The return-channel of a preceding stage in a multi-stage centrifugal compressor has a significant effect on the aerodynamic performance of the current and subsequent stages. However, due to the relatively complex nature of the return-channel configuration with many geometric parameters, no general design guidance is available in the literature. In this study, numerical methods are used to study the effects of different geometric parameters of a return-channel on the performance of a high-flow-coefficient centrifugal compressor. A multi-objective genetic algorithm is applied to optimize the return-channel. The effects of different geometric parameters on the performance are then studied using a sensitivity analysis method. Calculation results show that the residual vortex intensity at the outlet of the return-channel is affected by the geometric angles of the inlet and outlet of the return-channel blades. The flow uniformity at the stage outlet is primarily affected by the geometric angle of the blade outlet and the number of blades. The overall performance of the compressor stage is primarily affected by the geometric angle of the blade inlet and the lateral inclination angle of the cover plate. Calculation results for a two-stage compressor consisting of the optimized first stage and its following stage show that the outlet flow field of the first stage is more uniform than the original first stage. Additionally, at the design operating condition, the polytropic efficiency and pressure ratio of the entire unit increase by 1.07% and 4.07%, respectively. The polytropic efficiency and pressure ratio for the second stage increase by 2.34% and 3.51%, respectively. The impeller head coefficient increases by 7.33%. The theoretical analysis shows that for high-flow-coefficient centrifugal compressors, reducing the residual vortex intensity of the outlet flow field of the return-channel in a stage can significantly improve the off-design performance of the following stage.
{"title":"Effect of the Return-channel Geometric Parameters on the Performance of a Centrifugal Compressor with a High-flow Coefficient","authors":"K. Zhao, Y. Liu, Y. Zhang, Y. Sun, X. Liu, H. Shi","doi":"10.47176/jafm.17.3.2211","DOIUrl":"https://doi.org/10.47176/jafm.17.3.2211","url":null,"abstract":"The return-channel of a preceding stage in a multi-stage centrifugal compressor has a significant effect on the aerodynamic performance of the current and subsequent stages. However, due to the relatively complex nature of the return-channel configuration with many geometric parameters, no general design guidance is available in the literature. In this study, numerical methods are used to study the effects of different geometric parameters of a return-channel on the performance of a high-flow-coefficient centrifugal compressor. A multi-objective genetic algorithm is applied to optimize the return-channel. The effects of different geometric parameters on the performance are then studied using a sensitivity analysis method. Calculation results show that the residual vortex intensity at the outlet of the return-channel is affected by the geometric angles of the inlet and outlet of the return-channel blades. The flow uniformity at the stage outlet is primarily affected by the geometric angle of the blade outlet and the number of blades. The overall performance of the compressor stage is primarily affected by the geometric angle of the blade inlet and the lateral inclination angle of the cover plate. Calculation results for a two-stage compressor consisting of the optimized first stage and its following stage show that the outlet flow field of the first stage is more uniform than the original first stage. Additionally, at the design operating condition, the polytropic efficiency and pressure ratio of the entire unit increase by 1.07% and 4.07%, respectively. The polytropic efficiency and pressure ratio for the second stage increase by 2.34% and 3.51%, respectively. The impeller head coefficient increases by 7.33%. The theoretical analysis shows that for high-flow-coefficient centrifugal compressors, reducing the residual vortex intensity of the outlet flow field of the return-channel in a stage can significantly improve the off-design performance of the following stage.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" 11","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139392318","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cavitation-induced vibration presents a significant challenge in vortex pumps, leading to potential damage to hydraulic components and adverse effects on pump performance. This study aims to investigate the long-term implications of such phenomena. To capture the vibration signals caused by cavitation, we utilized vibration acceleration sensors on the vortex pump and collected data at five predetermined measuring points under three different operating conditions. The analysis used two prominent techniques, fast Fourier transform (FFT) and adaptive optimal kernel time-frequency representation (AOK-TFR), to explore the frequency-domain and time-frequency characteristics of the vibration signals. The findings reveal a notable increase in frequency amplitude at each monitoring point as the flow rate rises. Under cavitation conditions, pronounced vibration characteristics are observed along the y-axis and z-axis of the volute, with maximum vibration intensities of 1.83 m/s² and 1.80 m/s², respectively. The frequency amplitude exhibits non-constant behavior in the time series. Moreover, variations in the time-frequency characteristics are identified with changing flow rates. A distinct signal with a frequency of 750 Hz manifests in the x-axis and y-axis of the volute when the head experiences a 3% reduction from the cavitation level.
