To confirm the rheological characteristic of sewage in the research and application of urban sewage source heat pump system, the viscosity of sewage was investigated. The tube-type rheometer was used in this experimen...To confirm the rheological characteristic of sewage in the research and application of urban sewage source heat pump system, the viscosity of sewage was investigated. The tube-type rheometer was used in this experimental study, and the sewage was treated as homogeneous non-Newtonian fluid. In addition, the relational expression between viscosity parameters was developed, and the function of apparent viscosity was obtained. It is concluded that the viscosity characteristic of sewage is influenced largely by complex mixture in sewage, and the sewage has the characteristic of sheared densification fluid.展开更多
BACKGROUND: Delayed vitamin K deficiency is characterized by acute onset, severe illness and high fatality rate. 33%-50% survivors accompany with other various nervous system sequelas. Therefore, diagnosis and treatme...BACKGROUND: Delayed vitamin K deficiency is characterized by acute onset, severe illness and high fatality rate. 33%-50% survivors accompany with other various nervous system sequelas. Therefore, diagnosis and treatment of intracranial hemorrhage in time become a key factor for improving healing rate and reducing fatality rate and incidence of sequela. OBJECTIVE: To investigate the clinical situation, experimental characteristics, CT examination and terminative characteristics of infants with intracranial hemorrhage induced by delayed vitamin K deficiency. DESIGN: Case analysis. SETTING: Department of Pediatrics, Zhongshan Hospital Affiliated to Xiamen University. PARTICIPANTS: A total of 17 infants with intracranial hemorrhage induced by delayed vitamin K deficiency aged 1-3 months including 11 boys and 6 girls were selected from Department of Pediatrics, Zhongshan Hospital Affiliated to Xiamen University from January 1994 to December 2005. All infants had drowsiness, rejective milk, spiting milk, gaze of both eyes, tic, coma, full anterior fontanelle, high muscular tension and cerebral hernia, etc. Experimental examination demonstrated that infants had anemia at various degrees; prothrombin time and partial thromboplastin time were prolonged; platelet count was normal. CT examination indicated that screenages of subarachnoid hemorrhage, subdural hematoma, cerebral parenchyma hemorrhage and intraventricular hemorrage were changed. Hemorrhage was stopped by the application of vitamin K. All patients provided informed consent. METHODS: ① Clinical situation and physical sign of infants were observed after hospitalization and scanned with rapid spiral CT scanning system. The thickness and average space of layers were 8-10 mm and the scanning time was 5 s with window width of 30-80 Hu and window position of 28-35 Hu. ② After hospitalization, four items of blood coagulation was measured with Futura meter and biochemical indexes of blood, such as serum calcium, serum alkaline phosphatase, total bilirubin, direct bilirubin and indirect bilirubin, were detected with Roche Modular PPI automatic biochemistry analyzer. ③ After hospitalization, infants were given 5-10 mg vitamin K1 for 3-5 days, and then, they were transfused with 10-15 mL/kg fresh plasma or whole blood for 1-3 times and received other relative therapies. Therapeutic effects were evaluated based on clinical diagnosis and criteria. MAIN OUTCOME MEASURES: ① Clinical situation, physical sign and CT examination; ② results of experimental examination; ③ treatment and termination. RESULTS: A total of 17 infants with intracranial hemorrhage were involved in the final analysis. ① Clinical situation, physical sign and CT examination: All infants had pale facial expression and full or bossing anterior fontanelle. Among them, 13 infants had drowsiness or dysphoria, 12 rejective milk or emesis, 11 tic, 13 injection site hemorrhage, 2 gastrointestinal hemorrhage, 3 cerebral hernia, 11 high muscular tension and 6 cervical rigidity. CT examination demonstrated that most infants (88%, 15/17) had subarachnoid hemorrhage; 10 (59%, 10/17) had subdural hematoma; 8 (47%, 8/17) had cerebral parenchyma hemorrhage; few had intraventricular hemorrhage. In addition, results of CT examination also indicated that 17 infants had intracranial hemorrhage. Hemorrhage sites of 12 infants were equal to or more than 2, which was accounted for 70% (12/17); meanwhile, partial cases