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Entropy in Computational Fluid Dynamics II

A special issue of Entropy (ISSN 1099-4300).

Deadline for manuscript submissions: closed (15 June 2019) | Viewed by 23313

Special Issue Editor

Dr. Yan Jin

E-Mail Website
Guest Editor
Institute of Multiphase Flows, Hamburg University of Technology, 21073 Hamburg, Germany
Interests: interest: fluid mechanics; heat/mass transfer; direct numerical simulation; turbulence modeling; second law analysis; skin friction reduction; gas turbine; biological and physiological flows; nano- and micro-fluid flows
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Losses in a flow and heat transfer process, from a thermodynamics point of view, are due to irreversible processes. In order to better understand the physics of these loss-producing mechanisms, fluid mechanic and heat transfer considerations might be complemented by some thermodynamic concepts with respect to the irreversible processes involved. Basically, these are concepts that assess energy by its value in terms of its convertibility from one form to another.

The second law analysis (SLA) is often used in thermodynamics in order to assess an irreversible process. According to SLA, the quality of a flow and heat transfer process, and how reversible it is can only be assessed by the entropy generation rate. In our Special Issue, “Entropy in Computational Fluid Dynamics”, SLA is applied to both engineering applications and fundamental studies with respect to flow and heat transfer problems. The studies in the Special Issue show that SLA is a powerful tool for analyzing computational fluid dynamics (CFD) results.

The current Special Issue will further enhance knowledge about how to interpret CFD results with SLA. Analyses of irreversibility in traditional flow or heat transfer processes, e.g., evaluating irreversibility in gas turbines, are still a main topic of this Special Issue. In addition to traditional problems, irreversible processes in emerging subjects, such as nano- and micro-fluid flows, biological and physiological flows, are of particular interests.

Dr. Habil. Yan Jin
Guest Editor

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Keywords

  • Entropy generation in a flow
  • Entropy generation in a heat/mass transfer process
  • Assessing the irreversibility with high accuracy methods, e.g., DNS
  • Modeling the entropy generation due to turbulence
  • Optimization with the second law of thermodynamics
  • Skin friction reduction and heat transfer enhancement
  • Optimization of gas turbines with the second law of thermodynamics
  • Entropy generation in biological and physiological flows
  • Entropy generation in nano- and micro-fluid flows

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Published Papers (5 papers)

