在颗粒流动的动理学理论(Kinetic Theory of Granular Flow,KTGF)基础上,采用双流体模型(Two-Fluid Model,TFM)模拟风扇旋转作用下气体和颗粒的流动行为,分析摩擦应力模型和摩擦起始体积分数对颗粒携带效率的影响。结果表明,流场依据颗...在颗粒流动的动理学理论(Kinetic Theory of Granular Flow,KTGF)基础上,采用双流体模型(Two-Fluid Model,TFM)模拟风扇旋转作用下气体和颗粒的流动行为,分析摩擦应力模型和摩擦起始体积分数对颗粒携带效率的影响。结果表明,流场依据颗粒速度与体积分数分布被划分为诱导上流区、自由流动区和尾迹流动区。降低摩擦起始体积分数导致颗粒整体压力减小了3.9%。在摩擦起始体积分数分别为0.4和0.5的条件下,与Schaffer摩擦模型相比,Johnson-Jackson(JJ)模型预测风扇携带的颗粒质量分别增加了4.06 kg和1.08 kg。Johnson-Jackson模型下摩擦起始体积分数的影响要高于Schaffer模型,目前的数值模拟证实了气固双流体模型与颗粒动理学理论以及多重参考系法可以有效地应用于分析旋转风力驱动引起的颗粒夹带现象。展开更多
This article reports the findings on the adverse effect of the crosswind on the performance of natural draft cooling towers through numerical computation with the k-epsilon eddy-viscosity turbulence model. It is obser...This article reports the findings on the adverse effect of the crosswind on the performance of natural draft cooling towers through numerical computation with the k-epsilon eddy-viscosity turbulence model. It is observed here that the cause of the adverse effect of the crosswind on the cooling towers call be attributed to the around flow effect which destroys the radial inflow into the cooling towers when the wind is absent. Hence, a significant deterioration in the heat transfer from the heat exchangers at lateral sides occurs.展开更多
To investigate the natural frequencies and towing behaviors of a 3-bucket foundation platform at different drafts, the decay and towing experiments were carried out in a towing tank on a scale of 1:20. The air pressur...To investigate the natural frequencies and towing behaviors of a 3-bucket foundation platform at different drafts, the decay and towing experiments were carried out in a towing tank on a scale of 1:20. The air pressure inside the bucket foundations, the water pressure at the bottom of the bucket foundations, the acceleration of the platform and the towing force were determined in the test process. The time-history curves of the measured parameters were obtained, and the frequency responses of the parameters at different drafts were analyzed by means of fast Fourier transform(FFT). The results showed that the platform natural frequency of heave decreased slightly with the rise of draft. The natural frequencies of roll and pitch are much lower than that of heave, and they increased slightly with the increase of draft. When towing in the following sea, the maximum acceleration of surge, sway and heave has downward trends with the increase of draft, but the change range decreased gradually with the increase of draft. When the draft is 5.0 m(the ratio of draft to bucket height is 0.56), the towing dynamic responses achieve the maximum, which is not conducive to the towing of the platform. When the draft is 6.0 m(the ratio of draft to bucket height is 0.67), the towing dynamic responses are the most stable.展开更多
The value of form factor k at different drafts is important in predicting full-scale total resistance and speed for different types of ships. In the ITTC community, most organizations predict form factor k using a low...The value of form factor k at different drafts is important in predicting full-scale total resistance and speed for different types of ships. In the ITTC community, most organizations predict form factor k using a low-speed model test. However, this method is problematic for ships with bulbous bows and transom. In this article, a Computational Fluid Dynamics(CFD)-based method is introduced to obtain k for different type of ships at different drafts, and a comparison is made between the CFD method and the model test. The results show that the CFD method produces reasonable k values. A grid generating method and turbulence model are briefly discussed in the context of obtaining a consistent k using CFD.展开更多
Solid-liquid suspension in an agitated tank with a draft tube was investigated witha newly developed infrared turbidimeter for measuring solid concentration.The diameter of theflared inlet transition tube and the dist...Solid-liquid suspension in an agitated tank with a draft tube was investigated witha newly developed infrared turbidimeter for measuring solid concentration.The diameter of theflared inlet transition tube and the distance from the inlet to the tank bottom are two importantparameters for draft tube design The NAX-4 impeller,developed in this study,is characterized byits high flow efficiency and low power consumption.Some modifications are made to the Bald′smodel by considering the effects of solid concentration and fluid viscosity on the critical speed forcomplete off-bottom suspension.The modified equation fits the experimental data satisfactority andcan be used in scale-up展开更多
