Flow Field Visualization Research Articles

Effect of sweep angle on three-dimensional vortex dynamics over plunging wings

The effects of sweep angle and reduced frequency on the leading-edge vortex (LEV) structure over flapping swept wings in the Reynolds number (Re) range of O(104) are yet to be completely understood. With increasing interest in designing bio-inspired micro-air-vehicles, understanding LEV dynamics in such scenarios is imperative. This study investigates the effects of three different sweep angles (Λ=0°, 30°, and 60°) on LEV dynamics through high-fidelity improved delayed detached eddy simulation to analyze the underlying flow physics. Plunge ramp kinematics at two different reduced frequencies (k = 0.05 and 0.4) are studied to investigate the unsteady motion effects on LEV characteristics. The leading-edge suction parameter concept is applied to determine LEV initiation, and the results are verified against flow field visualization for swept-wing geometries. The force partitioning method is used to investigate the spanwise lift distribution resulting from the LEV. Distinct peaks in the lift coefficient occur for the high reduced frequency case due to the impulse-like plunging acceleration. This causes the LEV to detach from the leading edge more quickly and convect faster, significantly affecting the lift generated by the wing. As reduced frequency increases, the LEV breakdown mechanism switches from vortex bursting to LEV leg-induced instabilities. These results provide insights into the complex vortex structures surrounding swept wings at Re = 20 000, and the impact both sweep angle and reduced frequency have on the lift contribution of these flow features.

Visualization Method for Mesoscale Eddies Characteristics in Ocean Flow Fields Based on Variable Particle Systems

Visualization of ocean flow fields is a major area of interest in marine science. Existing visualization methods based on randomly generated particles tend to exhibit a uniform distribution. While this approach effectively represents ocean flow fields, it inadequately conveys the characteristic structures within the flow in an intuitive manner. Ocean eddies, as crucial components of ocean dynamics (Patrizio & Thompson, 2021), are key features in visualizing ocean flow fields. Mesoscale eddies, which contain 90% of the ocean's kinetic energy, play a vital role in transporting this energy. These eddies significantly influence local marine environments and are instrumental in understanding the kinetic energy of ocean flow fields, providing valuable insights for fields such as oceanography, meteorology, and climate research. The aim of this study is to establish a method based on variable particle systems. Initially, a feature set for mesoscale eddies and a parameter set for variable particles are defined. By mapping the feature set to the parameter set, we express the characteristic structure of mesoscale eddies dynamically. Using ocean flow field data, we demonstrate the method's ability to effectively highlight the characteristic structures of mesoscale eddies within the flow field through qualitative and quantitative evaluation metrics. By analyzing and visualizing ocean flow fields, we can gain a deeper understanding of their spatiotemporal evolution, thereby uncovering the patterns and regularities of their movement. This research approach not only facilitates the effective development, utilization, and sustainable management of marine resources but also aligns with the demands of digital ocean technology for visualizing marine spatial information.

Wire-to-two-drop plasma thruster: Experimental and numerical investigation of electroaerodynamic jet flow for micro aerial vehicle propulsion

Conventional micro aerial vehicles (MAVs) have primarily relied on complex, flapping-wing mechanisms for propulsion, often exhibiting limitations in terms of reliability and efficiency. To overcome these challenges, this study explores the potential of electroaerodynamic (EAD) thrusters as a novel propulsion system. By accelerating air molecules through ion collisions, EAD jet flow generates thrust, offering advantages such as noiseless operation and zero emissions due to its moving-part-free design. This research presents a comprehensive experimental and numerical investigation of a wire-to-two-drop thruster configuration to elucidate its electromechanical performance, plasma flow dynamics, and EAD jet characteristics. Experimental measurements of key parameters, including current, thrust, power, and effectiveness, were correlated with numerical simulations, demonstrating excellent agreement with a maximum error below 5%. These findings align strongly with established theoretical frameworks, revealing an inverse square root relationship between effectiveness and thrust. To optimize thruster performance, optimal operating voltages were identified at approximately 8.2, 9.4, and 11.6 kV for inter-electrode gap distances of 10, 15, and 20 mm, respectively, achieving a balanced trade-off between thrust and effectiveness. Detailed numerical visualizations of the plasma flow field, including velocity distribution, jet morphology, potential distribution, and electric field lines, provided valuable insights into the thruster's operation. Building upon these insights, a proof-of-concept EAD flier was constructed and tested, incorporating a serrated emitter electrode and lightweight materials. This flier achieved a mass of 0.5 g and generated a thrust of 0.77 g at 15 kV, resulting in a thrust-to-weight ratio of 1.54 and successful liftoff. This demonstration highlights the potential of EAD propulsion for practical MAV applications.

