Recirculating Flow Region Research Articles

Analyses of Reynolds and Mach number effects on Tollmien–Schlichting wave–bump interaction in subsonic flows

We investigated the effects of two-dimensional sharp-edged rectangular bumps on Tollmien–Schlichting (TS) wave evolution using direct numerical simulation. The bump height, $h$ , ranged from 5 % to 40 % of the local displacement thickness, $\delta ^*$ . Behind the bump, a recirculating flow region could be formed whose length increased nonlinearly with $h$ . The bump height effect on the TS wave, which was the dominant, scaled super-exponentially with $h$ . We also showed a substantial effect of the $\delta ^*$ -based Reynolds number, ${\textit {Re}} _{\delta ^*}$ . Firstly, the bump wake extended with ${\textit {Re}} _{\delta ^*}$ , promoting larger TS wave growth rates. The second effect is related to proximity to the upper branch of the instability loop, accounting for the influence of the TS frequency, as well. It dictates the bump impact increases as it gets closer to transition, either by the bump moving downstream or the transition moving upstream. For a 40 % high bump, for example, changing the ${\textit {Re}} _{\delta ^*}$ at the bump location from 1500 to 2000 increased $\Delta N$ by a factor of 2 ( $\Delta N$ represents a measure of a surface irregularity effect on the smooth plate N-factor). We also found that $(\Delta N)_{max}$ increases linearly with ${\textit {Re}} _{hh}$ . Results in the subsonic regime showed that the bump impact attenuates with Mach number up to 0.7 but above it, stabilisation is surpassed by the destabilising effect caused by the recirculation lengthening. This is mostly associated with the bump wake that extends with the pressure gradient which increases substantially towards the sonic speed. This is enhanced if the surface is adiabatic rather than isothermal.

Analysis of the flow induced vibration transition sustained by a hydrofoil

Hydrofoils sustain severe flow induced vibrations when a hydrodynamic excitation source couples with a natural frequency, a phenomenon called lock-in responsible for early fatigue and acoustic radiations. The present paper focuses on the fluid-structure interaction during the transition between a non-resonant and a lock-in regimes. Tests were performed in the hydrodynamic tunnel of the French Naval Academy Research Institute with a truncated NACA 66-306 hydrofoil for chord-based Reynolds numbers ranging between 255000 and 374000 at zero angle of attack. Laser vibrometry, particle image velocimetry and spectral proper orthogonal decomposition were used to investigate the fluid-structure interaction mechanisms. The analysis has highlighted a transition between a low magnitude vibration regime occurring at Reynolds 255000 and a lock-in regime occurring at Reynolds 374000. A primary excitation source has been associated with Karman vortex shedding. Also, during the lock-in, a specific type of vortices is observed at a characteristic frequency equal to twice the Karman vortex shedding frequency. Also, a flow recirculation region located in close vicinity of the trailing-edge is reinforced at this particular regime. The understanding of the mechanisms leading to high magnitude vibrations will reduce the acoustic radiations and enhance the efficiency of next generation hydrofoils.

A multi-directional redundant 3D-LPT system for ship–flight–deck wind interactions

In the past years, volumetric velocimetry measurements with helium-filled soap bubbles as tracer particles have been introduced in wind tunnel experiments and performed at large-scale, enabling the study of complex body aerodynamics. A limiting factor is identified in the field of wind engineering, where the flow around ships is frequently investigated. Considering multiple wind directions, the optical access for illumination and 3D imaging rapidly erodes the measurement regions due to shadows and incomplete triangulation. This work formalizes the concepts of volumetric losses and camera redundancy, and examines the performance of multi-directional illumination and imaging for monolithic and partitioned modes. The work is corroborated by experiments around a representative ship model. The study shows that a redundant system of cameras yields the largest measurement volume when partitioned into subsystems. The 3D measurements employing two illumination directions and seven cameras, yield the time-averaged velocity field around the ship. Regions of flow separation and recirculation are revealed, as well as sets of counter-rotating vortices in several stations from the ship bow to the flight–deck. The unsteady regime at the flight–deck is examined by proper orthogonal decomposition, indicating that the technique is suited for the analysis of large-scale unsteady flow features.

Hemodynamics of the VenusP Valve System™-an in vitro study.