气蚀引起的振动是旋涡泵面临的一个重大挑战，可能导致液压元件损坏，并对泵的性能产生不利影响。本研究旨在调查此类现象的长期影响。为了捕捉气蚀引起的振动信号，我们在涡旋泵上安装了振动加速度传感器，并在三种不同的工作条件下在五个预定测量点收集数据。分析中使用了快速傅立叶变换（FFT）和自适应最优核时频表示（AOK-TFR）这两种重要技术来探索振动信号的频域和时频特征。研究结果表明，随着流速的增加，各监测点的频率振幅也明显增加。在空化条件下，沿涡流的 y 轴和 z 轴观察到明显的振动特征，最大振动强度分别为 1.83 m/s² 和 1.80 m/s²。频率振幅在时间序列中表现为非恒定。此外，随着流量的变化，时间频率特性也会发生变化。当水头比空化水平降低 3% 时，在涡槽的 x 轴和 y 轴上会出现频率为 750 Hz 的明显信号。
{"title":"Analysis of Cavitation-induced Vibration Characteristics of a Vortex Pump Based on Adaptive Optimal Kernel Time-frequency Representation","authors":"Y. Wang, †. P.Zhou, C. Zhou, W. Zhou, J. Li","doi":"10.47176/jafm.17.3.2172","DOIUrl":"https://doi.org/10.47176/jafm.17.3.2172","url":null,"abstract":"Cavitation-induced vibration presents a significant challenge in vortex pumps, leading to potential damage to hydraulic components and adverse effects on pump performance. This study aims to investigate the long-term implications of such phenomena. To capture the vibration signals caused by cavitation, we utilized vibration acceleration sensors on the vortex pump and collected data at five predetermined measuring points under three different operating conditions. The analysis used two prominent techniques, fast Fourier transform (FFT) and adaptive optimal kernel time-frequency representation (AOK-TFR), to explore the frequency-domain and time-frequency characteristics of the vibration signals. The findings reveal a notable increase in frequency amplitude at each monitoring point as the flow rate rises. Under cavitation conditions, pronounced vibration characteristics are observed along the y-axis and z-axis of the volute, with maximum vibration intensities of 1.83 m/s² and 1.80 m/s², respectively. The frequency amplitude exhibits non-constant behavior in the time series. Moreover, variations in the time-frequency characteristics are identified with changing flow rates. A distinct signal with a frequency of 750 Hz manifests in the x-axis and y-axis of the volute when the head experiences a 3% reduction from the cavitation level.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"1 4","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139395009","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Samuel, A. Wicaksono, W. A. Kurniawan, E. S. Hadi, T. Tuswan, A. Trimulyono, M. Muryadin
This study discusses the inverted bow design on the combatant hull form. Changes in the shape of the stem angle and flare bow are used as analytical parameters to investigate the ship's performance. Ship resistance and motion will be predicted using the Computational Fluid Dynamics (CFD) approach using the Reynolds Averaged Navier Stokes (RANS) equation and the k-ε turbulence model. The volume of fluid (VOF) method is applied to simulate the change in the free surface between water and air using an overset mesh technique. The ship's movement is limited to sinkage and trim motions, so the movement's accuracy can be predicted. The results revealed that the inverted bow reduced the total resistance by 6.30%, whereas the trim and sinkage showed no significant changes. The breakdown of the reduction ratio showed that friction resistance components were reduced by 10.62%, wave resistance by 44.05%, and viscous-pressure resistance by 45.33%. This highlights the effectiveness of an inverted bow in optimizing wave and viscous pressure, enhancing overall ship performance.
