Turbulent Shear Stress Research Articles

Direct numerical simulations of a turbulent channel flow developing over convergent–divergent riblets

Direct numerical simulations of a turbulent channel flow developing over convergent–divergent (C–D) riblets at a Reynolds number of Reb=2800 are presented. It is found that, with a fixed normalized riblet height of h+=5, as the ratio of the riblet spacing and the height, s/h, increases from 2 to 10, the strength of the large-scale secondary flow motion Γ generated by the C–D riblets peaks around s/h=4 when the C–D riblets behavior lies between d- and k-type roughness. Compared to the baseline case with smooth walls, the turbulent activities and energy level increase significantly and peak at s/h=4 when Γ is the highest. It is shown that while the intense local turbulent kinetic energy (TKE) production occurring in the diverging region is caused by the high local velocity gradient due to the downwelling of the secondary flow, the strong local TKE production occurring in the converging region is caused by the high turbulent shear stress associated with upwelling. Furthermore, the TKE transport characteristics are significantly altered by the secondary flow motion, especially over the converging and diverging regions. The secondary flow is not caused by the local imbalance between turbulent kinetic energy production and dissipation but by the yawed riblets. It is then more appropriate to classify this flow as a Prandtl’s secondary flow of the first kind, also known as the geometry-driven secondary flow. Finally, in comparison with the baseline case, the drag increases for all the riblet cases examined, and a direct correlation between the amount of drag and intensity of the secondary flow exists, both peaking at s/h=4.

A coefficient adapted shear stress turbulence model to numerically simulate the internal transition phenomena in a case study of the nasal cavity

A coefficient adapted shear stress turbulence model to numerically simulate the internal transition phenomena in a case study of the nasal cavity

Impacts of Instrumented Bottom Frame on Flow and Turbulence Measurements

Abstract A series of laboratory experiments are carried out to demonstrate the impacts of instrumented bottom frame legs on flow and turbulence. The magnitudes of vertical velocity, turbulent kinetic energy, dissipation, and shear stress induced by the frame legs depend on several factors, including the diameter and number of the frame legs, distances between the legs and the observational location, and the magnitude of the incoming flow and its direction with respect to the layout of the frame. In situ observations were carried out near the mouth of the Yellow River using two acoustic Doppler velocimeters mounted on a bottom frame. The estimated vertical velocity and turbulent kinetic energy dissipation rate show a significant asymmetry with flood and ebb tidal flows. This asymmetry can be partly explained by the influences of the bottom frame legs. Finally, the design and deployment principles of bottom frames are discussed for the purpose of reducing the impacts of the frame legs. Significance Statement Instrumented bottom frames are widely used for observations in the oceanic bottom boundary layer and above. However, the impacts of frame legs on the observed flow and turbulence have rarely been investigated. A series of laboratory experiments demonstrate that frame legs can induce vertical flow and enhanced turbulence, and the magnitudes of these influences vary with the size and layout of the frame legs and the magnitude and direction of the background flow. The results of the laboratory experiments can partially explain an “asymmetry” behavior of the vertical flow and turbulent kinetic energy with the flood and ebb tidal flows, derived from in situ observations near the mouth of the Yellow River.

Large Eddy Simulation of trenched cylindrical film hole with backward compound angles

Many previous studies have demonstrated that both transverse trench and backward cooling injection are capable of improving jet lift-off problem of traditional cylindrical film hole at high blowing ratios. However, few studies have attempted to combine the above two cooling schemes to further alleviate the cooling deterioration phenomenon. This paper proposed two trenched film holes with different backward compound angles of β = 180° and 135°, and used highly-resolved Large Eddy Simulation method to explore in detail their unsteady flow fields including vortex structures, level of velocity fluctuation, turbulent shear stress, distributions of vorticity and adiabatic wall cooling effectiveness. The results are compared against those of the benchmark trenched film hole with β = 0°. The simulations were carried out under blowing ratio of 1.5, and the coolant to mainstream density ratio of 2.0.The detrimental symmetric counter-rotating vortex pair shown in the trench with β = 0° hole is replaced by an asymmetric vortex pair in the trench with β = 180° hole and only a single asymmetric vortex in the trench with β = 135° hole. Inside the trench, hairpin-like vortices are the dominant vortex structures for the trench with backward film holes. In the region downstream of the trench, the trench with β = 180° hole obtains the highest level of three velocity components fluctuations in the central region because of the direct intense collision between the coolant and mainstream, while the trench with β = 135° hole shows a highest level of lateral velocity component fluctuation in the lateral sides and a highest level of turbulent shear stress in the near wall region due to the significantly enhanced lateral motion of the coolant. The trenches with β = 180° and 135° holes significantly improve the lateral uniformity of the coolant, and respectively provide constantly high levels of 0.21 and 0.3 in laterally averaged cooling effectiveness on the wall downstream of the trench, compared to the trench with β = 0° hole with a low level of less than 0.2.

