over traditional approaches, using example of a patient with CSF loculation in prepontine/suprasellar cistern, causing third ventricular compression and hydrocephalus. The sequence depicted the surgical anatomy by showing the web/cyst wall as well as CSF flow entering the cyst potentially causing increased pressure.

A simplified discrete unified gas kinetic scheme for incompressible flow

The discrete unified gas kinetic scheme (DUGKS) is a new finite volume (FV) scheme for continuum and rarefied flows, which combines the benefits of both the lattice Boltzmann method and UGKS. By the reconstruction of the gas distribution function using particle velocity characteristic lines, the flux contains more detailed information of fluid flow and more concrete physical nature. In this work, a simplified DUGKS is proposed with the reconstruction stage on a whole time step instead of a half time step in the original DUGKS. Using the temporal/spatial integral Boltzmann Bhatnagar–Gross–Krook equation, the auxiliary distribution function with the inclusion of the collision effect is adopted. The macroscopic and mesoscopic fluxes of the cell on the next time step are predicted by the reconstruction of the auxiliary distribution function at interfaces along particle velocity characteristic lines. According to the conservation law, the macroscopic variables of the cell on the next time step can be updated through its flux, which is a moment of the predicted mesoscopic flux at cell interfaces. The equilibrium distribution function on the next time step can also be updated. The gas distribution function is updated by the FV scheme through its predicted mesoscopic flux in a time step. Compared with the original DUGKS, the computational process of the proposed method is more concise because of the omission of half time step flux calculation. The numerical time step is only limited by the Courant–Friedrichs–Lewy condition, and a relatively good stability has been preserved. Several test cases, including the Couette flow, lid-driven cavity flow, laminar flows over a flat plate, a circular cylinder, and an airfoil, and microcavity flow cases, are conducted to validate the present scheme. The observed numerical simulation results reasonably agree with the reported results.

Numerical Investigation of the Wake Vortex-Related Flow Mechanisms in Transonic Turbines

As the core equipment of the power generation system, a gas turbine is an indispensable energy-converting device in the national industry. The flow inside a high-pressure turbine (HPT) is highly unsteady, which has a great influence on the aerothermal performance and structural strength. To better clarify the flow mechanism and guide the advanced design, the basic flow characteristics of transonic turbines are investigated in the paper by a modified scale-adaptive simulation (SAS) model based on the shear stress transport (SST) turbulence model. The numerical results reveal the formation and development of the secondary flow structures such as wake vortex, pressure wave, shock wave, and the interactions among them. The length and frequency characteristics of wake are in good agreement with the large eddy simulation (LES) and the experimental data. Based on the detailed flow information, the local loss analysis is performed using the entropy generation rate. In summary, the wake vortex-related flow is the main origin of unsteadiness and entropy loss in high-pressure turbine cascade.

Steady-State Thermal-Hydraulic Model for Fluoride-Salt-Cooled Small Modular High-Temperature Reactors

A whole-core, steady-state, thermal-hydraulic model for the cylindrical pin-type fluoride-salt-cooled small modular advanced high-temperature reactor (SmAHTR) is developed. In this preconceptual reactor design initially proposed by Oak Ridge National Laboratory, each fuel assembly in the graphite-moderated core has the FLiBe coolant flowing parallel to a hexagonal array of fuel and moderator pins. The present study considers a slightly modified fuel assembly design with a hexagonal inner housing compared to the original cylindrical housing. Burnable poison pins and control rods are also included in the fuel assembly considered here. The thermal-hydraulic model employs finite volumes to solve three-dimensional conduction in the pins and the hexagonal graphite reflector regions in the core. Heat transfer between the fuel assemblies is also addressed. The finite volumes in the fluid region are modeled using a subchannel approach in which the fluid is discretized into edge, corner, and interior subchannels and the resulting mass, momentum, and energy equations are systematically solved. The subchannel model also includes the transport between adjacent subchannels both due to radial pressure gradient–driven cross flow and turbulent mixing. Appropriate closure models from the literature are used to quantify axial and lateral flow resistances, heat transfer from solid to fluid, and turbulent mixing. The resulting thermal-hydraulic model provides detailed temperature and flow information for the entire core at a modest computational cost. Preliminary verification studies are also performed and reported. Whole-core, steady-state results are presented for this SmAHTR core configuration for different power profiles. The effect of grid refinement and total mass flow rate into the core on the peak fuel temperature is also investigated. Fuel temperatures from a preliminary analysis with pin power distributions from a neutronic model are also included. The peak fuel temperature of ~1229°C in this illustrative case is below the steady-state operation limit for the SmAHTR.

