Different operating conditions (e.g. design and off-design) may lead to a significant difference in the hydrodynamics performance of a ship, especially in the total resistance and wake field of ships. This work inve...Different operating conditions (e.g. design and off-design) may lead to a significant difference in the hydrodynamics performance of a ship, especially in the total resistance and wake field of ships. This work investigated the hydrodynamic performance of the well-known KRISO 3600 TEU Container Ship (KCS) under three different operating conditions by means of Particle Image Velocimetry (P/V) and Computational Fluid Dynamics (CFD). The comparison results show that the use of PIV to measure a ship's nominal wake field is an important method which has the advantages of being contactless and highly accurate. Acceptable agreements between the results obtained by the two different methods are achieved. Results indicate that the total resistances of the KCS model under two off-design conditions are 23.88% and 13.92% larger than that under the designed condition, respectively.展开更多
<div style="text-align:justify;"> With the wide application of renewable energy, energy storage technology has become a research hotspot. In order to overcome the shortcomings of energy loss caused by ...<div style="text-align:justify;"> With the wide application of renewable energy, energy storage technology has become a research hotspot. In order to overcome the shortcomings of energy loss caused by compression heating in compressed air energy storage technology, a novel constant-pressure pumped hydro combined with compressed air energy storage system was proposed. To deepen the understanding of the system and make the analysis closer to reality, this paper adopted an off-design model of the compressor to calculate and analyze the effect of key parameters on system thermodynamics performance. In addition, the results of this paper were compared with previous research results, and it was found that the current efficiency considering the off-design model of compressor was generally 2% - 5% higher than the previous efficiency. With increased preset pressure or with decreased terminal pressure, both the previous efficiency and current efficiency of the system increased. The exergy destruction coefficient of the throttle valve reached 4%. System efficiency was more sensitive to changes in water pump efficiency and hydroturbine efficiency. </div>展开更多
Gas turbines are considered as one of the leading internal combustion engines in modern air transportation due to its favourable power to weight ratio and its continuous combustion process. Recent research focus has b...Gas turbines are considered as one of the leading internal combustion engines in modern air transportation due to its favourable power to weight ratio and its continuous combustion process. Recent research focus has been concerned with performance improvements aimed at reduced fuel consumption and hence reduced impact on the environment. This study is aimed at using theoretical and computational methods to model the operation and performance a turbojet gas turbine engine. The commercial software GasTurb13 was used for the theoretical simulation while Microsoft Excel was used for the analytical study. GasTurb13 solved the model using pseudo-perfect gas models i.e. component maps since the specific gas ratio could not be inputted into the solver. The effect of changes in the Mach number and altitude on the engine performance was studied. Also the effect of changes in the compressor pressure ratio, the turbine inlet temperature and the afterburner exit temperature were also studied. Results obtained showed the optimum pressure ratio at maximum thrust constraint to be 16.78 for the turbojet engine operating at Mach number (Ma) = 0.8 and altitude = 10,000 m, Turbine inlet temperature (TIT) = 1200 K and Afterburner exit temperature = 1800 K.展开更多
A theoretical calculation method of off-design performance is developed for an axial flow fan of oil cooling system in helicopter,including calculation of aerodynamic parameters and performance parameters.When calcula...A theoretical calculation method of off-design performance is developed for an axial flow fan of oil cooling system in helicopter,including calculation of aerodynamic parameters and performance parameters.When calculating inlet shock loss,the shock loss coefficient is obtained by comparing results of theoretical calculation,experimental and numerical calculation.The theoretical results and numerical results show that all air velocity components increase from hub to shroud in main flow area at rated condition.Tip leakage vortex moves downstream as flow rate increases.When flow rate decreases,Re decreases,and boundary layer thickness from hub to shroud area all increases gradually.Tip leakage vortex moves upstream,and secondary loss increases.Low speed area in the passage is widened along with high speed area moving to hub area,influenced by boundary layer separation.Consequently wake area and jet area at fan outlet are both larger than rated condition.Therefore optimization design for off-design performance of the fan is required on aerodynamic parameters influencing fan loss.A reliable method is supplied for estimating altitude performance of lubricating system in helicopter.展开更多
