The effect of tires on the overall aerodynamic drag in a car-tire assembly has been studied and deemed considerable from past studies. Previous studies focused on the tire attributes that have an impact on the aerodynamic performance of the vehicle. These tire attributes, however, have not been studied to the extent where one can get a better understanding of the impact of each of these attributes. This paper studies the impact that specific tire attributes have on the overall aerodynamic drag on the vehicle. A thorough and systematic sensitivity study of the effect of tire attributes of a standalone tire was performed to better understand the flow structures around the car body and the improvement in the aerodynamic performance of the vehicle. In this study, the DrivAer model is used due to the extensive research that has been done on the model. Ansys FLUENT is used to run the Simulations on the fastback configuration of the DrivAer model. Coefficient of Drag and coefficient of pressure results from the simulations are validated from experimental data. This is used to create a simulation procedure with appropriate meshing techniques and solution methods in order to simulate for the baseline tire-vehicle assembly and the optimized tire-vehicle assembly. Data from these simulations are used to conduct a sensitivity analysis of the tire-vehicle assembly model to get better insight into the modelling techniques for a car-tire assembly, as well as the impact of the individual parameters for future tire model optimization.
{"title":"Effects of Tire Attributes on the Aerodynamic Performance of a Generic Car-Tire Assembly1","authors":"Shubham Rath, A. Untaroiu","doi":"10.1115/1.4066192","DOIUrl":"https://doi.org/10.1115/1.4066192","url":null,"abstract":"\u0000 The effect of tires on the overall aerodynamic drag in a car-tire assembly has been studied and deemed considerable from past studies. Previous studies focused on the tire attributes that have an impact on the aerodynamic performance of the vehicle. These tire attributes, however, have not been studied to the extent where one can get a better understanding of the impact of each of these attributes. This paper studies the impact that specific tire attributes have on the overall aerodynamic drag on the vehicle. A thorough and systematic sensitivity study of the effect of tire attributes of a standalone tire was performed to better understand the flow structures around the car body and the improvement in the aerodynamic performance of the vehicle.\u0000 In this study, the DrivAer model is used due to the extensive research that has been done on the model. Ansys FLUENT is used to run the Simulations on the fastback configuration of the DrivAer model. Coefficient of Drag and coefficient of pressure results from the simulations are validated from experimental data. This is used to create a simulation procedure with appropriate meshing techniques and solution methods in order to simulate for the baseline tire-vehicle assembly and the optimized tire-vehicle assembly. Data from these simulations are used to conduct a sensitivity analysis of the tire-vehicle assembly model to get better insight into the modelling techniques for a car-tire assembly, as well as the impact of the individual parameters for future tire model optimization.","PeriodicalId":504378,"journal":{"name":"Journal of Fluids Engineering","volume":"5 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141920305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The physical mechanism, evolution process and control method on pulsation caused by flow-induced excitation vortex in axial flow pump are elaborated by numerical calculation and experiment. The mechanism formulation of flow-induced excitation vibration and the unique hydrodynamic design method of airfoil are proposed with three contrast models. According to the action law of inertial centrifugal force (ICF) in the rotor-stator interaction (RSI) region and guide vane airfoil, the evaluation method between vortex transport, turbulent kinetic energy and flow structure under transient and steady state of internal flow field is established, which navigates the instability of energy intensity determined by the uneven gradient distribution. The distribution characteristics of flow-induced excitation pulsation in the RSI region and the static region are quantitatively verified by experiment. Along the streamwise direction, the excitation loss changes from impact loss to flow loss, with the RSI vortex affected by wake-jet flow (WJF) vortices transforming into inter-vane vortex (IVV) in the guide vane. In pulsation evaluation, the excitation pulsation form changes from blade frequency fBPF to low frequency band. Overall, the generation analysis of the excitation pulsation is realized based on the hydrodynamic optimal design with the comparison of models, which provides guidance for the optimization design of the axial flow pump to reduce vibration and energy consumption of the cooling system.
