This article is aimed to experimentally validate the beneficial effects of boundary layer suction on improving the aerodynamic performance of a compressor cascade with a large camber angle. The flow field of the casca...This article is aimed to experimentally validate the beneficial effects of boundary layer suction on improving the aerodynamic performance of a compressor cascade with a large camber angle. The flow field of the cascade is measured and the ink-trace flow visualization is also presented. The experimental results show that the boundary layer suction reduces losses near the area of rnidspan in the cascade most effectively for all suction cases under test. Losses of the endwall could remarkably decrease only when the suction is at the position where the boundary layer has separated but still not departed far away from the blade surface. It is evidenced that the higher suction flow rate and the suction position closer to the trailing edge result in greater reduction in losses and the maximum reduction in the total pressure loss accounts to 16.5% for all cases. The suction position plays a greater role in affecting the total pressure loss than the suction flow rate does.展开更多
The thermal diffusion column represents one method of separating stable isotopes.This method is advantageous for smallscale operations because of the simplicity of the apparatus and small inventory,especially in gas-p...The thermal diffusion column represents one method of separating stable isotopes.This method is advantageous for smallscale operations because of the simplicity of the apparatus and small inventory,especially in gas-phase operations.Consequently,it has attracted attention for its applicability in tritium and noble gas separation systems.In this study,the R cascade was used to design and determine the number of columns.A square cascade was adopted for the final design because of its flexibility,and calculations were performed to separate 20Ne and 22Ne isotopes.All the R cascades that enriched the Ne isotopes by more than 99%were investigated,the number of columns was determined,and the square cascade parameters were optimized using the specified columns.Additionally,a calculation code“RSQ_CASCADE”was developed.A unit separation factor of three was considered,and the number of studied stages ranged from 10 to 20.The results showed that the column separation power,relative total flow rate,and required number of columns were linearly related to the number of stages.The separation power and relative total flow decreased and the number of columns increased as the stage number increased.Therefore,a cascade of 85 columns is recommended to separate the stable Ne isotopes.These calculations yielded a 17-stage square cascade with five columns in each stage.By changing the stage cut,feed point,and cascade feed flow rate,the best parameters for the square cascade were determined according to the cascade and column separation powers.As the column separation power had a maximum value in cascade feed 50,it was selected for separating Ne isotopes.展开更多
Maximizing the spread of influence is to select a set of seeds with specified size to maximize the spread of influence under a certain diffusion model in a social network. In the actual spread process, the activated p...Maximizing the spread of influence is to select a set of seeds with specified size to maximize the spread of influence under a certain diffusion model in a social network. In the actual spread process, the activated probability of node increases with its newly increasing activated neighbors, which also decreases with time. In this paper, we focus on the problem that selects k seeds based on the cascade model with diffusion decay to maximize the spread of influence in social networks. First, we extend the independent cascade model to incorporate the diffusion decay factor, called as the cascade model with diffusion decay and abbreviated as CMDD. Then, we discuss the objective function of maximizing the spread of influence under the CMDD, which is NP-hard. We further prove the monotonicity and submodularity of this objective function. Finally, we use the greedy algorithm to approximate the optimal result with the ration of 1 ? 1/e.展开更多
In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex ge...In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex generator with a special configuration and the longitudinal suction slot are adopted. The calculated results show that a reverse flow region, which is considered the main reason for occurring stall at 7.9° incidence, grows and collapses rapidly near the leading edge and leads to two critical points occurring on the end-wall with the increasing incidence in the baseline. As the micro-vortex generator is introduced in the baseline cascade, the corner separation is switched to a trailing edge separation by the thrust from the induced vortex. Meanwhile, the occurrence of failure is delayed due to the mixed low energy fluid and main flow. The synergistic effects between the micro-vortex generator and the boundary layer suction on the performance of the cascade are superior to the baseline at all the incidence conditions before the occurrence of failure, and the sudden deterioration of the cascade occurs at 10.3° incidence. The optimal results show that the farther upstream suction position, the lower total pressure loss of the cascade with vortex generator at the near stall condition. Moreover, the induced vortex with a leg can migrate the accumulated low energy fluid backward to delay the occurrence of stall.展开更多
