scholarly journals The Advantages of Viscous Dissipation Rate over Simplified Power Loss as a Fontan Hemodynamic Metric

2017 ◽  
Vol 46 (3) ◽  
pp. 404-416 ◽  
Author(s):  
Zhenglun Alan Wei ◽  
Michael Tree ◽  
Phillip M. Trusty ◽  
Wenjun Wu ◽  
Shelly Singh-Gryzbon ◽  
...  
Keyword(s):  
Viscous Dissipation ◽  
Dissipation Rate ◽  
Power Loss

Upper bounds on the energy dissipation in turbulent precession

1996 ◽  
Vol 321 ◽  
pp. 335-370 ◽  
Author(s):  
R. R. Kerswell
Keyword(s):  
Experimental Data ◽  
Energy Dissipation ◽  
Viscous Dissipation ◽  
Upper Bound ◽  
Dissipation Rate ◽  
Oblate Spheroid ◽  
Upper Bounds ◽  
Precession Rate ◽  
Long Cylinder

Rigorous upper bounds on the viscous dissipation rate are identified for two commonly studied precessing fluid-filled configurations: an oblate spheroid and a long cylinder. The latter represents an interesting new application of the upper-bounding techniques developed by Howard and Busse. A novel ‘background’ method recently introduced by Doering & Constantin is also used to deduce in both instances an upper bound which is independent of the fluid's viscosity and the forcing precession rate. Experimental data provide some evidence that the observed viscous dissipation rate mirrors this behaviour at sufficiently high precessional forcing. Implications are then discussed for the Earth's precessional response.

Experimental Study on Two-Oscillating Grid Turbulence With Polymer Additives

2015 ◽  
Author(s):  
Yue Wang ◽  
Wei-Hua Cai ◽  
Tong-Zhou Wei ◽  
Lu Wang ◽  
Feng-Chen Li
Keyword(s):  
Polymer Solution ◽  
Viscous Dissipation ◽  
Newtonian Fluid ◽  
Coherent Structures ◽  
Dissipation Rate ◽  
Close Relation ◽  
Space Distribution ◽  
Polymer Additives ◽  
Grid Turbulence ◽  
Solution Flow

In order to investigate the polymer effect on grid turbulence, the experiments study on grid turbulence has been built based on Particle Image Velocimetry. The Newtonian fluid flow and 200ppm polymer solution flow in grid turbulence were carried out at different grid oscillating frequency, such as 5Hz, 7.5Hz, 10Hz and 12.5Hz. The experimental results show that the viscous dissipation rate and vortex vector ωz is smaller and more regular in space distribution in polymer solution case at grid oscillating frequency with 5Hz. It indicates that the existence of polymer additives inhibits enormously the viscous dissipation rate and vortex vector, but this phenomenon can be attenuated with the increase of grid oscillating frequency. From this result, it shows that there exists a critical Reynolds number for the inhibition of polymer effect, which is the same as that in turbulent channel flows with polymers. Then, proper orthogonal decomposition (POD) has been used to extract coherent structures in grid turbulence. It is found that it needs 24 and 4 POD eigenfunctions to examine coherent structure in the Newtonian fluid and the polymer solution cases respectively at grid oscillating frequency with 10Hz. It suggests that the coherent structures can be inhibited due to the existence of polymers so as to the flow field to be more regular. But, with the increase of grid oscillating frequency, the number of POD eigenfunctions for the Newtonian fluid case and the polymer solution case respectively are approaching the same. Through this analysis, it can be also seen that the inhibition effect of polymers is close relation with the grid oscillating frequency.