This study aims to evaluate the fluid dynamic characteristics of the VenusP Valve System™ under varying cardiac outputs in vitro. A thorough hemodynamic study of the valve under physiological cardiac conditions was conducted and served as an independent assessment of the performance of the valve. Flow fields downstream of the valve near the pulmonary bifurcation were quantitatively studied by two-dimensional Particle Image Velocimetry (PIV). The obtained flow field was analyzed for potential regions of flow stasis and recirculation, and elevated shear stress and turbulence. High-speed en face imaging capturing the leaflet motion provided data for leaflet kinematic modeling. The experimental conditions for PIV studies were in accordance with ISO 5840-1:2021 standard, and two valves with different lengths and different orientations were studied. Results show good hemodynamics performance for the tested valves according to ISO 5840 standard without significant regions of flow stasis. Observed shear stress values are all well below established hemolysis limits.

Analysis of Confined Jet Impingement in Converging Annular Microchannel Heat Sinks

Jet impingement cooling is deemed an excellent choice for the thermal management of high-power electronics. However, high-pressure drop penalties and low local heat transfer coefficients in regions far from the jet zone are its drawbacks. Although it is reported that recirculation areas appear because of the entrainment, the effects of recirculation size on thermal behavior are not understood well enough. Here, jet impingement heat sinks with converging annular channels are employed in a numerical investigation to minimize the adverse cooling effects associated with an impinging jet in a microchannel. The realizable k−ε turbulent model is used for modeling thermal and turbulent flow fields (Re=5,000 to 25,000). It was found that the different flow recirculation zones in small scales are responsible for the enhanced heat transfer rate. While the thermal performance of a converging wall jet impingement heat sink is higher than its flat wall counterpart at low Re numbers, the thermal performance results are in favor of the flat wall jet impingement heat sink at high Re numbers. The flow recirculation area shrinks in converging channels at high Re numbers, thereby deteriorating the thermal performance of the converging channel compared with a flat wall jet heat sink. Also, it was found that employing steeper converging channels shrinks the flow recirculation region, resulting in up to 59% lower pressure drops at Re=25,000. The present study examines the role of flow recirculation at different Re numbers on the thermohydraulic performance of jet impingement converging annular heat sinks.

Flow field investigation of Confined Coaxial Swirling Jets by Stereo-PIV

This work analyses the isothermal flow field of a research burner exploiting both swirl and radially staged combustion air. The burner is composed of two coaxial co-rotating swirling jets, and the swirl level of the two jets can be controlled independently of each other. The influence of the swirl levels on the flow field is experimentally investigated under isothermal conditions using the Stereo-PIV technique, and the results evidence significant differences in the mean flow field at the different swirl levels. The vortex breakdown occurs in all the investigated cases, except for the combination of the lowest outer swirl level and the intermediate inner swirl level. Besides, the central recirculating flow region shape and size are affected by the momentum ratio and swirl level of the central jet. When the swirl intensities of the two coaxial jets are at their maximum, LDV measurements evidence on the burner axis tangential velocity fluctuations at a frequency of about 86 Hz; a POD-based phase average of the PIV maps allows recognizing the presence of a Precessing Vortex Core (PVC) which induces a periodic merging of the two jets. Those results can be of significance in the design of double swirl burners and for the control of the combustion process. Nevertheless, further tests are required to extend the current analysis to combustion conditions.

Scaling effects on experimentally obtained pressures on an idealized building: Possible implications towards asbestos containment

Atmospheric wind may affect mechanically-induced depressurization in asbestos containment zones set to prevent escape of hazardous fibers. The associated health risks necessitate investigation of wind effects on internal depressurization. This can be achieved by experiments in atmospheric boundary layer wind tunnels utilizing relatively large geometrical scaling ratios (e.g., 1:40), suitable for accommodating all components of the reduced-scale mechanical ventilation system. However, physical constraints in the wind-tunnel cross-section limit replicating large-scale turbulent structures, thus mispredicting exceedances of pressures responsible of containment breaches. Investigating the latter is the innovative goal of present study, for which external pressure characteristics and duration of a certain threshold pressure exceedance have been analyzed for an idealized low-rise cubic building with two geometrical scaling ratios (1:40 and 1:300). The 1:300 scaling ratio allows to represent turbulent structures of almost all relevant sizes of the ABL; whereas, with the 1:40, large-scale turbulent structures are missing. Overall, findings suggest that a larger scaling ratio of 1:40 can be effectively used for mechanical ventilation studies in scenarios where ventilation inlets or outlets are not installed on the roof. However, with the caution that the containment breach probability can be underpredicted at regions of flow reattachment and recirculation.

