Flow Visualization Research Articles

Prediction-focused machine learning-based visualization of compressor flow in a gas turbine engine digital twin

Sidewall visualization of flow boiling heat transfer dynamics in high-aspect-ratio rectangular channels

This study investigates the hydrodynamic behavior of rough cylinders, focusing on how surface roughness influences vortex shedding patterns and forces in cross-flow. To achieve this objective, a three-dimensional large-eddy simulation was conducted to study the hydrodynamic coefficients and flow fields of cylinders with different relative roughness, height, and coverage ratios at a Reynolds number of 3900. The results show that the coverage ratio plays a more significant role in determining hydrodynamic characteristics than relative roughness, with a critical coverage ratio identified at approximately 0.4. Below this threshold, both drag and lift coefficients exhibit a marked increase with higher relative roughness. However, beyond a 0.4 coverage ratio, the impact of roughness diminishes, with the coefficients approaching those of a smooth cylinder. Additionally, the Strouhal number decreases with increasing roughness height and increases with coverage ratio. Flow visualization shows that these changes are closely related to the position and magnitude of the wake vortex shedding in the wake region of a rough cylinder. These findings provide new insights into the fundamental mechanisms of the hydrodynamic characteristics and vortex shedding of rough cylinders and offer valuable guidance for optimizing engineering design and enhancing performance in practical applications.

ABSTRACT The study experimentally investigates the primary disintegration of a liquid sheet in an inside‐out effervescent atomizer using high‐speed flow visualization, focusing on the effects of bubbly flow. Key stability parameters, such as breakup length and frequencies, were analyzed in the Rayleigh zone (We g < 0.4) and the first wind‐induced regime (0.4 < We g < 5.4). For low gas Weber numbers, the disintegration process exhibited prolonged primary breakup events and shorter intermediate breakups. The coexistence of sinusoidal and dilatational modes of interfacial instability and their roles in these breakup processes were also examined. Increasing the gas Weber number promoted continuous bubble formation, eliminating intermediate breakup events and dilatational modes, thereby enhancing primary breakup efficiency. In the Rayleigh zone, liquid sheet disintegration is primarily driven by the liquid's inherent momentum. However, as gas velocities increase (We g > 0.4), the momentum of the gas bubbles becomes dominant. A gas‐to‐liquid momentum ratio, which accounts for the effective area of aeration holes where gas mixes with the co‐flowing liquid, was introduced. This ratio, replacing the traditional gas‐to‐liquid ratio, better captures the initial flow dynamics at the nozzle exit. Dimensionless stability characteristics plotted against this ratio enable data collapse and yield universal functions. Notably, a stronger correlation for breakup frequencies and disintegration length was achieved in the first wind‐induced zone compared to the Rayleigh zone, owing to the effective gas momentum. Though the Rayleigh zone generally results in larger droplets, the size can be fine‐tuned by modifying parameters like liquid viscosity, surface tension, and the gas‐to‐liquid ratio. This provides flexibility to tailor the atomization process to specific application needs. Additionally, integrating the Rayleigh zone with other regimes, such as wind‐induced breakup, can enable the development of hybrid atomization systems that achieve an optimal balance between energy efficiency and finer droplet size distributions.

The onset of turbulence in microsystems remains a fundamental scientific and engineering challenge due to the dominance of viscous forces at small confined scales. This study, therefore, experimentally demonstrates the concept of Turbulence-On-a-Chip by generating and characterizing turbulent-like flow regimes in microconfined environments under high-pressure transcritical conditions, without the addition of any external force or passive strategy. A custom-built microfluidic test rig is developed to operate with CO_2 at supercritical pressures and controlled temperature differences. Flow behavior is analyzed through external flow visualization and 2D time-resolved muPIV, revealing distinct laminar and turbulent-like regimes for the conditions evaluated. Laminar-like cases exhibit organized flow patterns and parabolic velocity profiles, while turbulent-like cases display irregular speckle patterns, particle migration, and optical distortions, indicative of flow destabilization through density-gradient effects. Complementary, direct numerical simulations provide deeper insight into the multiscale flow fluctuations, supporting the experimental results. These findings establish a new framework for microconfined turbulence generation, with ground-breaking implications for microfluidic mass transport and energy transfer.