Using the efficient,space-saving,and flexible supercritical carbon dioxide(sCO_(2)) Brayton cycle is a promising approach for improving the performance of nuclear-powered ships.The purpose of this paper is to design a...Using the efficient,space-saving,and flexible supercritical carbon dioxide(sCO_(2)) Brayton cycle is a promising approach for improving the performance of nuclear-powered ships.The purpose of this paper is to design and compare sCO_(2) cycle power systems suitable for nuclear-powered ships.Considering the characteristics of nuclear-powered ships,this paper uses different indicators to comprehensively evaluate the efficiency,cost,volume,and partial load performance of several nuclear-powered sCO_(2) cycles.Four load-following strategies are also designed and compared.The results show that the partial cooling cycle is most suitable for nuclear-powered ships because it offers both high thermal efficiency and low volume and cost,and can maintain relatively high thermal efficiency at partial loads.Additionally,the new load-following strategy that adjusts the turbine speed can keep the compressor away from the surge line,making the cycle more flexible and efficient compared to traditional inventory and turbine bypass strategies.展开更多
The comprehensive optimization of thermodynamic and economic performances is significant for the engineering application of ocean thermal energy conversion(OTEC).Motivated by this,this paper develops a thermo-economic...The comprehensive optimization of thermodynamic and economic performances is significant for the engineering application of ocean thermal energy conversion(OTEC).Motivated by this,this paper develops a thermo-economic OTEC model and conducts a sensitivity analysis of the OTEC system concerning its thermodynamic and economic performances.Specifically,the impact of warm-seawater temperature and cold-seawater pumping depth on the net thermal efficiency and the total investment cost are investigated.The results indicate that,an increase in warm-seawater temperature and cold-seawater pumping depth can improve the net thermal efficiency and a higher installed capacity is beneficial to the system economics.Building on these,a design optimization method with considering the on-design and off-design conditions is proposed in this paper,and the dynamic variation of warm-seawater temperature are considered in this method.In multi-objective optimization procedure,with the objective functions being the average net thermal efficiency and unit power cost within the operational cycle,the non-dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ) is employed to maximize the net thermal efficiency and minimize the unit power investment cost,resulting in the Pareto front.The net thermal efficiencies of OTEC systems using ammonia and R245fa as working fluids are 4.13% and 3.8%,respectively.This represents an improvement of 19.4% and 57.0%,respectively,compared to traditional optimization methods that do not account for off-design conditions.展开更多
Experimental investigations are performed in a three-stage low-speed axial compressor with variable inlet guide vanes(IGV) and adjustable stators.The characteristics of the compressor,especially the efficiency and sta...Experimental investigations are performed in a three-stage low-speed axial compressor with variable inlet guide vanes(IGV) and adjustable stators.The characteristics of the compressor,especially the efficiency and stall margin,are analyzed in design and off-design operation conditions by adjusting stagger angles of IGV and stators as well as changing the rotational speed.The experimental results show that the off-design performance of the multistage axial compressor is improved by restaggering of IGV and stators related to rotational speed.Considering the background of engineering applications,digital signal processing(DSP) technique is used to realize online adjustment of stagger angles according to the corresponding relations between incidence angles of rotor and rotational speed.展开更多