To further make clear vortex structures in diffusion cascades so as to help understand the mechanisms of vortex affecting loss production, the emergence, evolution and development of secondary flow vortexes, including...To further make clear vortex structures in diffusion cascades so as to help understand the mechanisms of vortex affecting loss production, the emergence, evolution and development of secondary flow vortexes, including horse shoe vortex, passage vortex and corner vortex and so on, were discussed mainly through using the topological analysis method and numerical calculation. The concept of a three-dimensional dividing surface between the low energy flow zone and the exterior flow zone was presented. The results show that concentrated shed vortex is located outside the dividing surface (in the outer flow zone) and horse shoe vortex, passage vortex and corner vortex are inside the dividing surface (in the low energy flow zone). Dissipation function is used to measure loss production instead of using entropy production. The results about loss analysis indicate that vortex motion directly causes loss production, namely, peak value of loss is generally located around the core of vortex and that maximal loss happens around the dividing surface other than in the low energy flow zone.展开更多
According to the previous experimental works on the low solidity circular cascade diffuser (LSD), a pressure recovery of a centrifugal blower was improved by the LSD significantly in a wide range of flow rate, and the...According to the previous experimental works on the low solidity circular cascade diffuser (LSD), a pressure recovery of a centrifugal blower was improved by the LSD significantly in a wide range of flow rate, and the pres-sure recovery was improved further by the LSD with a tandem cascade in comparison with the LSD with a sin-gle-row cascade. In the present study, the flow behavior in the LSD with the tandem cascade has been analyzed numerically by using the commercial CFD code of ANSYS-CFX12. It was shown clearly that the higher pressure recovery was achieved by applying the LSD with the tandem cascade, and the high pressure recovery is based on the high pressure rise in the vaneless space upstream of the LSD and the high blade loading of the front blade of the LSD. The high pressure recovery in the LSD could be achieved by controlling the flow separation on the suc-tion surface of the front blade and also on that of the rear blade due to formation of the favorable secondary flow and due to increase in mass flow passing through the slit section between the front and rear blades.展开更多
This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blowercharacteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip ...This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blowercharacteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip near theleading edge of the LSD blade. In order to clarify the mechanism of noise increase due to LSD and also to reducethe noise, the relationships between the noise increase based on the LSD, the LSD performance and the secondaryflow formed additionally by the tip-groove were investigated experimentally as well as numerically, especiallyanalyzing flow behaviors in the LSD in view points of flow separation on the suction surface of the LSD bladeand the secondary flow on the side walls. By reducing the stagnation region smaller near the root and/or tip of theLSD blade leading edge, the secondary flow behavior changes remarkably around the LSD blade, as a result, thenoise level and the blower characteristics vary. It can be concluded that, by means of a small tip-groove locatedonly at the shroud side near the LSD blade leading edge, the noise generated by the LSD can be reduced withoutdeteriorations of the LSD performance and the blower characteristics as well.展开更多
High-pressure ratio and wide operating range are highly required for compressors and blowers. The technical issue of the design is achievement of suppression of flow separation at small flow rate without deteriorating...High-pressure ratio and wide operating range are highly required for compressors and blowers. The technical issue of the design is achievement of suppression of flow separation at small flow rate without deteriorating the efficiency at design flow rate. A numerical simulation is very effective in design procedure, however, cost of the numerical simulation is generally high during the practical design process, and it is difficult to confn＇m the optimal design which is combined with many parameters. A multi-objective optimization technique is the idea that has been proposed for solving the problem in practical design process. In this study, a Low Solidity circular cascade Diffuser （LSD） in a centrifugal blower is successfully designed by means of multi-objective optimization technique. An optimization code with a meta-model assisted evolutionary algorithm is used with a commercial CFD code ANSYS-CFX. The optimization is aiming at improving the static pressure coefficient at design point and at low flow rate condition while constraining the slope of the lift coefficient curve. Moreover, a small tip clearance of the LSD blade was applied in order to activate and to stabilize the secondary flow effect at small flow rate condition. The optimized LSD blade has an extended operating range of 114 % towards smaller flow rate as compared to the baseline design without deteriorating the diffuser pressure recovery at design point. The diffuser pressure rise and operating flow range of the optimized LSD blade are experimentally verified by overall performance test. The detailed flow in the diffuser is also confirmed by means of a Particle Image Velocimeter. Secondary flow is clearly captured by PIV and it spreads to the whole area of LSD blade pitch. It is found that the optimized LSD blade shows good improvement of the blade loading in the whole operating range, while at small flow rate the flow separation on the LSD blade has been successfully suppressed by the secondary flow effect.展开更多