accompanied with a large area of focus of cerebral infarction or cerebral hypoxia-ischemia lesion. ② Results of experimental examination: There were 6 infants with elongation of prothrombin time, 5 with partial elongation of prothrombin time, 4 with decrease of serum calcium (1.69-2.25 mmol/L), 3 with increase of serum alkaline phosphatase, 3 with increase of total bilirubin, 3 with increase of direct bilirubin, and 3 with increase of indirect bilirubin. ③ Treatment and termination: After treatment, 12 infants were cured well, 3 improved, 1 given up and 1 died. Later, ten infants received CT re-examination at 3 months after treatment. The results indicated that 3 infants had simple subarachnoid hemorrhage and 4 had subarachnoid hemorrhage accompanying with subdural hematoma. Their focuses were absorbed well and not show as obvious sequela. One infant had subdural hematoma accompanying with subarachnoid hemorrhage, cerebral parenchyma hemorrhage, intraventricular hemorrage and cerebral hypoxia ischemia, and then, after hematom absorption, obvious cerebral malacia focus, hydrocephalus, brain atrophy and inferior accumulating fluid of dura mater were observed; 2 had subdural hematoma accompanying with subarachnoid hemorrhage and cerebral hypoxia ischemia, and then, after bleeding absorption, brain atrophy was changed remarkably; changes of hydrocephalus were observed in one infant. CONCLUSION: ① Symptoms of pale facial expression, full or bossing anterior fontanelle, drowsiness and dysphoria are observed in infants with delayed vitamin K deficiency . ② Experimental indexes demonstrate that prothrombin time and partial prothrombin time are prolonged, and numbers of infants having decrease of serum calcium are in the third place. ③ Poly-intracranial hemorrhage is a notable characteristic of CT examination. Partial infants who have poly-intracranial hemorrhage always accompany with cerebral hypoxia-ischemia lesion or cerebral infarction. Clinical situation and prognosis of infants who have a large area of intracranial hemorrhage and cerebral hypoxia-ischemia changes are poor; however, those of infants who have simple subarachnoid hemorrhage or combination of subarachnoid hemorrhage with subdural hematoma are well. ④ Effect of vitamin K on this kind of disease is well.展开更多
in this paper, an experimental research the effect of ablating material on the reflection and the transmission of microwaves in arc-heated plasma flow is presented by using the C band microwave measuring system. The ...in this paper, an experimental research the effect of ablating material on the reflection and the transmission of microwaves in arc-heated plasma flow is presented by using the C band microwave measuring system. The results show that the ablating material with accidented surface and its high temperature have remarkably affected the reflection and the transmission of microwaves. The experiment proves that the system has outstanding precision and reliability.展开更多
Microwave remote sensing has become the primary means for sea-ice research, and has been supported by a great deal of field experiments and theoretical studies regarding sea-ice microwave scattering. However, these st...Microwave remote sensing has become the primary means for sea-ice research, and has been supported by a great deal of field experiments and theoretical studies regarding sea-ice microwave scattering. However, these studies have been barely carried in the Bohai Sea. The sea-ice microwave scattering mechanism was first developed for the thin sea ice with slight roughness in the Bohai Sea in the winter of 2012, and included the backscattering coefficients which were measured on the different conditions of three bands（L, C and X）, two polarizations（HH and VV）, and incident angles of 20° to 60°, using a ground-based scatterometer and the synchronous physical parameters of the sea-ice temperature, density, thickness, salinity, and so on. The theoretical model of the sea-ice electromagnetic scattering is obtained based on these physical parameters. The research regarding the sea-ice microwave scattering mechanism is carried out through two means, which includes the comparison between the field microwave scattering data and the simulation results of the theoretical model, as well as the feature analysis of the four components of the sea-ice electromagnetic scattering. It is revealed that the sea-ice microwave scattering data and the theoretical simulation results vary in the same trend with the incident angles. Also, there is a visible variant in the sensitivity of every component to the different bands.For example, the C and X bands are sensitive to the top surface, the X band is sensitive to the scatterers, and the L and C bands are sensitive to the bottom surface, and so on. It is suggested that the features of the sea-ice surfaces and scatterers can be retrieved by the further research in the future. This experiment can provide an experimental and theoretical foundation for research regarding the sea-ice microwave scattering characteristics in the Bohai Sea.展开更多