Large-eddy simulation of helical- and straight-bladed vertical-axis wind turbines in boundary layer turbulence

Turbulent wake flows behind helical- and straight-bladed vertical axis wind turbines (VAWTs) in boundary layer turbulence are numerically studied using the large-eddy simulation (LES) method combined with the actuator line model. Based on the LES data, systematic statistical analyses are performed to explore the effects of blade geometry on the characteristics of the turbine wake. The time-averaged velocity fields show that the helical-bladed VAWT generates a mean vertical velocity along the center of the turbine wake, which causes a vertical inclination of the turbine wake and alters the vertical gradient of the mean streamwise velocity. Consequently, the intensities of the turbulent fluctuations and Reynolds shear stresses are also affected by the helical-shaped blades when compared with those in the straight-bladed VAWT case. The LES results also show that reversing the twist direction of the helical-bladed VAWT causes the spatial patterns of the turbulent wake flow statistics to be reversed in the vertical direction. Moreover, the mass and kinetic energy transports in the turbine wakes are directly visualized using the transport tube method, and the comparison between the helical- and straight-bladed VAWT cases show significant differences in the downstream evolution of the transport tubes.

The control mechanism of the soft trailing fringe on the flow characteristics over an airfoil

Inspired by the owl’s silent flight, we experimentally investigated the flow control mechanism of the soft trailing fringes (STFs) on the wake of the S833 airfoil at the Reynolds number of Re = 2 × 104. A high-speed Particle Image Velocimetry (PIV) system is employed to visualize and analyze the flow structures in the wake of the airfoil at different angles of attack (AOA). Furthermore, spectral proper orthogonal decomposition and bispectral mode decomposition are carried out to identify the coherent flow structures and reveal the control mechanism from the perspective of simplified models. PIV measurements’ results demonstrate that the STFs evidently suppress the turbulent quantities including turbulent kinetic energy and Reynolds shear stress in the airfoil wake. On the one hand, the STFs at low AOAs prevent the interaction between the upper and lower shear layers, and the leading- and trailing-edge vortices (TEVs) are significantly suppressed, thus destructing the von Karman vortex streets. On the other hand, the STFs at high AOAs divide the lower shear layer into two parts, markedly attenuating the TEVs and modifying the vortical structures in the wake. Besides, the quadrant analysis reveals that the STFs can mitigate the high-amplitude wall-pressure peaks, indicating that the STFs may manipulate the trailing-edge noise. However, the control effect is limited at median AOAs because the region with high triadic interactions moves upward in the interaction maps, which limits the impact of the STFs.

Numerical tripping of high-speed turbulent boundary layers

The influence of turbulence inflow generation on direct numerical simulations (DNS) of high-speed turbulent boundary layers at Mach numbers of 2 and 5.84 is investigated. Two main classes of inflow conditions are considered, based on the recycling/rescaling (RR) and the digital filtering (DF) approach, along with suitably modified versions. A series of DNS using very long streamwise domains is first carried out to provide reliable data for the subsequent investigation. A set of diagnostic parameters is then selected to verify achievement of an equilibrium state, and correlation laws for those quantities are obtained based on benchmark cases. Simulations using shorter domains, with extent comparable with that used in the current literature, are then carried out and compared with the benchmark data. Significant deviations from equilibrium conditions are found, to a different extent for the various flow properties, and depending on the inflow turbulence seeding. We find that the RR method yields superior performance in the evaluation of the inner-scaled wall pressure fluctuations and the turbulent shear stress. DF methods instead yield quicker adjustment and better accuracy in the prediction of wall friction and of the streamwise Reynolds stress in supersonic cases. Unrealistically high values of the wall pressure variance are obtained by the baseline DF method, while the proposed DF alternatives recover a closer agreement with respect to the benchmark. The hypersonic test case highlights that similar distribution of wall friction and heat transfer are obtained by both RR and DF baseline methods.Graphical abstract