{"title":"Hydrodynamic Design and Pulsation Evolution in an Axial-Flow Pump Based On Control Mechanism of Flow-Induced Excitation","authors":"Kexin Pu, Xiangsong Liu, Qipeng Li, Shangxiang Lu, Bin Huang, Dazhuan Wu","doi":"10.1115/1.4065962","DOIUrl":"https://doi.org/10.1115/1.4065962","url":null,"abstract":"\u0000 The physical mechanism, evolution process and control method on pulsation caused by flow-induced excitation vortex in axial flow pump are elaborated by numerical calculation and experiment. The mechanism formulation of flow-induced excitation vibration and the unique hydrodynamic design method of airfoil are proposed with three contrast models. According to the action law of inertial centrifugal force (ICF) in the rotor-stator interaction (RSI) region and guide vane airfoil, the evaluation method between vortex transport, turbulent kinetic energy and flow structure under transient and steady state of internal flow field is established, which navigates the instability of energy intensity determined by the uneven gradient distribution. The distribution characteristics of flow-induced excitation pulsation in the RSI region and the static region are quantitatively verified by experiment. Along the streamwise direction, the excitation loss changes from impact loss to flow loss, with the RSI vortex affected by wake-jet flow (WJF) vortices transforming into inter-vane vortex (IVV) in the guide vane. In pulsation evaluation, the excitation pulsation form changes from blade frequency fBPF to low frequency band. Overall, the generation analysis of the excitation pulsation is realized based on the hydrodynamic optimal design with the comparison of models, which provides guidance for the optimization design of the axial flow pump to reduce vibration and energy consumption of the cooling system.","PeriodicalId":504378,"journal":{"name":"Journal of Fluids Engineering","volume":" 13","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141824666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High fidelity simulation is conducted to investigate liquid jet in crossflow, specifically regarding the rectangular nozzle. The influence of aspect ratio (AR) of nozzles on the atomization characteristics of liquid column in the process of primary breakup is explored by the analysis of the flow structure of crossflow and liquid column. The aspect ratio is ranging from 1 to 8. The results indicate that as the increase of aspect ratio, the disturbance of crossflow to the liquid on the sides is weakened. While the thickness of liquid column also gradually decreases, which enables smaller disturbances to promote droplet shedding. Therefore, surface breakup first weakens and then strengthens. In the column breakup process, the increase of aspect ratio causes crossflow to become the main factor affecting column breakup, and the influence of air pressure gradually weakens. This indicates a shift in the mechanism of surface instability from “Rayleigh-Taylor” (R-T) instability to “Kelvin-Helmholtz” (K-H) instability.
{"title":"Numerical Investigation of the Impact of the Rectangular Nozzle Aspect Ratio On Liquid Jet in Crossflow","authors":"Meng Shao, Zhixia He, Qian Wang","doi":"10.1115/1.4065705","DOIUrl":"https://doi.org/10.1115/1.4065705","url":null,"abstract":"\u0000 High fidelity simulation is conducted to investigate liquid jet in crossflow, specifically regarding the rectangular nozzle. The influence of aspect ratio (AR) of nozzles on the atomization characteristics of liquid column in the process of primary breakup is explored by the analysis of the flow structure of crossflow and liquid column. The aspect ratio is ranging from 1 to 8. The results indicate that as the increase of aspect ratio, the disturbance of crossflow to the liquid on the sides is weakened. While the thickness of liquid column also gradually decreases, which enables smaller disturbances to promote droplet shedding. Therefore, surface breakup first weakens and then strengthens. In the column breakup process, the increase of aspect ratio causes crossflow to become the main factor affecting column breakup, and the influence of air pressure gradually weakens. This indicates a shift in the mechanism of surface instability from “Rayleigh-Taylor” (R-T) instability to “Kelvin-Helmholtz” (K-H) instability.","PeriodicalId":504378,"journal":{"name":"Journal of Fluids Engineering","volume":" 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141366081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wave rotor combustor technology is a new technical means to improve the thermal efficiency of aero-engine by using unsteady flow and constant volume combustion. In this article, the influence of wave rotor combustor channel structure on the mixture formation in the channel was studied by numerical simulation. The results showed that the internal flow field structure and change of any structure channel are similar. Flow separation will occur in all channels, and wake regions will be formed in the channels. The turbulence kinetic energy in the wake region was increased, and the velocity and pressure were decreased, resulted in the vortex in the channel. When the channel width was reduced to half of the original design, the Relative Standard Deviation (RSD) of the mixture was reduced by at least 54.92% compared to the original design, and the global fuel mass fraction in the channel was increased by at least 27.32%. In addition, the fluctuation of discharge pressure was also reduced. The reduction of the channel height does not lead to a significant improvement in the aforementioned results. This study can provide guidance for the structural design of wave rotor combustor channel.