Eight burn wound sepsis patients, in which 6 cases were diagnosed as MODS and two as septic shock, were treated consecutively in our hospital from September 1997 to October 1998. The plasma concentration of IL-6, IL-8...Eight burn wound sepsis patients, in which 6 cases were diagnosed as MODS and two as septic shock, were treated consecutively in our hospital from September 1997 to October 1998. The plasma concentration of IL-6, IL-8, TNFα and LPS were assayed before and after surgical intervention, as well as when the patients vital signs became stable. The results showed: ①The patients' conditions abruptly deteriorated when the burn wound sepsis emerged.展开更多
In this Letter, the loss and gain characteristics of an unconventional InxGa1-xAs∕Ga As asymmetrical step well structure consisting of variable indium contents of InxGa1-xAs materials are measured and analyzed for th...In this Letter, the loss and gain characteristics of an unconventional InxGa1-xAs∕Ga As asymmetrical step well structure consisting of variable indium contents of InxGa1-xAs materials are measured and analyzed for the first time, to the best of our knowledge. This special well structure is formed based on the indium-rich effect from the material growth process. The loss and gain are obtained by optical pumping and photoluminescence（PL）spectrum measurement at dual facets of an edge-emitting device. Unlike conventional quasi-rectangle wells, the asymmetrical step well may lead to a hybrid strain configuration containing both compressive and tensile strains and, thus, special loss and gain characteristics. The results will be very helpful in the development of multiple wavelength In Ga As-based semiconductor lasers.展开更多
The velocity profiles at six different cross sections and the development of the boundary layer over the surface of the overflow dam are given.Based on the experimental data using laser fcchnique the boundary layer th...The velocity profiles at six different cross sections and the development of the boundary layer over the surface of the overflow dam are given.Based on the experimental data using laser fcchnique the boundary layer thickness expression is derived.The velocity distributions within the boundary layer nearby the bottom of the dam are ana- lyzed.The fluctuating pressure on the overflow dam is compared with the fluctuating velocity nearby the bottom of the dam.展开更多
The pintle injector used for a liquid rocket engine is a newly re-attracted injection system famous for its wide throttle ability with high efficiency. The pintle injector has many variations with complex inner struct...The pintle injector used for a liquid rocket engine is a newly re-attracted injection system famous for its wide throttle ability with high efficiency. The pintle injector has many variations with complex inner structures due to its moving parts. In order to study the rotating flow near the injector tip, which was observed from the cold flow experiment using water and air, a numerical simulation was adopted and a verification of the numerical model was later conducted. For the verification process, three types of experimental data including velocity distributions of gas flows, spray angles and liquid distribution were all compared using simulated results. The numerical simulation was performed using a commercial simulation program with the Eulerian multiphase model and axisymmetric two dimensional grids. The maximum and minimum velocities of gas were within the acceptable range of agreement, however, the spray angles experienced up to 25% error when the momentum ratios were increased. The spray density distributions were quantitatively measured and had good agreement. As a result of this study, it was concluded that the simulation method was properly constructed to study specific flow characteristics of the pintle injector despite having the limitations of two dimensional and coarse grids.展开更多