A three-dimensional blade of a low solidity circular cascade diffuser in centrifugal blowers is designed by means of a multi-point optimization technique. The optimization aims at improving static pressure coefficient...A three-dimensional blade of a low solidity circular cascade diffuser in centrifugal blowers is designed by means of a multi-point optimization technique. The optimization aims at improving static pressure coefficient at a design point and at a small flow rate condition. Moreover, a clear definition of secondary flow expressed by positive radial velocity at hub side is taken into consideration in constraints. The number of design parameters for three-dimensional blade reaches to 10 in this study, such as a radial gap, a radial chord length and mean camber angle distribution of the LSD blade with five control points, control point between hub and shroud with two design freedom. Optimization results show clear Pareto front and selected optimum design shows good improvement of pressure rise in diffuser at small flow rate conditions. It is found that three-dimensional blade has advantage to stabilize the secondary flow effect with improving pressure recovery of the low solidity circular cascade diffuser.展开更多
Due to the high cost of data collection and limited experimental conditions,sonar images are often scarce and of poor quality,which hinders effective feature learning and limits the performance of existing detection m...Due to the high cost of data collection and limited experimental conditions,sonar images are often scarce and of poor quality,which hinders effective feature learning and limits the performance of existing detection methods.To address this,we propose an improved YOLO model,i.e.Swin transformer-cascaded group attention YOLO(STCYOLO),for sonar image target detection,which integrates diffusion-based sample generation with a Swin transformer and cascaded group attention(CGA)mechanism.First,we fine-tune stable diffusion via LoRA and incorporate semantic features from the bootstrapping language-image pre-training text model to generate high-quality and diverse sonar images for dataset expansion.Then,we introduce Swin transformer into the YOLOv8 backbone to enhance multi-scale feature extraction for small targets,while integrating the CGA mechanism into the C2f module to improve small object perception.Additionally,the skewed intersection-over-union(SIoU)loss function is utilized to better adapt to the complexities of underwater environments.Experimental results indicate that the trained generative model is capable of producing diverse and realistic samples even in data-scarce scenarios.Compared to the original YOLOv8 model,the enhanced STC-YOLO model exhibits a 5%increase in detection accuracy and a 12.6%improvement in mean average precision,achieving high-precision detection of small underwater targets.展开更多
基金National Basic Research Program of China (2007CB210100)National Natural Science Foundation of China (50876023)Chinese Specialized Research Fund for the Doctoral Program of Higher Education (20060213007)
文摘This article is aimed to experimentally validate the beneficial effects of boundary layer suction on improving the aerodynamic performance of a compressor cascade with a large camber angle. The flow field of the cascade is measured and the ink-trace flow visualization is also presented. The experimental results show that the boundary layer suction reduces losses near the area of rnidspan in the cascade most effectively for all suction cases under test. Losses of the endwall could remarkably decrease only when the suction is at the position where the boundary layer has separated but still not departed far away from the blade surface. It is evidenced that the higher suction flow rate and the suction position closer to the trailing edge result in greater reduction in losses and the maximum reduction in the total pressure loss accounts to 16.5% for all cases. The suction position plays a greater role in affecting the total pressure loss than the suction flow rate does.
文摘The thermal diffusion column represents one method of separating stable isotopes.This method is advantageous for smallscale operations because of the simplicity of the apparatus and small inventory,especially in gas-phase operations.Consequently,it has attracted attention for its applicability in tritium and noble gas separation systems.In this study,the R cascade was used to design and determine the number of columns.A square cascade was adopted for the final design because of its flexibility,and calculations were performed to separate 20Ne and 22Ne isotopes.All the R cascades that enriched the Ne isotopes by more than 99%were investigated,the number of columns was determined,and the square cascade parameters were optimized using the specified columns.Additionally,a calculation code“RSQ_CASCADE”was developed.A unit separation factor of three was considered,and the number of studied stages ranged from 10 to 20.The results showed that the column separation power,relative total flow rate,and required number of columns were linearly related to the number of stages.The separation power and relative total flow decreased and the number of columns increased as the stage number increased.Therefore,a cascade of 85 columns is recommended to separate the stable Ne isotopes.These calculations yielded a 17-stage square cascade with five columns in each stage.By changing the stage cut,feed point,and cascade feed flow rate,the best parameters for the square cascade were determined according to the cascade and column separation powers.As the column separation power had a maximum value in cascade feed 50,it was selected for separating Ne isotopes.