The turbulent flow in the draft tube of a Francis turbine is very complicated while working under off-design conditions. Although the off-design conditions were widely studied, the vortex core line in the draft tube o...The turbulent flow in the draft tube of a Francis turbine is very complicated while working under off-design conditions. Although the off-design conditions were widely studied, the vortex core line in the draft tube of a Francis turbine with splitter blades is not well understood, especially the vortex rope property. This letter presents a prediction of the behavior of the vortex rope in the draft tube of the Francis-99 turbine obtained by the computational fluid dynamics (CFD), where the Liutex/Rortex method, as the most recent vortex definition, is applied to analyze the periodical precession of the vortex rope in the draft tube cone. The advantage of this Liutex/Rortex method is shown by its enhanced ability to represent the vortex rope structurewith the vortex-core lines. Furthermore, since it seems to be very hard to define a sharp boundary surface for the whole vortex structure, it is advantageousfocusing only on the vortex core line,by which different vortex structures can be clearly differentiated. The evolution of the vortex core and the process of the vortex breakdown in the draft tube are revealed, which might help to comprehend the development of the turbulent flow in the draft tube.展开更多
离轴反射系统设计的关键环节是确定适用初始结构并进行优化,一般从同轴结构或者专利库中寻找相似的结构开始优化,这往往需要耗费大量的时间。以Seidel像差理论为依据,研究了一种获取离轴四反系统初始结构的设计方法。在设计之初引入视...离轴反射系统设计的关键环节是确定适用初始结构并进行优化,一般从同轴结构或者专利库中寻找相似的结构开始优化,这往往需要耗费大量的时间。以Seidel像差理论为依据,研究了一种获取离轴四反系统初始结构的设计方法。在设计之初引入视场偏置,通过追迹近轴光线给出五种单色像差的初级Seidel像差表示。以Seidel像差绝对值最小化作为目标函数,同时加入对光学和系统结构上的限制条件构建含有约束条件的单目标非线性优化模型,并通过粒子群优化算法进行求解。在此基础上,通过MATLAB调用CODE V API接口,判断此视场偏置情况下是否满足无遮拦的条件,并从中挑选出满足条件的初始结构。设计了一款焦距为1200 mm,视场1.2°×20°,F数为6的离轴四反光学系统,系统结构布局紧凑,成像质量良好,各项指标均满足设计要求。展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.41176074,51209048,51379043,and 51409063)the High Technology Ship Scientific Research Project of Ministry of Industry and Information Technology of China(Grant No.G014613002)
文摘Different operating conditions (e.g. design and off-design) may lead to a significant difference in the hydrodynamics performance of a ship, especially in the total resistance and wake field of ships. This work investigated the hydrodynamic performance of the well-known KRISO 3600 TEU Container Ship (KCS) under three different operating conditions by means of Particle Image Velocimetry (P/V) and Computational Fluid Dynamics (CFD). The comparison results show that the use of PIV to measure a ship's nominal wake field is an important method which has the advantages of being contactless and highly accurate. Acceptable agreements between the results obtained by the two different methods are achieved. Results indicate that the total resistances of the KCS model under two off-design conditions are 23.88% and 13.92% larger than that under the designed condition, respectively.
文摘<div style="text-align:justify;"> With the wide application of renewable energy, energy storage technology has become a research hotspot. In order to overcome the shortcomings of energy loss caused by compression heating in compressed air energy storage technology, a novel constant-pressure pumped hydro combined with compressed air energy storage system was proposed. To deepen the understanding of the system and make the analysis closer to reality, this paper adopted an off-design model of the compressor to calculate and analyze the effect of key parameters on system thermodynamics performance. In addition, the results of this paper were compared with previous research results, and it was found that the current efficiency considering the off-design model of compressor was generally 2% - 5% higher than the previous efficiency. With increased preset pressure or with decreased terminal pressure, both the previous efficiency and current efficiency of the system increased. The exergy destruction coefficient of the throttle valve reached 4%. System efficiency was more sensitive to changes in water pump efficiency and hydroturbine efficiency. </div>
文摘Gas turbines are considered as one of the leading internal combustion engines in modern air transportation due to its favourable power to weight ratio and its continuous combustion process. Recent research focus has been concerned with performance improvements aimed at reduced fuel consumption and hence reduced impact on the environment. This study is aimed at using theoretical and computational methods to model the operation and performance a turbojet gas turbine engine. The commercial software GasTurb13 was used for the theoretical simulation while Microsoft Excel was used for the analytical study. GasTurb13 solved the model using pseudo-perfect gas models i.e. component maps since the specific gas ratio could not be inputted into the solver. The effect of changes in the Mach number and altitude on the engine performance was studied. Also the effect of changes in the compressor pressure ratio, the turbine inlet temperature and the afterburner exit temperature were also studied. Results obtained showed the optimum pressure ratio at maximum thrust constraint to be 16.78 for the turbojet engine operating at Mach number (Ma) = 0.8 and altitude = 10,000 m, Turbine inlet temperature (TIT) = 1200 K and Afterburner exit temperature = 1800 K.
