AASHTO’s guideline for geometric design of highways and similar guidelines require that roadside areas on the inside of horizontal curves be cleared of high objects to provide stopping sight distance. The guidelines ...AASHTO’s guideline for geometric design of highways and similar guidelines require that roadside areas on the inside of horizontal curves be cleared of high objects to provide stopping sight distance. The guidelines have analytical models for determining the extent of clearance, known as the horizontal sightline offset or clearance offset, for simple curves. Researchers in the past have developed analytical models for clearance offsets for spiraled and reverse curves. Very few researchers developed analytical models for available sight distances for compound curves. Still missing are models for horizontal sightline offsets and locations of the offsets for compound curves. The objective of this paper is to present development of analytical models and charts for determining horizontal sightline offsets and their locations for compound curves. The paper considers curves whose component arcs are individually shorter than stopping sight distance. The resulting models and the charts have been verified with accurate values determined using graphical methods. The models and the charts will find application in geometric design of highway compound curves.展开更多
A new trough imaging solar collector with multiple compounding curved surfaces has been designed. Its working principle and design parameters have been introduced. The experimental curve of temperature rising of the s...A new trough imaging solar collector with multiple compounding curved surfaces has been designed. Its working principle and design parameters have been introduced. The experimental curve of temperature rising of the system with time under the real weather has been given. The system efficiency and the relation between efficiency and temperature have been calculated. The test result shows that the system has the advantages of high collecting temperature and not obvious variety of the collecting efficiency with the operating temperature. Therefore, this collector is a quite ideal medium temperature solar collector.展开更多
With the increasing of inlet temperature and pressure of the heavy-duty gas turbine, the flow conditions in the turbine become more complicated, and the aerodynamic loss inside the cascade also increases. This problem...With the increasing of inlet temperature and pressure of the heavy-duty gas turbine, the flow conditions in the turbine become more complicated, and the aerodynamic loss inside the cascade also increases. This problem is particularly serious in small aspect ratio blades. How to reduce the aerodynamic loss inside the cascade channel becomes quite urgent now. Based on previous studies, it can be seen that the positively curved blade can reduce the secondary flow loss at the blade end, but it will increase the profile loss, while the negatively curved blade behaves just in the opposite way of the positively curved blade. Therefore, this paper proposes a positively curved blade with negatively curving at blade end, and this design can help to reduce the negative effect of the positive curving modification on the middle of the blade. In this paper, the last stage of the GE-E3 high-pressure turbine is taken as the research object, and the composite curving modification of the last stage stator cascade is carried out. The influence of the positive curving and the composite curving on the flow field is compared by numerical simulation. The results show that within the scope of this study, the reduction amplitude of total pressure loss coefficient of composite curved blade is about 1.10 times that of positive curved blade, and the increasing amplitude of total to static efficiency is about 1.16 times that of positive curved blade. The composite curving modification greatly improves the turbine performance. The research results provide guidance for the design of high-performance turbine blades.展开更多
文摘AASHTO’s guideline for geometric design of highways and similar guidelines require that roadside areas on the inside of horizontal curves be cleared of high objects to provide stopping sight distance. The guidelines have analytical models for determining the extent of clearance, known as the horizontal sightline offset or clearance offset, for simple curves. Researchers in the past have developed analytical models for clearance offsets for spiraled and reverse curves. Very few researchers developed analytical models for available sight distances for compound curves. Still missing are models for horizontal sightline offsets and locations of the offsets for compound curves. The objective of this paper is to present development of analytical models and charts for determining horizontal sightline offsets and their locations for compound curves. The paper considers curves whose component arcs are individually shorter than stopping sight distance. The resulting models and the charts have been verified with accurate values determined using graphical methods. The models and the charts will find application in geometric design of highway compound curves.
基金Acknowledgments This work is supported by the National Natural Science Foundation of China （No.50576004） and National ＂863＂ Hi-Tech Development Program of China （No.2007AA05Z433）.
文摘A new trough imaging solar collector with multiple compounding curved surfaces has been designed. Its working principle and design parameters have been introduced. The experimental curve of temperature rising of the system with time under the real weather has been given. The system efficiency and the relation between efficiency and temperature have been calculated. The test result shows that the system has the advantages of high collecting temperature and not obvious variety of the collecting efficiency with the operating temperature. Therefore, this collector is a quite ideal medium temperature solar collector.
基金supported by National Science and Technology Major Project(HT-J2019-Ⅱ-0010-0030)National Science and Technology Major Project(HT-Y2019-Ⅰ-0002-0003)National Science and Technology Major Project(J2019-Ⅱ-0016-0037).
文摘With the increasing of inlet temperature and pressure of the heavy-duty gas turbine, the flow conditions in the turbine become more complicated, and the aerodynamic loss inside the cascade also increases. This problem is particularly serious in small aspect ratio blades. How to reduce the aerodynamic loss inside the cascade channel becomes quite urgent now. Based on previous studies, it can be seen that the positively curved blade can reduce the secondary flow loss at the blade end, but it will increase the profile loss, while the negatively curved blade behaves just in the opposite way of the positively curved blade. Therefore, this paper proposes a positively curved blade with negatively curving at blade end, and this design can help to reduce the negative effect of the positive curving modification on the middle of the blade. In this paper, the last stage of the GE-E3 high-pressure turbine is taken as the research object, and the composite curving modification of the last stage stator cascade is carried out. The influence of the positive curving and the composite curving on the flow field is compared by numerical simulation. The results show that within the scope of this study, the reduction amplitude of total pressure loss coefficient of composite curved blade is about 1.10 times that of positive curved blade, and the increasing amplitude of total to static efficiency is about 1.16 times that of positive curved blade. The composite curving modification greatly improves the turbine performance. The research results provide guidance for the design of high-performance turbine blades.