基金This paper was supported by the National Natural Science Foundation of China (61562091), Natural Science Foundation of Yunnan Province (2014FA023,201501CF00022), Program for Innovative Research Team in Yunnan University (XT412011), and Program for Excellent Young Talents of Yunnan University (XT412003).
文摘Maximizing the spread of influence is to select a set of seeds with specified size to maximize the spread of influence under a certain diffusion model in a social network. In the actual spread process, the activated probability of node increases with its newly increasing activated neighbors, which also decreases with time. In this paper, we focus on the problem that selects k seeds based on the cascade model with diffusion decay to maximize the spread of influence in social networks. First, we extend the independent cascade model to incorporate the diffusion decay factor, called as the cascade model with diffusion decay and abbreviated as CMDD. Then, we discuss the objective function of maximizing the spread of influence under the CMDD, which is NP-hard. We further prove the monotonicity and submodularity of this objective function. Finally, we use the greedy algorithm to approximate the optimal result with the ration of 1 ? 1/e.
基金co-supported by the National Natural Science Foundation of China(Grants Nos.51576162 and 51536006)
文摘In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex generator with a special configuration and the longitudinal suction slot are adopted. The calculated results show that a reverse flow region, which is considered the main reason for occurring stall at 7.9° incidence, grows and collapses rapidly near the leading edge and leads to two critical points occurring on the end-wall with the increasing incidence in the baseline. As the micro-vortex generator is introduced in the baseline cascade, the corner separation is switched to a trailing edge separation by the thrust from the induced vortex. Meanwhile, the occurrence of failure is delayed due to the mixed low energy fluid and main flow. The synergistic effects between the micro-vortex generator and the boundary layer suction on the performance of the cascade are superior to the baseline at all the incidence conditions before the occurrence of failure, and the sudden deterioration of the cascade occurs at 10.3° incidence. The optimal results show that the farther upstream suction position, the lower total pressure loss of the cascade with vortex generator at the near stall condition. Moreover, the induced vortex with a leg can migrate the accumulated low energy fluid backward to delay the occurrence of stall.
基金Supported by the National Natural Science Fundation of China (Grant No. 90718025)
文摘To further make clear vortex structures in diffusion cascades so as to help understand the mechanisms of vortex affecting loss production, the emergence, evolution and development of secondary flow vortexes, including horse shoe vortex, passage vortex and corner vortex and so on, were discussed mainly through using the topological analysis method and numerical calculation. The concept of a three-dimensional dividing surface between the low energy flow zone and the exterior flow zone was presented. The results show that concentrated shed vortex is located outside the dividing surface (in the outer flow zone) and horse shoe vortex, passage vortex and corner vortex are inside the dividing surface (in the low energy flow zone). Dissipation function is used to measure loss production instead of using entropy production. The results about loss analysis indicate that vortex motion directly causes loss production, namely, peak value of loss is generally located around the core of vortex and that maximal loss happens around the dividing surface other than in the low energy flow zone.
文摘According to the previous experimental works on the low solidity circular cascade diffuser (LSD), a pressure recovery of a centrifugal blower was improved by the LSD significantly in a wide range of flow rate, and the pres-sure recovery was improved further by the LSD with a tandem cascade in comparison with the LSD with a sin-gle-row cascade. In the present study, the flow behavior in the LSD with the tandem cascade has been analyzed numerically by using the commercial CFD code of ANSYS-CFX12. It was shown clearly that the higher pressure recovery was achieved by applying the LSD with the tandem cascade, and the high pressure recovery is based on the high pressure rise in the vaneless space upstream of the LSD and the high blade loading of the front blade of the LSD. The high pressure recovery in the LSD could be achieved by controlling the flow separation on the suc-tion surface of the front blade and also on that of the rear blade due to formation of the favorable secondary flow and due to increase in mass flow passing through the slit section between the front and rear blades.