{"title":"Numerical Study On the Effect of Channel Configuration On Mixture Formation of an Axial Flow Wave Rotor Combustor","authors":"Zhan Feng, Jianzhong Li, Erlei Gong, Qian Yao, Xinyu Chen, Yue Chen","doi":"10.1115/1.4065543","DOIUrl":"https://doi.org/10.1115/1.4065543","url":null,"abstract":"\u0000 Wave rotor combustor technology is a new technical means to improve the thermal efficiency of aero-engine by using unsteady flow and constant volume combustion. In this article, the influence of wave rotor combustor channel structure on the mixture formation in the channel was studied by numerical simulation. The results showed that the internal flow field structure and change of any structure channel are similar. Flow separation will occur in all channels, and wake regions will be formed in the channels. The turbulence kinetic energy in the wake region was increased, and the velocity and pressure were decreased, resulted in the vortex in the channel. When the channel width was reduced to half of the original design, the Relative Standard Deviation (RSD) of the mixture was reduced by at least 54.92% compared to the original design, and the global fuel mass fraction in the channel was increased by at least 27.32%. In addition, the fluctuation of discharge pressure was also reduced. The reduction of the channel height does not lead to a significant improvement in the aforementioned results. This study can provide guidance for the structural design of wave rotor combustor channel.","PeriodicalId":504378,"journal":{"name":"Journal of Fluids Engineering","volume":"1 10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140962174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A thrust bearing is a type of rotary bearing that permits rotation between parts and is designed to support a load parallel to the axis of rotation. There is a temperature drop region with the increase in speed. However, previous researchers mainly showed such temperature drop experimentally, and the physics causing such temperature drop is not understood. A full fluid-solid CFX model was developed for a center pivot, tilting pad, and fluid-film thrust-bearing experimental model to study the physics of temperature drop in the transitional region. A novel physics of causing temperature drop in the transitional region was proposed, analyzed, and verified.
{"title":"Study of Temperature Drop Region in Transitional Region in Fluid-film Thrust Bearings","authors":"Xin Deng","doi":"10.1115/1.4065542","DOIUrl":"https://doi.org/10.1115/1.4065542","url":null,"abstract":"\u0000 A thrust bearing is a type of rotary bearing that permits rotation between parts and is designed to support a load parallel to the axis of rotation. There is a temperature drop region with the increase in speed. However, previous researchers mainly showed such temperature drop experimentally, and the physics causing such temperature drop is not understood. A full fluid-solid CFX model was developed for a center pivot, tilting pad, and fluid-film thrust-bearing experimental model to study the physics of temperature drop in the transitional region. A novel physics of causing temperature drop in the transitional region was proposed, analyzed, and verified.","PeriodicalId":504378,"journal":{"name":"Journal of Fluids Engineering","volume":"41 24","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140966114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
H. Abitan, Yisheng Zhang, Simon Lautrup Ribergård, Clara Marika Velte
The trend to conduct volumetric Particle Tracking Velocimetry experiments with ever increasing volumes, at a given particle density, poses increasing challenges on the design of such experiments in terms of the power of the laser source and the image analysis. This, on one hand, requires a reliable model to estimate the signal level that is measured on a CMOS detector from a Mie scattering particle. On the other hand, it requires also a model for estimating the limiting factors upon the image resolution, where a large amount of particles within a 3D volume are mapped into a 2D image. Herein, we present a model that provides an analytical expression to estimate the signal level on a CMOS detector from a Mie scattering particle within an arbitrary large volume in a volumetric Particle Tracking Velocimetry experiment. We begin with a model for planar experiments and extend it into volumetric measurements. Our model considers the effect of the depth of field, particle density, Mie scattering signal and total Mie scattering loss, laser pulse-energy and relevant optical parameters. Later, we investigate the consequence of the Rayleigh criterion upon image resolution when it is applied to particles within a volume of interest. Finally, we demonstrate how we applied our model to estimate the signal level and the limit upon the spatial resolution in three experiments carried-out in our lab.
