The distribution of wind speed in the Atmospheric Boundary Layer - ABL has an essential role in the structural design and modeling of chimneys in thermal power plants. As a case study, the recently rehabilitated West Thermal Power Plant in Bucharest was selected. For the numerical modeling of the wind effect, a database was developed with the atmospheric parameters monitored for more than two years, in the selected area. The known pressure coefficients - Cp for a chimney are only valid for some conventional forms. In the present paper for the numerical modeling of the Cp coefficient and of the wind velocity coefficient, the real surface of the chimney was analyzed, considering also its roughness. A significant effect of the pressure distribution, known as the suction effect, was observed. The vertical distribution of the horizontal component of wind speed is strongly influenced by the presence of nearby buildings. They act as a roughness effect by producing air turbulence, separating the flow and inducing the “wake effect”. This phenomenon produces a variation of the average parameters of wind speed and turbulence, depending on the height and distribution of the buildings. For a proper modeling, some details are mentioned regarding the characteristics and dimensions of the analyzed chimney, associated with the land surface and its topography, with the wind speed and the structure of the chimney. Next, some criteria for modeling and selecting the geometric scale are mentioned, followed by some details on the meshing solution for the CFD modeling. A fine mesh is preferred for the inner and outer surface of the chimney in the bottom area, around the chimney, with a quality of about 0.75 for each model tested. The quality of the element is determined with a determinant of the Jacobian matrix, as a measure of the distortion of the shape of the elements. The inlet profile of dissipation rate ε produced by the turbulence was considered from the approximation of Richards and Hoxey. Knowing the wind velocity distribution and the coefficient of force exerted on the chimney, the acting force of the wind is determined. Some results obtained by numerical modeling are mentioned in the last part of the paper on wind velocity distribution, pressure values and force distribution, as altitude functions. The obtained results are in agreement with the experimental data, the highest difference being of approximately 3.43 %, in the top of the chimney, depending on the margin of the discretization field.
{"title":"Numerical Simulation of Wind Effect Over Industrial Chimneys in Cet West Bucharest","authors":"V. Radulescu","doi":"10.1115/fedsm2021-65618","DOIUrl":"https://doi.org/10.1115/fedsm2021-65618","url":null,"abstract":"\u0000 The distribution of wind speed in the Atmospheric Boundary Layer - ABL has an essential role in the structural design and modeling of chimneys in thermal power plants. As a case study, the recently rehabilitated West Thermal Power Plant in Bucharest was selected. For the numerical modeling of the wind effect, a database was developed with the atmospheric parameters monitored for more than two years, in the selected area. The known pressure coefficients - Cp for a chimney are only valid for some conventional forms. In the present paper for the numerical modeling of the Cp coefficient and of the wind velocity coefficient, the real surface of the chimney was analyzed, considering also its roughness. A significant effect of the pressure distribution, known as the suction effect, was observed. The vertical distribution of the horizontal component of wind speed is strongly influenced by the presence of nearby buildings. They act as a roughness effect by producing air turbulence, separating the flow and inducing the “wake effect”. This phenomenon produces a variation of the average parameters of wind speed and turbulence, depending on the height and distribution of the buildings. For a proper modeling, some details are mentioned regarding the characteristics and dimensions of the analyzed chimney, associated with the land surface and its topography, with the wind speed and the structure of the chimney. Next, some criteria for modeling and selecting the geometric scale are mentioned, followed by some details on the meshing solution for the CFD modeling. A fine mesh is preferred for the inner and outer surface of the chimney in the bottom area, around the chimney, with a quality of about 0.75 for each model tested. The quality of the element is determined with a determinant of the Jacobian matrix, as a measure of the distortion of the shape of the elements. The inlet profile of dissipation rate ε produced by the turbulence was considered from the approximation of Richards and Hoxey. Knowing the wind velocity distribution and the coefficient of force exerted on the chimney, the acting force of the wind is determined. Some results obtained by numerical modeling are mentioned in the last part of the paper on wind velocity distribution, pressure values and force distribution, as altitude functions. The obtained results are in agreement with the experimental data, the highest difference being of approximately 3.43 %, in the top of the chimney, depending on the margin of the discretization field.","PeriodicalId":23636,"journal":{"name":"Volume 2: Fluid Applications and Systems; Fluid Measurement and Instrumentation","volume":"36 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86802136","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 