The effects of a spur dike location in a 90° sharp channel bend on flow field: Focus on anisotropy degree and anisotropy nature

In this research, the flow features around a spur dike located in a 90˚ sharp channel bend have been studied experimentally in detail. Results showed that the effects of the spur dike on upstream sections increased by increasing α (spur dike location from the beginning of the bend). In addition, by increasing α, the horseshoe vortex (C3) and secondary flow in the channel bend (C1) strengthened. The energy and the Reynolds shear stress in the C3 region decreased by increasing α. It is recommended to use a Barycenteric Map (BM) instead of the normal Reynolds stresses to find the anisotropy nature accurately. A strong anisotropic condition was detected at the border of the recirculation flow region and the main flow. However, in the C3 and the interaction regions, the isotropy condition improved. In the main flow region, by increasing α, the isotropy degree improved. However, by increasing α, an increase in the development of the region with a high anisotropy degree towards the recirculation region was observed. The anisotropy degree in the near-bed layer region and the shear layer region is comparable. However, the anisotropy nature is different. The maximum error of the numerical simulation based on isotropic turbulence occurred at the shear layer region where the severe cigar-shaped turbulence occurred.

A hybrid experimental-computational study: Prediction of flow fields and full-field pressure distributions on measured shapes of three-tab asphalt roofing shingles subjected to hurricane velocity winds

A novel hybrid experimental-computational study is performed to predict the flow fields and pressure distributions on the measured three-dimensional shapes of flexible, three-tab asphalt roofing shingles undergoing increasing uplift when exposed to hurricane velocity winds for two hours. To quantify the evolution of shingle shapes, StereoDIC analysis is used to measure the transient, full-field deformed shapes of full-sized, three-tab asphalt shingles that did not show separation or failure when subjected to hurricane velocity winds for two hours. Based on physical observations during wind loading, the authors performed steady state computational fluid dynamics (CFD) simulations to predict the full-field pressure distributions on as-measured, uplifted three-dimensional shingle shapes at selected time instances during wind loading.Simulation predictions clearly show flow recirculation regions on both the front and top of the shingles that remain attached throughout wind loading and control the full-field uplift pressure distribution. For low velocity flow with maximum uplift ≤ 8.4 mm, CFD-predicted pressures are in good agreement with prior measurements. For both low and high-speed flows, the model predictions indicate that high pressures are formed at the leading-edge, upstream of the sealant layer, with maximum pressure occurring near the tab cutouts along the leading-edge of the shingle, providing a physical basis for the observed higher uplift and increased potential for shingle failure in these regions. The combined experimental-computational studies provide a contemporary way to eliminate the difficulties associated with attachment of pressure sensors to flexible materials that can alter shingle response, providing the basis for future design improvements by delineating the physical processes controlling pressure loading and shingle uplift in hurricane velocity winds.

Numerical investigation of electrohydrodynamically enhanced flow boiling inside minichannels: The seeding model

In the present study, three-dimensional numerical simulations are performed to examine the effect of applied direct current electric fields on the subcooled flow boiling heat transfer in a vertical minichannel. The volume of fluid model is used to capture the liquid–vapor interfaces, and the conservation laws, together with the electrohydrodynamic (EHD) equations, are solved using the finite volume method. Two mass transfer models of Lee and Fourier are evaluated, and a new seeding algorithm is developed based on the physics of the bubble formation and departure on the heated walls, integrated with the Fourier model. The early transition from slug to churn/annular flow regimes, due to EHD forces, is observed in the numerical solutions with both models, in agreement with the available experiment. Nevertheless, the Lee model tuned for the electric-free condition fails to predict the EHD-induced heat transfer enhancement, while the Fourier model with the new seeding algorithm captures this phenomenon with reasonable accuracy. Based on the present numerical results, this effect can be attributed to the migration of small bubbles toward the walls under the effect of electric fields, forming recirculating flow regions near the walls, augmenting the flow mixing, and mitigating hot spots.