Turbulent planar wakes of viscoelastic fluids analysed by direct numerical simulations

Direct numerical simulations employing the finitely extensible nonlinear elastic constitutive model closed with Peterlin's approximation (FENE-P) are used to investigate the far-field region of turbulent planar wakes of viscoelastic fluids and to develop the theory describing these flows. The theoretical results display excellent agreement with the simulations and provide new scaling laws for the evolution of the shear layer thickness $\delta (x) \sim x^{1/2}$ , mean velocity deficit ${\rm \Delta} U(x) \sim x^{-1/2}$ and, for very high Deborah numbers, of the maximum polymer shear stresses $\sigma ^{[p]}_c(x) \sim x^{-2}$ and averaged polymer chain extension $\textrm {tr}(\bar {C}(x) - \boldsymbol{\mathsf{I}}) \sim x^{-2}$ , where $x$ is the streamwise distance from the solid body generating the wake. The theory is able to show the existence of self-similarity for the profiles of mean velocity, mean polymer shear stress, averaged polymer chain extension and the conditions for similarity of the turbulent shear stress, and is very well supported by the numerical simulations. Similarly to the case of viscoelastic turbulent planar jets (Guimarães et al., J. Fluid Mech., vol. 899, 2020, p. A11), when the inlet Weissenberg and Deborah numbers are sufficiently large, turbulent viscoelastic wakes exhibit a considerable reduction of the spreading rate and of the normalised Reynolds stresses. However, for very large downstream locations the turbulent viscoelastic wake recovers the classical evolution laws observed for Newtonian turbulent planar wakes.

Maximizing the thermal performance index applying evolutionary multi-objective optimization approaches for double pipe heat exchanger

The thermal performance index (TPI) known as the efficiency parameter evaluates the highlight of the heat transfer for the same pumping power requirement. The optimum design of a heat exchanger with minimum pressure drops and efficient heat transfer is a big challenging task from an energy-saving point of view. One way to optimize this efficiency parameter is by changing the geometric parameters of the heat exchanger. For this purpose, the multi-objective reinforcement learner non-dominated sorting genetic algorithm (NSGA-RL) is employed maximizing TPI and Nusselt number and minimizing Fanning friction factor to the optimal design of a double pipe heat exchanger, with perforated baffles in the annulus side. Its performance is compared with a non-dominated sorting genetic algorithm - version II (NSGA-II), and a chaotic non-dominated sorting genetic algorithm (CNSGA). The calculations were carried out using the turbulent shear stress transport k-ω model. The multi-objective optimization techniques presented promising results in terms of the number of nondominated solutions, Euclidean distances to the origin point (reference point), and hypervolume indicators. However, in general, the results based on mean values indicate that the NSGA-RL outperforms the NSGA-II and CNSGA concerning the three performance indicators for the two double pipe heat exchanger evaluated cases. TPI increases 78% for case 1, and 108% for case 2 compared without baffles in a double pipe heat exchanger (DPHE). Numerical results revealed that DPHE employing internal perforated baffles improved heat transfer significantly with Nusselt number increased around 7.93–8.25 times and friction factor increased by 6.5–9.75 times compared with plain DPHE.

A new boundary layer integral method based on the universal velocity profile

A recently developed mixing length model of the turbulent shearing stress in wall bounded flows has been used to formulate a universal velocity profile (UVP) that provides an effective replacement for the widely used Coles wall-wake formulation. Comparisons with both direct numerical simulation and experimental data demonstrate the ability of the profile to approximate a wide variety of wall-bounded flows. The UVP is uniformly valid from the wall to the boundary layer edge and for all Reynolds numbers from zero to infinity. There is no presumption of logarithmic dependence of the velocity profile outside the viscous wall layer so the profile can accurately approximate low Reynolds number turbulent boundary layers. The effect of a pressure gradient is included in the UVP through the introduction of a modified Clauser parameter that correlates well with the parameters that determine the wake portion of the velocity profile. The inherent dependence of the UVP on Reynolds number, extended to include the effect of pressure gradient, enables it to be used as the basis of a new method for integrating the von Kármán boundary layer integral equation for a wide variety of attached wall bounded flows. To illustrate its application, the UVP is used to determine the zero-lift drag coefficient of the Joukowsky 0012 and NACA (National Advisory Committee for Aeronautics) 0012 airfoils over a wide range of chord Reynolds numbers.