Mixed convection heat transfer of supercritical pressure R1234yf in horizontal flow: Comparison study as alternative to R134a in organic Rankine cycles

The low GWP working fluid of R1234yf is a prospective alternative to the conventional R134a used in organic Rankine cycles. As studies regarding the heat transfer of supercritical pressure R1234yf are rare, supercritical heat transfer experiments of R1234yf were conducted for the first time to evaluate the feasibility of R1234yf in replacing R134a from the perspective of supercritical heat transfer performance. First, the effects of pressure, mass flux, and heat flux were analyzed. Subsequently, the supercritical heat transfer performances of the two fluids were compared experimentally and numerically. Results show that the heat transfer characteristics of R1234yf and R134a are similar at the same operating condition with the heat transfer coefficient of R1234yf being approximately 10% higher than that of R134a, while the pressure drop of R1234yf is higher. Numerical analyses on detailed flow and thermal field information show that the heat transfer difference between the two fluids is primarily caused by the difference in density, thereby causing a stronger buoyancy effect in R134a at the same operating condition. Finally, the applicability of the R134a-based buoyancy criterion and heat transfer correlation were evaluated for R1234yf, and results indicate that they can be used for R1234yf as well. • Supercritical heat transfer of low GWP fluid of R1234yf was studied. • Heat transfer of R134a and R1234yf was compared experimentally and numerically. • HTC and pressure drop of R1234yf are both higher compared with R134a. • Density difference dominates heat transfer difference between R134a and R1234yf. • R134a-based heat transfer correlation and buoyancy criteria is suitable for R1234yf.

Background Point Filtering of Low-Channel Infrastructure-Based LiDAR Data Using a Slice-Based Projection Filtering Algorithm.

A light detection and ranging (LiDAR) sensor can obtain richer and more detailed traffic flow information than traditional traffic detectors, which could be valuable data input for various novel intelligent transportation applications. However, the point cloud generated by LiDAR scanning not only includes road user points but also other surrounding object points. It is necessary to remove the worthless points from the point cloud by using a suitable background filtering algorithm to accelerate the micro-level traffic data extraction. This paper presents a background point filtering algorithm using a slice-based projection filtering (SPF) method. First, a 3-D point cloud is projected to 2-D polar coordinates to reduce the point data dimensions and improve the processing efficiency. Then, the point cloud is classified into four categories in a slice unit: Valuable object points (VOPs), worthless object points (WOPs), abnormal ground points (AGPs), and normal ground points (NGPs). Based on the point cloud classification results, the traffic objects (pedestrians and vehicles) and their surrounding information can be easily identified from an individual frame of the point cloud. We proposed an artificial neuron network (ANN)-based model to improve the adaptability of the algorithm in dealing with the road gradient and LiDAR-employing inclination. The experimental results showed that the algorithm of this paper successfully extracted the valuable points, such as road users and curbstones. Compared to the random sample consensus (RANSAC) algorithm and 3-D density-statistic-filtering (3-D-DSF) algorithm, the proposed algorithm in this paper demonstrated better performance in terms of the run-time and background filtering accuracy.

