Formation Of Secondary Flows Research Articles

Study on the Flow and Heat Transfer Performance of Microchannel Heat Exchangers With Different Elliptical Concave Cavities

AbstractEllipticity has a significant impact on the flow and heat transfer performance of microchannel heat exchangers (MHEs) with elliptical concave cavities. In this study, five types of MHEs with different elliptical concave cavities (ellipticities of 0.4, 0.6, 0.8, 1.0, and 1.2) were designed. The influence of ellipticity on the flow and heat transfer performance of MHEs was numerically investigated using ANSYS Fluent 21.0 R1. Moreover, MHEs with corresponding elliptical concave cavities structures were processed and manufactured, and then an experimental platform was designed and built for experimental verification. The results showed that the fluid velocity distribution in MHEs with elliptical concave cavities was symmetrical, and the formation of secondary flow in the elliptical concave cavities led to the continuous destruction and reconstruction of the flow and thermal boundary layer in the microchannel, which is conducive to mass and heat transfer in the MHEs with elliptical concave cavities. The inlet and outlet pressure drop of MHEs with elliptical concave cavities increased as the inlet flow rate increased. At the same inlet flow rate, the inlet and outlet pressure drop of the MHE with elliptical concave cavities first increased and then decreased with increasing ellipticity. At an ellipticity of 1.0, the inlet and outlet of MHE exhibited the lowest pressure drop indicating that the MHE with an ellipticity of 1.0 featured the highest pressure drop performance. The cold‐water outlet temperature of the MHEs with elliptical concave cavities first decreased and then increased as the inlet flow rate increased. At the same inlet flow rate, the cold‐water outlet temperature of the MHEs with elliptical concave cavities first increased and then decreased with increasing ellipticity, while the hot‐water outlet temperature of the MHEs first decreased and then increased with increasing flow rate. This indicated that the MHE with an ellipticity of 1.0 exhibited excellent heat transfer performance.

Investigation of the asymmetric flow structure in a hydrocyclone

AbstractThe flow field of a hydrocyclone was investigated using both computational fluid dynamics (CFD) and particle image velocimetry (PIV). A refractive index matching method was employed to improve the precision of the PIV measurements. The CFD results are in good agreement with PIV measurements. Detailed analysis reveals significant axial asymmetry in the velocity components, with the radial velocity component exhibiting notable disparities. This observation is supported by quantitative data comparing different sections of the hydrocyclone. It is further found that the asymmetry might be mainly attributed to the secondary vortexes with the single inlet of the hydrocyclone. And the secondary vortexes, superimposed on the primary flow rather than existing on its own, spiral downwards from near the inlet towards the underflow orifice. It is hypothesized that specific boundary effects and pressure gradients play a pivotal role in the formation of secondary flows. This assumption is grounded on both theoretical considerations and empirical observations, suggesting that these factors significantly influence the flow dynamics within the hydrocyclone. The insights gained from our measurement methodology and enhanced understanding of secondary flows within hydrocyclones are not only poised to serve as valuable references for fellow researchers but also have the potential to inform the design and operational optimization of hydrocyclones for improved efficiency and performance.

Comparative investigation on high-pressure flow accelerated corrosion at gradual contraction and gradual expansion pipes

In current study, the flow accelerated corrosion behaviors of X65 steel gradual contraction and gradual expansion pipes under high-pressure conditions were comparatively investigated by establishing dynamic in situ electrochemical tests under high CO2 partial pressure conditions in a loop apparatus. The findings indicate that the corrosion rate is reduced along the flowing direction of gradual contraction pipe. Nevertheless, the corrosion rate firstly descends and subsequently ascends along the flowing direction of gradual expansion pipe, and the lowest corrosion rate is presented in inclination segment close to the straight pipe with large diameter. The corrosion rate at the top wall of gradual contraction pipe is symmetrical to that at the bottom wall, while it is asymmetrically distributed at the top wall and the bottom wall of inclination segment in gradual expansion pipe. The distribution of corrosion rate is correlated with the flow fields at gradual contraction and gradual expansion pipes. Furthermore, the special corrosion rate distribution at inclination segment of gradual expansion pipe is ascribed to the formation of secondary flow and vortexes.