基金Foundation item: Supported by the National Natural Science Foundation of China (Grant Nos. 41176074, 51379043 and 51409063)Acknowledgement This project was supported by the National Natural Science Foundation of China (Grant Nos. 41176074,51379043 and 51409063) and was conducted in response to the great support received from a basic research project entitled "Multihull Ship Technology Key Laboratory of Fundamental Science for National Defence", which was conducted at Harbin Engineering University. The authors would like to extend their sincere gratitude to their colleagues in the towing tank laboratory.
文摘试验性的测试被进行评估 L 类型 podded propulsor 的水动力学性能在直向前,用一台开水的测量仪器的运动和离开设计条件为 podded propulsors 由作者发展了,拖引坦克的一个轮船模型,并且在水粒子图象 velocimetry (PIV ) 下面测量系统。在条件的三种类型下面, L 类型 podded propulsor 的主要参数被测量,包括推进器戳和转矩,以及整个豆荚单位的戳,方面力量,和时刻。另外,在推进器和神气之间的节上的流动领域被分析。试验性的结果证明动态 azimuthing 率和方向和转弯的方向在推进器和整个豆荚单位上影响力量。因为推进器旋转的效果,力量不均匀地在左、正确的 azimuthing 方向之间被散布。这研究的调查结果为关于 L 类型 podded propulsors 的进一步的研究提供一个基础。
基金National Aviation Science Foundation of China (No. 20080451014)
文摘A theoretical calculation method of off-design performance is developed for an axial flow fan of oil cooling system in helicopter,including calculation of aerodynamic parameters and performance parameters.When calculating inlet shock loss,the shock loss coefficient is obtained by comparing results of theoretical calculation,experimental and numerical calculation.The theoretical results and numerical results show that all air velocity components increase from hub to shroud in main flow area at rated condition.Tip leakage vortex moves downstream as flow rate increases.When flow rate decreases,Re decreases,and boundary layer thickness from hub to shroud area all increases gradually.Tip leakage vortex moves upstream,and secondary loss increases.Low speed area in the passage is widened along with high speed area moving to hub area,influenced by boundary layer separation.Consequently wake area and jet area at fan outlet are both larger than rated condition.Therefore optimization design for off-design performance of the fan is required on aerodynamic parameters influencing fan loss.A reliable method is supplied for estimating altitude performance of lubricating system in helicopter.
基金supported by the National Natural Science Foundation of China (52276150)。
文摘Using the efficient,space-saving,and flexible supercritical carbon dioxide(sCO_(2)) Brayton cycle is a promising approach for improving the performance of nuclear-powered ships.The purpose of this paper is to design and compare sCO_(2) cycle power systems suitable for nuclear-powered ships.Considering the characteristics of nuclear-powered ships,this paper uses different indicators to comprehensively evaluate the efficiency,cost,volume,and partial load performance of several nuclear-powered sCO_(2) cycles.Four load-following strategies are also designed and compared.The results show that the partial cooling cycle is most suitable for nuclear-powered ships because it offers both high thermal efficiency and low volume and cost,and can maintain relatively high thermal efficiency at partial loads.Additionally,the new load-following strategy that adjusts the turbine speed can keep the compressor away from the surge line,making the cycle more flexible and efficient compared to traditional inventory and turbine bypass strategies.