Space-Time Characterization of Ship Airwakes

The turbulent airwakes produced by a generic navy frigate (Simple Frigate Ship 2) was investigated in a low-speed wind tunnel. The frigate model was subjected to a headwind and immersed in a simulated atmospheric boundary layer. High-speed stereoscopic particle image velocimetry (PIV) was performed at six different spanwise planes over the flight deck. A spatio-temporal analysis of the PIV airwake measurements was conducted by applying the proper orthogonal decomposition (POD) to individual frequency bands of the airwake. Physical interpretations of the leading POD modes were substantiated by other complementary analyses. In particular, it was discovered that turbulent structures were shed from the funnel and superstructure edges. The flow recirculation region behind the superstructure exhibited a strongly three-dimensional bistable behavior. A pair of vortices near the stern also demonstrated low-frequency bistable dynamics. Notably, the bistable flow recirculation region appeared to influence or interact with the low-frequency behavior of the other major flow features.

Improved Thermal Performance of a Serpentine Cooling Channel by Topology Optimization Infilled with Triply Periodic Minimal Surfaces

The present study utilizes a density-based topology optimization method to design a serpentine channel under turbulent flow, solving a high pressure loss issue and enhancing heat transfer capability. In the topology optimization, the k–ε turbulence model is modified by adding penalization terms to reveal turbulence effects. Heat transfer modeling is included by setting the modified energy equation with additional terms related to topology optimization. The main objective is to minimize pressure loss while restricting heat transfer. The 2D simplified model is topologically optimized. Then, the optimal solution with intermediate results is extruded in the 3D system and interpreted with triply periodic minimal surfaces (TPMS) to further enhance heat transfer performance. Compared to the baseline serpentine channel, the optimized model infilled with the diamond-TPMS structure lowers pressure loss by 30.8% and significantly enhances total heat transfer by up to 45.8%, yielding thermal performance of 64.8% superior to the baseline. The temperature uniformity is also improved. The simulation results show that the curvatures in the optimized model with diamond-TPMS structure eliminate the large recirculation flow and low heat transfer regions. This model diminishes the effect of Dean’s vortices but promotes high turbulent kinetic energy, leading to better uniform flow and heat transfer distributions.

Millimeter-scale topography facilitates coral larval settlement in wave-driven oscillatory flow.

Larval settlement in wave-dominated, nearshore environments is the most critical life stage for a vast array of marine invertebrates, yet it is poorly understood and virtually impossible to observe in situ. Using a custom-built flume tank that mimics the oscillatory fluid flow over a shallow coral reef, we isolated the effect of millimeter-scale benthic topography and showed that it increases the settlement of slow-swimming coral larvae by an order of magnitude relative to flat substrates. Particle tracking velocimetry of flow fields revealed that millimeter-scale ridges introduced regions of flow recirculation that redirected larvae toward the substrate surface and decreased the local fluid speed, effectively increasing the window of time for larvae to settle. Regions of recirculation were quantified using the Q-criterion method of vortex identification and correlated with the settlement locations of larvae for the first time. In agreement with experiments, computational fluid dynamics modeling and agent-based larval simulations also showed significantly higher settlement onto ridged substrates. Additionally, in contrast to previous reports on the effect of micro-scale substrate topography, we found that these topographies did not produce key hydrodynamic features linked to increased settlement. These findings highlight how physics-based substrate design can create new opportunities to increase larval recruitment for ecosystem restoration.

Experimental Investigations and Numerical Assessment of Liquid Velocity Profiles and Turbulence for Single- and Two-phase Flow in a Constricted Vertical Pipe

In this work, the capabilities of state-of-the-art turbulence models are compared for a three-dimensional flow (3D) field within a constricted vertical pipe. The considered flow domain is a vertical pipe section with a baffle-shaped flow constriction which leads to the development of a jet flow through and a recirculation flow region behind the constriction. Different Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) models were tested for single- and two-phase flow simulations. In the two-phase simulations, bubble-induced turbulence (BIT) was also considered by adding source terms in the k and ε/ω equations. The results are validated against experimental data. We employed hot-film anemometry (HFA) for liquid velocity measurement and combined it with ultrafast X-ray computed tomography (UFXCT), which provides gas phase data. Based on the local phase-indicator function obtained from the tomographic image data, we can correct HFA signals, which become corrupted by bubble contacts. We found that for single-phase flow all RANS models predict axial velocity well while radial velocity prediction is inadequate. LES models, however, achieve a better prediction of the latter. For two-phase flow, the axial component of the liquid velocity is well captured by all RANS models and the radial component of the liquid velocity is predicted better than for single-phase flow. In general, the computationally less costly RNG k-ε model performs similar to the SSG RSM model and can therefore be recommended for simulation of complex flow scenarios.