Nuclear Mechanosensation and Mechanotransduction in Vascular Cells.

Vascular cells are constantly subjected to physical forces associated with the rhythmic activities of the heart, which combined with the individual geometry of vessels further imposes oscillatory, turbulent, or laminar shear stresses on vascular cells. These hemodynamic forces play an important role in regulating the transcriptional program and phenotype of endothelial and smooth muscle cells in different regions of the vascular tree. Within the aorta, the lesser curvature of the arch is characterized by disturbed, oscillatory flow. There, endothelial cells become activated, adopting pro-inflammatory and athero-prone phenotypes. This contrasts the descending aorta where flow is laminar and endothelial cells maintain a quiescent and atheroprotective phenotype. While still unclear, the specific mechanisms involved in mechanosensing flow patterns and their molecular mechanotransduction directly impact the nucleus with consequences to transcriptional and epigenetic states. The linker of nucleoskeleton and cytoskeleton (LINC) protein complex transmits both internal and external forces, including shear stress, through the cytoskeleton to the nucleus. These forces can ultimately lead to changes in nuclear integrity, chromatin organization, and gene expression that significantly impact emergence of pathology such as the high incidence of atherosclerosis in progeria. Therefore, there is strong motivation to understand how endothelial nuclei can sense and respond to physical signals and how abnormal responses to mechanical cues can lead to disease. Here, we review the evidence for a critical role of the nucleus as a mechanosensor and the importance of maintaining nuclear integrity in response to continuous biophysical forces, specifically shear stress, for proper vascular function and stability.

A study on coronary bifurcation lesions and procedural outcome at Manmohan cardiothoracic vascular and transplant center, Kathmandu, Nepal

Background and Aims: Coronary bifurcation lesions are associated with high atherosclerotic plaque burden due to turbulent blood flow and high shear stress. There are various strategies for bifurcation stenting however, they are often prone to major cardiac events during percutaneous coronary intervention. The aim of this study was to assess the clinical profile and procedural outcome of patients with coronary bifurcation lesions.
 Methods: This retrospective study was carried out at Manmohan Cardiothoracic Vascular and Transplant center, Kathmandu, Nepal. Two hundred and eight patients were enrolled in this study who had coronary bifurcation lesions seen on invasive coronary angiography from August 2017 to October 2021. The procedural complications were assessed.
 Results: The mean age of patients with coronary bifurcation lesions was 61.48±11.19 years. Out of total 208 patients, 77% were males. True bifurcation lesion was seen in 65.4% of patients. Left anterior descending artery with diagonal was the most common bifurcation lesion (67.3%). The provisional stenting was done in 80.8% of patients and rest underwent 2-stent strategy. The complications mainly observed during the provisional stenting were plaque shift and side branch dissection.
 Conclusion: The provisional stenting is the most preferred and suitable technique for most bifurcation lesions if technically feasible.

Vertical structure of conventionally neutral atmospheric boundary layers

SignificanceThe presented model describes the vertical structure of conventionally neutral atmospheric boundary layers. Due to the complicated interplay between buoyancy, shear, and Coriolis effects, analytical descriptions have been limited to the mean wind speed. We introduce an analytical approach based on the Ekman equations and the basis function of the universal potential temperature flux profile that allows one to describe the wind and turbulent shear stress profiles and hence capture features like the wind veer profile. The analytical profiles are validated against high-fidelity large-eddy simulations and atmospheric measurements. Our findings contribute to the scientific community's fundamental understanding of atmospheric turbulence with direct relevance for weather forecasting, climate modeling, and wind energy applications.

