The role of large-scale vortical structures in transient convective heat transfer augmentation

Hubble, David; Vlachos, Pavlos P.; Diller, Thomas E.

doi:10.1017/jfm.2012.589

Cited by 31 publications

(24 citation statements)

References 38 publications

(50 reference statements)

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“…Additionally, it is of great interest that the center of the main vortices are very close to the peaks obtained in the distribution of exponent m, while the peaks of heat transfer appear closer to the centreline of the channel (y/L = 0), as forced by the rotation of each branch of the vortex. According to Hubble et al [20], high levels of convection correspond to the downwash regions of vortices and not to the location of the maximum shear stress point, which is located beneath the vortex and agrees with exponent m distribution.…”

Section: Local Exponent M Vs H Distributionssupporting

confidence: 66%

A method to visualise near wall fluid flow patterns using locally resolved heat transfer experiments

Terzis¹,

Wolfersdorf²,

Ott³

2015

Experimental Thermal and Fluid Science

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Section: Local Exponent M Vs H Distributionssupporting

confidence: 66%

A method to visualise near wall fluid flow patterns using locally resolved heat transfer experiments

Terzis¹,

Wolfersdorf²,

Ott³

2015

Experimental Thermal and Fluid Science

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“…Recently, Nguyen et al (2015) have demonstrated the separation between near wall species with different Sc numbers. This separation could also happen due to the partitioning effect of the repelling WSS LCS as demonstrated in Fig 3. From a design perspective, it would be interesting to manipulate these structures to obtain a WSS pattern with a desired outcome of wall concentration/temperature distribution, in similar fashion to Hubble et al (2013), who investigated the effect of vortical structures near the boundary layer on heat transfer augmentation. Finally, the bearing of these structures on near wall transport of turbulent flows remains to be investigated.…”

Section: Discussionmentioning

confidence: 99%

Lagrangian wall shear stress structures and near-wall transport in high-Schmidt-number aneurysmal flows

et al. 2016

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The wall shear stress (WSS) vector field provides a signature for near wall convective transport, and can be scaled to obtain a first order approximation of the near wall fluid velocity. The near wall flow field governs mass transfer problems in convection dominated open flows with high Schmidt number, in which case a flux at the wall will lead to a thin concentration boundary layer. Such near wall transport is of particular interest in cardiovascular flows whereby hemodynamics can initiate and progress biological events at the vessel wall. In this study we consider mass transfer processes in pulsatile blood flow of abdominal aortic aneurysms resulting from complex WSS patterns. Specifically, the Lagrangian surface transport of a species released at the vessel wall was advected in forward and backward time based on the near wall velocity field. Exposure time and residence time measures were defined to quantify accumulation of trajectories, as well as the time required to escape the near wall domain. The effect of diffusion and normal velocity was investigated. The trajectories induced by the WSS vector field were observed to form attracting and repelling coherent structures that delineated species distribution inside the boundary layer consistent with exposure and residence time measures. The results indicate that Lagrangian wall shear stress structures can provide a template for near wall transport.

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“…PIV processing was performed using Prana (available at 'http://sourceforge.net/projects/qi-tools/'), an in-house, open-source software program which has been thoroughly validated in several publications. 6,19,34,46 First, processing was conducted using ensemble and multi-frame correlation techniques to resolve the large dynamic range in the flow fields. As described above, multi-frame correlation utilizes multiple frame separations to resolve high and low velocities.…”

Section: Piv Processing Methodologymentioning

confidence: 99%

Time-Resolved Particle Image Velocimetry Measurements with Wall Shear Stress and Uncertainty Quantification for the FDA Nozzle Model

Raben

Hariharan

Robinson

et al. 2015

Cardiovasc Eng Tech

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We present advanced particle image velocimetry (PIV) processing, post-processing, and uncertainty estimation techniques to support the validation of computational fluid dynamics analyses of medical devices. This work is an extension of a previous FDA-sponsored multi-laboratory study, which used a medical device mimicking geometry referred to as the FDA benchmark nozzle model. Experimental measurements were performed using time-resolved PIV at five overlapping regions of the model for Reynolds numbers in the nozzle throat of 500, 2000, 5000, and 8000. Images included a twofold increase in spatial resolution in comparison to the previous study. Data was processed using ensemble correlation, dynamic range enhancement, and phase correlations to increase signal-to-noise ratios and measurement accuracy, and to resolve flow regions with large velocity ranges and gradients, which is typical of many blood-contacting medical devices. Parameters relevant to device safety, including shear stress at the wall and in bulk flow, were computed using radial basis functions. In addition, in-field spatially resolved pressure distributions, Reynolds stresses, and energy dissipation rates were computed from PIV measurements. Velocity measurement uncertainty was estimated directly from the PIV correlation plane, and uncertainty analysis for wall shear stress at each measurement location was performed using a Monte Carlo model. Local velocity uncertainty varied greatly and depended largely on local conditions such as particle seeding, velocity gradients, and particle displacements. Uncertainty in low velocity regions in the sudden expansion section of the nozzle was greatly reduced by over an order of magnitude when dynamic range enhancement was applied. Wall shear stress uncertainty was dominated by uncertainty contributions from velocity estimations, which were shown to account for 90-99% of the total uncertainty. This study provides advancements in the PIV processing methodologies over the previous work through increased PIV image resolution, use of robust image processing algorithms for near-wall velocity measurements and wall shear stress calculations, and uncertainty analyses for both velocity and wall shear stress measurements. The velocity and shear stress analysis, with spatially distributed uncertainty estimates, highlights the challenges of flow quantification in medical devices and provides potential methods to overcome such challenges.

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The role of large-scale vortical structures in transient convective heat transfer augmentation

Cited by 31 publications

References 38 publications

A method to visualise near wall fluid flow patterns using locally resolved heat transfer experiments

A method to visualise near wall fluid flow patterns using locally resolved heat transfer experiments

Lagrangian wall shear stress structures and near-wall transport in high-Schmidt-number aneurysmal flows

Time-Resolved Particle Image Velocimetry Measurements with Wall Shear Stress and Uncertainty Quantification for the FDA Nozzle Model

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