A visual digital twin framework based on residual-based fourier neural operator online simulation method

ABSTRACT To enjoy a wonderful cooking experience in a smart kitchen, users and designers need a visual interaction platform. This paper proposes a DT framework incorporating data processing, flow field online simulation, equipment monitoring, interaction and visualization. Specifically, the DT online simulation and visualization of the kitchen fume flow field serve as the foundation for appliance design and control. Additionally, users can gain deeper insight into the state and change trends of the kitchen. To address the online simulation of the flow field, a RFNO online simulation method is proposed. In addition, this paper proposes an Echarts-based 2D and UE5-based 3D flow field visualization method to enable dynamic visualization and interaction of the flow field. The proposed DT framework was successfully verified in the case of the smart kitchen, demonstrating its efficiency and effectiveness.

Effect of porosity and pore heterogeneity on heat transfer performance of polyimide aerogels

The effects of porosity and pore distribution on the heat transfer performance of polyimide (PI) aerogel under natural convection were investigated through a combination of experimental and numerical simulations. The governing equations of heat transfer were analyzed in detail. A novel heterogeneity factor (η) was introduced to quantify internal pore distribution. PI aerogels exhibiting a range of porosities and heterogeneity factors were synthesized and characterized. The natural convection heat transfer coefficient of PI aerogels was measured experimentally, providing empirical data. A porous model was developed by integrating Voronoi technique with a two-scale generation method, allowing for comprehensive numerical simulations of heat transfer. The numerical results demonstrated strong concordance with the experimental data, validating the model’s accuracy. The results revealed that the heat transfer performance of the aerogels diminished markedly with increasing porosity when heterogeneity was held constant. Conversely, with fixed porosity, the heat transfer performance improved significantly with greater heterogeneity. Numerical simulations further enabled the visualization of internal temperature and flow fields, elucidating that the effect of porosity and heterogeneity on natural convection heat transfer performance is predominantly driven by variations in internal permeability.

Effect of turbulence intensity on bubble-particle detachment mechanism in a confined vortex

Bubble-particle detachment induced by turbulence is the primary factor for the low recovery of coarse particles, which has attracted much attention in recent years. The prevailing centrifugal detachment theory has achieved broad consensus. However, due to the complexity of bubble-particle aggregate motion in the turbulent field, the influence of turbulence intensity on bubble-particle detachment mechanism remains unclear. In this study, a controlled rotating vortex was generated using a custom-made fluid channel to systematically investigate the effect of turbulence intensity on bubble-particle centrifugal detachment. Firstly, detachment behaviours of bubble-particle aggregates were captured using high-speed cameras, followed by flow field visualization of bubble-particle detachment processes using Computational Fluid Dynamics (CFD). Experimental results reveal three typical detachment modes of bubble-particle aggregates in the confined vortex: fluid shear, bubble oscillation, and particle centrifugal motion, with particle centrifugal detachment becoming dominant with increasing turbulence intensity. This shift is attributed to changes in turbulence intensity directly affecting the trajectories of bubble/aggregates and indirectly influencing the detachment mode of bubble-particle. Compared to low turbulence intensity, bubble-particle aggregates exhibit smaller rotational radii under high turbulence intensity, reducing the probability of fluid shear and bubble oscillation detachment by mitigating the influence of high-speed shear zones at the top of the cavity. Conversely, particles located at the edge of aggregates are more susceptible to acceleration by sidewall flow fields, favouring detachment through particle centrifugal motion. Moreover, unlike traditional centrifugal detachment theories, particles do not merely undergo independent circumferential motion on the bubble surface but participate as a whole with bubbles in centrifugal motion governed by vortices. These findings are expected to provide fundamental insights into the bubble-particle detachment mechanism in turbulent fields.