Traffic parameter estimation and control system based on machine vision

With the rapid development of urbanization in the world, it has brought enormous pressure on urban traffic management and control such as traffic congestion. An excellent urban traffic management and control system consists of three critical aspects: obtaining traffic parameters, developing traffic control scheme, and evaluating traffic control scheme. Intersection signal timing is one of the most important parts in urban traffic control. This paper proposed an intersection signal timing system based on traffic video which consists of three parts: acquisition of video-based traffic parameters, calculation of traffic flow-based signal timing scheme, and evaluation of intersection signal timing scheme. In the first part, we used advanced techniques such as deep learning and image processing to obtain traffic parameters such as traffic flow, vehicle type, composition of different vehicle types, and speed of vehicles passing through a scene in a traffic video. In the second part, we calculated the signal timing scheme of the video at the traffic scene through the obtained traffic flow information with Webster method. In the third part, the detailed traffic parameters and signal timing scheme were input into the VISSIM software for traffic microscopic simulation, which was used to evaluate the signal timing scheme. The experimental results show that the accuracy of the detailed traffic flow information obtained by the proposed system can reach more than 90%, the accuracy of composition of different vehicle types can be achieved more than 98%, and the vehicle speed accuracy can reach more than 95%. Therefore, the system improves the reliability and adaptability of the whole signal timing network. At the same time, the simulation results show that the proposed system integrates the acquisition of traffic parameters and the calculation and evaluation of signal timing schemes, and provides a good solution for solving research problems and actual needs such as signal timing optimization.

Numerical and Experimental Investigation on Radiated Noise Characteristics of the Multistage Centrifugal Pump

The radiated noise of the centrifugal pump acts as a disturbance in many applications. The radiated noise is closely related to the hydraulic design. The hydraulic parameters in the multistage pump are complex and the flow interaction among different stages is very strong, which in turn causes vibration and noise problems because of the strong hydraulic excitation. Hence, the mechanism of radiated noise and its relationship with hydraulics must be studied clearly. In order to find the regular pattern of the radiated noise at different operational conditions, a hybrid numerical method was proposed to obtain the flow-induced noise source based on Lighthill acoustic analogy theory, which divided the computational process into two parts: computational fluid dynamics (CFD) and computational acoustics (CA). The unsteady flow field was solved by detached eddy simulation using the commercial CFD code. The detailed flow information near the surface of the vane diffusers and the calculated flow-induced noise source was extracted as the hydraulic exciting force, both of which were used as acoustic sources for radiated noise simulation. The acoustic simulation employed the finite element method code to get the sound pressure level (SPL), frequency response, directivity, et al. results. The experiment was performed inside a semi-anechoic room with a closed type pump test rig. The pump performance and acoustic parameters of the multistage pump at different flow rates were gathered to verify the numerical methods. The computational and experimental results both reveal that the radiated noise exhibits a typical dipole characteristic behavior and its directivity varies with the flowrate. In addition, the sound pressure level (SPL) of the radiated noise fluctuates with the increment of the flow rate and the lowest SPL is generated at 0.8Qd, which corresponds to the maximum efficiency working conditions. Furthermore, the experiment detects that the sound pressure level of the radiated noise in the multistage pump rises linearly with the increase of the rotational speed. Finally, an example of a low noise pump design is processed based on the obtained noise characteristics.

Modelling and validation of fluid flow inside a dissipative ladle shroud and a continuous casting tundish

Fluid flow plays a significant role in the continuous casting of molten steel. In this paper, two Reynolds Averaged Naiver-Stokes (RANS) models and a Large Eddy Simulation (LES) model were comparatively employed to characterize the fluid flow inside a dissipative ladle shroud and a tundish. LES model was proved to be powerful to characterize the turbulence structure inside the ladle shroud. The effect of meshing density on the computational accuracy was considered using the LES model. The fine-mesh model can capture multiscale vortices inside the ladle shroud; while, the coarse-mesh model disables the LES to obtain the detailed flow information. The experiment of particle image velocimetry (PIV) was used to verify the flow field obtained by the LES model inside the tundish. The PIV and the LES results agree well in terms of flow pattern and velocity vector.