文摘在颗粒流动的动理学理论(Kinetic Theory of Granular Flow,KTGF)基础上,采用双流体模型(Two-Fluid Model,TFM)模拟风扇旋转作用下气体和颗粒的流动行为,分析摩擦应力模型和摩擦起始体积分数对颗粒携带效率的影响。结果表明,流场依据颗粒速度与体积分数分布被划分为诱导上流区、自由流动区和尾迹流动区。降低摩擦起始体积分数导致颗粒整体压力减小了3.9%。在摩擦起始体积分数分别为0.4和0.5的条件下,与Schaffer摩擦模型相比,Johnson-Jackson(JJ)模型预测风扇携带的颗粒质量分别增加了4.06 kg和1.08 kg。Johnson-Jackson模型下摩擦起始体积分数的影响要高于Schaffer模型,目前的数值模拟证实了气固双流体模型与颗粒动理学理论以及多重参考系法可以有效地应用于分析旋转风力驱动引起的颗粒夹带现象。
基金The project supported by the National Natural Science Foundation of China (19725208) and the National Climbing project of China
文摘This article reports the findings on the adverse effect of the crosswind on the performance of natural draft cooling towers through numerical computation with the k-epsilon eddy-viscosity turbulence model. It is observed here that the cause of the adverse effect of the crosswind on the cooling towers call be attributed to the around flow effect which destroys the radial inflow into the cooling towers when the wind is absent. Hence, a significant deterioration in the heat transfer from the heat exchangers at lateral sides occurs.
基金Supported by the National Natural Science Foundation of China(No.51309179)Tianjin Municipal Natural Science Foundation(No.14JCQNJC07000)the State Key Laboratory of Hydraulic Engineering Simulation and Safety(Tianjin University)
文摘To investigate the natural frequencies and towing behaviors of a 3-bucket foundation platform at different drafts, the decay and towing experiments were carried out in a towing tank on a scale of 1:20. The air pressure inside the bucket foundations, the water pressure at the bottom of the bucket foundations, the acceleration of the platform and the towing force were determined in the test process. The time-history curves of the measured parameters were obtained, and the frequency responses of the parameters at different drafts were analyzed by means of fast Fourier transform(FFT). The results showed that the platform natural frequency of heave decreased slightly with the rise of draft. The natural frequencies of roll and pitch are much lower than that of heave, and they increased slightly with the increase of draft. When towing in the following sea, the maximum acceleration of surge, sway and heave has downward trends with the increase of draft, but the change range decreased gradually with the increase of draft. When the draft is 5.0 m(the ratio of draft to bucket height is 0.56), the towing dynamic responses achieve the maximum, which is not conducive to the towing of the platform. When the draft is 6.0 m(the ratio of draft to bucket height is 0.67), the towing dynamic responses are the most stable.
基金Supported by Ministry of Industry and Information(No.K24097)
文摘The value of form factor k at different drafts is important in predicting full-scale total resistance and speed for different types of ships. In the ITTC community, most organizations predict form factor k using a low-speed model test. However, this method is problematic for ships with bulbous bows and transom. In this article, a Computational Fluid Dynamics(CFD)-based method is introduced to obtain k for different type of ships at different drafts, and a comparison is made between the CFD method and the model test. The results show that the CFD method produces reasonable k values. A grid generating method and turbulence model are briefly discussed in the context of obtaining a consistent k using CFD.
文摘Solid-liquid suspension in an agitated tank with a draft tube was investigated witha newly developed infrared turbidimeter for measuring solid concentration.The diameter of theflared inlet transition tube and the distance from the inlet to the tank bottom are two importantparameters for draft tube design The NAX-4 impeller,developed in this study,is characterized byits high flow efficiency and low power consumption.Some modifications are made to the Bald′smodel by considering the effects of solid concentration and fluid viscosity on the critical speed forcomplete off-bottom suspension.The modified equation fits the experimental data satisfactority andcan be used in scale-up