{"title":"Optical Considerations for Designing Laser-Based Volumetric Particle Tracking Velocimetry","authors":"H. Abitan, Yisheng Zhang, Simon Lautrup Ribergård, Clara Marika Velte","doi":"10.1115/1.4065544","DOIUrl":"https://doi.org/10.1115/1.4065544","url":null,"abstract":"\u0000 The trend to conduct volumetric Particle Tracking Velocimetry experiments with ever increasing volumes, at a given particle density, poses increasing challenges on the design of such experiments in terms of the power of the laser source and the image analysis. This, on one hand, requires a reliable model to estimate the signal level that is measured on a CMOS detector from a Mie scattering particle. On the other hand, it requires also a model for estimating the limiting factors upon the image resolution, where a large amount of particles within a 3D volume are mapped into a 2D image. Herein, we present a model that provides an analytical expression to estimate the signal level on a CMOS detector from a Mie scattering particle within an arbitrary large volume in a volumetric Particle Tracking Velocimetry experiment. We begin with a model for planar experiments and extend it into volumetric measurements. Our model considers the effect of the depth of field, particle density, Mie scattering signal and total Mie scattering loss, laser pulse-energy and relevant optical parameters. Later, we investigate the consequence of the Rayleigh criterion upon image resolution when it is applied to particles within a volume of interest. Finally, we demonstrate how we applied our model to estimate the signal level and the limit upon the spatial resolution in three experiments carried-out in our lab.","PeriodicalId":504378,"journal":{"name":"Journal of Fluids Engineering","volume":"8 20","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141127117","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Maximilian Schenk, G. Giamagas, A. Roccon, A. Soldati, F. Zonta
In this work, we develop a dual-grid approach for the direct numerical simulations (DNS) of tur- bulent multiphase flows in the framework of the phase-field method (PFM). With the dual-grid approach, the solution of the Navier-Stokes equations (flow-field) and of the Cahn-Hilliard equa- tion (phase-field) are performed on two different computational grids. In particular, a base grid - fine enough to resolve the flow down to the Kolmogorov scale - is used for the solution of the Navier-Stokes equations, while a refined grid - required to improve the description of small interfacial structures - is used for the solution of the Cahn-Hilliard equation (phase-field method). The proposed approach is validated, and its computational efficiency is evaluated considering the deformation of a drop in a two-dimensional shear flow. Analyzing the computational time and memory usage, we observe a reduction between ≃30% and ≃40% (with respect to the single-grid approach), depending on the grid refinement factor employed for the phase-field variable. The applicability of the approach to a realistic three-dimensional case is also discussed, by focusing on the breakage of a thin liquid sheet inside a turbulent channel flow. Indications on the grid resolution representing a good compromise between accuracy and computational efficiency in drop-laden turbulence are also provided.
{"title":"Computationally Efficient and Interface Accurate Dual-Grid Phase-Field Simulation of Turbulent Drop-Laden Flows","authors":"Maximilian Schenk, G. Giamagas, A. Roccon, A. Soldati, F. Zonta","doi":"10.1115/1.4065504","DOIUrl":"https://doi.org/10.1115/1.4065504","url":null,"abstract":"\u0000 In this work, we develop a dual-grid approach for the direct numerical simulations (DNS) of tur- bulent multiphase flows in the framework of the phase-field method (PFM). With the dual-grid approach, the solution of the Navier-Stokes equations (flow-field) and of the Cahn-Hilliard equa- tion (phase-field) are performed on two different computational grids. In particular, a base grid - fine enough to resolve the flow down to the Kolmogorov scale - is used for the solution of the Navier-Stokes equations, while a refined grid - required to improve the description of small interfacial structures - is used for the solution of the Cahn-Hilliard equation (phase-field method). The proposed approach is validated, and its computational efficiency is evaluated considering the deformation of a drop in a two-dimensional shear flow. Analyzing the computational time and memory usage, we observe a reduction between ≃30% and ≃40% (with respect to the single-grid approach), depending on the grid refinement factor employed for the phase-field variable. The applicability of the approach to a realistic three-dimensional case is also discussed, by focusing on the breakage of a thin liquid sheet inside a turbulent channel flow. Indications on the grid resolution representing a good compromise between accuracy and computational efficiency in drop-laden turbulence are also