ABSTRACTMelt rupture of a bimodal molecular weight distribution polyethylene is studied under simple shear via flow visualization techniques for the first time. We demonstrated that this catastrophic failure is not exclusive to extensional flows. It was found that melt rupture is a time‐dependent phenomenon occurring after steady‐state plateau in slip velocity and stress. The rupture happens at the three‐phase (polymer‐air‐plate) common line and propagates through the specimen. The common line recedes slightly and stops slipping just before the onset of rupture. The presence of polytetrafluoroethylene lubrication (low surface energy coating) changes the nature of the slip mechanism toward adhesive failure and accelerates melt rupture in terms of time‐to‐rupture‐onset (at the same nominal shear rate). Surface roughness reduces the time to rupture onset but without affecting the nature of the slip. A time‐dependent phenomenon at the interface like fractionation or changes in conformation and entanglement density of the interfacial chains is likely the reason for the transition from slip to melt rupture. This conclusion holds substantial industrial relevance, especially since the prevailing approach to prevent rupture involves promoting slip and reducing stress. However, our research demonstrates that even after achieving a relatively high steady‐state slip velocity, rupture can occur.

Static mixers are commonly used for process intensification in a wide range of industrial applications. For the design and selection of a static mixer, an accurate prediction of the hydraulic performance, particularly the pressure drop, is essential. This experimental study examines the pressure drop for turbulent single-phase and gas–liquid two-phase flows through a Komax triple-action static mixer placed on a horizontal pipeline. New values of friction factor and z-factor are reported for fully turbulent liquid single-phase flow (11,700 ≤ ReL ≤ 18,700). For two-phase flow, the pressure drop for stratified and intermittent flows (0.07 m/s ≤ UL ≤ 0.28 m/s and 0.46 m/s ≤ UG ≤ 3.05 m/s) is modeled using the Lockhart–Martinelli approach, with a coefficient, C, correlated to the homogenous void fraction. Conversely, the analysis of power dissipation reveals a dependence on both liquid and gas superficial velocities. For conditions corresponding to intermittent flow upstream of the mixer, flow visualization revealed the emergence of a swirling flow in the Komax static mixer. It is interesting to note that an increase in slug frequency leads to an increase, followed by stabilization of the pressure drop. The results offer valuable insights for improving the design and optimization of Komax static mixers operating under single-phase and two-phase flow conditions. In particular, the reported correlations can serve as practical tools for predicting hydraulic losses during the design and scale-up. Moreover, the observed influence of the slug frequency on the pressure drop provides guidance for selecting operating conditions that minimize energy consumption while ensuring efficient mixing.

Computational fluid dynamics modelling was performed to obtain additional information about the flow of irrigant in the root canal system. The interaction between the flow rate of the irrigant, the size and taper of the root canal apex, and the type, size and depth of insertion of the endodontic needle was studied. Aim. The aim of the study was to conduct an experimental study using computer modelling of the unsteady leakage of irrigation solution in the root canal. Materials and methods. Computer modelling of the unsteady leakage of irrigation solution was performed using three-dimensional Reynolds-mediated Navier-Stokes equations of continuity -Stokes equations for an incompressible viscous fluid for a position corresponding to the distance from the tip of the endodontic needle to the apical opening of the root canal - 1 mm. Results. Visualisation of the irrigant flow is presented in the form of isolines on the surfaces of the canal and in cross-sections of the calculated area, surface (boundary) and spatial flows, as well as projections of velocity vectors on the surfaces of cross-sections, and the distribution of flow parameters along the lines of the graph. Conclusions. The study showed that the location of the irrigation needle opening towards the large diameter of the root canal, hypothetically, provides a better washing capacity for the irrigation solution

In transcritical CO2 refrigeration systems, replacing the throttle valve with a two-phase ejector markedly enhances energy recovery during the expansion process. This study comprehensively reviews the application of supersonic flow visualization techniques in two-phase ejectors. The first section elucidates the internal flow states of the two-phase ejector and summarizes key indicators of interest in visualization experiments. The second section details various visualization methods applied to two-phase ejectors and synthesizes the main findings from previous experiments. The third section critically evaluates the advantages and limitations of each visualization approach. Finally, the conclusion outlines insights regarding the future integration of visualization techniques in CO2 refrigeration systems employing two-phase ejectors and emphasizes opportunities for further improvement and innovation.