Turbulence characteristics of the ship air-wake with two different topside arrangements and inflow conditions

We investigate the effect of the Atmospheric Boundary Layer (ABL) and vessel topside arrangement on ship air-wake flow. The investigation is performed by comparing experimental results with two inflow conditions: a simulated ABL and a smooth-wall flat-plate turbulent boundary layer; and two simplified ship models: Simplified Frigate Ship model 2 (SFS2) and NATO-Generic Destroyer (NATO-GD). Particle Image Velocimetry (PIV) and point measurements over the landing deck center-line show that the ABL inflow increases the flow fluctuations but reduces the length of the wake. Furthermore, we observed an enhancement of turbulence energy on the ship landing deck when the ABL is simulated. The data also show that the topside arrangement, especially at the hangar elevation upstream of the landing deck, plays an essential role in the air-wake over the ship center line. There are significant differences in the flow re-circulation regions, turbulence structure and energy content. Based on a turbulence structure and energy spectrum analysis, we highlight regions with a possible increased safety risk for both models. Over the SFS2 center line, regions with an increased safety risk are located directly above the landing deck. Meanwhile, on the NATO-GD center line, these regions are located above the hangar elevation.

Experimental and Numerical Investigation of Fluid Flow in Hydraulic Filters

Hydraulic systems are extensively used in industries. However, these systems must be free of contaminants to ensure their durability. When the contaminants entering the system are not removed with a suitable filter, sensitive parts such as pumps, motors, and actuators would be damaged. Therefore, hydraulic filters are critical elements in hydraulic systems. In this study, the flow and pressure drop in hydraulic filters were investigated experimentally and numerically. Although the main function of this device is to filter oil, it has many other functions in the system. Experiments were performed at eight Reynolds numbers in the range of 1250 ‒ 2350 at a constant viscosity. In the experiments, the pressure between the inlet and outlet of the filter was measured differently. The numerical results were used for detailed analysis of the flow after experimental verification. The analyses were performed using eight Reynolds numbers at laminar boundaries to examine the flow in the hydraulic filter. The results show that all surface areas of the filter element are not used homogeneously for fluid passage. The resultant pressure drop is due to the Dean vortex formed at the outlet of the hydraulic filter. The findings of this study can help better understand the flow recirculation regions that produce pressure drops and contaminant accumulation regions throughout a hydraulic filter from the inlet to the outlet of the flow path.

Particle inhalability of a standing mannequin with large airways in a ventilated room

This study presents a series of numerical simulations for airflow field and particle dispersion and deposition around a mannequin inside a ventilated room. A 3-D airway system of a volunteer subject with a large respiratory system was reconstructed from the nostril inlet to the end of the tracheobronchial tree 4th generation and was integrated into a standing mannequin at the center of a room. The room ventilation system supplied air through a diffuser and expelled air via a damper in three modes. The airflow field was first evaluated by solving the governing equations and the k-ω SST transitional turbulence model using the Ansys-Fluent software. Then spherical particles with various diameters were released into the room, and their trajectories were evaluated using the Lagrangian approach. Aspiration fraction and particle deposition for inhalation flow rates of 15 and 30 L/min were analyzed using a modified discrete random walk (DRW) stochastic model using a user-defined function (UDF) coupled to the Ansys-Fluent discrete phase model. For the first ventilation mode, a recirculation flow region formed behind the mannequin that led the airflow streamlines to the breathing zone. A recirculation flow formed in front of the face for the second ventilation mode that led the airflow streamlines out of the mannequin breathing zone. For the third mode, however, there was no strong recirculation flow zone around the mannequin. Simulation results showed that the aspiration fraction in the first ventilation mode was higher than the other modes. In addition, the regional deposition rates and deposition patterns of particles inside the respiratory system were presented for each region. Accordingly, most large particles were trapped in the nasal passage; however, some large particles penetrated deeper into the airway due to the large airway size. For the higher breathing rate, the percentage of large escaped particles from the lobe branches dropped by a factor of 7 compared to the lower breathing rate.