The centrifugal pumps usually work at various rotational speeds. The variation in the rotational speeds will affect the internal flow, the external performance, and the anti-cavitation performance of the pump. In orde...The centrifugal pumps usually work at various rotational speeds. The variation in the rotational speeds will affect the internal flow, the external performance, and the anti-cavitation performance of the pump. In order to improve the anti-cavitation performance of the centrifugal pumps, variable-pitch inducers are placed upstream of the impeller. Because the rotational speeds directly affect the flow and the performance of the pump, it is essential to characterize the performance of the pump with a variable-pitch inducer at various rotational speeds. In this paper, the simulations and the experimental tests of a centrifugal pump with a variable-pitch inducer are designed and carried out under various rotational speed conditions. Navier-Stokes equations, coupled with a Reynolds average simulation approach, are used in the simulations. In the experimental tests, the external and anti-cavitation performances of the pump are investigated in a closed system. The following results are obtained from the simulations. Firstly, the velocity in the passage of the inducer rises with the increase of the rotational speed. Secondly, the static pressure escalates on the inducer and the impeller with the increase of the rotational speed. Thirdly, the static pressure distribution on the inducer and the impeller is asymmetric. Fourthly, the anti-cavitation performance of the pump deteriorates with the increase of the rotational speed. Additional results are gathered from an analysis of the experiments. H-Q curves are similar parabolas at various rotational speeds, while η-Q curves are similar parabolas only when n ≤6 000 r/min. The anti-cavitation performance of the pump deteriorates with the increase of the rotational speed. Finally, the simulation results are found to be consistent with the experimental results.展开更多
The clear differences between the atmosphere of Mars and the Earth coupled with the lack of a domestic research basis were significant challenges for the aerodynamic prediction and verification of Tianwen-1.In additio...The clear differences between the atmosphere of Mars and the Earth coupled with the lack of a domestic research basis were significant challenges for the aerodynamic prediction and verification of Tianwen-1.In addition,the Mars entry,descent,and landing(EDL)mission led to specific requirements for the accuracy of the aerodynamic deceleration performance,stability,aerothermal heating,and various complex aerodynamic coupling problems of the entry module.This study analyzes the key and difficult aerodynamic and aerothermodynamic problems related to the Mars EDL process.Then,the study process and results of the design and optimization of the entry module configuration are presented along with the calculations and experiments used to obtain the aerodynamic and aerothermodynamic characteristics in the Martian atmosphere.In addition,the simulation and verification of the low-frequency free oscillation characteristics under a large separation flow are described,and some special aerodynamic coupling problems such as the aeroelastic buffeting response of the trim tab are discussed.Finally,the atmospheric parameters and aerodynamic characteristics obtained from the flight data of the Tianwen-1 entry module are compared with the design data.The data obtained from the aerodynamic design,analysis,and verification of the Tianwen-1 entry module all meet the engineering requirements.In particular,the flight data results for the atmospheric parameters,trim angles of attack,and trim axial forces are within the envelopes of the prediction deviation zones.展开更多
基金Sponsored by the National Natural Science Foundation of China (Grant No.50578048)
文摘To confirm the rheological characteristic of sewage in the research and application of urban sewage source heat pump system, the viscosity of sewage was investigated. The tube-type rheometer was used in this experimental study, and the sewage was treated as homogeneous non-Newtonian fluid. In addition, the relational expression between viscosity parameters was developed, and the function of apparent viscosity was obtained. It is concluded that the viscosity characteristic of sewage is influenced largely by complex mixture in sewage, and the sewage has the characteristic of sheared densification fluid.