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Research

19 pages, 4255 KiB  
Article
Model Development and Exergy Analysis of a Microreactor for the Steam Methane Reforming Process in a CFD Environment
by Zia ur Rahman, Iftikhar Ahmad, Manabu Kano and Jawad Mustafa
Entropy 2019, 21(4), 399; https://doi.org/10.3390/e21040399 - 15 Apr 2019
Cited by 8 | Viewed by 4560
Abstract
Steam methane reforming (SMR) is a dominant technology for hydrogen production. For the highly energy-efficient operation, robust energy analysis is crucial. In particular, exergy analysis has received the attention of researchers due to its advantage over the conventional energy analysis. In this work, [...] Read more.
Steam methane reforming (SMR) is a dominant technology for hydrogen production. For the highly energy-efficient operation, robust energy analysis is crucial. In particular, exergy analysis has received the attention of researchers due to its advantage over the conventional energy analysis. In this work, an exergy analysis based on the computational fluid dynamics (CFD)-based method was applied to a monolith microreactor of SMR. Initially, a CFD model of SMR was developed using literature data. Then, the design and operating conditions of the microreactor were optimized based on the developed CFD model to achieve higher conversion efficiency and shorter length. Exergy analysis of the optimized microreactor was performed using the custom field function (CFF) integrated with the CFD environment. The optimized catalytic monolith microreactor of SMR achieved higher conversion efficiency at a smaller consumption of energy, catalyst, and material of construction than the reactor reported in the literature. The exergy analysis algorithm helped in evaluating length-wise profiles of all three types of exergy, namely, physical exergy, chemical exergy, and mixing exergy, in the microreactor. Full article
(This article belongs to the Special Issue Entropy in Computational Fluid Dynamics II )
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19 pages, 14823 KiB  
Article
Evaluating the Transient Energy Dissipation in a Centrifugal Impeller under Rotor-Stator Interaction
by Ran Tao, Xiaoran Zhao and Zhengwei Wang
Entropy 2019, 21(3), 271; https://doi.org/10.3390/e21030271 - 11 Mar 2019
Cited by 20 | Viewed by 4308
Abstract
In fluid machineries, the flow energy dissipates by transforming into internal energy which performs as the temperature changes. The flow-induced noise is another form that flow energy turns into. These energy dissipations are related to the local flow regime but this is not [...] Read more.
In fluid machineries, the flow energy dissipates by transforming into internal energy which performs as the temperature changes. The flow-induced noise is another form that flow energy turns into. These energy dissipations are related to the local flow regime but this is not quantitatively clear. In turbomachineries, the flow regime becomes pulsating and much more complex due to rotor-stator interaction. To quantitatively understand the energy dissipations during rotor-stator interaction, the centrifugal air pump with a vaned diffuser is studied based on total energy modeling, turbulence modeling and acoustic analogy method. The numerical method is verified based on experimental data and applied to further simulation and analysis. The diffuser blade leading-edge site is under the influence of impeller trailing-edge wake. The diffuser channel flow is found periodically fluctuating with separations from the blade convex side. Stall vortex is found on the diffuser blade trailing-edge near outlet. High energy loss coefficient sites are found in the undesirable flow regions above. Flow-induced noise is also high in these sites except in the stall vortex. Frequency analyses show that the impeller blade frequency dominates in the diffuser channel flow except in the outlet stall vortexes. These stall vortices keep their own stall frequency which is about 1/5 impeller frequency with high energy loss coefficient but low noise level. Results comparatively prove the energy dissipation mechanism in the centrifugal air pump under rotor-stator interaction. Results also provide the quantitative basis for turbomachinery’s loss reduction design. Full article
(This article belongs to the Special Issue Entropy in Computational Fluid Dynamics II )
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15 pages, 12593 KiB  
Article
Entropy Generation and Heat Transfer Performance in Microchannel Cooling
by Jundika C. Kurnia, Desmond C. Lim, Lianjun Chen, Lishuai Jiang and Agus P. Sasmito
Entropy 2019, 21(2), 191; https://doi.org/10.3390/e21020191 - 18 Feb 2019
Cited by 11 | Viewed by 5529
Abstract
Owing to its relatively high heat transfer performance and simple configurations, liquid cooling remains the preferred choice for electronic cooling and other applications. In this cooling approach, channel design plays an important role in dictating the cooling performance of the heat sink. Most [...] Read more.
Owing to its relatively high heat transfer performance and simple configurations, liquid cooling remains the preferred choice for electronic cooling and other applications. In this cooling approach, channel design plays an important role in dictating the cooling performance of the heat sink. Most cooling channel studies evaluate the performance in view of the first thermodynamics aspect. This study is conducted to investigate flow behaviour and heat transfer performance of an incompressible fluid in a cooling channel with oblique fins with regards to first law and second law of thermodynamics. The effect of oblique fin angle and inlet Reynolds number are investigated. In addition, the performance of the cooling channels for different heat fluxes is evaluated. The results indicate that the oblique fin channel with 20° angle yields the highest figure of merit, especially at higher Re (250–1000). The entropy generation is found to be lowest for an oblique fin channel with 90° angle, which is about twice than that of a conventional parallel channel. Increasing Re decreases the entropy generation, while increasing heat flux increases the entropy generation. Full article
