The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens.The blades are the key components of offshore wind turbines,and their dynamic characteristics directly determine t...The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens.The blades are the key components of offshore wind turbines,and their dynamic characteristics directly determine the effectiveness of offshore wind turbines.With different rotating speeds and blade length,the rotating blades generate various centrifugal stiffening effects.To directly analyze the centrifugal stiffening effect of blades,the Rayleigh energy method (REM) was used to derive the natural frequency equation of the blade,including the centrifugal stiffening effect and the axial force calculation formula.The axial force planes and the first to third order natural frequency planes which vary with the rotating speed and length were calculated in three-dimensional coordinates.The centrifugal stiffening coefficient was introduced to quantitatively study the relationship between the centrifugal stiffening degree and the rotating speed,and then the fundamental frequency correction formula was built based on the rotating speed and the blade length.The analysis results show that the calculation results of the fundamental frequency correction formula agree with the theoretical calculation results.The error of calculation results between them is less than 0.5%.展开更多
A commercial Navier-Stokes flow solver has been employed for simulating steady subsonic flow characteristics and analyzing the comparative features of flow fields between straight and bowed blades applied to the stato...A commercial Navier-Stokes flow solver has been employed for simulating steady subsonic flow characteristics and analyzing the comparative features of flow fields between straight and bowed blades applied to the stator of a high pressure steam turbine. For comparison, we have studied the effects of bowed blades on the wakes of stator trailing edge and horse shoe vortex in the rotor. It was found that the position of wakes for bowed blades is shifted toward the blade suction side. Also, we have discussed and compared the entropy generation and energy loss caused by dissipation mechanism within the boundary layers on the hub and shroud; and temperature gradient in meridional plane.展开更多
In this study, a vertical axis tidal turbine with flexible blades is investigated. The focus is on analyzing the effect of flexible airfoils types and blade flexibility on turbine net output power. To this end, five d...In this study, a vertical axis tidal turbine with flexible blades is investigated. The focus is on analyzing the effect of flexible airfoils types and blade flexibility on turbine net output power. To this end, five different flexible airfoils （Symmetric and Non-symmetric） are employed. The results show that the use of a thick flexible symmetric airfoil can effectively increase output power compared to that achievable with a conventional rigid blade. Moreover, the use of highly flexible blades, as opposed to less flexible or rigid blades, is not recommended.展开更多
In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the...In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the characteristics were compared with those of background noise received from a real hydraulic turbine unit. It is found that the AE parameters such as the energy and duration can qualitatively describe the fatigue state of the blades. The correlations of crack propagation rates and acoustic emission count rates vs stress intensity factor (SIF) range are also obtained. At the same time, for the specimens of 20SiMn under the given testing conditions, it is noted that the rise time and duration of events emitted from the fatigue process are lower than those from the background noise; amplitude range is 49-74 dB, which is lower than that of the noise (90-99 dB); frequency range of main energy of crack signals is higher than 60 kHz while that in the noise is lower than 55 kHz. Thus, it is possible to extract the useful crack signals from the noise through appropriate signal processing methods and to represent the crack status of blade materials by AE parameters. As a result, it is feasible to monitor the safety of runners using AE technique.展开更多
For a certain type of transonic axial fan, the flow field of a fan rotor with splitter blade was computed by numerical simulation, and the shape of the rotor was modified. The effects of different circumferential dist...For a certain type of transonic axial fan, the flow field of a fan rotor with splitter blade was computed by numerical simulation, and the shape of the rotor was modified. The effects of different circumferential distributions concerning the splitter cascades upon the aerodynamic performance were investigated. The studies show that the optimum splitter cascade is not very close to the suction side of main blade. The load between the main blade and the splitter blade can be soundly distributed in terms of the adjustment of circumferential position of the splitter blade. The best aerodynamic performance can be successfully obtained according to the optimum shape of the expanding fluid channel reasonably formed by the splitter blade and the main blade.展开更多
This paper presents an approach that utilizes the recently developed tools for analyzing wind blade properties resulting from geometric shape and geographical site characteristics to find possible blade design improve...This paper presents an approach that utilizes the recently developed tools for analyzing wind blade properties resulting from geometric shape and geographical site characteristics to find possible blade design improvements. A set of blade shapes with a certain deviation of chord distribution from the initial geometry was investigated for WindPACT 1.5 MW turbine. The results showed that the original blade geometry can be improved based on individual site wind characteristics, giving better aerodynamic efficiency and reduced cost.展开更多