Aerothermal Loads on a Representative Porous Mesostructure at Flight Conditions Using Direct Simulation Monte Carlo

Spacecraft require thermal protection systems (TPS) in order to survive the extreme conditions present during atmospheric entry missions. Porous ablators are a class of TPS materials that have been used successfully on several entry missions, although they can be difficult to model because of their complex nature at the micro- and mesoscales. Specifically, the processes that lead to mechanical erosion (spallation) of these materials are poorly understood. In order to gain insight into the spallation process, the current work computes aerothermal loads on a mesostructure representative of FiberForm (the substrate of phenolic impregnated carbon ablator) by leveraging a simulation framework involving loosely coupled Computational Fluid Dynamics-Direct Simulation Monte Carlo (CFD-DSMC) simulations of hypersonic boundary layers. CFD boundary layers are extracted from two altitudes, 68.9 and 81 km, along the Stardust entry trajectory and are imposed as boundary conditions on a DSMC simulation over an artificially generated mesostructure, which is representative of the charred layer of the TPS material. In order to produce high-quality results, the DSMC boundary conditions require careful consideration; specifically, Chapman–Enskog distributions are needed to account for large velocity and temperature gradients. Visualizations of the DSMC flowfield indicate excellent agreement with the original CFD data, and the aerothermal loads (heat flux and traction force) on the surface were examined using probability density functions. Additionally, the effects of pyrolysis blowing through the mesostructure on the surface properties are also determined.

Airflow collision characteristics of double square column attachment ventilation

In the square column attachment ventilation (S-CAV) mode, the introduction of multiple airflows attached to the column into the horizontal diffusion zone inevitably leads to various “airflow collision” phenomena. However, after the floor-attached airflow collides, the indoor air distribution may deviate from the design goal. In this paper, the layout of the axisymmetric and non-axisymmetric arrangement of double columns is summarized. The airflow collision mechanism and flow characteristics for different column layouts are analyzed via experiments and computational fluid dynamics (CFD) simulations, and a new partition form is proposed to more effectively control the indoor environment. A 1:2 scale model was employed for the velocity verification experiments and flow field visualization. The results indicated that the airflow collision area can be divided into impact, transition, and collision zones with axisymmetric double-column layouts. In the range of 1–3 m/s, any variation in the supply air velocity, irrespective of the occurrence of airflow collision, may be considered negligible with respect to its impact on the attenuation trend of the axial velocities. At the same absolute value of the air supply temperature difference, the cooling condition experiences a 3.1 times greater kinetic energy loss due to collision than does the heating condition. In a nonsymmetric arrangement of two columns, the curve formed by the stagnation point rotates, and the direction of rotation is biased toward the side of the column that is farther away. The findings provide a solid theoretical basis for the engineering application and optimal design of CAV modes.

Wake mode identification of rotating triangle with machine learning approaches

The moving body usually leaves different forms of wake trails in fluids, and these wake fields contain physical information such as the state and geometry of the moving body. Recognizing and extracting these information from the wake can provide new insights for non-acoustic detection technology. Traditional methods do not easily extract the flow state, geometry, and other information directly from the wake structure. This work mainly uses convolutional neural network algorithms for intelligent recognition of the wake types of rotating triangles. Based on the flow field visualization technology of the soap film tunnel, the wake types of the flow around a structure controlled by external excitation of sinusoidal rotation are studied. The winding characteristics of the rotating triangle and the variation rule of the wake with control parameters are analyzed. At last, the recognition rate of the wake types on the test set is above 90%. The recognition rates of the experimental data not involved in the training conditions are all above 80%, demonstrating the generalizability of the model. This method provides a reference for further utilizing artificial intelligence in extracting physical information from wakes, playing a crucial role in advancing wake detection technology.