wind-tunnel experimental study was performed to investigate the impact of the surge and sway motions of a wind turbine model on the power output, rotor thrust and wake characteristics. A wind turbine model was mounted on a translation platform to simulate the surge and sway motions under given amplitude and frequency. The power output and rotor thrust of the turbine model subjected to surge and sway motions were measured by using a DC variable electronic load and a six-component force sensor, respectively. For comparison, these measurements were also performed in a bottom-fixed wind turbine. The results show that the mean power output and mean rotor thrust of the turbine model under surge and sway motions are almost the same as those of the bottom-fixed turbine. However, the thrust fluctuation amplitude of the turbine model under surge motion is significantly higher than those of the turbine model under sway motion and the bottom-fixed turbine. In addition, the wake characteristics of the turbine model were also investigated by using a particle image velocimetry system. The results show that the surge and sway motions have slight effect on the near and intermediate wake of the turbine model in the horizontal plane at the rotor hub height.
{"title":"Aerodynamic Performance and Wake Characteristics of a Wind Turbine Model Subjected to Surge and Sway Motions","authors":"Haoran Meng, Hao Su, Jia Guo, T. Qu, Li-ping Lei","doi":"10.1115/fedsm2021-65608","DOIUrl":"https://doi.org/10.1115/fedsm2021-65608","url":null,"abstract":"\u0000 A wind-tunnel experimental study was performed to investigate the impact of the surge and sway motions of a wind turbine model on the power output, rotor thrust and wake characteristics. A wind turbine model was mounted on a translation platform to simulate the surge and sway motions under given amplitude and frequency. The power output and rotor thrust of the turbine model subjected to surge and sway motions were measured by using a DC variable electronic load and a six-component force sensor, respectively. For comparison, these measurements were also performed in a bottom-fixed wind turbine. The results show that the mean power output and mean rotor thrust of the turbine model under surge and sway motions are almost the same as those of the bottom-fixed turbine. However, the thrust fluctuation amplitude of the turbine model under surge motion is significantly higher than those of the turbine model under sway motion and the bottom-fixed turbine. In addition, the wake characteristics of the turbine model were also investigated by using a particle image velocimetry system. The results show that the surge and sway motions have slight effect on the near and intermediate wake of the turbine model in the horizontal plane at the rotor hub height.","PeriodicalId":23636,"journal":{"name":"Volume 2: Fluid Applications and Systems; Fluid Measurement and Instrumentation","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85442550","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}
Puyuan Wu, Jun Chen, P. Sojka, Yang Li, Hongjun Cao
Hundreds of millions of Air conditioning (AC) systems are produced each year. Many of them, especially small AC appliances, use rotary compressors as the system’s heat pump due to their simple structure and high efficiency in a small system. Lubricant oil is used in the rotary compressor to lubricate the moving parts, such as the crankshaft and the rolling piston, and to seal the clearance between the sliding parts, e.g., the clearance between the rolling piston and the cylinder, and the vane and the cylinder. As the compressed refrigerant vapor is discharged from the cylinder through the discharge port, part of lubricant oil in the cylinder would be carried by the vapor and atomize into small droplets in the lower cavity during the discharge process, which is complicated and highly-coupled. Some of these oil droplets would ultimately be exhausted from the compressor and enter other parts in the system, reducing the compressor reliability and deteriorating the heat transfer of the condenser and the evaporator in the system. Our previous research studied the atomization of the lubricant oil during the discharge process in the compressor’s lower cavity. However, the oil droplets’ behavior downstream of the lower cavity is unknown. Thus, studying the oil droplets’ behavior after passing through the rotor/stator can help understand how the rotor/stator would affect the droplet size distribution and movement, thus controlling the flow rate of escaped oil droplets. In this study, a hot gas bypass test rig is built to run a modified rotary compressor with sapphire windows right above the rotor/stator. The oil droplets’ size distribution and movement along the radial direction are obtained at the shaft’s rotating frequency of 30 and 60 Hz by shadowgraph. It is found that droplet size at 30 and 60 Hz varies little in the inner region of the rotor/stator clearance and would increase sharply above the clearance and keep increasing in the outer region of the clearance. More importantly, droplet velocity has a downward velocity component at the inner region and an upward velocity component at the outer region of the rotor/stator clearance. With the result of droplet size distribution and droplet velocity above the rotor/stator, we propose the model of the oil droplet’s path above the rotor/stator, which can be understood as the coupling of a swirling jet and a rotating disk.