Examination of air flow characteristics over an open rectangular cavity between the plates

Air flow characteristics of an open cavity have been numerically examined by using different turbulence models of Detached Eddy Simulation (DES), k-ε Realizable, k-ω Shear Stress Transport (SST) and Large Eddy Simulation (LES) based on an experimental study of open literature. Numerical results of transient analyses have been compared to experimental results at cavity length-based Reynolds number of Re = 4600. Pressure distributions, streamline patterns, streamwise velocity components, mean velocity values and their vectors have been given in terms of contour graphics. Moreover, velocity profiles have been presented. Pressure fluctuations have been triggered by flow separation and its reattachment. Due to upstream separation of boundary layer, there was curved boundary layer obtained between the outer potential-flow-like and the recirculation zones. As a result, negative velocity values are evidence for rotational flows affected by formation of secondary flows in the cavity. Furthermore, lower pressure region has been observed as a result of rotational flow which was powerful in the open cavity. Numerical results of DES and LES turbulence models are in good agreement with the results of reference study. As the numerical results obtained by LES turbulence model are approximately same with those of experimental reference study, LES turbulence model is mostly recommended. As an option to these turbulence models, k-ω SST model could be utilized for limited computer capacity. However, k-ε Realizable model is not sufficient for capturing rotational flows which are very effective in terms of present case.

Numerical Simulation of 3D- Flow Structure and Heat Transfer for Longitudinal Riblet Upstream of Leading Edge Endwall Junction of Nozzle Guide Vane

The simulation have been made for 3D flow structure and heat transfer with and without
 longitudinal riblet upstream of leading edge vane endwall junction of first stage nozzle guide vane .The research explores concept of weakening the secondary flows and reducing their harmful effects.Numerical investigation involved examination of the secondary flows ,velocity and heat transfer rates by solving the governing equations (continuity, Navier -stokes and energy equations ) using the known package FLUENT version (12.1).The governing equations were solved for three dimentional, turbulent flowe, incompressible with an appropriate turbulent model (k-ω,SST) .The numerical solution was carried out for 25 models of V-groove riblet with wide ranges of height (h) and space (s). The results indicated that, the riblet endwall junction was a powerful tool for controlling the flow structure, reducing secondary flow formation,and elimination the effect of heat transfer at leading edg and passage . The drag reduction produced by riblet was proportional with their height and space. V-groove riblet with dimension of (h=1.35mm and s=2.26mm) was found to be the most effective in reduction of drag (2.7%) and heat transfer (21%) so it was selected as an optimum dimension of riblet model. The results also showed that the drag reduction produced by riblet was proportional to their size. The riblet model had a great effect in elimination spanwise ,pitchwise velocities ,but strength the streamwise velocity .At leading edge ,the effect of secondary flow was extended up to 23% from span height and 35% upstream leading edge .The riblet model caused an increase in momentom at a region very close to leading edge and to move stagnation point very close to the leading edge.

A numerical study on thermo-hydraulic performance of micro pin-fin heat sink using hybrid pin-fins arrangement for electronic cooling devices

PurposeThis study aims to examine the effect of a combination of hybrid pin-fin patterns on a heat sink's performance using numerical techniques. Also, flow characteristics have been studied, such as secondary flow formation and flow-wall interaction.Design/methodology/approachIn this study, the effect of hybrid arrangements of elliptical and hexagonal pin-fins with different distribution percentages on flow characteristics and performance evaluation criteria in laminar flow was investigated. Ansys-Fluent software solves the governing equations using the finite volume method. Also, the accuracy of obtained results was compared with the experimental results of other similar papers.FindingsThe results of this study highlighted that hybrid arrangements show higher overall performance than single pin-fin patterns. Among the hybrid arrangements, case 3 has the highest values of performance evaluation criteria, that is, 1.84 in Re = 900. The results revealed that, with the instantaneous change in the pattern from elliptic to hexagonal, the secondary flow increases in the cross-sectional area of the channels, and the maximum velocity in the cross-section of the channel increases. The important advantages of case 3 are its highest overall performance and a lower chip surface temperature of up to about 2% than other hybrid patterns.Originality/valuePrior research has shown that in the single pin-fin pattern, the cooling power at the end of the heat sink decreases with increasing fluid temperature. Also, a review of previous studies showed that existing papers had not investigated hybrid pin-fin patterns by considering the effect of changing distribution percentages on overall performance, which is the aim of this paper.