文摘This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blowercharacteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip near theleading edge of the LSD blade. In order to clarify the mechanism of noise increase due to LSD and also to reducethe noise, the relationships between the noise increase based on the LSD, the LSD performance and the secondaryflow formed additionally by the tip-groove were investigated experimentally as well as numerically, especiallyanalyzing flow behaviors in the LSD in view points of flow separation on the suction surface of the LSD bladeand the secondary flow on the side walls. By reducing the stagnation region smaller near the root and/or tip of theLSD blade leading edge, the secondary flow behavior changes remarkably around the LSD blade, as a result, thenoise level and the blower characteristics vary. It can be concluded that, by means of a small tip-groove locatedonly at the shroud side near the LSD blade leading edge, the noise generated by the LSD can be reduced withoutdeteriorations of the LSD performance and the blower characteristics as well.
基金financially supported by Japan Society for the Promotion of Science(JSPS) program of"Strategic young researcher overseas visits program for accelerating brain circulation"
文摘High-pressure ratio and wide operating range are highly required for compressors and blowers. The technical issue of the design is achievement of suppression of flow separation at small flow rate without deteriorating the efficiency at design flow rate. A numerical simulation is very effective in design procedure, however, cost of the numerical simulation is generally high during the practical design process, and it is difficult to confn＇m the optimal design which is combined with many parameters. A multi-objective optimization technique is the idea that has been proposed for solving the problem in practical design process. In this study, a Low Solidity circular cascade Diffuser （LSD） in a centrifugal blower is successfully designed by means of multi-objective optimization technique. An optimization code with a meta-model assisted evolutionary algorithm is used with a commercial CFD code ANSYS-CFX. The optimization is aiming at improving the static pressure coefficient at design point and at low flow rate condition while constraining the slope of the lift coefficient curve. Moreover, a small tip clearance of the LSD blade was applied in order to activate and to stabilize the secondary flow effect at small flow rate condition. The optimized LSD blade has an extended operating range of 114 % towards smaller flow rate as compared to the baseline design without deteriorating the diffuser pressure recovery at design point. The diffuser pressure rise and operating flow range of the optimized LSD blade are experimentally verified by overall performance test. The detailed flow in the diffuser is also confirmed by means of a Particle Image Velocimeter. Secondary flow is clearly captured by PIV and it spreads to the whole area of LSD blade pitch. It is found that the optimized LSD blade shows good improvement of the blade loading in the whole operating range, while at small flow rate the flow separation on the LSD blade has been successfully suppressed by the secondary flow effect.
基金financially supported by Harada memorial foundation and Japan Science and Technology Agency
文摘A three-dimensional blade of a low solidity circular cascade diffuser in centrifugal blowers is designed by means of a multi-point optimization technique. The optimization aims at improving static pressure coefficient at a design point and at a small flow rate condition. Moreover, a clear definition of secondary flow expressed by positive radial velocity at hub side is taken into consideration in constraints. The number of design parameters for three-dimensional blade reaches to 10 in this study, such as a radial gap, a radial chord length and mean camber angle distribution of the LSD blade with five control points, control point between hub and shroud with two design freedom. Optimization results show clear Pareto front and selected optimum design shows good improvement of pressure rise in diffuser at small flow rate conditions. It is found that three-dimensional blade has advantage to stabilize the secondary flow effect with improving pressure recovery of the low solidity circular cascade diffuser.
基金supported by the National Natural Science Foundation of China(U2441254,62571179).
文摘Due to the high cost of data collection and limited experimental conditions,sonar images are often scarce and of poor quality,which hinders effective feature learning and limits the performance of existing detection methods.To address this,we propose an improved YOLO model,i.e.Swin transformer-cascaded group attention YOLO(STCYOLO),for sonar image target detection,which integrates diffusion-based sample generation with a Swin transformer and cascaded group attention(CGA)mechanism.First,we fine-tune stable diffusion via LoRA and incorporate semantic features from the bootstrapping language-image pre-training text model to generate high-quality and diverse sonar images for dataset expansion.Then,we introduce Swin transformer into the YOLOv8 backbone to enhance multi-scale feature extraction for small targets,while integrating the CGA mechanism into the C2f module to improve small object perception.Additionally,the skewed intersection-over-union(SIoU)loss function is utilized to better adapt to the complexities of underwater environments.Experimental results indicate that the trained generative model is capable of producing diverse and realistic samples even in data-scarce scenarios.Compared to the original YOLOv8 model,the enhanced STC-YOLO model exhibits a 5%increase in detection accuracy and a 12.6%improvement in mean average precision,achieving high-precision detection of small underwater targets.