文摘BACKGROUND: Delayed vitamin K deficiency is characterized by acute onset, severe illness and high fatality rate. 33%-50% survivors accompany with other various nervous system sequelas. Therefore, diagnosis and treatment of intracranial hemorrhage in time become a key factor for improving healing rate and reducing fatality rate and incidence of sequela. OBJECTIVE: To investigate the clinical situation, experimental characteristics, CT examination and terminative characteristics of infants with intracranial hemorrhage induced by delayed vitamin K deficiency. DESIGN: Case analysis. SETTING: Department of Pediatrics, Zhongshan Hospital Affiliated to Xiamen University. PARTICIPANTS: A total of 17 infants with intracranial hemorrhage induced by delayed vitamin K deficiency aged 1-3 months including 11 boys and 6 girls were selected from Department of Pediatrics, Zhongshan Hospital Affiliated to Xiamen University from January 1994 to December 2005. All infants had drowsiness, rejective milk, spiting milk, gaze of both eyes, tic, coma, full anterior fontanelle, high muscular tension and cerebral hernia, etc. Experimental examination demonstrated that infants had anemia at various degrees; prothrombin time and partial thromboplastin time were prolonged; platelet count was normal. CT examination indicated that screenages of subarachnoid hemorrhage, subdural hematoma, cerebral parenchyma hemorrhage and intraventricular hemorrage were changed. Hemorrhage was stopped by the application of vitamin K. All patients provided informed consent. METHODS: ① Clinical situation and physical sign of infants were observed after hospitalization and scanned with rapid spiral CT scanning system. The thickness and average space of layers were 8-10 mm and the scanning time was 5 s with window width of 30-80 Hu and window position of 28-35 Hu. ② After hospitalization, four items of blood coagulation was measured with Futura meter and biochemical indexes of blood, such as serum calcium, serum alkaline phosphatase, total bilirubin, direct bilirubin and indirect bilirubin, were detected with Roche Modular PPI automatic biochemistry analyzer. ③ After hospitalization, infants were given 5-10 mg vitamin K1 for 3-5 days, and then, they were transfused with 10-15 mL/kg fresh plasma or whole blood for 1-3 times and received other relative therapies. Therapeutic effects were evaluated based on clinical diagnosis and criteria. MAIN OUTCOME MEASURES: ① Clinical situation, physical sign and CT examination; ② results of experimental examination; ③ treatment and termination. RESULTS: A total of 17 infants with intracranial hemorrhage were involved in the final analysis. ① Clinical situation, physical sign and CT examination: All infants had pale facial expression and full or bossing anterior fontanelle. Among them, 13 infants had drowsiness or dysphoria, 12 rejective milk or emesis, 11 tic, 13 injection site hemorrhage, 2 gastrointestinal hemorrhage, 3 cerebral hernia, 11 high muscular tension and 6 cervical rigidity. CT examination demonstrated that most infants (88%, 15/17) had subarachnoid hemorrhage; 10 (59%, 10/17) had subdural hematoma; 8 (47%, 8/17) had cerebral parenchyma hemorrhage; few had intraventricular hemorrhage. In addition, results of CT examination also indicated that 17 infants had intracranial hemorrhage. Hemorrhage sites of 12 infants were equal to or more than 2, which was accounted for 70% (12/17); meanwhile, partial cases accompanied with a large area of focus of cerebral infarction or cerebral hypoxia-ischemia lesion. ② Results of experimental examination: There were 6 infants with elongation of prothrombin time, 5 with partial elongation of prothrombin time, 4 with decrease of serum calcium (1.69-2.25 mmol/L), 3 with increase of serum alkaline phosphatase, 3 with increase of total bilirubin, 3 with increase of direct bilirubin, and 3 with increase of indirect bilirubin. ③ Treatment and termination: After treatment, 12 infants were cured well, 3 improved, 1 given up and 1 died. Later, ten infants received CT re-examination at 3 months after treatment. The results indicated that 3 infants had simple subarachnoid hemorrhage and 4 had subarachnoid hemorrhage accompanying with subdural hematoma. Their focuses were absorbed well and not show as obvious sequela. One infant had subdural hematoma accompanying with subarachnoid hemorrhage, cerebral parenchyma hemorrhage, intraventricular hemorrage and cerebral hypoxia ischemia, and then, after hematom absorption, obvious cerebral malacia focus, hydrocephalus, brain atrophy and inferior accumulating fluid of dura mater were observed; 2 had subdural hematoma accompanying with subarachnoid hemorrhage and cerebral hypoxia ischemia, and then, after bleeding absorption, brain atrophy was changed remarkably; changes of hydrocephalus were observed in one infant. CONCLUSION: ① Symptoms of pale facial expression, full or bossing anterior fontanelle, drowsiness and dysphoria are observed in infants with delayed vitamin K deficiency . ② Experimental indexes demonstrate that prothrombin time and partial prothrombin time are prolonged, and numbers of infants having decrease of serum calcium are in the third place. ③ Poly-intracranial hemorrhage is a notable characteristic of CT examination. Partial infants who have poly-intracranial hemorrhage always accompany with cerebral hypoxia-ischemia lesion or cerebral infarction. Clinical situation and prognosis of infants who have a large area of intracranial hemorrhage and cerebral hypoxia-ischemia changes are poor; however, those of infants who have simple subarachnoid hemorrhage or combination of subarachnoid hemorrhage with subdural hematoma are well. ④ Effect of vitamin K on this kind of disease is well.