Based on the nonlinear continuum damage model （CDM） developed by Chaboehe, a modified model for high cycle fatigue of TC4 alloy was proposed. Unsymmetrical cycle fatigue tests were conducted on rod specimens at room...Based on the nonlinear continuum damage model （CDM） developed by Chaboehe, a modified model for high cycle fatigue of TC4 alloy was proposed. Unsymmetrical cycle fatigue tests were conducted on rod specimens at room temperature. Then the material parameters needed in the CDM were obtained by the fatigue tests, and the stress distribution of the specimen was calculated by FE method. Compared with the linear damage model （LDM）, the dam- age results and the life prediction of the CDM show a better agreement with the test and they are more precise than the LDM. By applying the CDM developed in this study to the life prediction of aeroengine blades, it is concluded that the root is the most dangerous region of the whole blade and the shortest life is 58 211 cycles. Finally, the Cox propor- tional hazard model of survival analysis was applied to the analysis of the fatigue reliability. The Cox model takes the covariates into consideration, which include diameter, weight, mean stress and tensile strength. The result shows that the mean stress is the only factor that accelerates the fracture process.展开更多
It is important to study the pressure distribution on the blade and in the adjacent area while searching the power augmentation theory with adding a tip vane to the wind turbine. This paper shows the CFD simulation re...It is important to study the pressure distribution on the blade and in the adjacent area while searching the power augmentation theory with adding a tip vane to the wind turbine. This paper shows the CFD simulation relationship of the pressure distribution on the rotor blade and in the adjacent area, after calculating the pressure of the different chordwise and spanwise point on the blade with the tip vane-V（8.8×8） and without the tip vane under tip speed ratio λ 4.5. Combining the isobaric section figure in certain location, it can be seen that the tip vane improve the pressure difference between pressure and suction surface. The most influenced zone is found and these can further display the power augmentation theory of the wind turbine using the tip vane. The simulation calculation was based on N-S equations. 3-D, steady, implicit solver was chosen. Turbulence model was k-ω SST. Discretization scheme is SECOND ORDER UPWIND. Pressure-velocity coupling was a typical SIMPLE scheme. In the whole grid system, two-divided grid formation was adopted, that is, inner region and outer region. Inner region including rectangular solid blade and neighboring, outer region is semi-cylinder. There were together 720,000 nodes with tetra-prism unstructured mesh.展开更多
This paper presents the study of the flow structure and heat transfer,and also their correlations on the four walls of a radial cooling passage model of a gas turbine blade.The investigations focus on heat transfer an...This paper presents the study of the flow structure and heat transfer,and also their correlations on the four walls of a radial cooling passage model of a gas turbine blade.The investigations focus on heat transfer and aerodynamic measurements in the channel,which is an accurate representation of the configuration used in aeroengines.Correlations for the heat transfer coefficient and the pressure drop used in the design of radial cooling passages are often developed from simplified models.It is important to note that real engine passages do not have perfect rectangular cross sections,but include coiner fillet,ribs with fillet radii and special orientation.Therefore,this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which possesses very realistic features.展开更多
Recently, it has been reported that physisorbed adsorbates can be trapped between the bottom surface of twodimensional(2D) materials and supported substrate to form2 D confined films. However, the influence of such 2D...Recently, it has been reported that physisorbed adsorbates can be trapped between the bottom surface of twodimensional(2D) materials and supported substrate to form2 D confined films. However, the influence of such 2D confined adsorbates on the properties of 2D materials is rarely explored. Herein, we combined atomic force microscopy(AFM), Kelvin probe force microscopy(KPFM) and Raman spectroscopy especially the ultralow frequency(ULF) Raman spectroscopy to explore the influence of 2D confined organic adlayer thickness on the ULF breathing modes of few-layer MoS2 and WSe2nanosheets. As the thickness of organic adlayers increased, red shift, coexistence of blue and red shifts as well as blue shift of ULF breathing mode was observed. KPFM measurement confirmed the enhanced n-doping and p-doping behaviors of organic adlayers as their thickness increased,respectively. Our results will provide new insights into the interaction between 2D confined adsorbates and bottom surface of 2D nanosheets, which could be useful for modulating properties of 2D materials.展开更多