{"title":"Experimental Measurement of Oil Droplets Size and Velocity Above the Rotor/Stator in a Rotary Compressor","authors":"Puyuan Wu, Jun Chen, P. Sojka, Yang Li, Hongjun Cao","doi":"10.1115/fedsm2021-65874","DOIUrl":"https://doi.org/10.1115/fedsm2021-65874","url":null,"abstract":"\u0000 Hundreds of millions of Air conditioning (AC) systems are produced each year. Many of them, especially small AC appliances, use rotary compressors as the system’s heat pump due to their simple structure and high efficiency in a small system. Lubricant oil is used in the rotary compressor to lubricate the moving parts, such as the crankshaft and the rolling piston, and to seal the clearance between the sliding parts, e.g., the clearance between the rolling piston and the cylinder, and the vane and the cylinder. As the compressed refrigerant vapor is discharged from the cylinder through the discharge port, part of lubricant oil in the cylinder would be carried by the vapor and atomize into small droplets in the lower cavity during the discharge process, which is complicated and highly-coupled. Some of these oil droplets would ultimately be exhausted from the compressor and enter other parts in the system, reducing the compressor reliability and deteriorating the heat transfer of the condenser and the evaporator in the system. Our previous research studied the atomization of the lubricant oil during the discharge process in the compressor’s lower cavity. However, the oil droplets’ behavior downstream of the lower cavity is unknown. Thus, studying the oil droplets’ behavior after passing through the rotor/stator can help understand how the rotor/stator would affect the droplet size distribution and movement, thus controlling the flow rate of escaped oil droplets. In this study, a hot gas bypass test rig is built to run a modified rotary compressor with sapphire windows right above the rotor/stator. The oil droplets’ size distribution and movement along the radial direction are obtained at the shaft’s rotating frequency of 30 and 60 Hz by shadowgraph. It is found that droplet size at 30 and 60 Hz varies little in the inner region of the rotor/stator clearance and would increase sharply above the clearance and keep increasing in the outer region of the clearance. More importantly, droplet velocity has a downward velocity component at the inner region and an upward velocity component at the outer region of the rotor/stator clearance. With the result of droplet size distribution and droplet velocity above the rotor/stator, we propose the model of the oil droplet’s path above the rotor/stator, which can be understood as the coupling of a swirling jet and a rotating disk.","PeriodicalId":23636,"journal":{"name":"Volume 2: Fluid Applications and Systems; Fluid Measurement and Instrumentation","volume":"31 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75639630","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}
M. Lewandowski, Paul J. Kristo, Abdullah G. Weiss, M. Kimber
The near field mixing phenomenon created by a round jet with three slot lobes exhausting into a crossflow are investigated at a velocity ratio of 0.5. Time-resolved particle image velocimetry measurements provide instantaneous velocity fields of the slotted jet in crossflow, allowing for evaluation of the first and second order turbulent statistics in two perpendicular planes of interest. The independently controlled jet exit and crossflow inlet are first characterized extensively to confirm the velocity ratio and anticipated momentum exchanges. Spanwise and transverse mean velocity profiles reveal that the interaction of the three slot lobes and the center round jet primarily occur in the immediate jet exit region, though residual effects are also found in the wake. Evaluation of the Reynold stresses aims to quantify the near region mixing between the jets collated geometric features and their interaction with the crossflow. Frequency analysis reveals that low-frequency harmonics in the wake region provide greater energy contributions than that of the higher-frequency harmonics found along the leading edge shear layer. This behavior is attributed to the low velocity ratio, where the freestream velocity is twice as large as the jet exit velocity. The experimental data and observations herein serve analogous computational modeling efforts for the slotted jet in crossflow at low velocity ratios, with ample information to inform necessary boundary conditions, fluid properties, and flow fields for validation.