Scale-Adaptive Simulation of the Unsteady Turbulent Flow in a High-Speed Centrifugal Compressor with a Wedge-Type Vaned Diffuser

The present work investigates the details of unsteady flow behavior in a transonic centrifugal compressor with vaned diffuser. The analysis is based on solving three-dimensional, compressible, unsteady Navier-Stokes equations. The computational model is a high-compression ratio centrifugal compressor (4:1) consisting of an inlet duct, impeller, and diffuser vane. The hybrid scale-adaptive simulation (SAS) turbulent model is used to provide detailed flow information and characterize the transient flow structures within the compressor passages. A numerical sensitivity test is performed to validate the computational results in terms of pressure ratio and compressor efficiency. Instantaneous and mean flow field analyses are presented in the impeller and the vaned diffuser passages. Applying transient simulations, it is shown that the interaction between the pressure waves and the surface pressure of the diffuser blades leads to a pulsating behavior within the diffuser. Moreover, spectral analysis is evaluated to analyze the blade passing frequency (BPF) tonal noise as the main noise source of centrifugal compressors. In addition, the current SAS results are compared with those of the URANS-SST (shear stress transport) approach to show the ability of the SAS approach in the prediction of turbulent structures, where the SAS model leads to a much better resolution of the unsteady fluctuations. This study shows that the current SAS approach is promising in terms of the prediction of transient phenomena like LES, but offers a substantially reduced turn-around time.

A Study on the Motion of Partial Air Cushion Support Catamaran in Regular Head Waves

In this paper, the motion of partial air cushion support catamaran (PACSCAT) sailing in regular waves was firstly investigated by the experimental method. The monitored histories of heave, pitch, midship acceleration, and air cushion pressure in towing tests are performed to analyze the influence of air cushion on the periodicity feature of hull body motion. Subsequently, using the finite volume method (FVM)-based CFD software Star-ccm, numerical simulations are carried out for the PACSCAT model with a simplification of the air cushion system. The detailed flow information of wave evolution, pressure, and velocity distribution is investigated. The calculated oscillation characteristics of different motion parameters are compared with those from experiment and show good agreement. The numerical method also has good capacity in the prediction of amplitude response of heave and midship acceleration; however, large error is found when calculating resistance and amplitude response of pitch.

Assessing the interaction of air from a jet diffuser on a thermal plume in a room using two-dimensional particle image velocimetry

Traditional design of airflow distributions in large spaces does not consider the interference of thermal plumes on jets. In order to quantitatively describe the indoor environment, it is first necessary to quantify how the airflow gets distributed. In this study, a two-dimensional particle image velocimetry (PIV) system for measuring a wide indoor flow field was established. A total of 24 sub-regions (each with a size of 400 mm × 350 mm) were accurately measured in an unmanned room, and the overall cross-sectional flow field was obtained by splicing. Uncertainty analysis proved the rationality of this experimental method. According to the damage extent of the jet structure introduced by the thermal plume, two groups were divided, i.e. Groups A and B. The distribution of velocity fields, trajectories and velocity attenuation of jet centerlines, and velocity magnitude profiles at nozzle and head levels were compared and analyzed in detail. Through this investigation, detailed information of indoor air flow in large spaces can be effectively characterized, which can be useful to help understand the indoor physics and validate CFD models. Practical application: The key to creating a comfortable and healthy indoor thermal environment is the rational design of the airflow distribution. This paper proposes a method for quantitatively describing the airflow distribution in an enclosed space. The equation of the non-dimensional velocity attenuation of jet centerlines is obtained by using advanced technology (PIV), which provides theoretical basis and useful reference for the design of airflow distribution.

Video-Based Vehicle Counting Framework

The continuous development in the construction of transportation infrastructure has brought enormous pressure to traffic control. Accurate and detailed traffic flow information is valuable for an effective traffic control strategy. This paper proposes a video-based vehicle counting framework using a three-component process of object detection, object tracking, and trajectory processing to obtain the traffic flow information. First, a dataset for vehicle object detection (VDD) and a standard dataset for verifying the vehicle counting results (VCD) were established. The object detection was then completed by deep learning with VDD. Using this detection, a matching algorithm was designed to perform multi-object tracking in combination with a traditional tracking method. Trajectories of the moving objects were obtained using this approach. Finally, a trajectory counting algorithm based on encoding is proposed. The vehicles were counted according to the vehicle categories and their moving route to obtain detailed traffic flow information. The results demonstrated that the overall accuracy of our method for vehicle counting can reach more than 90%. The running rate of the proposed framework is 20.7 frames/s on the VCD. Therefore, the proposed vehicle counting framework is capable of acquiring reliable traffic flow information, which is likely applicable to intelligent traffic control and dynamic signal timing.