To improve the aerodynamic performance of small axial flow fan, in this paper the design of a small axial flow fan with splitter blades is studied. The RNG k-e turbulence model and SIMPLE algorithm were applied to the...To improve the aerodynamic performance of small axial flow fan, in this paper the design of a small axial flow fan with splitter blades is studied. The RNG k-e turbulence model and SIMPLE algorithm were applied to the steady simulation calculation of the flow field, and its result was used as the initial field of the large eddy simulation to calculate the unsteady pressure field. The FW-H noise model was adopted to predict aerodynamic noise in the six monitoring points. Fast Fourier transform algorithm was applied to process the pressure signal. Experiment of noise testing was done to further investigate the aerodynamic noise of fans. And then the results obtained from the numerical simulation and experiment were described and analyzed. The results show that the static characteristics of small axial fan with splitter blades are similar with the prototype fan, and the static characteristics are improved within a certain range of flux. The power spectral density at the six monitoring points of small axial flow fan with splitter blades have decreased to some extent. The experimental results show sound pressure level of new fan has reduced in most frequency bands by comparing with prototype fan. The research results will provide a proof for parameter optimization and noise prediction of small axial flow fans with high performance.展开更多
As we approach the exascale era in supercomputing, designing a balanced computer system with a powerful computing ability and low power requirements has becoming increasingly important. The graphics processing unit（...As we approach the exascale era in supercomputing, designing a balanced computer system with a powerful computing ability and low power requirements has becoming increasingly important. The graphics processing unit（GPU） is an accelerator used widely in most of recent supercomputers. It adopts a large number of threads to hide a long latency with a high energy efficiency. In contrast to their powerful computing ability, GPUs have only a few megabytes of fast on-chip memory storage per streaming multiprocessor（SM）. The GPU cache is inefficient due to a mismatch between the throughput-oriented execution model and cache hierarchy design. At the same time, current GPUs fail to handle burst-mode long-access latency due to GPU＇s poor warp scheduling method.Thus, benefits of GPU＇s high computing ability are reduced dramatically by the poor cache management and warp scheduling methods, which limit the system performance and energy efficiency. In this paper, we put forward a coordinated warp scheduling and locality-protected（CWLP） cache allocation scheme to make full use of data locality and hide latency. We first present a locality-protected cache allocation method based on the instruction program counter（LPC） to promote cache performance. Specifically, we use a PC-based locality detector to collect the reuse information of each cache line and employ a prioritised cache allocation unit（PCAU） which coordinates the data reuse information with the time-stamp information to evict the lines with the least reuse possibility. Moreover, the locality information is used by the warp scheduler to create an intelligent warp reordering scheme to capture locality and hide latency. Simulation results show that CWLP provides a speedup up to 19.8% and an average improvement of 8.8% over the baseline methods.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No.50708015the foundation of State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology
文摘The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens.The blades are the key components of offshore wind turbines,and their dynamic characteristics directly determine the effectiveness of offshore wind turbines.With different rotating speeds and blade length,the rotating blades generate various centrifugal stiffening effects.To directly analyze the centrifugal stiffening effect of blades,the Rayleigh energy method (REM) was used to derive the natural frequency equation of the blade,including the centrifugal stiffening effect and the axial force calculation formula.The axial force planes and the first to third order natural frequency planes which vary with the rotating speed and length were calculated in three-dimensional coordinates.The centrifugal stiffening coefficient was introduced to quantitatively study the relationship between the centrifugal stiffening degree and the rotating speed,and then the fundamental frequency correction formula was built based on the rotating speed and the blade length.The analysis results show that the calculation results of the fundamental frequency correction formula agree with the theoretical calculation results.The error of calculation results between them is less than 0.5%.
文摘A commercial Navier-Stokes flow solver has been employed for simulating steady subsonic flow characteristics and analyzing the comparative features of flow fields between straight and bowed blades applied to the stator of a high pressure steam turbine. For comparison, we have studied the effects of bowed blades on the wakes of stator trailing edge and horse shoe vortex in the rotor. It was found that the position of wakes for bowed blades is shifted toward the blade suction side. Also, we have discussed and compared the entropy generation and energy loss caused by dissipation mechanism within the boundary layers on the hub and shroud; and temperature gradient in meridional plane.
文摘In this study, a vertical axis tidal turbine with flexible blades is investigated. The focus is on analyzing the effect of flexible airfoils types and blade flexibility on turbine net output power. To this end, five different flexible airfoils （Symmetric and Non-symmetric） are employed. The results show that the use of a thick flexible symmetric airfoil can effectively increase output power compared to that achievable with a conventional rigid blade. Moreover, the use of highly flexible blades, as opposed to less flexible or rigid blades, is not recommended.