{"title":"Time Resolved PIV Measurements of a Slot Lobed Jet Issuing Into a Crossflow","authors":"M. Lewandowski, Paul J. Kristo, Abdullah G. Weiss, M. Kimber","doi":"10.1115/fedsm2021-65783","DOIUrl":"https://doi.org/10.1115/fedsm2021-65783","url":null,"abstract":"\u0000 The near field mixing phenomenon created by a round jet with three slot lobes exhausting into a crossflow are investigated at a velocity ratio of 0.5. Time-resolved particle image velocimetry measurements provide instantaneous velocity fields of the slotted jet in crossflow, allowing for evaluation of the first and second order turbulent statistics in two perpendicular planes of interest. The independently controlled jet exit and crossflow inlet are first characterized extensively to confirm the velocity ratio and anticipated momentum exchanges. Spanwise and transverse mean velocity profiles reveal that the interaction of the three slot lobes and the center round jet primarily occur in the immediate jet exit region, though residual effects are also found in the wake. Evaluation of the Reynold stresses aims to quantify the near region mixing between the jets collated geometric features and their interaction with the crossflow. Frequency analysis reveals that low-frequency harmonics in the wake region provide greater energy contributions than that of the higher-frequency harmonics found along the leading edge shear layer. This behavior is attributed to the low velocity ratio, where the freestream velocity is twice as large as the jet exit velocity. The experimental data and observations herein serve analogous computational modeling efforts for the slotted jet in crossflow at low velocity ratios, with ample information to inform necessary boundary conditions, fluid properties, and flow fields for validation.","PeriodicalId":23636,"journal":{"name":"Volume 2: Fluid Applications and Systems; Fluid Measurement and Instrumentation","volume":"47 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77358466","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}
It is well known that Rayleigh-Benard convection with perturbations yields Lagrangian chaotic transport, and the mechanism of inducing chaotic transport has been numerically clarified by lobe dynamics [2]. On the other hand, the mechanism of such Lagrangian transport has not been enough studied by experiments. In our previous work [16], we made an experimental study to investigate the Lagrangian transport appeared in the two-dimensional Rayleigh-Benard convection by giving oscillation on the velocity fields and showed that there exist Lagrangian Coherent Structures (LCSs) which correspond to invariant manifolds of non-autonomous systems. We also showed that the LCSs entangle with each other around cell boundaries. In this paper, we further explore the global invariant structures of the perturbed Rayleigh-Benard convection by clarifying the details on the LCSs and explain how the fluid transport obeys lobe dynamics. Finally, we propose a novel Hamiltonian model for the two-dimensional perturbed Rayleigh-Benard convection that enables to elucidate the global structures detected by experiments.
