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14 results on '"Unsteady phenomena"'

1. Simulation of solidification for saving energy with using nanomaterial involving conduction heat transfer

Author

Mashhour A. Alazwari, Ali Basem, Hussein A.Z. AL-bonsrulah, Nidal H. Abu-Hamdeh, Mahmood Shaker Albdeiri, and Galal A.Ahmed Alashaari

Subjects
Storage of cold energy, Galerkin method, Nanomaterial, Unsteady phenomena, Diameter of powder, Engineering (General). Civil engineering (General), TA1-2040
Abstract

The current article studies the improvement of the discharging rate in cold storage systems by modifying the tank configuration and incorporating additives. Specifically, the study inspects how varying the diameter (dp) and fraction (ϕ) of nano-powders affects the process duration. The governing equations, derived under the assumption of negligible slip velocity of nanoparticles and convection terms, were solved using the Galerkin method. The computational grid was modified owing to location of the ice front, and unsteady terms were discretized using an unconditionally stable approach. The results indicate that initially, increasing dp decreases the process duration by approximately 20.01 %, but further increases in dp lead to a 49.53 % rise in the duration. As the process time increases, the amount of ice produced also increases, with nanoparticle loading resulting in a significantly higher ice yield. Specifically, the incorporation of nanoparticles enhances the storage rate by approximately 41.37 %.

Published
2024
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2. Analysis of conduction mode in cold energy storage using a tank filled with nanomaterial

Author

Mashhour A. Alazwari, Ali Basem, Hussein A.Z. Al-bonsrulah, Khalid H. Almitani, Nidal H. Abu-Hamdeh, Mahmood Shaker Albdeiri, and Galal A.Ahmed Alashaari

Subjects
Freezing process, NEPCM, Unsteady phenomena, Mesh adaption, Galerkin method, Engineering (General). Civil engineering (General), TA1-2040
Abstract

The intensification of freezing rates through the incorporation of nano-sized powders and fins through a cold storage unit was examined. The Galerkin method with special meshing was utilized to solve equations, which were based on the supposition of conduction mode dominance. Additives of varying diameters (dp) and three different concentration levels (ϕ) were implemented. The findings are presented through ice front visualization, contour plots, and scalar curves. The computational code demonstrated high accuracy during the validation phase. The results reveal that as the dp increases, the solidification time initially drops by approximately 20 %, then subsequently increases by about 49.45 %. The optimal solidification time of 2951.17 s was achieved with medium-sized powders. Furthermore, an intensification in (ϕ) leads to a significant decrement in freezing time by about 41.43 %, with the most pronounced effect observed for nano-powders with dp = 40 nm.

Published
2024
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3. Analysis of the Inner Fluid-Dynamics of Scroll Compressors and Comparison between CFD Numerical and Modelling Approaches

Author

Giovanna Cavazzini, Francesco Giacomel, Alberto Benato, Francesco Nascimben, and Guido Ardizzon

Subjects
positive displacement machine, scroll, CFD analysis, unsteady phenomena, axial gap, turbulent model, Technology
Abstract

Scroll compressors are widely adopted machines in both refrigeration systems and heat pumps. However, their efficiency is basically poor and constitutes the main bottleneck for improving the overall system performance. In fact, due to the complex machine fluid dynamics, scroll design is mainly based on theoretical and/or semi-empirical approaches. Designs strategies that do not guarantee an in-depth analysis of the machine behavior can be supplemented with a Computation Fluid Dynamics (CFD) approach. To this purpose, in the present work, the scroll compressor inner fluid dynamics is numerically analyzed in detail using two CFD software and two different modelling strategies for the axial gap. The analysis of the fluid evolution within the scroll wraps reveals unsteady phenomena developing during the suction and discharge phases, amplified by the axial clearance with negative impact on the main fluid flow (e.g., −13% of average mass flow rate for an axial gap of 30 μ) and on the scroll performance (e.g., +26% of average absorbed power for an axial gap of 30 μ). In terms of accuracy, the k-ε offers good performance on the estimation of average quantities but proves to be inadequate for capturing the complexity of the unsteady phenomena caused by the axial gap (e.g., −19% of the absorbed power in case of perfect tip seal). The need for considering specific geometric details in design procedures is highlighted, and guidelines on the choice of the most suitable numerical model are provided depending on the analysis needs.