{"title":"Investigation of An Inverted Bow on Frigate Hull Resistance","authors":"S. Samuel, A. Wicaksono, W. A. Kurniawan, E. S. Hadi, T. Tuswan, A. Trimulyono, M. Muryadin","doi":"10.47176/jafm.17.1.2122","DOIUrl":"https://doi.org/10.47176/jafm.17.1.2122","url":null,"abstract":"This study discusses the inverted bow design on the combatant hull form. Changes in the shape of the stem angle and flare bow are used as analytical parameters to investigate the ship's performance. Ship resistance and motion will be predicted using the Computational Fluid Dynamics (CFD) approach using the Reynolds Averaged Navier Stokes (RANS) equation and the k-ε turbulence model. The volume of fluid (VOF) method is applied to simulate the change in the free surface between water and air using an overset mesh technique. The ship's movement is limited to sinkage and trim motions, so the movement's accuracy can be predicted. The results revealed that the inverted bow reduced the total resistance by 6.30%, whereas the trim and sinkage showed no significant changes. The breakdown of the reduction ratio showed that friction resistance components were reduced by 10.62%, wave resistance by 44.05%, and viscous-pressure resistance by 45.33%. This highlights the effectiveness of an inverted bow in optimizing wave and viscous pressure, enhancing overall ship performance.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"77 2","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139128812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The study proposes a new method called MTRMC to simulate flow in rarefied regimes, which are important in various industrial and engineering applications. This new method utilizes a modified collision function with smaller number of inter-molecular collisions, making it more computationally efficient than the widely used direct simulation Monte Carlo (DSMC) method. The MTRMC method is used to analyze the flow over a flat nano-plate at various free stream velocities, ranging from low to supersonic speeds. The results are compared with those from DSMC and time relaxed Monte Carlo (TRMC) schemes, and the findings show that the MTRMC method is in good agreement with the standard schemes, with a significant reduction in computational expense, up to 51% in some cases.
{"title":"On an Efficient Solution of the Boltzmann Equation Using the Modified Time Relaxed Monte Carlo (MTRMC) Scheme","authors":"M. Eskandari, †. S.S.Nourazar","doi":"10.47176/jafm.17.1.1922","DOIUrl":"https://doi.org/10.47176/jafm.17.1.1922","url":null,"abstract":"The study proposes a new method called MTRMC to simulate flow in rarefied regimes, which are important in various industrial and engineering applications. This new method utilizes a modified collision function with smaller number of inter-molecular collisions, making it more computationally efficient than the widely used direct simulation Monte Carlo (DSMC) method. The MTRMC method is used to analyze the flow over a flat nano-plate at various free stream velocities, ranging from low to supersonic speeds. The results are compared with those from DSMC and time relaxed Monte Carlo (TRMC) schemes, and the findings show that the MTRMC method is in good agreement with the standard schemes, with a significant reduction in computational expense, up to 51% in some cases.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"9 4","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139129341","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A novel approach is presented for predicting compressible turbulent flow fields using a neural network-based data-driven method. Accurate prediction in turbulent regions heavily relies on the resolution of available data. Traditional methods, employing image-based techniques by mapping scattered computational fluid dynamics (CFD) data onto Cartesian grids, encounter data scarcity in critical areas such as the boundary layer and wake. Recently, convolutional neural networks (CNN) have gained prominence as the most widely referenced technique in fluid dynamics, utilizing flow field images as datasets for flow field prediction. However, CNN requires datasets with a high pixel density to enhance training accuracy in crucial regions, thereby increasing the input data volume and machine training time. To address this challenge, our proposed method deviates from using flow field images and instead generates datasets directly from the flow field properties of CFD grid points. By employing this approach, several advantages are realized. Firstly, the network benefits from the favorable characteristics of unstructured grids, such as varying point spacing near the object surface and in the far field, which effectively reduces the amount of input data and consequently the machine training cost. Secondly, the construction of the training dataset eliminates the need for interpolation or extrapolation, thereby preserving the accuracy of CFD data. In this case, a simple multilayer perceptron can be trained using the proposed dataset. Various flow field properties, including static pressure, turbulent kinetic energy, and velocity components, can be predicted with high accuracy within a few seconds.