{"title":"Experimental Investigation of Lagrangian Coherent Structures and Lobe Dynamics in Perturbed Rayleigh-Benard Convection","authors":"Masahito Watanabe, Hiroaki Yoshimura","doi":"10.1115/fedsm2021-64945","DOIUrl":"https://doi.org/10.1115/fedsm2021-64945","url":null,"abstract":"\u0000 It is well known that Rayleigh-Benard convection with perturbations yields Lagrangian chaotic transport, and the mechanism of inducing chaotic transport has been numerically clarified by lobe dynamics [2]. On the other hand, the mechanism of such Lagrangian transport has not been enough studied by experiments. In our previous work [16], we made an experimental study to investigate the Lagrangian transport appeared in the two-dimensional Rayleigh-Benard convection by giving oscillation on the velocity fields and showed that there exist Lagrangian Coherent Structures (LCSs) which correspond to invariant manifolds of non-autonomous systems. We also showed that the LCSs entangle with each other around cell boundaries. In this paper, we further explore the global invariant structures of the perturbed Rayleigh-Benard convection by clarifying the details on the LCSs and explain how the fluid transport obeys lobe dynamics. Finally, we propose a novel Hamiltonian model for the two-dimensional perturbed Rayleigh-Benard convection that enables to elucidate the global structures detected by experiments.","PeriodicalId":23636,"journal":{"name":"Volume 2: Fluid Applications and Systems; Fluid Measurement and Instrumentation","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80376149","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 pressure distribution on sluice gate walls was investigated in this paper, based on CFD simulations. The flow characteristics impacting the pressure distribution were analyzed. Based on this analyzation, a new parametrization approach for the gate pressure distribution is derived for both, standard sluice gates and inclined sluice gates. Based on these investigations the impact of 3D flow characteristics on the pressure profile at the sluice gate wall is presented and discussed in detail.
{"title":"Impact of Flow Characteristics on the Pressure Distribution on Sluice Gates","authors":"M. Steppert, P. Epple, A. Malcherek","doi":"10.1115/fedsm2021-65396","DOIUrl":"https://doi.org/10.1115/fedsm2021-65396","url":null,"abstract":"\u0000 The pressure distribution on sluice gate walls was investigated in this paper, based on CFD simulations. The flow characteristics impacting the pressure distribution were analyzed. Based on this analyzation, a new parametrization approach for the gate pressure distribution is derived for both, standard sluice gates and inclined sluice gates. Based on these investigations the impact of 3D flow characteristics on the pressure profile at the sluice gate wall is presented and discussed in detail.","PeriodicalId":23636,"journal":{"name":"Volume 2: Fluid Applications and Systems; Fluid Measurement and Instrumentation","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84296813","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}
Present work aims to investigate the hydro acoustic behavior of a typical low specific speed radial type centrifugal pump with narrow channel impeller passage. The blade design parameters play an important role in hydraulic noise generation by a low specific speed radial pump with narrow impeller channels. Though, these pumps are hydraulically efficient for a given design point, the hydraulic noise production may be higher at duty point. The blade passage length along with the outlet width of the impeller are the two main design parameters of a radial impeller with narrow channels, which can impact the flow quality along the impeller blade passage. To understand the effect of the narrow channel, initially steady state simulation is conducted to predict and validate the hydraulic performance. Then transient simulations were conducted using Detached Eddy Simulation (DES) using STAR-CCM+ to predict the hydro acoustic behavior of the pump in terms of pressure fluctuations and far field noise spectra of the pump at specific points. The velocity profiles along the impeller channels, shows the formation of wake region, which strongly affects the jet wake flow phenomenon near impeller trailing edge. This results in high pressure fluctuations near impeller outlet.