Published
2021
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4. Wind Effects, Unsteady Behaviors, and Regimes of Propagation of Surface Fires in Open Field.

Author

Morvan, Dominique

Subjects
COMPUTER simulation, WIND speed, GRASSLANDS, BOUNDARY value problems, SPECTRUM analysis, FLAME, WILDFIRES
Abstract

The subject of this article concerns the unsteady effects (fire intensity, wind) upon the propagation and, more generally, the behavior of surface fires in open fields. The study focused on two sources of unsteadiness: the first one resulting from the regime of propagation (wind driven or plume dominated), which can affect greatly the behavior of the flame front and consequently the fire intensity, the second one resulting from the wind gusts associated with the conditions of flow of wind in real conditions. The study was based on numerical simulations, using a multiphase formulation, and on spectral analysis of the time evolution of the fire line intensity. The calculations were performed in 2D for a homogeneous vegetation layer (grassland) and for a large interval of wind conditions (10 m open wind velocity U10ranged between 1 m/s and 25 m/s). The results have highlighted the link between the unsteady character of flame front behavior and the regime of propagation (plume dominated, wind driven). A particular interest was focused on the role played by two potential sources of instabilities, namely the Kelvin-Helmholtz instability (wind effects) and the thermo-convective instability (plume effects), upon the behavior of fires. A second set of simulations has been carried out using unsteady wind conditions, reproduced using sinusoidal boundary conditions for the streamwise velocity, with a frequency ranging between 0.5 Hz and 3 Hz. [ABSTRACT FROM PUBLISHER]

Published
2014
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5. NUMERICAL INVESTIGATION OF FLOW IN MIXED-FLOW PUMP WITH VOLUTE

Author

MILAN SEDLAR

Subjects
CFD, separated flow, cavitation, unsteady phenomena, mixed-flow pump, volute, Information technology, T58.5-58.64
Abstract

This work deals with modelling of flow in a complete mixed-flow pump with volute, including the tip leakage flows, using both the quasi-steady and true transient models of rotor/stator interaction. The CFX-TASCflow CFD package from AEA Technology is applied to calculate flows for a wide range of flow rates from about 0.2 to 1.4 Qopt. Fairly detailed flow structures have been predicted based on the flow rates, especially the impeller inlet recirculation and separations on the suction side of the blades for the suboptimal rates of flow, as well as strong secondary flows and separations in the volute for off-design conditions. The rotor/stator interaction influence on flow phenomena both in the impeller and volute have been investigated with very interesting results, providing a good insight into the dynamics of flow close to the volute tongue. Based on the computational results, pump performance curves (Q-H, Q-nh and Q-P, nh being the hydraulic efficiency) have been obtained. The data from this numerical investigation have been used to improve the inlet part of the impeller blades, especially close to the tip. The geometry modifications have resulted in reducing cavitation in the impeller as well as the noise at suboptimal rates of flow.

Published
2001

6. Analysis of the Inner Fluid-Dynamics of Scroll Compressors and Comparison between CFD Numerical and Modelling Approaches.

Author

Cavazzini, Giovanna, Giacomel, Francesco, Benato, Alberto, Nascimben, Francesco, and Ardizzon, Guido

Subjects
COMPUTATIONAL fluid dynamics, FLUID dynamics, HEAT pumps, MACHINE dynamics, FLUID flow, COMPRESSORS
Abstract