{"title":"A Data-Driven Machine Learning Approach for Turbulent Flow Field Prediction Based on Direct Computational Fluid Dynamics Database","authors":"M. Nemati, †. A.Jahangirian","doi":"10.47176/jafm.17.1.2109","DOIUrl":"https://doi.org/10.47176/jafm.17.1.2109","url":null,"abstract":"A novel approach is presented for predicting compressible turbulent flow fields using a neural network-based data-driven method. Accurate prediction in turbulent regions heavily relies on the resolution of available data. Traditional methods, employing image-based techniques by mapping scattered computational fluid dynamics (CFD) data onto Cartesian grids, encounter data scarcity in critical areas such as the boundary layer and wake. Recently, convolutional neural networks (CNN) have gained prominence as the most widely referenced technique in fluid dynamics, utilizing flow field images as datasets for flow field prediction. However, CNN requires datasets with a high pixel density to enhance training accuracy in crucial regions, thereby increasing the input data volume and machine training time. To address this challenge, our proposed method deviates from using flow field images and instead generates datasets directly from the flow field properties of CFD grid points. By employing this approach, several advantages are realized. Firstly, the network benefits from the favorable characteristics of unstructured grids, such as varying point spacing near the object surface and in the far field, which effectively reduces the amount of input data and consequently the machine training cost. Secondly, the construction of the training dataset eliminates the need for interpolation or extrapolation, thereby preserving the accuracy of CFD data. In this case, a simple multilayer perceptron can be trained using the proposed dataset. Various flow field properties, including static pressure, turbulent kinetic energy, and velocity components, can be predicted with high accuracy within a few seconds.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"43 11","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139127960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The plunger valve has an important role in a large compressor system as its operating characteristics directly affect the aerodynamic boundary condition of the compressor equipment. In this study, dynamic modeling and analysis method of the plunger valve are proposed for an accurate control of the system. By considering the interaction between the dynamic flow in the valve and actuator action, a lumped parameter model for the fluid–structure interaction force and multibody dynamic model of the actuator are developed based on intrinsic correlation parameters. A combination analysis to simultaneously predict valve flow and actuator dynamic characteristics is proposed. The predicted results are in a good agreement with experimental data, which validates the proposed model and analysis method. The analysis results show that the coupling effect between the valve flow and actuator is significant and has an important role in valve control, particularly when the valve opening is smaller. Compared to the experimental data and computational fluid dynamics results, the presented methods are accurate for valve control and effective for prediction of flow rate.