{"title":"Influence of the Blade Design Parameters on Hydraulic Noise Generation by a Low Specific Speed Radial Pump With Narrow Channel Flow","authors":"Rajavamsi Gangipamula, Pritanshu Ranjan, R. Patil","doi":"10.1115/fedsm2021-65670","DOIUrl":"https://doi.org/10.1115/fedsm2021-65670","url":null,"abstract":"\u0000 Present work aims to investigate the hydro acoustic behavior of a typical low specific speed radial type centrifugal pump with narrow channel impeller passage. The blade design parameters play an important role in hydraulic noise generation by a low specific speed radial pump with narrow impeller channels. Though, these pumps are hydraulically efficient for a given design point, the hydraulic noise production may be higher at duty point. The blade passage length along with the outlet width of the impeller are the two main design parameters of a radial impeller with narrow channels, which can impact the flow quality along the impeller blade passage. To understand the effect of the narrow channel, initially steady state simulation is conducted to predict and validate the hydraulic performance. Then transient simulations were conducted using Detached Eddy Simulation (DES) using STAR-CCM+ to predict the hydro acoustic behavior of the pump in terms of pressure fluctuations and far field noise spectra of the pump at specific points. The velocity profiles along the impeller channels, shows the formation of wake region, which strongly affects the jet wake flow phenomenon near impeller trailing edge. This results in high pressure fluctuations near impeller outlet.","PeriodicalId":23636,"journal":{"name":"Volume 2: Fluid Applications and Systems; Fluid Measurement and Instrumentation","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77168185","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}
Propeller exciting force is divided into bearing force and surface force according to the transfer path, and they are essential for radiated noise of the underwater vehicle. Surface force is an increasingly important issue in radiated noise because of the appearance of guide vanes and ducts. But the related questions about surface force are not thoroughly considered. Here we show spectral characteristics of surface force and its formation mechanism. Computational Fluid Dynamics is used in this paper. One of the important results is that there is a significant blade passing frequency (BPF) line spectrum in the radial component of surface force which does not appear in the axial direction; Another one is that the frequency amplitude at BPF of the duct is ten times that of the stator blades, which shows that the duct mainly contributes to the surface force. We also found that the amplitude of the duct surface force is equivalent to the rotor bearing force, which illustrates the importance of surface force research. It is demonstrated that the tip leakage vortex is the reason for the duct surface force by the analysis of the flow field. By adjusting the size of the tip clearance to control the tip leakage vortex, we found that the uniformity of the flow field has a significant effect on the surface force of the duct. The result obtained by this study can be used to reduce the radiated noise of underwater vehicles.
{"title":"Research on Formation Mechanism and Suppression Method of Surface Force Caused by Pump Jet Propeller","authors":"Y. Zhang, Dazhuan Wu","doi":"10.1115/fedsm2021-65423","DOIUrl":"https://doi.org/10.1115/fedsm2021-65423","url":null,"abstract":"\u0000 Propeller exciting force is divided into bearing force and surface force according to the transfer path, and they are essential for radiated noise of the underwater vehicle. Surface force is an increasingly important issue in radiated noise because of the appearance of guide vanes and ducts. But the related questions about surface force are not thoroughly considered. Here we show spectral characteristics of surface force and its formation mechanism. Computational Fluid Dynamics is used in this paper. One of the important results is that there is a significant blade passing frequency (BPF) line spectrum in the radial component of surface force which does not appear in the axial direction; Another one is that the frequency amplitude at BPF of the duct is ten times that of the stator blades, which shows that the duct mainly contributes to the surface force. We also found that the amplitude of the duct surface force is equivalent to the rotor bearing force, which illustrates the importance of surface force research. It is demonstrated that the tip leakage vortex is the reason for the duct surface force by the analysis of the flow field. By adjusting the size of the tip clearance to control the tip leakage vortex, we found that the uniformity of the flow field has a significant effect on the surface force of the duct. The result obtained by this study can be used to reduce the radiated noise of underwater vehicles.","PeriodicalId":23636,"journal":{"name":"Volume 2: Fluid Applications and Systems; Fluid Measurement and Instrumentation","volume":"31 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89604884","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}
At off-design operations, flow instabilities such as vortex breakdown, reverse flows, and stagnant regions are observed in Francis turbines. The present work shows the numerical flow field investigations of a Francis turbine at two different part loads (PL) by employing a vortex identification algorithm. The analysis has been performed at various locations in the draft tube by extracting the velocity fields at different time steps of the simulation. The first operating point involves a fully developed rotating vortex rope (RVR) in the draft tube, which precesses at a frequency of 0.28 times of the runner rotation. The present algorithm is able to identify the regions along with the eccentric local rotation center. The second operating regime shows characteristics of deep part load with central solid body rotation in the draft tube flow field. The results show highly swirling flows with very low axial velocity. The flow is confined primarily near the walls. The analysis shows that the extent of stagnation region at deep part load is more and no inner shear layer is present as compared to the part-load operation. The spatial harmonic decomposition (SHD) of the pressure data is also performed to evaluate the synchronous and asynchronous components of pressure pulsations.