Scroll compressors are widely adopted machines in both refrigeration systems and heat pumps. However, their efficiency is basically poor and constitutes the main bottleneck for improving the overall system performance. In fact, due to the complex machine fluid dynamics, scroll design is mainly based on theoretical and/or semi-empirical approaches. Designs strategies that do not guarantee an in-depth analysis of the machine behavior can be supplemented with a Computation Fluid Dynamics (CFD) approach. To this purpose, in the present work, the scroll compressor inner fluid dynamics is numerically analyzed in detail using two CFD software and two different modelling strategies for the axial gap. The analysis of the fluid evolution within the scroll wraps reveals unsteady phenomena developing during the suction and discharge phases, amplified by the axial clearance with negative impact on the main fluid flow (e.g., −13% of average mass flow rate for an axial gap of 30 μ) and on the scroll performance (e.g., +26% of average absorbed power for an axial gap of 30 μ). In terms of accuracy, the k-ε offers good performance on the estimation of average quantities but proves to be inadequate for capturing the complexity of the unsteady phenomena caused by the axial gap (e.g., −19% of the absorbed power in case of perfect tip seal). The need for considering specific geometric details in design procedures is highlighted, and guidelines on the choice of the most suitable numerical model are provided depending on the analysis needs. [ABSTRACT FROM AUTHOR]

Published
2021
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7. Large-Eddy Simulation of a Mixed-Flow Pump at Off-Design Conditions

Author

Antonio Lippolis, Elias Balaras, and Antonio Posa

Subjects
Physics, Suction, Turbulence, Mechanical Engineering, Large eddy simulation, Thermodynamics, Mechanics, Off design, Kinetic energy, Turbulent flow, Physics::Fluid Dynamics, Impeller, Mixed flow, Immersed boundary, Machine design, Off design condition, Unsteady phenomena
Abstract

The flow through turbopumps is characterized by highly unsteady phenomena at part load conditions, involving large separation and generation of vortical structures. This behavior is strongly dependent on the interaction between rotating and steady parts, which is significantly modified, compared to the one at the design flow rate. Therefore, at off-design conditions, eddy-resolving computations are more suitable to analyze the complex physics occurring inside turbomachinery channels. In this work the large eddy simulation (LES), coupled with an immersed-boundary (IB) method, is utilized to study a mixed-flow pump at a reduced flow rate, equivalent to 40% of the nominal one. The present approach has been already validated in a previous study, where a satisfactory agreement with two-dimensional (2D) particle image velocimetry (PIV) experiments has been shown at design conditions. In this paper a comparison with the LES results at the optimal flow rate is also proposed, in order to understand the important modifications of the flow occurring at part loads.

Published
2015
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8. Wind effects, unsteady behaviors, and regimes of propagation of surface fires in open field

Author

Dominique Morvan, Laboratoire de Mécanique, Modélisation et Procédés Propres (M2P2), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), UNIMECA, and Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Wind gradient, Meteorology, General Chemical Engineering, Flow (psychology), General Physics and Astronomy, Energy Engineering and Power Technology, Wind stress, 020101 civil engineering, 02 engineering and technology, Wind effects, 7. Clean energy, Wind speed, 0201 civil engineering, Physics::Fluid Dynamics, Wind profile power law, Fire modeling, Wind shear, Wildfire behavior, [SPI.GPROC]Engineering Sciences [physics]/Chemical and Process Engineering, Unsteady phenomena, Physics::Atmospheric and Oceanic Physics, 040101 forestry, 04 agricultural and veterinary sciences, General Chemistry, Mechanics, Plume, Fuel Technology, 13. Climate action, 0401 agriculture, forestry, and fisheries, Environmental science, Intensity (heat transfer)
Abstract

International audience; The subject of this article concerns the unsteady effects (fire intensity, wind) upon the propagation and, more generally, the behavior of surface fires in open fields. The study focused on two sources of unsteadiness: the first one resulting from the regime of propagation (wind driven or plume dominated), which can affect greatly the behavior of the flame front and consequently the fire intensity, the second one resulting from the wind gusts associated with the conditions of flow of wind in real conditions. The study was based on numerical simulations, using a multiphase formulation, and on spectral analysis of the time evolution of the fire line intensity. The calculations were performed in 2D for a homogeneous vegetation layer (grassland) and for a large interval of wind conditions (10 m open wind velocity U10 ranged between 1 m/s and 25 m/s). The results have highlighted the link between the unsteady character of flame front behavior and the regime of propagation (plume dominated, wind driven). A particular interest was focused on the role played by two potential sources of instabilities, namely the Kelvin-Helmholtz instability (wind effects) and the thermo-convective instability (plume effects), upon the behavior of fires. A second set of simulations has been carried out using unsteady wind conditions, reproduced using sinusoidal boundary conditions for the streamwise velocity, with a frequency ranging between 0.5 Hz and 3 Hz.