(This article belongs to the Special Issue Entropy in Computational Fluid Dynamics II )
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23 pages, 8811 KiB  
Article
Entropy Analysis of the Flat Tip Leakage Flow with Delayed Detached Eddy Simulation
by Hui Li, Xinrong Su and Xin Yuan
Entropy 2019, 21(1), 21; https://doi.org/10.3390/e21010021 - 28 Dec 2018
Cited by 26 | Viewed by 4402
Abstract
In unshrouded turbine rotors, the tip leakage vortices develop and interact with the passage vortices. Such complex leakage flow causes the major loss in the turbine stage. Due to the complex turbulence characteristics of the tip leakage flow, the widely used Reynolds Averaged [...] Read more.
In unshrouded turbine rotors, the tip leakage vortices develop and interact with the passage vortices. Such complex leakage flow causes the major loss in the turbine stage. Due to the complex turbulence characteristics of the tip leakage flow, the widely used Reynolds Averaged Navier–Stokes (RANS) approach may fail to accurately predict the multi-scale turbulent flow and the related loss. In order to effectively improve the turbine efficiency, more insights into the loss mechanism are required. In this work, a Delayed Detached Eddy Simulation (DDES) study is conducted to simulate the flow inside a high pressure turbine blade, with emphasis on the tip region. DDES results are in good agreement with the experiment, and the comparison with RANS results verifies the advantages of DDES in resolving detailed flow structures of leakage flow, and also in capturing the complex turbulence characteristics. The snapshot Proper Orthogonal Decomposition (POD) method is used to extract the dominant flow features. The flow structures and the distribution of turbulent kinetic energy reveal the development of leakage flow and its interaction with the secondary flow. Meanwhile, it is found that the separation bubble (SB) is formed in tip clearance. The strong interactions between tip leakage vortex (TLV) and the up passage vortex (UPV) are the main source of unsteady effects which significantly enhance the turbulence intensity. Based on the DDES results, loss analysis of tip leakage flow is conducted based on entropy generation rates. It is found that the viscous dissipation loss is much stronger than heat transfer loss. The largest local loss occurs in the tip clearance, and the interaction between the leakage vortex and up passage vortex promotes the loss generation. The tip leakage flow vortex weakens the strength of up passage vortex, and loss of up passage flow is reduced. Comparing steady and unsteady effects to flow field, we found that unsteady effects of tip leakage flow have a large influence on flow loss distribution which cannot be ignored. To sum up, the current DDES study about the tip leakage flow provides helpful information about the loss generation mechanism and may guide the design of low-loss blade tip. Full article
(This article belongs to the Special Issue Entropy in Computational Fluid Dynamics II )
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16 pages, 7627 KiB  
Article
Quantification and Analysis of the Irreversible Flow Loss in a Linear Compressor Cascade
by Zhiyuan Li, Juan Du, Xavier Ottavy and Hongwu Zhang
Entropy 2018, 20(7), 486; https://doi.org/10.3390/e20070486 - 22 Jun 2018
Cited by 15 | Viewed by 3712
Abstract
A local loss model and an integral loss model are proposed to study the irreversible flow loss mechanism in a linear compressor cascade. The detached eddy simulation model based on the Menter shear stress transport turbulence model (SSTDES) was used to perform the [...] Read more.
A local loss model and an integral loss model are proposed to study the irreversible flow loss mechanism in a linear compressor cascade. The detached eddy simulation model based on the Menter shear stress transport turbulence model (SSTDES) was used to perform the high-fidelity simulations. The flow losses in the cascade with an incidence angle of 2°, 4° and 7° were analyzed. The contours of local loss coefficient can be explained well by the three-dimensional flow structures. The trend of flow loss varying with incidence angle predicted by integral loss is the same as that calculated by total pressure loss coefficient. The integral loss model was used to evaluate the irreversible loss generated in different regions and its varying trend with the flow condition. It as found that the boundary layer shear losses generated near the endwall, the pressure surface and the suction surface are almost identical for the three incidence angles. The secondary flow loss in the wake-flow and blade-passage regions changes dramatically with the flow condition due to the occurrence of corner stall. For this cascade, the secondary flow loss accounts for 26.1%, 48.3% and 64.3% of the total loss for the flow when the incidence angles are 2°, 4° and 7°, respectively. Lastly, the underlying reason for the variation of the secondary flow loss with the incidence angle is explained using the Lc iso-surface method. Full article
(This article belongs to the Special Issue Entropy in Computational Fluid Dynamics II )
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