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Entropy
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Entropy Production in Turbulent Flow II
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Entropy Production in Turbulent Flow II

A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Multidisciplinary Applications".

Deadline for manuscript submissions: closed (31 January 2021) | Viewed by 12338

Special Issue Editor

Dr. T.-W. Lee

E-Mail Website
Guest Editor
Mechanical and Aerospace Engineering, SEMTE, Arizona State University, Tempe, AZ 85287, USA
Interests: energy system analysis; thermal and fluid process characterization; fuel property measurements for energy systems
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Turbulence is one of the difficult and interesting problems in fluid physics, with ubiquitous applications in engineering and science. Numerics are predominantly used in modern solutions and analysis of turbulent flows. Even in this regard, additional measures such as entropy and related principles can lead to advances or even breakthroughs. An example is the use of the maximum entropy principle in determining the turbulence kinetic energy spectra or the spatial distribution in wall-bounded flows. It can even be said that existing methods have reached an asymptote where colorful results may be obtained from super-simulations, and yet the rate of approach to new insights or solutions has decelerated. Therefore, it is a timely endeavor to seek new insights toward turbulent flows, and one interesting and useful measure is the entropy and related principles.

We open this forum and invite articles on this topic, where ideas and approaches based on sound physics of entropy and turbulent flows will receive careful considerations regardless of their novelty. The topics are broadly on entropy and related principles applied toward turbulent flows and are inclusive of single- and multiphase flows (e.g., spray atomization), reacting flows, and large-scale flows (atmospheric turbulence or industrial processes). System-level entropy analyses of processes involving turbulent flows are also of interest.

Dr. T.-W. Lee
Guest Editor

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Published Papers (4 papers)