Origin of self-ignition in transient release of pressurized hydrogen into a rectangular tube: Flow visualization and numerical research

Experimental research of a high specific speed low-head model Francis turbine – A case study with emphasis on flow visualisation under runner using PIV method and energy production analysis

This study investigates the effect of surface slip on the unsteady vortex dynamics around the National Advisory Committee for Aeronautics (NACA) 64-618 airfoil using unsteady Reynolds-averaged Navier–Stokes simulation. The Reynolds number, based on the chord length and freestream velocity, was 1.3 × 106 and at an angle of attack of 12°. A Navier-slip boundary condition, modeled to mimic a superhydrophobic coating, was implemented on the walls of the airfoil to assess its impact on turbulent flow dynamics. Four slip lengths (Ls = 100 μm, Ls = 140 μm, Ls = 185 μm, and Ls = 400 μm) in addition to the base no-slip condition were examined. The spatiotemporal dynamics and the interactions between the small-scale Kelvin–Helmholtz vortices and the energetic large-scale von-Karman vortices are examined using frequency spectra and the proper orthogonal decomposition (POD). The mean flow topology revealed distinct separation bubbles at the trailing edge in the baseline no-slip case. Regardless of the slip length considered, suppression of the separation bubble was observed, resulting in greater acceleration of the flow in the wake region. Also, instantaneous flow visualization showed that the shear-layer instability was enhanced, causing an early vortex roll-up in the wake when the slip was imposed. Frequency analysis conducted along the separated shear layer further revealed the migration of dominant frequencies to the lower frequency range, especially for Ls = 400 μm. Based on the results from the POD analysis, it can be concluded that slip significantly increases the turbulent kinetic energy in the wake and concentrates this energy within the identified mode pairs.

The present study examines turbulent flow around a three-dimensional tripile submerged foundation experimentally, using laser Doppler velocimetry, and numerically, using Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) techniques. The study is conducted at a Reynolds number of 104 with a tripile spacing ratio of 3. Flow measurements are compared to assess the predictive capabilities of the selected turbulence models. All RANS models succeeded in predicting primary mean flow phenomena, including flow detachment, vortex recirculation, and downstream reattachment. The LES model performed adequately well both near-wake and far-wake regions. Within the near wake region, the standard k−ϵ model exhibited the largest deviation from experimental data, although it performed appropriately well in the far-wake region. The k−ω shear stress transport model overpredicted the wake recovery. The observed discrepancies are likely due to limitations in modeling flows with large pressure gradients. Also, detailed structural analysis was conducted using the instantaneous flow data obtained from the LES simulations. Key flow features such as the horseshoe vortex, arch vortex, and a dipole structure composed of counter-rotating vortices are identified, exhibiting qualitative agreement with previous high-Reynolds number studies on an isolated cylinder. Instantaneous flow visualization revealed an antler-shaped vortex structure in the downstream wake, which resulted from the interaction of streamwise and spanwise vortices. Time-averaged surface streamlines were used to identify saddle points, attachment nodes, and swirl patterns on the tripiles. Notably, visualization at the free end of the downstream cylinder showed inward-shifted foci and a crescent-shaped recirculation region.

Flow visualization of adjoint-optimized pin fin arrays fabricated by additive manufacturing

Internal flow visualization and performance characteristics of a disc pump under gas-liquid two-phase flow conditions

This study presents high-fidelity, two-way coupled fluid–structure interaction (FSI) simulations to investigate the dynamic behavior of tandem perforated elastic vortex generators (EVGs) across a wide range of bending rigidity, mass ratio, and porosity, at a fixed Reynolds number and interspacing. Comparative simulations with non-perforated EVGs are also performed. Three response modes—Lodging, Vortex-Induced Vibration (VIV), and Static Reconfiguration—are observed in both configurations, while a distinct Cavity Oscillation mode emerges exclusively in non-perforated tandem EVGs. This mode is entirely suppressed with porosity due to disruption of the low-pressure cavity and increased flow transmission through pores. Frequency analyses reveal that VIV is consistently locked onto the second natural frequency, whereas the Cavity Oscillation mode is locked onto the first natural frequency and closely aligns with the first Rossiter mode, underscoring its distinct physical origin. Perforation modifies the natural frequency of the EVGs, shifting the lock-in and mode transitions toward lower bending rigidity and higher mass ratio values, and reducing oscillation amplitudes due to motion damping. Drag analysis shows consistently higher upstream drag due to wake shielding, while porosity reduces upstream drag and increases downstream drag by restoring streamwise momentum. Flow visualizations demonstrate that vortex shedding originates at the EVG tips, with perforated configurations producing smaller, more dissipative vortical structures. These results establish that porosity fundamentally alters dynamic regimes, suppresses cavity-driven instabilities, and enables passive modulation of wake dynamics in tandem EVG systems.