{"title":"Dynamic Modeling and Combination Analysis of Plunger Valve Considering Both Flow and Actuator","authors":"Y. Ren, C. Bai, H. Zhang","doi":"10.47176/jafm.17.1.1998","DOIUrl":"https://doi.org/10.47176/jafm.17.1.1998","url":null,"abstract":"The plunger valve has an important role in a large compressor system as its operating characteristics directly affect the aerodynamic boundary condition of the compressor equipment. In this study, dynamic modeling and analysis method of the plunger valve are proposed for an accurate control of the system. By considering the interaction between the dynamic flow in the valve and actuator action, a lumped parameter model for the fluid–structure interaction force and multibody dynamic model of the actuator are developed based on intrinsic correlation parameters. A combination analysis to simultaneously predict valve flow and actuator dynamic characteristics is proposed. The predicted results are in a good agreement with experimental data, which validates the proposed model and analysis method. The analysis results show that the coupling effect between the valve flow and actuator is significant and has an important role in valve control, particularly when the valve opening is smaller. Compared to the experimental data and computational fluid dynamics results, the presented methods are accurate for valve control and effective for prediction of flow rate.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"18 12","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139128957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The aim of the present research work is to understand the intricacies of fluid flow through a rectangular channel that has been partially filled with a metal foam block of different blockage ratio (0.16-1), with a pore density (5–30 Pores Per Inch i.e. PPI), along with varying inlet velocity (6.5–12.5 m/s). For the porous region, numerical solutions are acquired using the Darcy Extended Forchheimer model. The Navier-Stokes equation is used in the non-porous zone. Different flow behaviours were seen as a function of PPI, height, and inlet velocity. The pressure drop increases with inlet velocity, PPI, and block height, with a maximum value of approximately 4.5 kPa for the case of 30 PPI, 12.5 m/s, and a blockage ratio of 1. Results show that the existence and location of the formation of eddies depends on the inlet velocity, PPI, and blockage ratio. Such studies have been reported less and will aid research on forced convection through a channel partially filled with metal foam and optimisation studies between increased heat transmission and the additional pressure drop for the same by providing a detailed fluid flow analysis.
{"title":"3D Numerical Modelling of Turbulent Flow in a Channel Partially Filled with Different Blockage Ratios of Metal Foam","authors":"A. Narkhede, †. N.Gnanasekaran","doi":"10.47176/jafm.17.3.2189","DOIUrl":"https://doi.org/10.47176/jafm.17.3.2189","url":null,"abstract":"The aim of the present research work is to understand the intricacies of fluid flow through a rectangular channel that has been partially filled with a metal foam block of different blockage ratio (0.16-1), with a pore density (5–30 Pores Per Inch i.e. PPI), along with varying inlet velocity (6.5–12.5 m/s). For the porous region, numerical solutions are acquired using the Darcy Extended Forchheimer model. The Navier-Stokes equation is used in the non-porous zone. Different flow behaviours were seen as a function of PPI, height, and inlet velocity. The pressure drop increases with inlet velocity, PPI, and block height, with a maximum value of approximately 4.5 kPa for the case of 30 PPI, 12.5 m/s, and a blockage ratio of 1. Results show that the existence and location of the formation of eddies depends on the inlet velocity, PPI, and blockage ratio. Such studies have been reported less and will aid research on forced convection through a channel partially filled with metal foam and optimisation studies between increased heat transmission and the additional pressure drop for the same by providing a detailed fluid flow analysis.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"3 6","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139395511","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Xue, B. Cui, Z. Zhu, R. Wang, Z. Yang, J. Hu, X. Su
The hydraulic turbine has been used extensively in the field of energy conservation. For turbines that have low heads and large discharge, improving recovery efficiency and stability is crucial due to their significant hydraulic impact. This paper provides a detailed analysis of the correlation between the influence of radial guide vanes on the stability of low-head, large-discharge turbines focusing on hydraulic performance and energy dissipation before and after the implementation of guide vanes. Moreover, in this paper, two types of turbines, with and without guide vanes, were designed considering the desulfurization scenario. Hydraulic efficiency, radial force, and internal flow field mechanics were numerically studied, and validated through experiments. The results reveal that the working range of the hydraulic turbine could be widened and the energy recovery efficiency improved by a maximum of 3.11% in the small flow rate under the action of guide vanes. Furthermore, it results in a substantial reduction in the radial force of the impeller. Subsequently, the variation in entropy production of different components under full flow rate conditions was compared between the models with and without guide vanes. The total energy consumption decreases sharply under overall working conditions due to the flow control ability of guide vanes affecting the flow state. The entropy production rate of the impeller remains the largest regardless of the presence of a guide vane in the turbine. The vortices inside the guide vanes increase obviously with the flow rate increase.