文摘in this paper, an experimental research the effect of ablating material on the reflection and the transmission of microwaves in arc-heated plasma flow is presented by using the C band microwave measuring system. The results show that the ablating material with accidented surface and its high temperature have remarkably affected the reflection and the transmission of microwaves. The experiment proves that the system has outstanding precision and reliability.
基金The National Science Foundation for Young Scientists of China under contract No.41306193the National Special Research Fund for Non-Profit Marine Sector under of China under contract No.201105016the European Space Agency-Ministry of Science and Technology of the People’s Republic of China(ESA-MOST)Dragon 3 Cooperation Programme under contract No.10501
文摘Microwave remote sensing has become the primary means for sea-ice research, and has been supported by a great deal of field experiments and theoretical studies regarding sea-ice microwave scattering. However, these studies have been barely carried in the Bohai Sea. The sea-ice microwave scattering mechanism was first developed for the thin sea ice with slight roughness in the Bohai Sea in the winter of 2012, and included the backscattering coefficients which were measured on the different conditions of three bands（L, C and X）, two polarizations（HH and VV）, and incident angles of 20° to 60°, using a ground-based scatterometer and the synchronous physical parameters of the sea-ice temperature, density, thickness, salinity, and so on. The theoretical model of the sea-ice electromagnetic scattering is obtained based on these physical parameters. The research regarding the sea-ice microwave scattering mechanism is carried out through two means, which includes the comparison between the field microwave scattering data and the simulation results of the theoretical model, as well as the feature analysis of the four components of the sea-ice electromagnetic scattering. It is revealed that the sea-ice microwave scattering data and the theoretical simulation results vary in the same trend with the incident angles. Also, there is a visible variant in the sensitivity of every component to the different bands.For example, the C and X bands are sensitive to the top surface, the X band is sensitive to the scatterers, and the L and C bands are sensitive to the bottom surface, and so on. It is suggested that the features of the sea-ice surfaces and scatterers can be retrieved by the further research in the future. This experiment can provide an experimental and theoretical foundation for research regarding the sea-ice microwave scattering characteristics in the Bohai Sea.
文摘Eight burn wound sepsis patients, in which 6 cases were diagnosed as MODS and two as septic shock, were treated consecutively in our hospital from September 1997 to October 1998. The plasma concentration of IL-6, IL-8, TNFα and LPS were assayed before and after surgical intervention, as well as when the patients vital signs became stable. The results showed: ①The patients' conditions abruptly deteriorated when the burn wound sepsis emerged.
基金supported by the National Natural Science Foundation of China under Grant Nos.61376067 and61474118
文摘In this Letter, the loss and gain characteristics of an unconventional InxGa1-xAs∕Ga As asymmetrical step well structure consisting of variable indium contents of InxGa1-xAs materials are measured and analyzed for the first time, to the best of our knowledge. This special well structure is formed based on the indium-rich effect from the material growth process. The loss and gain are obtained by optical pumping and photoluminescence（PL）spectrum measurement at dual facets of an edge-emitting device. Unlike conventional quasi-rectangle wells, the asymmetrical step well may lead to a hybrid strain configuration containing both compressive and tensile strains and, thus, special loss and gain characteristics. The results will be very helpful in the development of multiple wavelength In Ga As-based semiconductor lasers.
文摘The velocity profiles at six different cross sections and the development of the boundary layer over the surface of the overflow dam are given.Based on the experimental data using laser fcchnique the boundary layer thickness expression is derived.The velocity distributions within the boundary layer nearby the bottom of the dam are ana- lyzed.The fluctuating pressure on the overflow dam is compared with the fluctuating velocity nearby the bottom of the dam.