Research on the blockage effect in a shock tube

The shock tube is a crucial experimental apparatus in the field of explosive impact. Limited research has been conducted on the visualization of the internal flow field in shock tubes under blockage conditions, and there is a lack of comprehensive understanding of the mechanisms behind blockage effects. This paper presents experimental and numerical investigations into the propagation of shock waves inside a shock tube and their interaction with obstructive elements. Blockage effect experiments were conducted on a shock tube test platform, where pressure data were obtained through a pressure monitoring system. Additionally, schlieren imaging technology was employed to visualize the evolution of shock wave fronts. A two-dimensional numerical model of the shock tube was established using Fluent software, and the computed results exhibited excellent agreement with the experimental data, confirming the accuracy of the numerical model. The mechanism of the blockage effect was revealed through analysis of pressure-time curves and images depicting the evolution of shock wave fronts. Furthermore, adjustments to parameters on the validated numerical model allowed for analysis and comparison of different blockage ratios. The results indicate that the disturbance to the flow field caused by the blockage effect is primarily due to the reflection of shock waves between the front surface of the obstructive element and the shock tube wall. This reflection leads to differences in pressure curves compared to free-field conditions, and such differences increase with higher blockage ratios.

Effect of length and attack angle of the splitter plates on circular cylinder piezoelectric water energy harvester

With the micro-miniaturization of offshore wireless sensors, signal lights, and other devices and the emergence of the problem of self-powering in the distant sea, how to harvest energy from low-speed currents has become a hot spot of research nowadays. To improve the energy output power and conversion efficiency of low-speed water flow, we propose a vertical cantilever beam circular cylinders fitted with a rigid splitter plate piezoelectric energy harvester (CSPPEH). In this paper, the influence of the length and the attack angle of the splitter plate on CSPPEH has been experimentally investigated. The vibration response mechanism involving the mutual transition between vortex-induced vibration and galloping was analyzed through particle image velocimetry flow field visualization. The experimental results indicate that the vibration and piezoelectric characteristics of the CSPPEH increase initially and then decrease with the length of the splitter plates (L/D = 0–2.4) at the attack angle of 0°, which can be explained by the theoretical model of the energy harvester. It is found that the optimal vibration and piezoelectric characteristics occur at a rigid splitter plate length of 1.40D with an attack angle of 90°. The maximum values for amplitude, vibration swing angle, voltage, power, and power density are 4.96D, 21.7°, 42.68 V, 910.81 μW, and 1.94 mW/cm3, respectively. Efficiency was up to 2.2% at 0.4D length and 90° attack angle of the splitter plate. Compared to the bare circular cylinder energy harvester, the output power and efficiency are significantly improved. The demonstration of continuous charging and discharging of capacitors and light emitting diode lights is performed to show the practicability of the designed CSPPEH. Overall, the present study enables the applications of CSPPEH for realizing self-powered wireless sensing and signal lights under low-water-speed environments.

Study on the application of 3D imaging based on the γ-photon silk thread method for visualisation and detection of flow fields

As a flow display technique, the silk thread method can clearly show the state of the flow field. However, displaying the state of the flow field in industrial closed metal cavities is impossible, and results of the traditional silk thread method fail to present depth information. To address these limitations, we propose a display method based on γ-photon silk thread 3D imaging. Firstly, a flow field visualization experimental platform applicable for industrial closed metal cavity was designed. Then, aiming at the shortcomings of insufficient γ-photon scanning data and limited imaging quality in flow field visualization, an adaptive sinogram interpolation-iterative filtering reconstruction algorithm was proposed to expand the data via the adaptive interpolation processing of the sinogram in image reconstruction. Beltrami filtering was also embedded in the iterative algorithm to effectively reduce noise and artifacts in the imaging image. Finally, the internal flow field inspection of the NACA0018 airfoil and the industrial confinement turbine were used as examples to visualise the wing upper surface flow and turbine blade passage secondary flow, respectively, and the results were consistent with those of the numerical simulation analysis. As the angle of attack of the wing increased, laminar flow separation occurred, and the silk thread structure state changed to the point where the aircraft stalled. After the imaging map analysis, the stall angle ranged between (15°,19°), which is consistent with the simulation results. In the turbine blade passage secondary flow detection, the imaging map formed a horseshoe vortex with airflow separation at the central saddle point and silk threads clearly presenting the structural state of the flow field along different directions.