Experimental investigation of turbulent flow in a rectangular bonneted slide gate and eliminating random fluctuating loads

Bonneted slide gates are widely used in dam bottom outlets for flow regulation. High kinetic energy flow generates turbulence, which induces vibrations in bonneted slide gates under partially open conditions. Significant vibrations can indicate problems and cause damage or expedited deterioration of the gate if left unchecked. This experimental study focuses on two aspects: turbulent flow formation due to rectangular bonneted slide gates and elimination of random fluctuating loads on the gate using a turbulence inhibitor. Five reservoir heads were combined with nine gate openings (10%–90%) to produce 45 different discharges of 12–182 l/s. The different types of the gate flow create different turbulence and random loads based on the water–air mixture and the kinetic energy of the flow. Flow analysis indicates considerable random static pressure fluctuations under the slide gate. The results show the formation of swirling secondary flows in the gate's side guide slots, and their movement and collision with the gate are the leading cause of the turbulent multiphase flow and random fluctuations in static pressure. Also, the use of turbulence inhibitors on the gate can prevent the formation of secondary flows, which results in a 98.92% reduction in the amplitude of random static pressure fluctuations and the elimination of the random fluctuating loads on the slide gate. After removing the swirling secondary flows, a stable air boundary layer was formed under the gate. Finally, the gate flow changed from a turbulent two-phase flow to a steady single-phase jet of water.

Characteristics of secondary flow and separation zone with different junction angle and flow ratio at river confluences

Confluences are widespread in natural rivers where pollutants, sediment and fish tend to accumulate (especially separation zone), and studying their three-dimensional (3D) structure can provide guidance for improving river environmental health. In the current study, a flume experiment was conducted, and a 3D confluence model was built. Three turbulent models were compared based on the experimental results, which confirmed the applicability of the RNG k-ε model. The effects of junction angles and flow ratios on the formation and evolution of secondary flow and separation zone were investigated by the established model. The results indicated that the separation zone with low flow velocity, high turbulence kinetic energy and low pressure is formed downstream of the junction while two secondary flows form on the sides of the shear plane downstream. The shapes of the separation zone and secondary flow at the confluence were defined in a new way. The secondary flow formation process is reversed within the separation zone and highly complicated when the junction angle and flow ratio change. This study can provide a scientific basis for the utilization of confluences to improve water quality and aquatic animal ecology at natural river confluences.

A recent state of art review on heat transfer enhanced characteristics and material selection of SCTHX

The shell and coil tube heat exchangers (SCTHX) are widely used to transfer heat energy from one medium to another effecting medium, such as refrigeration and air conditioning system, chemical reactor, solar heater and steam power plant. The helical tubes are one of the passive heat transfer enhancement technique in heat exchanger, which are adopted in industries due to higher rate of heat transfer and simplicity in manufacturing. It has been widely employed that heat transfer coefficient in helical coils are higher compare to straight pipe by several researchers. The reason is behind that the formation of secondary flow of nano fluid. It is leading by dean vortex which is imposed to primary flow. Furthermore research on segmental and helical baffle geometry can improve the heat transfer rate in helical coil tube heat exchanger. This study is concerned with the enhancement of convective heat transfer interaction between fluid and solid surface of helical coil. The detailed descriptions of material selection, nano fluid flow physics and heat transfer enhancement inside helical coil tube are very less in open literature. A state of art review indicates that further research work can be carried out by modifying the geometry of SCTHX and enhance factors of fluid property. The heat transfer can also be enhanced by polymer additives added in nano fluids, effect of super hydrophobic surfaces and fluid bubbles generation from roughened heating surface. Finally new ideas are presented in this paper to improve the heat transfer rate and material selection for low cost manufacturing with minimum size.

Numerical investigation of centrifuge-trapping technique for generating gas–liquid flows in microchannels

We have recently presented a novel approach (called the centrifuge-trapping method) based on a microfluidic structure for the generation of stratified flow and slug flow for biochemical applications based on centrifugal microfluidics. The technique relies on stratifying liquid into a spiral channel using centrifugal force and trapping bubbles between liquid plugs to form a slug flow. In this study, we comprehensively characterize the fluidic behavior of the system using a multiphase numerical model. The model is first validated by experiments and then used to evaluate the hydrodynamical effects of the system. Pressure fluctuation of the liquid plugs in the microchannel shows high stability of slug flow in rotational velocity ranging from 350 to 1000 RPM. The mixing efficiency of two liquids injected into the spiral channel is evaluated in generated stratified and slug flows. The results show that slug flow can be effectively utilized to enhance the mixing efficiency by more than 30% compared to single-phase or stratified flow. The formation of secondary flows into the liquid plugs is the main reason for elevated mixing.