基金Project(50465002) supported by the National Natural Science Foundation of China
文摘In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the characteristics were compared with those of background noise received from a real hydraulic turbine unit. It is found that the AE parameters such as the energy and duration can qualitatively describe the fatigue state of the blades. The correlations of crack propagation rates and acoustic emission count rates vs stress intensity factor (SIF) range are also obtained. At the same time, for the specimens of 20SiMn under the given testing conditions, it is noted that the rise time and duration of events emitted from the fatigue process are lower than those from the background noise; amplitude range is 49-74 dB, which is lower than that of the noise (90-99 dB); frequency range of main energy of crack signals is higher than 60 kHz while that in the noise is lower than 55 kHz. Thus, it is possible to extract the useful crack signals from the noise through appropriate signal processing methods and to represent the crack status of blade materials by AE parameters. As a result, it is feasible to monitor the safety of runners using AE technique.
文摘For a certain type of transonic axial fan, the flow field of a fan rotor with splitter blade was computed by numerical simulation, and the shape of the rotor was modified. The effects of different circumferential distributions concerning the splitter cascades upon the aerodynamic performance were investigated. The studies show that the optimum splitter cascade is not very close to the suction side of main blade. The load between the main blade and the splitter blade can be soundly distributed in terms of the adjustment of circumferential position of the splitter blade. The best aerodynamic performance can be successfully obtained according to the optimum shape of the expanding fluid channel reasonably formed by the splitter blade and the main blade.
文摘This paper presents an approach that utilizes the recently developed tools for analyzing wind blade properties resulting from geometric shape and geographical site characteristics to find possible blade design improvements. A set of blade shapes with a certain deviation of chord distribution from the initial geometry was investigated for WindPACT 1.5 MW turbine. The results showed that the original blade geometry can be improved based on individual site wind characteristics, giving better aerodynamic efficiency and reduced cost.
基金Supported by National Natural Science Foundation of China(No.60879002)Key Technologies R and D Program of Tianjin (No.10ZCKFGX03800)
文摘Based on the nonlinear continuum damage model （CDM） developed by Chaboehe, a modified model for high cycle fatigue of TC4 alloy was proposed. Unsymmetrical cycle fatigue tests were conducted on rod specimens at room temperature. Then the material parameters needed in the CDM were obtained by the fatigue tests, and the stress distribution of the specimen was calculated by FE method. Compared with the linear damage model （LDM）, the dam- age results and the life prediction of the CDM show a better agreement with the test and they are more precise than the LDM. By applying the CDM developed in this study to the life prediction of aeroengine blades, it is concluded that the root is the most dangerous region of the whole blade and the shortest life is 58 211 cycles. Finally, the Cox propor- tional hazard model of survival analysis was applied to the analysis of the fatigue reliability. The Cox model takes the covariates into consideration, which include diameter, weight, mean stress and tensile strength. The result shows that the mean stress is the only factor that accelerates the fracture process.
基金Project 50566001 supported by NSFCProject 200308020207 supported by Inner Mongolia Autono- mous Region Natural Science Foundation of China.
文摘It is important to study the pressure distribution on the blade and in the adjacent area while searching the power augmentation theory with adding a tip vane to the wind turbine. This paper shows the CFD simulation relationship of the pressure distribution on the rotor blade and in the adjacent area, after calculating the pressure of the different chordwise and spanwise point on the blade with the tip vane-V（8.8×8） and without the tip vane under tip speed ratio λ 4.5. Combining the isobaric section figure in certain location, it can be seen that the tip vane improve the pressure difference between pressure and suction surface. The most influenced zone is found and these can further display the power augmentation theory of the wind turbine using the tip vane. The simulation calculation was based on N-S equations. 3-D, steady, implicit solver was chosen. Turbulence model was k-ω SST. Discretization scheme is SECOND ORDER UPWIND. Pressure-velocity coupling was a typical SIMPLE scheme. In the whole grid system, two-divided grid formation was adopted, that is, inner region and outer region. Inner region including rectangular solid blade and neighboring, outer region is semi-cylinder. There were together 720,000 nodes with tetra-prism unstructured mesh.
基金funding from the European Union Seventh Framework Programme(FP7/2007-2013) under Grant Agreement No. 233799(ERICKA)
文摘This paper presents the study of the flow structure and heat transfer,and also their correlations on the four walls of a radial cooling passage model of a gas turbine blade.The investigations focus on heat transfer and aerodynamic measurements in the channel,which is an accurate representation of the configuration used in aeroengines.Correlations for the heat transfer coefficient and the pressure drop used in the design of radial cooling passages are often developed from simplified models.It is important to note that real engine passages do not have perfect rectangular cross sections,but include coiner fillet,ribs with fillet radii and special orientation.Therefore,this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which possesses very realistic features.