A deep-learning super-resolution reconstruction model of turbulent reacting flow

Super-resolution reconstruction using deep-learning techniques is a valuable tool for enhancing computational and experimental visualization of flow fields to recover detailed features from coarse results. In this study, we propose the Pyramid Res U Super Resolution (PRUSR) network as a flow reconstruction model that upgrades the basic architecture of the Downsampled Skip-Connection Multi-Scale (DSC/MS) model with the pre-activated residual block (PRB). To improve the model accuracy, we also implement a new loss function called Mean Square Structure Similarity (MSSSIM), which combines the Mean Square Error (MSE) and Structure Similarity (SSIM). We test the model on a practical problem of visualizing the three-dimensional turbulent jet flame and find that the PRUSR model accurately reconstructs the super-resolution flow field, particularly in large downsampling ratio conditions, outperforming the original DSC/MS model and traditional interpolation algorithms such as bilinear and bicubic even with fewer input data. Additionally, the PRUSR model is capable of reconstructing sub-grid turbulent flow and flame thickness by inferring high-frequency information in the inertial subrange, making it a powerful post-processing tool for turbulent flow visualization and analysis.

An investigation of flow regimes and mixing in a novel arrow-shaped jet reactor

Fluid mixing plays a vital role in the industry of chemical engineering. In this work, a novel arrow-shaped jet reactor by varying the angle of fluid impingement in the inlet channel was investigated. Flow field visualization experiments using Planar Laser-Induced Fluorescence (PLIF) technique were carried out to study various flow regimes and mixing performance. Results show that differentiated flow patterns of engulfment flow regimes appear within the arrow-shaped jet reactor. Particularly, vortex ring shedding was found in the unsteady engulfing flow regime, which promoted the mixing significantly. Besides, the mechanism of the variation of fluid impinging angle on mixing in an arrow-shaped jet reactor was investigated by numerical simulation. The results indicate that the transformation from double-leg vortex to single-leg vortex and the increase of the volume of vortex clusters caused by vortex ring shedding are the main reasons for the improvement of the mixing of engulfment flow regime.

Study on the Cooling Performance of a Focused Ultrasonic Radiator for Electrical Heating Elements.

In this work, a focused ultrasonic radiator is proposed for cooling the electrical heating elements in the focal region, and its working characteristics are investigated. The analyses of the FEM computational and flow field visualization test results indicate that focused ultrasound can generate forced convective heat transfer by the acoustic streaming in the focal region, which can cool the heating elements effectively. Experiments show that when the input voltage is 30Vp-p and the ambient temperature is 25 °C, the focused ultrasonic radiator can cause the surface temperature of the heating element (high-temperature alumina ceramic heating plate with a diameter of 5 mm) in the focal region to drop from 100 °C to about 55 °C. When the diameter of the electrical heating element is changed from 5 mm to 30 mm, the cooling effect is similar in the focal region. Compared with a fan, the focused ultrasound radiator has a shorter cooling time and a more concentrated cooling area. The focused ultrasonic radiator proposed in this work is suitable for some special environments.

Visualization of post-detonation fireball flowfields and comparison to CFD modeling

Visualization of flow structures within post-detonation fireballs has been performed for benchmark validation of numerical simulations. Custom pressed PETN explosives with a 12-mm diameter hemispherical form factor were used to produce a spherically symmetric post-detonation flow with low soot yield. Hydroxyl-radical planar laser induce fluorescence (OH-PLIF) was employed to visualize the structure ranging from approximately 10μs to 35μs after shock breakout from the explosive pellet. Fireball simulations were performed using the HyBurn Computational Fluid Dynamics (CFD) package. Experimental OH-PLIF results were compared to synthetic OH-PLIF from post-processing of CFD simulations. From the comparison of experimental and synthetic OH-PLIF images, CFD is shown to replicate much of the flow structure observed in the experiments, revealing potential differences in turbulent length scales and OH kinetics. Results provide significant advancement in experimental resolution of these harsh turbulent combustion environments and validate physical models thereof.

A Study on the Application of Multi-sensory Interaction Technology in Enhancing Concert Audience Immersion

Abstract The progress of multi-sensory interaction technology provides technical support for creating immersive concerts full of participation and experience. Based on multi-sensory interaction technology, this study proposes the design idea of immersive concerts and outlines the application process of multi-sensory interaction technology in immersive concerts. It builds a concert virtual reality scene through emotion recognition and evocation in the virtual reality scene, designs a gesture interaction interface based on immersive flow field visualization, realizes the construction of an immersive concert, and carries out application evaluation. The model's emotion recognition rate is as high as 93.04%, and after the resting state adjustment, the subjects’ pleasantness and arousal are on the rise, and the ability to evoke emotions is consistent with the expectation. The experimental expectations were met as the mean values of realism and immersion scores were not below 7.6. The percentage of user agreement for clicking and pinching gestures is concentrated in rank 4 and rank 3, and the percentage of voting for comfort is concentrated in rank 2 and reaches 96% and 91%, respectively, which can meet the interaction needs of immersive concerts. This paper presents technical ideas for using multisensory interaction technology in immersive concerts.