Published
2014
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9. CFD simulace poryvu bočního větru

Author

Čavoj, Ondřej, Vančura, Jan, Kroupa, Michal, Čavoj, Ondřej, Vančura, Jan, and Kroupa, Michal

Abstract

Tato diplomová práce se zabývá zkoumáním nestacionárních aerodynamických jevů při průjezdu vozidla poryvem bočního větru. V první části byla pro CFD simulace vytvořena funkce popisující průběh boční složky rychlosti v čase a prostoru. V další části byl srovnán kontinuální poryv s trapézovým poryvem. Srovnání nestacionárních a kvazi-stacionárních průběhů aerodynamických silových účinků pomocí anulovaných sil, povrchového tlaku vozidla a proudového pole kolem vozidla bylo úkolem další části. V předposlední části bylo zkoumáno nestacionární chování odporové síly a na závěr byl zkoumán vliv zadní části geometrie na nestacionární jevy., This thesis deals with the investigation of unsteady effects on vehicle that has been exposed to a crosswind gust. First crosswind velocity function was created, which is a function of both time and space. A comparison of continual and trapeze gust model was carried out. Next step was to compare unsteady and quasi-steady evolution of the aerodynamic loads using accumulated forces, surface pressures and flow field around the car. The penultimate part deals with investigation of unsteady behaviour of drag and in the last part the influence of rear geometry of the car on unsteady phenomena was investigated.

10. CFD simulace poryvu bočního větru

Author

Čavoj, Ondřej, Vančura, Jan, Kroupa, Michal, Čavoj, Ondřej, Vančura, Jan, and Kroupa, Michal

Abstract

Tato diplomová práce se zabývá zkoumáním nestacionárních aerodynamických jevů při průjezdu vozidla poryvem bočního větru. V první části byla pro CFD simulace vytvořena funkce popisující průběh boční složky rychlosti v čase a prostoru. V další části byl srovnán kontinuální poryv s trapézovým poryvem. Srovnání nestacionárních a kvazi-stacionárních průběhů aerodynamických silových účinků pomocí anulovaných sil, povrchového tlaku vozidla a proudového pole kolem vozidla bylo úkolem další části. V předposlední části bylo zkoumáno nestacionární chování odporové síly a na závěr byl zkoumán vliv zadní části geometrie na nestacionární jevy., This thesis deals with the investigation of unsteady effects on vehicle that has been exposed to a crosswind gust. First crosswind velocity function was created, which is a function of both time and space. A comparison of continual and trapeze gust model was carried out. Next step was to compare unsteady and quasi-steady evolution of the aerodynamic loads using accumulated forces, surface pressures and flow field around the car. The penultimate part deals with investigation of unsteady behaviour of drag and in the last part the influence of rear geometry of the car on unsteady phenomena was investigated.

11. CFD simulace poryvu bočního větru

Author

Čavoj, Ondřej, Vančura, Jan, Čavoj, Ondřej, and Vančura, Jan

Abstract

Tato diplomová práce se zabývá zkoumáním nestacionárních aerodynamických jevů při průjezdu vozidla poryvem bočního větru. V první části byla pro CFD simulace vytvořena funkce popisující průběh boční složky rychlosti v čase a prostoru. V další části byl srovnán kontinuální poryv s trapézovým poryvem. Srovnání nestacionárních a kvazi-stacionárních průběhů aerodynamických silových účinků pomocí anulovaných sil, povrchového tlaku vozidla a proudového pole kolem vozidla bylo úkolem další části. V předposlední části bylo zkoumáno nestacionární chování odporové síly a na závěr byl zkoumán vliv zadní části geometrie na nestacionární jevy., This thesis deals with the investigation of unsteady effects on vehicle that has been exposed to a crosswind gust. First crosswind velocity function was created, which is a function of both time and space. A comparison of continual and trapeze gust model was carried out. Next step was to compare unsteady and quasi-steady evolution of the aerodynamic loads using accumulated forces, surface pressures and flow field around the car. The penultimate part deals with investigation of unsteady behaviour of drag and in the last part the influence of rear geometry of the car on unsteady phenomena was investigated.