{"title":"Effect of the Guide Vane on the Hydraulic Stability of a Low-head, Large-discharge Industrial Hydraulic Turbine","authors":"L. Xue, B. Cui, Z. Zhu, R. Wang, Z. Yang, J. Hu, X. Su","doi":"10.47176/jafm.17.3.2056","DOIUrl":"https://doi.org/10.47176/jafm.17.3.2056","url":null,"abstract":"The hydraulic turbine has been used extensively in the field of energy conservation. For turbines that have low heads and large discharge, improving recovery efficiency and stability is crucial due to their significant hydraulic impact. This paper provides a detailed analysis of the correlation between the influence of radial guide vanes on the stability of low-head, large-discharge turbines focusing on hydraulic performance and energy dissipation before and after the implementation of guide vanes. Moreover, in this paper, two types of turbines, with and without guide vanes, were designed considering the desulfurization scenario. Hydraulic efficiency, radial force, and internal flow field mechanics were numerically studied, and validated through experiments. The results reveal that the working range of the hydraulic turbine could be widened and the energy recovery efficiency improved by a maximum of 3.11% in the small flow rate under the action of guide vanes. Furthermore, it results in a substantial reduction in the radial force of the impeller. Subsequently, the variation in entropy production of different components under full flow rate conditions was compared between the models with and without guide vanes. The total energy consumption decreases sharply under overall working conditions due to the flow control ability of guide vanes affecting the flow state. The entropy production rate of the impeller remains the largest regardless of the presence of a guide vane in the turbine. The vortices inside the guide vanes increase obviously with the flow rate increase.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"48 5","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139395884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Lu, Q. Liu, Z. Lu, R. Tao, F. Jin, D. Zhu, R. Xiao
An oscillating water column (OWC) is typical of axial rotor turbines, which are used to convert ocean wave energy into electrical energy. This device impacts downstream pressure pulsations when its rotor becomes eccentric. This study compared the details of pressure pulsations downstream of eccentric and non-eccentric rotors under three operating conditions: low flow A, high-efficiency flow B, and high flow C. Computational fluid dynamics (CFD) simulations based on the pulsation tracking network (PTN) method were used for the OWC device to compare the experimental results. The results indicate downstream pressure pulsations were mostly dominated by the blade frequency in non-eccentric low-flow cases. In the other eccentric operating conditions, downstream pressure pulsations were mainly dominated by the 2-, 3.6-, 6-, and 7-times rotation frequencies and the 0.5-times blade frequency. The phase change of downstream pressure pulsations in eccentric and non-eccentric conditions is consistent with the flow direction. The phase change is relatively uniform and steady before eccentricity and becomes turbulent after eccentricity, which affects its steadiness. In this study, the OWC device did not significantly change with or without rotor eccentricity at a 1-time blade frequency intensity; however, at a 1-time rotation frequency, the OWC device showed a significant increase in the pressure pulsation amplitude after rotor eccentricity. The study of the dominant frequency, amplitude, and phase of pressure pulsations in OWC devices with eccentric rotors can help prevent excessive pressure pulsations that can lead to incidents.