Study of flow and heat transfer characteristics of a liquid jet impinging on a heat sink with discontinuous staggered ring ribs

The temperature uniformity of the bottom surface of the heat sink is one of the hot research topics in the field of jet impingement heat transfer enhancement. In this study, jet impingement on a heat sink with novel discontinuous staggered ring ribs in the wall jet region is put forward to improve the local heat transfer by combining a single micro-jet impact with the secondary flow channel. The flow and heat transfer characteristics of the confined liquid jet impinging on the ribbed head sink under different structural parameters of ribs and jet Reynolds numbers are numerically studied. The V2F turbulence model is used for numerical calculation and the obtained results are compared with the experimental results. The results show that discontinuous staggered ring ribs in the wall jet region of the heat sink promote the formation of secondary flow and strengthen the fluid-solid conjugate heat transfer, that effectively improve the temperature uniformity of the entire heat sink. The temperature difference of the ring-ribbed heat sink is about 91.82% lower than that of the flat plate heat sink when the Reynolds number is 8000. When the outlet shrinkage ratio decreases, or when the position radius of the first layer of ribs or arc angle of a rib on the first layer increases, the temperature uniformity of the ring-ribbed heat sink is gradually improved. However, the lifting range of the outer edge of the heat sink decreases. Also, when the jet Reynolds number increases to 20,000, the maximum temperature difference of the heat sink decreases down to 1.6 K.

Utilising fractional porous interface for high thermal performance of serpentine wavy channel solar air heater

This work investigates the thermohydraulic performance of a porous serpentine wavy channel solar air heater. Comprehensive illustration on the effect of fractional porous interface (25%≤ξ≤100%), channel porosity (90%≤φ≤100%) and Reynolds number 2000≤Re≤11000 on the thermohydraulic performance of solar air heater design is presented. Experiments are performed and numerical results are validated to conduct further investigations for the optimization of the input variables. This study is a unique idea that broadly presents the scope of thermal performance improvement by utilizing the porous media in fraction and varying porosity in solar air heater channel and highly useful for the researchers of this field. Finite volume method based computational fluid dynamics tool is used to conduct numerical investigations, Forchheimer equation is used to account the effect of porous media and surface to surface (S2S) radiation model to capture the effect of shape factor and emitted radiation in collector channel. It is obtained that ξ of 25% and φ of 93% delineated the best thermohydraulic performance (THPP) of 4.52 for the present solar air heater design. While, the obtained thermohydraulic performance is 186% times higher compared to the smooth design. The excellent results that come into the light from numerical investigation are the secondary flow formation in the porous and flow zones at higher Reynolds number and lower fraction of porous region (ξ), and for all configurations of ξ at large channel porosity (φ). Hence, results of this investigation not only present the best operational configuration to obtain higher thermal performance, but also present the measures to reduce the material cost of porous media and consequently pumping power.

Three-Dimensional Computational Fluid Flow Analysis of Bio-inspired Corrugated wing at Low Reynolds Number.

A computational study was performed to analyze the airflow over bio-inspired corrugated wings. The bio-inspired corrugated wing profiles were derived from the mid-span section of the forewing of Aeshna Cyanea dragonfly species. Additionally, a hybrid non-corrugated profile was also created possessing geometric similarities with the corrugated airfoils to compare and visualize the effects of corrugation on the fluid flow. The computational analysis was conducted for 4,8-, and 12-degrees angles of attack. Streamlines obtained from the computational analysis results (carried out on ANSYS CFX) showed the formation of secondary flows or vortices that are trapped in the valleys of the corrugated wings which was not observed in the hybrid airfoil. This study also compares the effects of corrugation geometry on fluid flow behavior. It was also seen that the intensity and quantity of the secondary flows increased with the increase in the angle of attack.