{"title":"Flow Field Investigation in Draft Tube of Francis Turbine at Off-Design Operation Using a Vortex Identification Algorithm","authors":"Sandeep Kumar, S. Khullar, B. Gandhi","doi":"10.1115/fedsm2021-65742","DOIUrl":"https://doi.org/10.1115/fedsm2021-65742","url":null,"abstract":"\u0000 At off-design operations, flow instabilities such as vortex breakdown, reverse flows, and stagnant regions are observed in Francis turbines. The present work shows the numerical flow field investigations of a Francis turbine at two different part loads (PL) by employing a vortex identification algorithm. The analysis has been performed at various locations in the draft tube by extracting the velocity fields at different time steps of the simulation. The first operating point involves a fully developed rotating vortex rope (RVR) in the draft tube, which precesses at a frequency of 0.28 times of the runner rotation. The present algorithm is able to identify the regions along with the eccentric local rotation center. The second operating regime shows characteristics of deep part load with central solid body rotation in the draft tube flow field. The results show highly swirling flows with very low axial velocity. The flow is confined primarily near the walls. The analysis shows that the extent of stagnation region at deep part load is more and no inner shear layer is present as compared to the part-load operation. The spatial harmonic decomposition (SHD) of the pressure data is also performed to evaluate the synchronous and asynchronous components of pressure pulsations.","PeriodicalId":23636,"journal":{"name":"Volume 2: Fluid Applications and Systems; Fluid Measurement and Instrumentation","volume":"98 1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78109787","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}
Ang Li, Yijie Wang, Jun Chen, G. Jensen, Haiyan Zhang
Hydrokinetic power is the most efficient and reliable source of renewable energy and it has been utilized to produce power for centuries. The cycloidal water turbine is a subset of the H-bar type Darrieus turbines that are designed to actively controls the pitch angle of blades to improve turbine efficiency. However, the traditional cycloidal turbine has some shortcomings. For example, the torque and power coefficient vary significantly as the turbine rotates, which means the produced power is not uniform in one revolution. The associated hydrodynamic load will lead to fatigue of the turbine structure that will shorten the turbine lifespan. To solve this problem, a concept of the multi-sectional cycloidal water turbine is proposed. In the present study, computational fluid dynamic (CFD) simulations are applied to investigate the performance of the multi-sectional cycloidal turbine. A cycloidal turbine with three identical sections is designed. Each section consists of three blades and NACA0021 is chosen as the hydrofoil. Structured mesh with sliding interfaces is generated and arbitrary Mesh Interface (AMI) technique is employed. Unsteady RANS simulations with SST k–ω model are conducted to compute the flow field and torque generated by the turbine, and then power coefficient is computed. The results demonstrates that the three-section turbine has uniform performance in one revolution. At the design condition, the power coefficients of the one-section turbine and the three-section turbine are similar; when the TSR is much larger or less than the desired value, the three-section turbine has better performance.
水动力是最有效、最可靠的可再生能源，几个世纪以来一直被用于发电。摆线水轮机是H-bar型Darrieus水轮机的一个子集，旨在主动控制叶片的俯仰角，以提高涡轮效率。然而，传统的摆线水轮机存在一些不足。例如，随着涡轮机旋转，扭矩和功率系数变化很大，这意味着在一次旋转中产生的功率不是均匀的。伴随的水动力载荷将导致涡轮结构的疲劳，从而缩短涡轮的使用寿命。为解决这一问题，提出了多截面摆线水轮机的概念。本文采用计算流体动力学(CFD)方法对多截面摆线涡轮的性能进行了研究。设计了一种三等分截面摆线涡轮。每个部分由三个叶片组成，选择NACA0021作为水翼。采用任意网格界面(AMI)技术，生成具有滑动界面的结构化网格。采用SST k -ω模型进行非定常RANS仿真，计算涡轮产生的流场和转矩，进而计算功率系数。结果表明，三段式水轮机在一转内具有均匀的性能。在设计工况下，单段式水轮机与三段式水轮机的功率系数相近;当TSR较大或较小时，三段式水轮机性能较好。
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