Viscous dissipation rate in concentrated suspensions

1994 ◽  
Vol 6 (9) ◽  
pp. 3189-3191 ◽  
Author(s):  
B. Seifu ◽  
A. Nir ◽  
R. Semiat
Keyword(s):  
Viscous Dissipation ◽  
Dissipation Rate ◽  
Concentrated Suspensions

scholarly journals Characterization of the Martian Convective Boundary Layer

2009 ◽  
Vol 66 (7) ◽  
pp. 2044-2058 ◽  
Author(s):  
Germán Martínez ◽  
Francisco Valero ◽  
Luis Vázquez
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Standard Deviation ◽  
Wind Speed ◽  
Viscous Dissipation ◽  
Mixed Layer ◽  
Dissipation Rate ◽  
Horizontal Wind

Abstract The authors have carried out an extensive characterization of the Martian mixed layer formed under convective conditions. The values of the mixed layer height, convective velocity scale, convective temperature scale, mean temperature standard deviation, mean horizontal and vertical velocity standard deviations, and mean turbulent viscous dissipation rate have been obtained during the strongest convective hours for the mixed layer. In addition, the existing database of the surface layer has been improved by recalculating some parameters (e.g., Monin–Obukhov length, friction velocity, or scale temperature) that had already been obtained in previous papers by other means and also by calculating new ones, such as the standard deviation of the vertical wind speed velocity, the turbulent viscous dissipation rate, and eddy transfer coefficients for momentum and heat. The Earth counterparts of all these magnitudes are also shown. In this paper, a comprehensive database concerning the whole convective planetary boundary layer on Mars is displayed, and a detailed terrestrial comparison is established. The inputs of this work are hourly in situ temperature, hourly in situ horizontal wind speed, and hourly simulated ground temperature for specific selected Sols of the Viking and Pathfinder landers. These data correspond to typical low and midlatitude northern summertime conditions, with weak prevailing winds. To handle this set of data, surface layer and mixed layer similarity theory have been used at the strongest convective hours. In addition, the inclusion of a parameterization of a molecular sublayer and prescribed values of the surface roughness has been considered.

Noninvasive Fluid Dynamic Power Loss Assessments for Total Cavopulmonary Connections Using the Viscous Dissipation Function: A Feasibility Study

2001 ◽  
Vol 123 (4) ◽  
pp. 317-324 ◽  
Author(s):  
Timothy M. Healy ◽  
Carol Lucas ◽  
Ajit P. Yoganathan
Keyword(s):  
Cardiac Output ◽  
Viscous Dissipation ◽  
Velocity Gradient ◽  
Power Loss ◽  
Control Volume ◽  
Fluid Dynamic ◽  
Dissipation Function ◽  
Power Losses ◽  
Dynamic Power ◽  
The Right

The total cavopulmonary connection (TCPC) has shown great promise as an effective palliation for single-ventricle congenital heart defects. However, because the procedure results in complete bypass of the right-heart, fluid dynamic power losses may play a vital role in postoperative patient success. Past research has focused on determining power losses using control volume methods. Such methods are not directly applicable clinically without highly invasive pressure measurements. This work proposes the use of the viscous dissipation function as a tool for velocity gradient based estimation of fluid dynamic power loss. To validate this technique, numerical simulations were conducted in a model of the TCPC incorporating a 13.34 mm (one caval diameter) caval offset and a steady cardiac output of 2 Ls˙min−1. Inlet flow through the superior vena cava was 40 percent of the cardiac output, while outflow through the right pulmonary artery (RPA) was varied between 30 and 70 percent, simulating different blood flow distributions to the lungs. Power losses were determined using control volume and dissipation function techniques applied to the numerical data. Differences between losses computed using these techniques ranged between 3.2 and 9.9 percent over the range of RPA outflows studied. These losses were also compared with experimental measurements from a previous study. Computed power losses slightly exceeded experimental results due to different inlet flow conditions. Although additional experimental study is necessary to establish the clinical applicability of the dissipation function, it is believed that this method, in conjunction with velocity gradient information derived from imaging modalities such as magnetic resonance imaging, can provide a noninvasive means of assessing power losses within the TCPC in vivo.

scholarly journals A model for the viscous dissipation rate in stably stratified, sheared turbulence

2013 ◽  
Vol 40 (14) ◽  
pp. 3744-3749 ◽  
Author(s):  
H. E. Fossum ◽  
E. M. M. Wingstedt ◽  
B. A. P. Reif
Keyword(s):  
Viscous Dissipation ◽  
Dissipation Rate

Direct particle–fluid simulation of Kolmogorov-length-scale size particles in decaying isotropic turbulence