Modelling spanwise heterogeneous roughness through a parametric forcing approach

Inhomogeneous rough surfaces in which strips of roughness alternate with smooth-wall strips are known to generate large-scale secondary motions. Those secondary motions are strongest if the strip width is of the order of the half-channel height and they generate a spatial wall shear stress distribution whose mean value can significantly exceed the area-averaged mean value of a homogeneously smooth and rough surface. In the present paper it is shown that a parametric forcing approach (Busse & Sandham, J. Fluid Mech., vol. 712, 2012, pp. 169–202; Forooghi et al., Intl J. Heat Fluid Flow, vol. 71, 2018, pp. 200–209), calibrated with data from turbulent channel flows over homogeneous roughness, can capture the topological features of the secondary motion over protruding and recessed roughness strips (Stroh et al., J. Fluid Mech., vol. 885, 2020, R5). However, the results suggest that the parametric forcing approach roughness model induces a slightly larger wall offset when applied to the present heterogeneous rough-wall conditions. Contrary to roughness-resolving simulations, where a significantly higher resolution is required to capture roughness geometry, the parametric forcing approach can be applied with usual smooth-wall direct numerical simulation resolution resulting in less computationally expensive simulations for the study of localized roughness effects. Such roughness model simulations are employed to systematically investigate the effect of the relative roughness protrusion on the physical mechanism of secondary flow formation and the related drag increase. It is found that strong secondary motions present over spanwise heterogeneous roughness with geometrical height difference generally lead to a drag increase. However, the physical mechanism guiding the secondary flow formation, and the resulting secondary flow topology, is different for protruding roughness strips and recessed roughness strips separated by protruding smooth surface strips.

Numerical investigation on separated turbulent flow in a three-dimensional U-turn duct with spanwise diverging

The flow in a U-turn duct with a 180-degree curved section is a typical model of various applications such as the bend and return channel in multi-stage radial turbo-machines. The flow exhibits complex patterns including the separation on the inner wall, highly sheared flow in the curved and downstream sections, and recovery of deficit flow to uniform flow. Most of current researches focus on the simplified models of two-dimensional plane duct or three-dimensional duct with constant cross-section, while in realistic circumstances the duct can be varying in the shape and area of the cross-section to meet the design requirement. In this work, we performed a numerical investigation on the turbulent flow in a U-turn duct with spanwise diverging at Reynolds number Re = 106. The effect of diverging, as represented by the height of the duct, on the formation of secondary flow, flow separation and recovery is explored, and the three-dimensionality of the separated flow is quantitatively assessed. Numerical results reveal that with stronger spanwise diverging, the flow separates earlier from the inner wall and the size of the separated vortex is larger; the primary characteristics of the secondary flow also change significantly. The three-dimensional separated flow substantially affects the flow in the downstream straight duct that both streamwise and radial velocities exhibit fluctuating patterns as a result of the spatially non-uniform separation. The characteristics of boundary layer flow on all solid walls are also analyzed and discussed regarding the pressure field and local shearing.

Comparison of Film Cooling Performance for Different Purge Slot Configurations in a Cylindrical and State-of-the-Art Nozzle Guide Vane

Abstract This comparative study is concerned with the advances in nozzle guide vane (NGV) design developments and their influence on endwall film cooling performance by injecting coolant through the purge slot. This experimental study compares the film cooling effectiveness and the aerodynamic effects for different purge slot configurations on both a flat and an axisymmetrically contoured endwall of a NGV. While the flat endwall cascade was equipped with cylindrical vanes, the contoured endwall cascade consisted of modern NGVs, which represent state-of-the-art high-pressure turbine design standards. Geometric variations, e.g., the slot width and injection angle, as well as different blowing ratios were realized. The mainstream flow parameters were set to meet real engine conditions with regard to Reynolds and Mach numbers. Pressure-sensitive paint was used to determine the adiabatic film cooling effectiveness. Five-hole probe measurements were performed to measure the flow field in the vane wake region. For a more profound insight into the origin of the secondary flows, oil dye visualizations were carried out. The results show that the advances in NGV design have a significantly positive influence on the distribution of the coolant. This has to be attributed to lesser disturbance of the coolant propagation by secondary flow for the optimized NGV design, since the design features are intended to suppress the formation of secondary flow. Therefore, it is advisable to take these effects into account when designing the film cooling system of a modern high-pressure turbine.

Numerical Predictions of Turbine Cascade Secondary Flows and Heat Transfer With Inflow Turbulence