Electrokinetic behavior of an individual liquid metal droplet in a rotating electric field

The interfacial tension gradient forms tangential stress that drives fluid flow at a liquid–liquid interface, known as the Marangoni convection. In this study, we report on the electrocapillary-driven Marangoni flow at the polarizable interface between a gallium-based liquid metal droplet (LMD) and electrolytes, activated by the rotating electric field. When the electric field frequency exceeds 50 Hz, the amplitude of the oscillatory movement of LMD decays to zero, resulting in a stationary droplet. Utilizing micrometer-resolution particle image velocimetry (micro-PIV), we investigate the flow patterns around the LMD in detail. The visualized flow fields reveal two distinct flow patterns in the surrounding fluid at the central cross section of LMD, which vary with changes in frequency: normal flow (50–200 Hz) and tangential flow (300–1000 Hz). To reveal this flow mechanism, we first analyzed the fluid configuration in a linear electric field. Subsequently, we employ the stream functions to theoretically derive the slip velocity of the Marangoni flow in a rotating electric field. By combining this with the numerical simulations, we arrive at the following conclusions: At high frequencies (f≥50 Hz), the time-averaged part of the interfacial tension gradient dominates the in-phase Marangoni flow, leading to normal flow; while the frequency increases (f≥300 Hz), the electrorotation due to the out-of-phase charging accounts for the transformation of the flow pattern. Our work systematically studied the Marangoni flow under linear and rotating electric fields, which is vital in electrokinetic flows and of fundamental interest for the fluid dynamics society.

Construction of Intelligent Practice System of Visual Arts Based on VR Technology in Information Age

Abstract Taking visual art intelligence as an entry point, this paper describes the transformation brought by the information age to the expression of visual art. Based on VR technology to build a practice system of visual art intelligence, VR positioning technology is used to locate the three-dimensional coordinates of the operator in order to realize the independent positioning of multiple operators in a large space and avoid positioning interference. Through the eye movement multi-channel interaction algorithm based on head-eye synergy, the two-dimensional interaction task in flow field visualization is completed, and then gesture interaction is added to complete the three-dimensional interaction task. The constructed system was implemented in the teaching of art majors at College Z, and the data were analyzed. The results show that the total average scores of innovative theoretical ideas, interactive experience feeling, symbolic integration of creative content and infinite extension of the multidimensional spatial field are 82.42, 83.57, 80.84 and 80.28, respectively. The data show that teachers, students and parents recognize the intelligent system of visual arts and believe that it improves students’ innovative ability in art creation, enhances the interactive experience feeling of visual arts, and provides data support for the continuous research and exploration of contemporary visual arts.

Experimental study on evolution of longitudinal vortex rolls subject to the duct tilted in the spanwise direction

An experiment was performed in this study to investigate the effect of duct spanwise inclinations on the longitudinal vortex pattern in an air mixed convective flow. Key parameters, including Reynolds (Re) numbers from 20 to 30 and Grashof (Gr) numbers from 4071 to 10,855, are investigated. The spatial and temporal attributes of longitudinal vortex rolls (LVRs) are examined via flow field visualization and transient temperature measurement in details. Compared with the corresponding non-sloping case, the duct inclination significantly influences the LVR evolution. Due to the non-zero spanwise buoyancy, the vortex roll tends to be asymmetrical across the span and causes the delayed onset of lower LVRs. The temperature fluctuates significantly with time adjacent to the upper sidewall at the larger tilt angle. In an inclined duct, lower LVRs will stretch spanwise to squeeze upper vortex rolls with a decrease in Re number. Increasing the Gr number is beneficial to LVR formation for a smaller spanwise-inclined angle. However, the increase in either Gr number or tilt angle makes the vortex flow relatively unstable. We also provide an empirical expression to determine the vortex onset as a function of Re, Pr, Gr numbers, and the tilted angle.