Drag reduction in wall-bounded turbulence by synthetic jet sheets

A turbulent drag-reduction method employing synthetic jet sheets in a turbulent channel flow is investigated by direct numerical simulations. The jet sheets are wall-parallel and produced by periodic blowing and suction from pairs of thin slots aligned with the main streamwise flow. By varying the slot height and the jet-sheet angle with respect to the spanwise direction, drag-reduction margins between $10\,\%$ and $30\,\%$ are obtained for jet-sheet angles between $45 ^{\circ }$ and $75 ^{\circ }$ , while a drag increase of almost 100 % is computed when the jet sheets are spanwise-oriented. When global skin-friction drag reduction occurs, the wall-shear stress near the jet-sheet exits increases during suction and decreases during blowing, while the velocity fluctuations weaken during suction and intensify during blowing. The global drag-reduction effect is produced by a finite counter flow induced by the nonlinear interaction between the jet-sheet flow and the main flow, although the turbulent intensity and Reynolds shear stresses increase. The power spent to generate the jet sheets is computed by modelling numerically the actuator underneath the channel flow as a piston oscillating sinusoidally along the spanwise direction in a round-shaped cavity from which the fluid is released into the channel through the cavity exits. A power balance leads to the computation of the efficiency of the actuator system, quantifying the portion of the piston power that is lost as internal power fluxes and heat transfer through the cavity walls. For the tested configurations, the power consumed by the piston to generate the jet sheets is larger than the power saved thanks to the drag reduction.

An experimental investigation of turbulent free-surface flows over a steep permeable bed

Steep streams involve shallow, supercritical turbulent flows over a permeable bed made up of coarse particles. They usually exhibit higher flow resistance and stronger mass and momentum exchanges between the stream and subsurface flow than low-gradient streams. Describing their flow dynamics using generalised Manning–Strickler equations has led to empirical relationships with weak predictive power (errors between predictions and data of over one order of magnitude). We studied shallow turbulent flows by employing a mesoscopic approach based on the double-averaged Navier–Stokes equations. More specifically, we were concerned with the possibility of modelling the turbulent and dispersive shear stress equations using simple algebraic equations. To that end, we studied shallow, supercritical turbulent flows over a sloping bed made up of randomly packed spherical particles. Using visualisation techniques based on particle velocimetry imaging and refractive index matched scanning, we were able to reconstruct the velocity field throughout the bed and stream, far from the sidewalls, and estimate the contributions of the dispersive and turbulent shear stresses to the total shear stress. The dispersive shear stress represented less than 20 % of the turbulent shear stress, but because it was concentrated within a thin layer (called the roughness layer) where it outweighed the turbulent shear stress, it had a significant influence on the mean velocity profile. We proposed an algebraic closure equation for dispersive shear stress, based on the mixing-length model used for turbulent shear stress, and we found that it captured closely the mean-velocity and turbulence-intensity profiles of shallow flows over horizontal or sloping permeable beds. Our data suggest that flow dynamics was affected largely by turbulence damping, drag forces and dispersion within the roughness layer, which may explain why steep streams differ from low-gradient streams.

Large-Scale Production of Size-Adjusted β-Cell Spheroids in a Fully Controlled Stirred-Tank Reactor

For β-cell replacement therapies, one challenge is the manufacturing of enough β-cells (Edmonton protocol for islet transplantation requires 0.5–1 × 106 islet equivalents). To maintain their functionality, β-cells should be manufactured as 3D constructs, known as spheroids. In this study, we investigated whether β-cell spheroid manufacturing can be addressed by a stirred-tank bioreactor (STR) process. STRs are fully controlled bioreactor systems, which allow the establishment of robust, larger-scale manufacturing processes. Using the INS-1 β-cell line as a model for process development, we investigated the dynamic agglomeration of β-cells to determine minimal seeding densities, spheroid strength, and the influence of turbulent shear stress. We established a correlation to exploit shear forces within the turbulent flow regime, in order to generate spheroids of a defined size, and to predict the spheroid size in an STR by using the determined spheroid strength. Finally, we transferred the dynamic agglomeration process from shaking flasks to a fully controlled and monitored STR, and tested the influence of three different stirrer types on spheroid formation. We achieved the shear stress-guided production of up to 22 × 106 ± 2 × 106 viable and functional β-cell spheroids per liter of culture medium, which is sufficient for β-cell therapy applications.

A Detailed Study to Discover the Trade between Left Atrial Blood Flow, Expression of Calcium-Activated Potassium Channels and Valvular Atrial Fibrillation.