2017 ◽  
Vol 819 ◽  
pp. 188-227 ◽  
Author(s):  
Lennart Schneiders ◽  
Matthias Meinke ◽  
Wolfgang Schröder
Keyword(s):  
Kinetic Energy ◽  
Strain Rate ◽  
Viscous Dissipation ◽  
Dissipation Rate ◽  
Isotropic Turbulence ◽  
Bulk Flow ◽  
Small Scale ◽  
Length Scale ◽  
Kolmogorov Length Scale ◽  
Scale Size

The modulation of decaying isotropic turbulence by 45 000 spherical particles of Kolmogorov-length-scale size is studied using direct particle–fluid simulations, i.e. the flow field over each particle is fully resolved by direct numerical simulations of the conservation equations. A Cartesian cut-cell method is used by which the exchange of momentum and energy at the fluid–particle interfaces is strictly conserved. It is shown that the particles absorb energy from the large scales of the carrier flow while the small-scale turbulent motion is determined by the inertial particle dynamics. Whereas the viscous dissipation rate of the bulk flow is attenuated, the particles locally increase the level of dissipation due to the intense strain rate generated near the particle surfaces due to the crossing-trajectory effect. Analogously, the rotational motion of the particles decouples from the local fluid vorticity and strain-rate field at increasing particle inertia. The high level of dissipation is partially compensated by the transfer of momentum to the fluid via forces acting at the particle surfaces. The spectral analysis of the kinetic energy budget is supported by the average flow pattern about the particles showing a nearly universal strain-rate distribution. An analytical expression for the instantaneous rate of viscous dissipation induced by each particle is derived and subsequently verified numerically. Using this equation, the local balance of fluid kinetic energy around a particle of arbitrary shape can be precisely determined. It follows that two-way coupled point-particle models implicitly account for the particle-induced dissipation rate via the momentum-coupling terms; however, they disregard the actual length scales of the interaction. Finally, an analysis of the small-scale flow topology shows that the strength of vortex stretching in the bulk flow is mitigated due to the presence of the particles. This effect is associated with the energy conversion at small wavenumbers and the reduced level of dissipation at intermediate wavenumbers. Consequently, it damps the spectral flux of energy to the small scales.

scholarly journals Characterization of the Martian Surface Layer

2009 ◽  
Vol 66 (1) ◽  
pp. 187-198 ◽  
Author(s):  
Germán Martínez ◽  
Francisco Valero ◽  
Luis Vázquez
Keyword(s):  
Surface Layer ◽  
Viscous Dissipation ◽  
Dissipation Rate ◽  
Friction Velocity ◽  
Temperature Scale ◽  
Surface Heat ◽  
Martian Surface ◽  
Transfer Coefficients ◽  
Obukhov Length

Abstract The authors have estimated the diurnal evolution of Monin–Obukhov length, friction velocity, temperature scale, surface heat flux, eddy-transfer coefficients for momentum and heat, and turbulent viscous dissipation rate on the Martian surface layer for a complete sol belonging to the Pathfinder mission. All these magnitudes have been derived from in situ wind and temperature measurements at around 1.3-m height and simulated ground temperature (from 0600 sol 25 to 0600 sol 26). Previously, neither values of turbulent viscous dissipation rate and eddy-transfer coefficients from in situ measurements for the Martian surface layer nor diurnal evolutions of all the previously mentioned turbulent parameters for the Pathfinder had been obtained. Monin–Obukhov similarity theory for stratified surface layers has been applied to obtain the results. The values assigned to the surface roughness and the applied parameterization of the interfacial sublayer will be discussed in detail with respect to the results’ sensitivity to them. The authors have found similarities concerning the order of magnitude and qualitative behavior of Monin–Obukhov length, friction velocity, and turbulent viscous dissipation rate on Earth and on Mars. However, quantities directly related to the lower Martian atmospheric density and thermal inertia, like temperature scale and hence surface heat flux, range over different orders of magnitude. Additionally, turbulent exchanges in the first few meters have been found to be just two orders of magnitude higher than the molecular ones, whereas on Earth around five orders of magnitude separate both mechanisms.

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