ABSTRACT This paper focuses on an innovative cartographic visualisation of key aspects of spatial mobility, specifically daily mobility flows and the travel behaviour of students in Czechia. It represents mobility flows through the key attributes of intensity, direction, and proportionality, with an emphasis on the dominance of the main direction. This method enables the clear and effective visualisation of daily mobility flows within a single map. Additionally, we examine the differentiation in the use of various transport modes as a foundation for analysing the travel behaviour of young residents. These differences are further visualised in an original manner using 3D plots of the distance-decay function. The presented map cartographically illustrates the complex issue of daily mobility and travel behaviour of students and has the potential to be utilised for research, planning, or educational purposes.

This paper introduces the core role of BIM technology in intelligent construction systems, and analyzes its information flow, collaborative work and data visualization functions in the project life cycle. Then, an integrated model based on the K-means clustering algorithm is proposed to optimize resource scheduling and task allocation during the construction process. By clustering data from different construction scenarios, the model can automatically identify and optimize resource allocation, improve construction efficiency and project progress. Again, this paper constructs a multi-dimensional algorithm framework, covering key steps such as data preprocessing, feature extraction, and cluster analysis. Through simulation experiments, the application effect of the integrated system in actual civil engineering is evaluated. The experimental results show that the K-means clustering algorithm can effectively improve the accuracy and real-time performance of resource allocation, significantly reduce resource waste during construction, optimize construction progress, and the model has good robustness and adaptability. The data analysis results also prove the wide applicability of the system in different construction site environments.

The mechanism of fluid dynamics is essential for the rational clinical application of the root canal irrigation technique. This study aimed to explore the dynamic characteristics of bubble fluid in the apical canal during ultrasound-activated irrigation. Ultrasound-activated irrigation was performed in canal models with different sizes as group #30/0.04 and #30/0.06. High-speed flow visualization technology was used to capture real-time images at 4000 frames per second. The air bubble behavior in the apical region was observed and analyzed via ImageJ and MATLAB software. The bubble movement distance and the bubble lock formation time and length were recorded. The dimensionless cavitation area was calculated. Fluid activated by ultrasound in the apical canal presented initiation, growth and stability stages. In stage initiation, numerous small cavitation bubbles were generated within 1ms at the file tip. Concurrent with small bubble generation, certain bubbles underwent coalescence, forming individual larger bubbles approximately 100μm in diameter within 1s. The presence of multiscale-size bubbles from micrometres to millimetres indicated the stage growth. Fate of most bubbles ended up with collapse, while aggregation was captured. When the large bubble diameter reached the root canal diameter, new small bubbles could not break and pass through the bubble layer. This was denoted as the bubble lock formation and stage stability starting at 9.80 ± 2.74s in group #30/0.06 and 5.00 ± 2.26s in group #30/0.04 (P < 0.05). Taper size of the root canal could influence the bubble fluid dynamics during ultrasound-activated irrigation. Larger canal taper with an apical diameter of 0.30mm significantly prolonged bubble lock formation time and enhanced apical bubble movement distance during ultrasound-activated irrigation.

The peculiarities of air distribution in a limited free space under compressed conditions of thermally stressed technological premises require consideration of the interaction of supply jets and convective flows in the heated surfaces of technological equipment. Similar problems of interaction of compact turbulent jets with vertical surfaces also occur in technological equipment. The development of supply jets of various types, which are laid on a flat surface, has been sufficiently studied both theoretically and experimentally since XX century. In addition, there is also a body of experimental research on the interaction of convective flows in vertical heat-dissipating surfaces of equipment with transverse air-jet overlap to minimize temperature stratification along the height of the premises. Analysis of modern developments on this problem showed that there is no data on the thermal and aerodynamic characteristics of the conditions of interaction of compact turbulent jets with vertical heated surfaces of equipment, although as noted above, these issues are relevant for applied problems of aerodynamics and hydraulics. The article presents the results of a comprehensive study of the interaction of a compact turbulent jet with a convective flow formed near a heated vertical surface. Special attention is paid to identifying key factors that determine the intensity of this interaction, in particular: the geometric parameters of the jet, temperature conditions, and properties of the working environment. Experimental studies conducted using modern methods of flow visualization and thermal anemometry allowed us to establish a criterion dependence of the relative level of interaction on the Archimedes number (Ar). This dependence quantitatively characterizes the influence of the conditions of jet flow onto the plate on the processes of heat and mass transfer in the system. The obtained results have important theoretical and applied significance. Based on them, an improved model of flow interaction was developed and the boundary conditions of interaction were established for different values of the Ar criterion. The results of the study may be useful for heat engineers, designers of ventilation systems and developers of technological equipment where similar combined flows occur.