Background: The present study aimed to explore the correlation between calcium-activated potassium channels, left atrial flow field mechanics, valvular atrial fibrillation (VAF), and thrombosis. The process of transforming mechanical signals into biological signals has been revealed, which offers new insights into the study of VAF. Methods: Computational fluid dynamics simulations use numeric analysis and algorithms to compute flow parameters, including turbulent shear stress (TSS) and wall pressure in the left atrium (LA). Real-time PCR and western blotting were used to detect the mRNA and protein expression of IKCa2.3/3.1, ATK1, and P300 in the left atrial tissue of 90 patients. Results: In the valvular disease group, the TSS and wall ressure in the LA increased, the wall pressure increased in turn in all disease groups, mainly near the mitral valve and the posterior portion of the LA, the increase in TSS was the most significant in each group near the mitral valve, and the middle and lower part of the back of the LA and the mRNA expression and protein expression levels of IKCa2.3/3.1, AKT1, and P300 increased (p < 0.05) (n = 15). The present study was preliminarily conducted to elucidate whether there might be a certain correlation between IKCa2.3 and LA hemodynamic changes. Conclusions: The TSS and wall pressure changes in the LA are correlated with the upregulation of mRNA and protein expression of IKCa2.3/3.1, AKT1, and P300.

Large-eddy simulation of a planar offset wall-jet with heat transfer: Characterization, turbulent kinetic energy and Reynolds shear stress budgets

Planar wall-attaching offset jets can be found in a variety of engineering applications. In the present work, a planar turbulent offset wall-jet, at a Reynolds number of 7500 and an offset-ratio of 5, with heat transfer is numerically studied using large-eddy simulation (LES). First, a grid sensitivity study is performed and the quality of the mesh used is assessed using LES index of quality of resolution and an appropriate mesh is selected. Next, the solver is validated for mean streamwise velocity, streamwise Reynolds normal stress, and the evolution of coefficient of pressure on the wall, using reference experimental data from the literature. Thereafter, the unsteady flow features of the jet, maximum velocity decay and jet-spread, statistical features of flow and temperature, and turbulent kinetic energy (TKE) budgets and in-plane component of Reynolds shear stress are studied. The streamwise evolution of Nusselt number on the wall shows three distinct peaks and the location of these peaks correlates with a change-of-sign of the wall skin-friction coefficient. The domain can be categorized into three distinct regions namely, the recirculation, impingement and wall-jet regions. Distinct flow and thermal characteristics are observed depending on the region of interest. The peak magnitudes of Reynolds normal and shear stresses increase as one moves from the recirculation region to the impingement region and decreases thereafter attaining a lowest value in the wall-jet region. The heat transfer from the wall is observed to be most effective in the recirculation region. The production of TKE is dominant in all the three regions of the flow, whereas the Reynolds shear stress budgets indicate that the production and velocity–pressure-gradient terms are dominant and balance each other in all the three regions of the flow.

Effect of secondary currents on the flow and turbulence in partially filled pipes

Large-eddy simulations of turbulent flow in partially filled pipes are conducted to investigate the effect of secondary currents on the friction factor, first- and second-order statistics and large-scale turbulent motion. The method is validated first and simulated profiles of the mean streamwise velocity, normal stresses and turbulent kinetic energy (TKE) are shown to be in good agreement with experimental data. The secondary flow is stronger in half- and three-quarters full pipes compared with quarter full or fully filled pipe flows, respectively. The origin of the secondary flow is examined by both the TKE budget and the steamwise vorticity equation, providing evidence that secondary currents originate from the corner between the free surface and the pipe walls, which is where turbulence production is larger than the sum of the remaining terms of the TKE budget. An extra source of streamwise vorticity production is found at the free surface near the centreline bisector, due to the two-component asymmetric turbulence there. The occurrence of dispersive stresses (due to secondary currents) reduces the contribution of the turbulent shear stress to the friction factor, which results in a reduction of the total friction factor of flows in half and three-quarters full pipes in comparison to a fully filled pipe flow. Furthermore, the presence of significant secondary currents inhibits very-large-scale motion (VLSM), which in turn reduces the strength and scales of near-wall streaks. Subsequently, near-wall coherent structures generated by streak instability and transient growth are significantly suppressed. The absence of VLSM and less coherent near-wall turbulence structures is supposedly responsible for the drag reduction in partially filled pipe flows relative to a fully filled pipe flow at an equivalent Reynolds number.

Turbulent Kinetic Energy Loss and Shear Stresses Before and After Transcatheter Aortic Valve Replacement

Blood flow and shear stresses were quantified using 4-dimensional flow cardiac magnetic resonance and 3-dimensional particle velocimetry before and after transcatheter aortic valve replacement (TAVR). TAVR reduced turbulent kinetic energy by 47% and shear stresses by 33%, illustrating that the benefit of TAVR extends beyond a simple reduction in transvalvular gradients. (Level of Difficulty: Advanced.)