基金supported by Advanced Research Center Program(NRF-2013R1A5A1073861)through the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIP)contracted through Advanced Space Propulsion Research Center at Seoul National University
文摘The pintle injector used for a liquid rocket engine is a newly re-attracted injection system famous for its wide throttle ability with high efficiency. The pintle injector has many variations with complex inner structures due to its moving parts. In order to study the rotating flow near the injector tip, which was observed from the cold flow experiment using water and air, a numerical simulation was adopted and a verification of the numerical model was later conducted. For the verification process, three types of experimental data including velocity distributions of gas flows, spray angles and liquid distribution were all compared using simulated results. The numerical simulation was performed using a commercial simulation program with the Eulerian multiphase model and axisymmetric two dimensional grids. The maximum and minimum velocities of gas were within the acceptable range of agreement, however, the spray angles experienced up to 25% error when the momentum ratios were increased. The spray density distributions were quantitatively measured and had good agreement. As a result of this study, it was concluded that the simulation method was properly constructed to study specific flow characteristics of the pintle injector despite having the limitations of two dimensional and coarse grids.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51406185,51579225)the Third Level 151 Talent Project in Zhejiang Province
文摘The centrifugal pumps usually work at various rotational speeds. The variation in the rotational speeds will affect the internal flow, the external performance, and the anti-cavitation performance of the pump. In order to improve the anti-cavitation performance of the centrifugal pumps, variable-pitch inducers are placed upstream of the impeller. Because the rotational speeds directly affect the flow and the performance of the pump, it is essential to characterize the performance of the pump with a variable-pitch inducer at various rotational speeds. In this paper, the simulations and the experimental tests of a centrifugal pump with a variable-pitch inducer are designed and carried out under various rotational speed conditions. Navier-Stokes equations, coupled with a Reynolds average simulation approach, are used in the simulations. In the experimental tests, the external and anti-cavitation performances of the pump are investigated in a closed system. The following results are obtained from the simulations. Firstly, the velocity in the passage of the inducer rises with the increase of the rotational speed. Secondly, the static pressure escalates on the inducer and the impeller with the increase of the rotational speed. Thirdly, the static pressure distribution on the inducer and the impeller is asymmetric. Fourthly, the anti-cavitation performance of the pump deteriorates with the increase of the rotational speed. Additional results are gathered from an analysis of the experiments. H-Q curves are similar parabolas at various rotational speeds, while η-Q curves are similar parabolas only when n ≤6 000 r/min. The anti-cavitation performance of the pump deteriorates with the increase of the rotational speed. Finally, the simulation results are found to be consistent with the experimental results.
基金This research comes from the Tianwen-1 Mars exploration mission.The authors gratefully acknowledge the contributions of the entire Tianwen-1 design team.
文摘The clear differences between the atmosphere of Mars and the Earth coupled with the lack of a domestic research basis were significant challenges for the aerodynamic prediction and verification of Tianwen-1.In addition,the Mars entry,descent,and landing(EDL)mission led to specific requirements for the accuracy of the aerodynamic deceleration performance,stability,aerothermal heating,and various complex aerodynamic coupling problems of the entry module.This study analyzes the key and difficult aerodynamic and aerothermodynamic problems related to the Mars EDL process.Then,the study process and results of the design and optimization of the entry module configuration are presented along with the calculations and experiments used to obtain the aerodynamic and aerothermodynamic characteristics in the Martian atmosphere.In addition,the simulation and verification of the low-frequency free oscillation characteristics under a large separation flow are described,and some special aerodynamic coupling problems such as the aeroelastic buffeting response of the trim tab are discussed.Finally,the atmospheric parameters and aerodynamic characteristics obtained from the flight data of the Tianwen-1 entry module are compared with the design data.The data obtained from the aerodynamic design,analysis,and verification of the Tianwen-1 entry module all meet the engineering requirements.In particular,the flight data results for the atmospheric parameters,trim angles of attack,and trim axial forces are within the envelopes of the prediction deviation zones.