Investigation on effects of varying geometrical configurations on thermal hydraulics flow in a 3D corrugated pipe

In this numerical investigation, the flow behavior, pressure drop, and heat transfer enhancement for the fluid in a corrugated pipe with varying geometrical configurations arrangements by supporting the computational simulation technique are analyzed. Also, correlations expressions for friction factor (f) and Nusselt number (Nu) with different corrugated geometrical parameters are developed. The numerical modeling is applied using computational fluid dynamics (CFD), and flow field patterns with different structural parameters are predicted. The numerical simulation results are validated with available experimental data. The numerical approach combined with the varying qualitatively and quantitatively analysis are used. The computational investigations are carried out for a different range of Reynolds numbers (Re) with varying corrugated geometrical configurations, including corrugated pipe ratio (PCR) of 20, 40, 60, 80, and 100%, a number of the corrugated ring (NCR) of 2, 3 and 4 as well as the corrugated diameter ring (CDR) of 1, 2 and 3 mm respectively. The outcomes illustrate that as in similar Re number increases, the Nu number increases. When the corrugated geometrical increases, the mixing, and recirculation flow regions start to high rise along the corrugated pipe. Then the flow becomes more undisturbed near and closes to the corrugated rings, and hence the pressure drop (PD), Turbulent kinetic energy (TKE), and vorticity also increase. Moreover, as the PCR increases, the friction factor increases and the f for PCR of 100% is considerably higher than other models. The friction factor for PCR is higher than other models by about 7.05, 24.3, 40.7, and 67.1%. Furthermore, the performance evaluation factor is greater than unity.

Assessment of RANS turbulence closure models for predicting airflow in neutral ABL over hilly terrain

AbstractImplementing wind farms in heights of a hilly terrain where wind speed is expected to be large may be viewed as a means to increase wind energy production without occupying fertile lands. Micro sitting of a wind farm in these conditions can gain dramatically from CFD simulation of fluid flow in the ABL above complex topography. However, this issue still poses tough challenges regarding the turbulence model to be used and the way to operate the near wall treatment in the presence eventually of separation. In this work, prediction capacity of RANS turbulence models was studied for a typical hill under the assumption of steady state and incompressible airflow regime in neutral ABL. Two models were analyzed by using COMSOL Multiphysics software packages. These included standard , and shear-stress transport . The most up-to-date procedures dedicated to near wall treatment were applied along with refined closer coefficients adjusted for the particular case of ABL. Considering wind tunnel test data, performance of the previous models was discussed in terms of converging mesh, computational time, reattachment point position and propensity of the model to retrieve the right level of turbulence flow in conditions of neutral stratifications. Then, a numerical simulation of the turbulent airflow over two slopes shapes of the symmetry hill by the validation of the experimental data has been then carried out. Both turbulence models agree well with air-velocity tested windward of the hills H3 and H5. Therefore, it was found that the standard model performs very well at the different positions of the low slope hill, and at the summit of a steep hill, but it over-predicts wind speed close to the wall, which requires an improvement of the near-wall treatment. However, the model in neutral case of the ABL was given consistent simulation results with experimental data for prediction of the flow separation and recirculation region at the leeward side of a steep hill, whereas standard model under the neutral condition and the model by using standard coefficients were failed to predict accurately detailed characteristics of recirculation region process.

Combining 4D Flow MRI and Complex Networks Theory to Characterize the Hemodynamic Heterogeneity in Dilated and Non-dilated Human Ascending Aortas

Motivated by the evidence that the onset and progression of the aneurysm of the ascending aorta (AAo) is intertwined with an adverse hemodynamic environment, the present study characterized in vivo the hemodynamic spatiotemporal complexity and organization in human aortas, with and without dilated AAo, exploring the relations with clinically relevant hemodynamic and geometric parameters. The Complex Networks (CNs) theory was applied for the first time to 4D flow magnetic resonance imaging (MRI) velocity data of ten patients, five of them presenting with AAo dilation. The time-histories along the cardiac cycle of velocity-based quantities were used to build correlation-based CNs. The CNs approach succeeded in capturing large-scale coherent flow features, delimiting flow separation and recirculation regions. CNs metrics highlighted that an increasing AAo dilation (expressed in terms of the ratio between the maximum AAo and aortic root diameter) disrupts the correlation in forward flow reducing the correlation persistence length, while preserving the spatiotemporal homogeneity of secondary flows. The application of CNs to in vivo 4D MRI data holds promise for a mechanistic understanding of the spatiotemporal complexity and organization of aortic flows, opening possibilities for the integration of in vivo quantitative hemodynamic information into risk stratification and classification criteria.