provided.","PeriodicalId":504378,"journal":{"name":"Journal of Fluids Engineering","volume":" 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140997312","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Despite the observation of change in the cavitation regime on a heated surface, the specific section of the wall surface that plays a more dominant role in this transition phenomenon remains unknown. This study experimentally investigated the effect of surface temperature of different regions on the cavitating flow in terms of the cavitation regime. The experiments were conducted using a convergent-divergent Venturi nozzle comprising two parts that could be heated independently. The Venturi nozzle could be fully or selectively heated at either the front, where the leading edge of the cavity sheet was located, or the rear, where the cavity sheet developed. The cavitation behavior under different heating conditions was investigated using high-speed visualization and fluctuating pressure measurements. Compared with the non-heated case, which exhibited a sheet-cloud cavitation regime, the cavitation regime on the completely heated Venturi nozzle exhibited transient cavitation. The same transition phenomenon was observed when only the front of the Venturi nozzle was heated. A liquid film was observed beneath the cavity sheet of transient cavitation when only the front portion was heated. In contrast, heating the rear part alone did not induce a change in the cavitation regime. Thus, it appeared that the transition of the cavitation regime on a heated surface was mainly influenced by the temperature increase at the leading edge of the cavity sheet.
{"title":"Experimental Study of the Cavitating Flow on an Independently Heated Venturi Nozzle","authors":"Ning Yang, J. Okajima, Y. Iga","doi":"10.1115/1.4065505","DOIUrl":"https://doi.org/10.1115/1.4065505","url":null,"abstract":"\u0000 Despite the observation of change in the cavitation regime on a heated surface, the specific section of the wall surface that plays a more dominant role in this transition phenomenon remains unknown. This study experimentally investigated the effect of surface temperature of different regions on the cavitating flow in terms of the cavitation regime. The experiments were conducted using a convergent-divergent Venturi nozzle comprising two parts that could be heated independently. The Venturi nozzle could be fully or selectively heated at either the front, where the leading edge of the cavity sheet was located, or the rear, where the cavity sheet developed. The cavitation behavior under different heating conditions was investigated using high-speed visualization and fluctuating pressure measurements. Compared with the non-heated case, which exhibited a sheet-cloud cavitation regime, the cavitation regime on the completely heated Venturi nozzle exhibited transient cavitation. The same transition phenomenon was observed when only the front of the Venturi nozzle was heated. A liquid film was observed beneath the cavity sheet of transient cavitation when only the front portion was heated. In contrast, heating the rear part alone did not induce a change in the cavitation regime. Thus, it appeared that the transition of the cavitation regime on a heated surface was mainly influenced by the temperature increase at the leading edge of the cavity sheet.","PeriodicalId":504378,"journal":{"name":"Journal of Fluids Engineering","volume":" 40","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140996032","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Windage loss and flow characteristics in a disk-type gap featuring scalloped structures are investigated in this paper. Special attention is paid to the size of the scallops and the associated loss models. The respective losses and scallop effects in the gap are explored with various combinations of depths, quantities, and rotating speeds. The results indicate that scallop structures positively contribute to increased windage losses, accounting for more than 60% of the overall losses. An internal spiral vortex band is formed along the scallop wall, with the scallop depth ratio exerting influences on loss, reaching a maximum of 8.1%. The current scallop loss model overlooks the consideration of the total arc length ratio of scallops to the circumference, presenting a limitation, and the maximum relative deviation from numerical simulation results is observed to be 111.4%. An increase in arc length ratio results in a higher total loss, although the loss per individual scallop is diminished, manifesting in reduced vortices and pressure differences. Furthermore, a modified model is proposed to increase the precision of the current loss model. The maximal relative deviations of 13.8% confirm that the modified model is accepted to predict the windage loss in disk-type gaps with scallops. The conclusions offer valuable insights into the structural design of impellers and high-speed electrical machines with superior efficiency.