基金supported by the National Natural Science Foundation of China (21571101 and 51322202)the Natural Science Foundation of Jiangsu Province in China (BK20161543 and BK20130927)+1 种基金the Joint Research Fund for Overseas Chinese, Hong Kong and Macao Scholars (51528201)Natural Science Foundation of Jiangsu Higher Education Institutions of China (15KJB430016)
文摘Recently, it has been reported that physisorbed adsorbates can be trapped between the bottom surface of twodimensional(2D) materials and supported substrate to form2 D confined films. However, the influence of such 2D confined adsorbates on the properties of 2D materials is rarely explored. Herein, we combined atomic force microscopy(AFM), Kelvin probe force microscopy(KPFM) and Raman spectroscopy especially the ultralow frequency(ULF) Raman spectroscopy to explore the influence of 2D confined organic adlayer thickness on the ULF breathing modes of few-layer MoS2 and WSe2nanosheets. As the thickness of organic adlayers increased, red shift, coexistence of blue and red shifts as well as blue shift of ULF breathing mode was observed. KPFM measurement confirmed the enhanced n-doping and p-doping behaviors of organic adlayers as their thickness increased,respectively. Our results will provide new insights into the interaction between 2D confined adsorbates and bottom surface of 2D nanosheets, which could be useful for modulating properties of 2D materials.
基金supported by grants from the National Natural Science Foundation of China (No.51076144)the Major Special Project of Technology Office in Zhejiang Province (No.2011C11073, No.2011C16038)
文摘To improve the aerodynamic performance of small axial flow fan, in this paper the design of a small axial flow fan with splitter blades is studied. The RNG k-e turbulence model and SIMPLE algorithm were applied to the steady simulation calculation of the flow field, and its result was used as the initial field of the large eddy simulation to calculate the unsteady pressure field. The FW-H noise model was adopted to predict aerodynamic noise in the six monitoring points. Fast Fourier transform algorithm was applied to process the pressure signal. Experiment of noise testing was done to further investigate the aerodynamic noise of fans. And then the results obtained from the numerical simulation and experiment were described and analyzed. The results show that the static characteristics of small axial fan with splitter blades are similar with the prototype fan, and the static characteristics are improved within a certain range of flux. The power spectral density at the six monitoring points of small axial flow fan with splitter blades have decreased to some extent. The experimental results show sound pressure level of new fan has reduced in most frequency bands by comparing with prototype fan. The research results will provide a proof for parameter optimization and noise prediction of small axial flow fans with high performance.
基金Project supported by the National Natural Science Foundation of China(No.61170083)the Specialized Research Fund for the Doctoral Program of Higher Education,China(No.20114307110001)
文摘As we approach the exascale era in supercomputing, designing a balanced computer system with a powerful computing ability and low power requirements has becoming increasingly important. The graphics processing unit（GPU） is an accelerator used widely in most of recent supercomputers. It adopts a large number of threads to hide a long latency with a high energy efficiency. In contrast to their powerful computing ability, GPUs have only a few megabytes of fast on-chip memory storage per streaming multiprocessor（SM）. The GPU cache is inefficient due to a mismatch between the throughput-oriented execution model and cache hierarchy design. At the same time, current GPUs fail to handle burst-mode long-access latency due to GPU＇s poor warp scheduling method.Thus, benefits of GPU＇s high computing ability are reduced dramatically by the poor cache management and warp scheduling methods, which limit the system performance and energy efficiency. In this paper, we put forward a coordinated warp scheduling and locality-protected（CWLP） cache allocation scheme to make full use of data locality and hide latency. We first present a locality-protected cache allocation method based on the instruction program counter（LPC） to promote cache performance. Specifically, we use a PC-based locality detector to collect the reuse information of each cache line and employ a prioritised cache allocation unit（PCAU） which coordinates the data reuse information with the time-stamp information to evict the lines with the least reuse possibility. Moreover, the locality information is used by the warp scheduler to create an intelligent warp reordering scheme to capture locality and hide latency. Simulation results show that CWLP provides a speedup up to 19.8% and an average improvement of 8.8% over the baseline methods.
基金supported by the Inner Mongolia Autonomous Region Open Major Basic Research Project(Grant No.20120905)the National Natural Science Foundation of China(Grant No.51666014)
文摘Wind tunnel experiments of the wake characteristics of a two-blade wind turbine, in the downstream region of 0