12. CFD simulace poryvu bočního větru

Author

Čavoj, Ondřej, Vančura, Jan, Čavoj, Ondřej, and Vančura, Jan

Abstract

Tato diplomová práce se zabývá zkoumáním nestacionárních aerodynamických jevů při průjezdu vozidla poryvem bočního větru. V první části byla pro CFD simulace vytvořena funkce popisující průběh boční složky rychlosti v čase a prostoru. V další části byl srovnán kontinuální poryv s trapézovým poryvem. Srovnání nestacionárních a kvazi-stacionárních průběhů aerodynamických silových účinků pomocí anulovaných sil, povrchového tlaku vozidla a proudového pole kolem vozidla bylo úkolem další části. V předposlední části bylo zkoumáno nestacionární chování odporové síly a na závěr byl zkoumán vliv zadní části geometrie na nestacionární jevy., This thesis deals with the investigation of unsteady effects on vehicle that has been exposed to a crosswind gust. First crosswind velocity function was created, which is a function of both time and space. A comparison of continual and trapeze gust model was carried out. Next step was to compare unsteady and quasi-steady evolution of the aerodynamic loads using accumulated forces, surface pressures and flow field around the car. The penultimate part deals with investigation of unsteady behaviour of drag and in the last part the influence of rear geometry of the car on unsteady phenomena was investigated.

13. CFD simulace poryvu bočního větru

Author

Čavoj, Ondřej, Vančura, Jan, Čavoj, Ondřej, and Vančura, Jan

Abstract

Tato diplomová práce se zabývá zkoumáním nestacionárních aerodynamických jevů při průjezdu vozidla poryvem bočního větru. V první části byla pro CFD simulace vytvořena funkce popisující průběh boční složky rychlosti v čase a prostoru. V další části byl srovnán kontinuální poryv s trapézovým poryvem. Srovnání nestacionárních a kvazi-stacionárních průběhů aerodynamických silových účinků pomocí anulovaných sil, povrchového tlaku vozidla a proudového pole kolem vozidla bylo úkolem další části. V předposlední části bylo zkoumáno nestacionární chování odporové síly a na závěr byl zkoumán vliv zadní části geometrie na nestacionární jevy., This thesis deals with the investigation of unsteady effects on vehicle that has been exposed to a crosswind gust. First crosswind velocity function was created, which is a function of both time and space. A comparison of continual and trapeze gust model was carried out. Next step was to compare unsteady and quasi-steady evolution of the aerodynamic loads using accumulated forces, surface pressures and flow field around the car. The penultimate part deals with investigation of unsteady behaviour of drag and in the last part the influence of rear geometry of the car on unsteady phenomena was investigated.

14. CFD simulace poryvu bočního větru

Author

Čavoj, Ondřej, Vančura, Jan, Kroupa, Michal, Čavoj, Ondřej, Vančura, Jan, and Kroupa, Michal

Abstract

Tato diplomová práce se zabývá zkoumáním nestacionárních aerodynamických jevů při průjezdu vozidla poryvem bočního větru. V první části byla pro CFD simulace vytvořena funkce popisující průběh boční složky rychlosti v čase a prostoru. V další části byl srovnán kontinuální poryv s trapézovým poryvem. Srovnání nestacionárních a kvazi-stacionárních průběhů aerodynamických silových účinků pomocí anulovaných sil, povrchového tlaku vozidla a proudového pole kolem vozidla bylo úkolem další části. V předposlední části bylo zkoumáno nestacionární chování odporové síly a na závěr byl zkoumán vliv zadní části geometrie na nestacionární jevy., This thesis deals with the investigation of unsteady effects on vehicle that has been exposed to a crosswind gust. First crosswind velocity function was created, which is a function of both time and space. A comparison of continual and trapeze gust model was carried out. Next step was to compare unsteady and quasi-steady evolution of the aerodynamic loads using accumulated forces, surface pressures and flow field around the car. The penultimate part deals with investigation of unsteady behaviour of drag and in the last part the influence of rear geometry of the car on unsteady phenomena was investigated.

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