基金supported by National Key R&D Program of China(No.2019YFB1504301).
文摘The comprehensive optimization of thermodynamic and economic performances is significant for the engineering application of ocean thermal energy conversion(OTEC).Motivated by this,this paper develops a thermo-economic OTEC model and conducts a sensitivity analysis of the OTEC system concerning its thermodynamic and economic performances.Specifically,the impact of warm-seawater temperature and cold-seawater pumping depth on the net thermal efficiency and the total investment cost are investigated.The results indicate that,an increase in warm-seawater temperature and cold-seawater pumping depth can improve the net thermal efficiency and a higher installed capacity is beneficial to the system economics.Building on these,a design optimization method with considering the on-design and off-design conditions is proposed in this paper,and the dynamic variation of warm-seawater temperature are considered in this method.In multi-objective optimization procedure,with the objective functions being the average net thermal efficiency and unit power cost within the operational cycle,the non-dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ) is employed to maximize the net thermal efficiency and minimize the unit power investment cost,resulting in the Pareto front.The net thermal efficiencies of OTEC systems using ammonia and R245fa as working fluids are 4.13% and 3.8%,respectively.This represents an improvement of 19.4% and 57.0%,respectively,compared to traditional optimization methods that do not account for off-design conditions.
基金supported by the Key Program of the National Natural Science Foundation of China (Grant No 50736007)
文摘Experimental investigations are performed in a three-stage low-speed axial compressor with variable inlet guide vanes(IGV) and adjustable stators.The characteristics of the compressor,especially the efficiency and stall margin,are analyzed in design and off-design operation conditions by adjusting stagger angles of IGV and stators as well as changing the rotational speed.The experimental results show that the off-design performance of the multistage axial compressor is improved by restaggering of IGV and stators related to rotational speed.Considering the background of engineering applications,digital signal processing(DSP) technique is used to realize online adjustment of stagger angles according to the corresponding relations between incidence angles of rotor and rotational speed.
文摘The turbulent flow in the draft tube of a Francis turbine is very complicated while working under off-design conditions. Although the off-design conditions were widely studied, the vortex core line in the draft tube of a Francis turbine with splitter blades is not well understood, especially the vortex rope property. This letter presents a prediction of the behavior of the vortex rope in the draft tube of the Francis-99 turbine obtained by the computational fluid dynamics (CFD), where the Liutex/Rortex method, as the most recent vortex definition, is applied to analyze the periodical precession of the vortex rope in the draft tube cone. The advantage of this Liutex/Rortex method is shown by its enhanced ability to represent the vortex rope structurewith the vortex-core lines. Furthermore, since it seems to be very hard to define a sharp boundary surface for the whole vortex structure, it is advantageousfocusing only on the vortex core line,by which different vortex structures can be clearly differentiated. The evolution of the vortex core and the process of the vortex breakdown in the draft tube are revealed, which might help to comprehend the development of the turbulent flow in the draft tube.
文摘离轴反射系统设计的关键环节是确定适用初始结构并进行优化,一般从同轴结构或者专利库中寻找相似的结构开始优化,这往往需要耗费大量的时间。以Seidel像差理论为依据,研究了一种获取离轴四反系统初始结构的设计方法。在设计之初引入视场偏置,通过追迹近轴光线给出五种单色像差的初级Seidel像差表示。以Seidel像差绝对值最小化作为目标函数,同时加入对光学和系统结构上的限制条件构建含有约束条件的单目标非线性优化模型,并通过粒子群优化算法进行求解。在此基础上,通过MATLAB调用CODE V API接口,判断此视场偏置情况下是否满足无遮拦的条件,并从中挑选出满足条件的初始结构。设计了一款焦距为1200 mm,视场1.2°×20°,F数为6的离轴四反光学系统,系统结构布局紧凑,成像质量良好,各项指标均满足设计要求。