{"title":"Influence of Scallops On Windage Loss and Flow Characteristics in Disk-type Gap","authors":"Zhuobin Zhao, Qinghua Deng, Jun Li, Zhenping Feng","doi":"10.1115/1.4065450","DOIUrl":"https://doi.org/10.1115/1.4065450","url":null,"abstract":"\u0000 Windage loss and flow characteristics in a disk-type gap featuring scalloped structures are investigated in this paper. Special attention is paid to the size of the scallops and the associated loss models. The respective losses and scallop effects in the gap are explored with various combinations of depths, quantities, and rotating speeds. The results indicate that scallop structures positively contribute to increased windage losses, accounting for more than 60% of the overall losses. An internal spiral vortex band is formed along the scallop wall, with the scallop depth ratio exerting influences on loss, reaching a maximum of 8.1%. The current scallop loss model overlooks the consideration of the total arc length ratio of scallops to the circumference, presenting a limitation, and the maximum relative deviation from numerical simulation results is observed to be 111.4%. An increase in arc length ratio results in a higher total loss, although the loss per individual scallop is diminished, manifesting in reduced vortices and pressure differences. Furthermore, a modified model is proposed to increase the precision of the current loss model. The maximal relative deviations of 13.8% confirm that the modified model is accepted to predict the windage loss in disk-type gaps with scallops. The conclusions offer valuable insights into the structural design of impellers and high-speed electrical machines with superior efficiency.","PeriodicalId":504378,"journal":{"name":"Journal of Fluids Engineering","volume":"74 9","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141008495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A series of laboratory experiments was conducted to investigate the effects of impact energy and other initial controlling parameters on the motion of particle clouds in stagnant water. Experiments were performed for two median sand diameters of D50 = 0.52 mm and 0.74 mm and nozzle diameters of do = 6 mm and 8 mm. Sand masses were converted to an equivalent pipe length with the same diameter as the nozzle, Lo, and a wide range of aspect ratios, Lo/do, between 2 and 93 was tested. The impact energy of sand particles was controlled by the release height of sand particles, and it was quantified by the non-dimensional release height, η, ranging from 1 to 21.5. It was found that particle clouds with higher impact energy had smaller concentration and velocity decay rates. This indicated that by increasing the release height, the momentum transfer between sand particles and the ambient water decreases. The time-series of instantaneous sand velocity were used to determine velocity fluctuations and turbulence intensity of sand particles and a direct correlation was found between sand velocity fluctuations and aspect ratio in particle clouds. The effects of impact energy on the anatomy of the resulted particle clouds were examined in this study. It was found that the cloud width increased dramatically when the impact energy of sand particles with high aspect ratios (i.e., Lo/do > 39) increased. Furthermore, the dispersion of sand particle began earlier as the kinetic energy of sand particles increased at the water surface.
{"title":"Effects of Impact Energy and Aspect Ratio on the Motion of Particle Clouds in Stagnant Water","authors":"Maliheh Sabershahraki, Amir Azimi","doi":"10.1115/1.4065475","DOIUrl":"https://doi.org/10.1115/1.4065475","url":null,"abstract":"\u0000 A series of laboratory experiments was conducted to investigate the effects of impact energy and other initial controlling parameters on the motion of particle clouds in stagnant water. Experiments were performed for two median sand diameters of D50 = 0.52 mm and 0.74 mm and nozzle diameters of do = 6 mm and 8 mm. Sand masses were converted to an equivalent pipe length with the same diameter as the nozzle, Lo, and a wide range of aspect ratios, Lo/do, between 2 and 93 was tested. The impact energy of sand particles was controlled by the release height of sand particles, and it was quantified by the non-dimensional release height, η, ranging from 1 to 21.5. It was found that particle clouds with higher impact energy had smaller concentration and velocity decay rates. This indicated that by increasing the release height, the momentum transfer between sand particles and the ambient water decreases. The time-series of instantaneous sand velocity were used to determine velocity fluctuations and turbulence intensity of sand particles and a direct correlation was found between sand velocity fluctuations and aspect ratio in particle clouds. The effects of impact energy on the anatomy of the resulted particle clouds were examined in this study. It was found that the cloud width increased dramatically when the impact energy of sand particles with high aspect ratios (i.e., Lo/do > 39) increased. Furthermore, the dispersion of sand particle began earlier as the kinetic energy of sand particles increased at the water surface.","PeriodicalId":504378,"journal":{"name":"Journal of Fluids Engineering","volume":"49 8","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141007980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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