Abstract Turbine passage secondary flows are studied for a large rounded leading edge airfoil geometry considered in the experimental investigation of Varty et al. (“Vane Suction Surface Heat Transfer in Regions of Secondary Flows: The Influence of Turbulence Level, Reynolds Number, and the Endwall Boundary Condition,” ASME J. Turbomach., 140(2), p. 021010) using high resolution large eddy simulation. The complex nature of secondary flow formation and evolution are affected by the approach boundary layer characteristics, components of pressure gradients tangent and normal to the passage flow, surface curvature, and inflow turbulence. This paper presents a detailed description of the secondary flows and heat transfer in a linear vane cascade at exit chord Reynolds number of 5 × 105 at low and high inflow turbulence. Initial flow turning at the leading edge of the inlet boundary layer leads to a pair of counter-rotating flow circulation in each half of the cross plane that drives the evolution of the pressure side and suction side of the near-wall vortices such as the horseshoe and leading edge corner vortex. The passage vortex for the current large leading edge vane is formed by the amplification of the initially formed circulation closer to the pressure side (PPC) which strengthens and merges with other vortex systems while moving towards the suction side. The predicted suction surface heat transfer shows good agreement with the measurements and properly captures the augmented heat transfer due to the formation and lateral spreading of the secondary flows towards the vane midspan downstream of the vane passage. Effects of various components of the secondary flows on the endwall and vane heat transfer are discussed in detail.

Prandtl\u2019s Secondary Flows of the Second Kind. Problems of Description, Prediction, and Simulation

—The occurrence of turbulent pulsations in straight pipes of noncircular cross-section leads to the situation, when the average velocity field includes not only the longitudinal component but also transverse components that form a secondary flow. This hydrodynamic phenomenon discovered at the twenties of the last century (J. Nikuradse, L. Prandtl) has been the object of active research to the present day. The intensity of the turbulent secondary flows is not high; usually, it is not greater than 2–3% of the characteristic flow velocity. Nevertheless, their contribution to the processes of transverse transfer of momentum and heat is comparable to that of turbulent pulsations. In this paper, a review of experimental, theoretical, and numerical studies of secondary flows in straight pipes and channels is given. Emphasis is placed on the issues of revealing the physical mechanisms of secondary flow formation and developing the models of the apriori assessment of their forms. The specific features of the secondary flow development in open channels and channels with inhomogeneously rough walls are touched upon. The approaches of semiempirical simulation of turbulent flows in the presence of secondary flows are discussed.

Turbulent secondary flows in channels with no-slip and shear-free boundaries

Abstract

Altered hemodynamics by 4D flow cardiovascular magnetic resonance predict exercise intolerance in repaired coarctation of the aorta: an in vitro study

BackgroundCoarctation of the aorta (CoA) is associated with decreased exercise capacity despite successful repair. Altered flow patterns have been identified due to abnormal aortic arch geometry. Our previous work demonstrated aorta size mismatch to be associated with exercise intolerance in this population. In this study, we studied aortic flow patterns during simulations of exercise in repaired CoA using 4D flow cardiovascular magnetic resonance (CMR) using aortic replicas connected to an in vitro flow pump and correlated findings with exercise stress test results to identify biomarkers of exercise intolerance.MethodsPatients with CoA repair were retrospectively analyzed after CMR and exercise stress test. Each aorta was manually segmented and 3D printed. Pressure gradient measurements from ascending aorta (AAo) to descending aorta (DAo) and 4D flow CMR were performed during simulations of rest and exercise using a mock circulatory flow loop. Changes in wall shear stress (WSS) and secondary flow formation (vorticity and helicity) from rest to exercise were quantified, as well as estimated DAo Reynolds number. Parameters were correlated with percent predicted peak oxygen consumption (VO2max) and aorta size mismatch (DAAo/DDAo).ResultsFifteen patients were identified (VO2max 47 to 126% predicted). Pressure gradient did not correlate with VO2max at rest or exercise. VO2max correlated positively with the change in peak vorticity (R = 0.55, p = 0.03), peak helicity (R = 0.54, p = 0.04), peak WSS in the AAo (R = 0.68, p = 0.005) and negatively with peak WSS in the DAo (R = − 0.57, p = 0.03) from rest to exercise. DAAo/DDAo correlated strongly with change in vorticity (R = − 0.38, p = 0.01), helicity (R = − 0.66, p = 0.007), and WSS in the AAo (R = − 0.73, p = 0.002) and DAo (R = 0.58, p = 0.02). Estimated DAo Reynolds number negatively correlated with VO2max for exercise (R = − 0.59, p = 0.02), but not rest (R = − 0.28, p = 0.31). Visualization of streamline patterns demonstrated more secondary flow formation in aortic arches with better exercise capacity, larger DAo, and lower Reynolds number.ConclusionsThere are important associations between secondary flow characteristics and exercise capacity in repaired CoA that are not captured by traditional pressure gradient, likely due to increased turbulence and inefficient flow. These 4D flow CMR parameters are a target of investigation to identify optimal aortic arch geometry and improve long term clinical outcomes after CoA repair.