The entrainment behavior of a turbulent axisymmetric jet in a viscous host fluid

Chhabra, Sudhaker; Shipman, Thomas; Prasad, Ajay K.

doi:10.1007/s00348-004-0888-x

Cited by 11 publications

(3 citation statements)

References 14 publications

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“…A previous study of a turbulent jet issuing into a more viscous fluid than the jet fluid has shown a dependence of the decay constant, a, on entrainment. 6 This study showed that increased entrainment of the relatively stagnant fluid by the jet results in a lower jet decay constant, and, consequently, the jet decays more quickly than expected. This faster decay is due to the higher laminar shear stresses that cause the jet decay to deviate from the normal behavior of a turbulent jet.…”

Section: Discussionmentioning

confidence: 76%

Procoagulant Properties of Flow Fields in Stenotic and Expansive Orifices

et al. 2007

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In the United States, over 125,000 mechanical heart valves (MHVs) are implanted each year. Flow through the MHV hinge can cause thromboemboli formation. The purpose of this study was to examine various orifice geometries representing the MHV hinge region and how these geometries may contribute to platelet activation and thrombin generation. We also characterized these flow fields with digital particle image velocimetry (DPIV). Citrated human blood at room temperature was forced through the orifices (400 and 800 microm ID) with a centrifugal bypass pump, continuously infusing calcium chloride to partially reverse the citrate anticoagulant. Blood samples were tested for the presence of thrombin-antithrombin complex (TAT) and platelet factor 4 (PF4). Velocity and shear stress were measured with DPIV using a blood analog fluid seeded with fluorescent microbeads. The results indicate that small changes in geometry, although they do not affect the bulk flow, change the coagulation propensity as blood flows through the orifices. A more abrupt geometry allows more stagnation to occur resulting in more thrombin generation. PF4 measurements indicated similar levels of platelet activation for all orifices. DPIV showed differences in the jets with respect to entrainment of stagnant fluid. These results help to pinpoint the important parameters that lead to flow stasis and subsequent thrombus formation.

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Section: Discussionmentioning

confidence: 76%

Procoagulant Properties of Flow Fields in Stenotic and Expansive Orifices

et al. 2007

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“…Most studies reported in literature have focused on the impact of variable viscosity on the large scales. Chhabra et al (2005) and Talbot et al (2013) studied turbulent jet flows, where the viscosity between jet fluid and host fluid differs. They observed, compared to a flow with uniform viscosity, that the relationship between production and dissipation of turbulent energy is altered and that the entrainment and the spreading rates of the jet flow are changed.…”

Section: Introductionmentioning

confidence: 99%

One-point and two-point statistics of homogeneous isotropic decaying turbulence with variable viscosity

Gauding

Danaila

Varéa

2018

International Journal of Heat and Fluid Flow

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The decay of homogeneous isotropic turbulence in a variable viscosity fluid with a viscosity ratio up to 15 is analyzed by means of highly resolved direct numerical simulations (DNS) at low Reynolds numbers. The question addressed by the present work is how quantities such as the kinetic energy and the associated dissipation rate, as well as the inter-scale transport mechanism of turbulence are changed by local fluctuations of the viscosity. From the one-point budget equation of the turbulent kinetic energy, it is shown that the mean dissipation rate is nearly unchanged by variable viscosity effects. This result is explained by a negative correlation between the local viscosity and the local velocity gradients. However, the dissipation is a highly fluctuating quantity with a strong level of intermittency. From a statistical analysis it is shown that turbulent flows with variable viscosity are characterized by an enhanced level of small-scale intermittency, which results in the presence of smaller length scales and a modified turbulent mixing. The effect of variable viscosity on the turbulent cascade is analyzed by a budget equation for the velocity structure function. From DNS it is shown that viscosity gradients contribute to the inter-scale transport mechanism in the form of an inverse transport, where information propagates from the small scales to the large scales.

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“…Moreover, flows with viscosity variations have been studied mainly for mixing involving liquids, for which the viscosity ratios varies over several orders of magnitude, e.g. Chhabra [6]. Indeed, in chemical industry and nature, it is the most encountered configuration.…”

Section: Introductionmentioning

confidence: 99%

On the similarity of variable viscosity flows

et al. 2016

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Turbulent mixing is ubiquitous in both nature and industrial applications. Most of them concern different fluids, therefore with variable physical properties (density and/or viscosity). The focus here is on variable viscosity flows and mixing, involving density-matched fluids. The issue is whether or not these flows may be self-similar, or self-preserving. The importance of this question stands on the predictability of these flows; self-similar dynamical systems are easier tractable from an analytical viewpoint. More specifically, self-similar analysis is applied to the scale-by-scale energy transport equations, which represent the transport of energy at each scale and each point of the flow. Scale-by-scale energy budget equations are developed for inhomogeneous and anisotropic flows, in which the viscosity varies as a result of heterogeneous mixture or temperature variations. Additional terms are highlighted, accounting for the viscosity gradients, or fluctuations. These terms are present at both small and large scales, thus rectifying the common belief that viscosity is a small-scale quantity. Scale-by-scale energy budget equations are then adapted for the particular case of a round jet evolving in a more viscous host fluid. It is further shown that the condition of self-preservation is not necessarily satisfied in variable-viscosity jets. Indeed, the jet momentum conservation, as well as the constancy of the Reynolds number in the central region of the jet, cannot be satisfied simultaneously. This points to the necessity of considering less stringent conditions (with respect to classical, single-fluid jets) when analytically tackling these flows and reinforces the idea that viscosity variations must be accounted for when modelling these flows.

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The entrainment behavior of a turbulent axisymmetric jet in a viscous host fluid

Cited by 11 publications

References 14 publications

Procoagulant Properties of Flow Fields in Stenotic and Expansive Orifices

Procoagulant Properties of Flow Fields in Stenotic and Expansive Orifices

One-point and two-point statistics of homogeneous isotropic decaying turbulence with variable viscosity

On the similarity of variable viscosity flows

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