{"title":"Pressure Pulsation Analysis of Oscillating Water Column Rotor Eccentricity Based on the Pulsation Tracking Network Method","authors":"J. Lu, Q. Liu, Z. Lu, R. Tao, F. Jin, D. Zhu, R. Xiao","doi":"10.47176/jafm.17.3.2070","DOIUrl":"https://doi.org/10.47176/jafm.17.3.2070","url":null,"abstract":"An oscillating water column (OWC) is typical of axial rotor turbines, which are used to convert ocean wave energy into electrical energy. This device impacts downstream pressure pulsations when its rotor becomes eccentric. This study compared the details of pressure pulsations downstream of eccentric and non-eccentric rotors under three operating conditions: low flow A, high-efficiency flow B, and high flow C. Computational fluid dynamics (CFD) simulations based on the pulsation tracking network (PTN) method were used for the OWC device to compare the experimental results. The results indicate downstream pressure pulsations were mostly dominated by the blade frequency in non-eccentric low-flow cases. In the other eccentric operating conditions, downstream pressure pulsations were mainly dominated by the 2-, 3.6-, 6-, and 7-times rotation frequencies and the 0.5-times blade frequency. The phase change of downstream pressure pulsations in eccentric and non-eccentric conditions is consistent with the flow direction. The phase change is relatively uniform and steady before eccentricity and becomes turbulent after eccentricity, which affects its steadiness. In this study, the OWC device did not significantly change with or without rotor eccentricity at a 1-time blade frequency intensity; however, at a 1-time rotation frequency, the OWC device showed a significant increase in the pressure pulsation amplitude after rotor eccentricity. The study of the dominant frequency, amplitude, and phase of pressure pulsations in OWC devices with eccentric rotors can help prevent excessive pressure pulsations that can lead to incidents.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"95 9","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139454288","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this study, the Large Eddy Simulation (LES) model in OpenFOAM was used to investigate the scale effects in the physical modeling of recirculating shallow flow at low Froude numbers. A laboratory test of turbulent flow through a submerged conical island with a Reynolds number of 6,210 was selected. The lab prototype was scaled with factors of 3 and 10 for both undistorted and distorted models. Our study employed the Froude similarity as the gravitational force is more dominant than the others (viscous, drag, and cohesion forces). Because the fluid (water) used for the prototype and model is the same, it is impossible to match the Reynolds, Weber, and Froude numbers simultaneously, resulting in the scale effects. For a scale of 1:1, the LES model could simulate the experimental data by appropriately capturing the vortices behind the conical island. For the undistorted models with scales of 3 and 10, the numerical model captured weaker magnitudes of vortices than the 1:1 scale, indicated by the discrepancies in velocity. In fact, the magnitudes of vortices became weaker with the distorted models. We also observed a significant increment in energy loss behind the conical island (where recirculating flows exist) as the scale increased. However, no significant discrepancies in velocity were observed between the results of the 1:1 scale and the scaled models in front of the conical island, where vortices were absent. These results indicate that the scale effects due to the Froude similarity are quite significant provided that recirculating turbulent flow occurs.
{"title":"Scale Effects Investigation in Physical Modeling of Recirculating Shallow Flow Using Large Eddy Simulation Technique","authors":"R. A. Tartandyo, B. M. Ginting, J. Zulfan","doi":"10.47176/jafm.17.1.1980","DOIUrl":"https://doi.org/10.47176/jafm.17.1.1980","url":null,"abstract":"In this study, the Large Eddy Simulation (LES) model in OpenFOAM was used to investigate the scale effects in the physical modeling of recirculating shallow flow at low Froude numbers. A laboratory test of turbulent flow through a submerged conical island with a Reynolds number of 6,210 was selected. The lab prototype was scaled with factors of 3 and 10 for both undistorted and distorted models. Our study employed the Froude similarity as the gravitational force is more dominant than the others (viscous, drag, and cohesion forces). Because the fluid (water) used for the prototype and model is the same, it is impossible to match the Reynolds, Weber, and Froude numbers simultaneously, resulting in the scale effects. For a scale of 1:1, the LES model could simulate the experimental data by appropriately capturing the vortices behind the conical island. For the undistorted models with scales of 3 and 10, the numerical model captured weaker magnitudes of vortices than the 1:1 scale, indicated by the discrepancies in velocity. In fact, the magnitudes of vortices became weaker with the distorted models. We also observed a significant increment in energy loss behind the conical island (where recirculating flows exist) as the scale increased. However, no significant discrepancies in velocity were observed between the results of the 1:1 scale and the scaled models in front of the conical island, where vortices were absent. These results indicate that the scale effects due to the Froude similarity are quite significant provided that recirculating turbulent flow occurs.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"96 7","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139126108","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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