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Research

18 pages, 2707 KiB  
Article
Entropy Generation for Negative Frictional Pressure Drop in Vertical Slug and Churn Flows
by Lei Liu, Dongxu Liu and Na Huang
Entropy 2021, 23(2), 156; https://doi.org/10.3390/e23020156 - 27 Jan 2021
Cited by 5 | Viewed by 1950
Abstract
It is widely accepted that the frictional pressure drop is impossible to be negative for pipe flow. However, the negative frictional pressure drops were observed for some cases of two-phase slug and churn flows in pipes, challenging the general sense of thermodynamic irreversibility. [...] Read more.
It is widely accepted that the frictional pressure drop is impossible to be negative for pipe flow. However, the negative frictional pressure drops were observed for some cases of two-phase slug and churn flows in pipes, challenging the general sense of thermodynamic irreversibility. In order to solve this puzzling problem, theoretical investigations were performed for the entropy generation in slug and churn flows. It is found that the frictional pressure drop along with a buoyancy-like term contributes to the entropy generation due to mechanical energy loss for steady, incompressible slug and churn flows in vertical and inclined pipes. Experiments were conducted in a vertical pipe with diameter as 0.04 m for slug and churn flows. Most of the experimental data obtained for frictional pressure drop are negative at high gas–liquid ratios from 100 to 10,000. Entropy generation rates were calculated from experimental data. The results show that the buoyancy-like term is positive and responsible for a major part of entropy generation rate while the frictional pressure drop is responsible for a little part of entropy generation rate, because of which the overall entropy generation due to mechanical energy loss is still positive even if the frictional pressure drop is negative in vertical slug and churn flows. It is clear that the negative frictional pressure drops observed in slug and churn flows are not against the thermodynamics irreversibility. Full article
(This article belongs to the Special Issue Entropy Production in Turbulent Flow II)
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11 pages, 2229 KiB  
Article
Lognormality in Turbulence Energy Spectra
by Taewoo Lee
Entropy 2020, 22(6), 669; https://doi.org/10.3390/e22060669 - 17 Jun 2020
Cited by 6 | Viewed by 4015
Abstract
The maximum entropy principle states that the energy distribution will tend toward a state of maximum entropy under the physical constraints, such as the zero energy at the boundaries and a fixed total energy content. For the turbulence energy spectra, a distribution function [...] Read more.
The maximum entropy principle states that the energy distribution will tend toward a state of maximum entropy under the physical constraints, such as the zero energy at the boundaries and a fixed total energy content. For the turbulence energy spectra, a distribution function that maximizes entropy with these physical constraints is a lognormal function due to its asymmetrical descent to zero energy at the boundary lengths scales. This distribution function agrees quite well with the experimental data over a wide range of energy and length scales. For turbulent flows, this approach is effective since the energy and length scales are determined primarily by the Reynolds number. The total turbulence kinetic energy will set the height of the distribution, while the ratio of length scales will determine the width. This makes it possible to reconstruct the power spectra using the Reynolds number as a parameter. Full article
(This article belongs to the Special Issue Entropy Production in Turbulent Flow II)
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14 pages, 6213 KiB  
Article
Numerical Investigation on the Thermodynamic Characteristics of a Liquid Film upon Spray Cooling Using an Air-Blast Atomization Nozzle
by Jia-Xin Li, Yun-Ze Li, En-Hui Li and Tong Li
Entropy 2020, 22(3), 308; https://doi.org/10.3390/e22030308 - 9 Mar 2020
Cited by 11 | Viewed by 3129
Abstract
This paper developed a three-dimensional model to simulate the process of atomization and liquid film formation during the air-blast spray cooling technological process. The model was solved using the discrete phase model method. Several factors including the thermodynamic characteristics of the liquid film [...] Read more.
This paper developed a three-dimensional model to simulate the process of atomization and liquid film formation during the air-blast spray cooling technological process. The model was solved using the discrete phase model method. Several factors including the thermodynamic characteristics of the liquid film as well as the spray quality with different spray mass flow rates under different spray heights were numerically investigated and discussed. The results show that the varied spray height has little effect on the Sauter Mean Diameter (d32) of the spray droplet, while the thermodynamic characteristics of liquid film including the liquid film height, the liquid film velocity, and the liquid film generation rate are sensitive to the change of the spray height. With the growth of spray mass flow rates, d32, the liquid film generation rate and liquid film height become larger, while the liquid film velocity with different spray mass flow rates has a similar velocity distribution, indicating that the spray mass flow rate has little effect on the liquid film velocity. The average d32 of droplet size shows a sharp drop when sprayed from the nozzle in a short period of time (<1.5 ms), then approaching smoothness, below a value of 40 μ m , the spray status tends to be stable. Full article
(This article belongs to the Special Issue Entropy Production in Turbulent Flow II)
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16 pages, 13528 KiB  
Article
Effect of Incidence Angle on Entropy Generation in the Boundary Layers on the Blade Suction Surface in a Compressor Cascade
by Lei Shi and Hongwei Ma
Entropy 2019, 21(11), 1049; https://doi.org/10.3390/e21111049 - 27 Oct 2019
Cited by 13 | Viewed by 2787
Abstract
The entropy generation that occurs within boundary layers over a C4 blade at a Reynolds number of 24,000 and incidence angles (i) of 0°, 2.5°, 5°, 7.5°, and 10° are investigated experimentally using a particle image velocimetry (PIV) technique. To clarify the entropy [...] Read more.
The entropy generation that occurs within boundary layers over a C4 blade at a Reynolds number of 24,000 and incidence angles (i) of 0°, 2.5°, 5°, 7.5°, and 10° are investigated experimentally using a particle image velocimetry (PIV) technique. To clarify the entropy generation process, the distribution of the entropy generation rates (EGR) and the unsteady flow structures within the PIV snapshots are analyzed. The results identify that for a higher incidence angle, the separation and transition occur further upstream, and the entropy generation in the boundary layer increases. When the separation takes place at the aft portion of the blade, the integral EGR decrease near the leading edge, remain minimal values in the middle portion of the blade, and increase sharply in the vicinity of the mean transition. More than 35% of the entropy generation is generated at the region downstream of the mean transition. When the separation occurs at the fore portion of the blade, the contributions of mean-flow viscous dissipation decrease to less than 20%. The entropy generation with elevated value can be detected over the entire blade. The entire integral entropy generation in the boundary layer increases sharply when the laminar separation bubble moves upstream to the leading edge. Full article
(This article belongs to the Special Issue Entropy Production in Turbulent Flow II)
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