从理论分析和数值计算两方面研究不同背压下的液体离心喷嘴内液膜厚度.在经典理论的基础上建立的包含气液界面摩擦作用的损失系数理论模型并不足以体现背压对液膜厚度的改变;通过使用旋转轴对称模型在自适应网格中求解耦合VOF(volume of...从理论分析和数值计算两方面研究不同背压下的液体离心喷嘴内液膜厚度.在经典理论的基础上建立的包含气液界面摩擦作用的损失系数理论模型并不足以体现背压对液膜厚度的改变;通过使用旋转轴对称模型在自适应网格中求解耦合VOF(volume of fluid)方程的Navier-Stokes方程组的数值模拟表明,随气体密度增加而减小的气液界面附近过渡区域中的平均速度分布是导致液膜厚度增加的原因.展开更多
直接空冷凝汽器积灰和迎面风速降低是影响机组背压上升的主要因素,机组背压升高会影响机组出力。以某330 MW直接空冷机组为例,分析了积灰和迎面风速对传热系数和机组背压的影响规律,并提出了防治措施。结果表明:当积灰厚度达到1.0 mm时...直接空冷凝汽器积灰和迎面风速降低是影响机组背压上升的主要因素,机组背压升高会影响机组出力。以某330 MW直接空冷机组为例,分析了积灰和迎面风速对传热系数和机组背压的影响规律,并提出了防治措施。结果表明:当积灰厚度达到1.0 mm时,机组背压由设计值34.0 k Pa升高到49.0 k Pa,机组功率降低了8.6 MW;迎面风速由设计值2.2 m/s降低到1.6 m/s,机组背压由设计值34.0 k Pa升高到50.1 k Pa,机组功率减小了9.4 MW。展开更多
In this paper,a correlation model between centrifugal compressor and its piping system is built based on plenum chamber model and throttle valve model.This model could be used to conduct numerical analysis of compress...In this paper,a correlation model between centrifugal compressor and its piping system is built based on plenum chamber model and throttle valve model.This model could be used to conduct numerical analysis of compressor systems from steady to surge operating points.Three dimensional unsteady numerical simulations were performed to predict the performance of a centrifugal compressor.The flow structures in blade passage and diffuser were plotted and analyzed.The fluctuations of pressure and mass flow rate over time at the outlet of diffuser are obtained at surge condition.The characteristic changes of compressor-pipe network under the surge condition were carried out,and the effects of model characteristics including valve coefficient and backpressure on surge were analyzed.展开更多
Experimental investigations are conducted on an axisymmetric hypersonic inlet to evaluate the effects of trips on oscillatory flows. The model exit is throttled with a fixed block to generate oscillatory flows at a fr...Experimental investigations are conducted on an axisymmetric hypersonic inlet to evaluate the effects of trips on oscillatory flows. The model exit is throttled with a fixed block to generate oscillatory flows at a freestream Mach number of 6 in a conventional wind tunnel and a shock tunnel. Schlieren imaging and pressure measurements are adopted to record unsteady flow features.Results indicate that trips with a 1 mm thickness prominently suppress external separations, shorten oscillatory cycles, and modify pressure magnitudes. Trips can reduce the upstream movement ranges of separated shocks from nose regions to locations axially 142 mm downstream. The oscillatory cycles are shortened from 3.75 ms to 3.25 ms and from 4 ms to 3.13 ms in two facilities.Tripped cases generally exhibit higher pressure magnitudes than those of untripped cases, of which the increment is up to 21 times the freestream static pressure for the farthest downstream transducer in the shock tunnel. The effects of trips are related to the streamwise vortexes in wake flows, in which interactions between external separations modify the separated flow patterns and enhance the sustainment of the forebody boundary layers to backpressure. Flow processes causing increments of oscillatory frequencies and pressure magnitudes are analyzed, while the flow mechanisms dominating the processes still need to be clarified in the future.展开更多
Due to the limited output capability of piezoelectric diaphragm pumps, the driving voltage is frequently increased to obtain the desired output. However, the excessive voltage application may lead to a large deformati...Due to the limited output capability of piezoelectric diaphragm pumps, the driving voltage is frequently increased to obtain the desired output. However, the excessive voltage application may lead to a large deformation in the piezoelectric ceramics, which could cause it to breakdown or become damaged. Therefore, increasing the number of chambers to obtain the desired output is proposed. Using a check-valve quintuple-chamber pump with quintuple piezoelectric actuators, the characteristics of the pump under different driving modes are investigated through experiments. By changing the number and connection mode of working actuators, pump performances in terms of flow rate and backpressure are tested at a voltage of 150 V with a frequency range of 60 Hz -400 Hz. Experiment results indicate that the properties of the multiple-chamber pump change significantly with distinct working chambers even though the number of pumping chambers is the same. Pump performance declines as the distance between the working actuators increases. Moreover, pump performance declines dramatically when the working piezoelectric actuator closest to the outlet is involved. The maximum backpressures of the pump with triple, quadruple, and quintuple actuators are increased by 39%, 83%, and 128%, respectively, compared with the pump with double working actuators; the corresponding maximum flow rates of the pumps are simply increased by 25.9%, 49.2%, and 67.8%, respectively. The proposed research offers practical guidance for the effective utilization of the multiple-chamber pumps under different driving modes.展开更多
随着大量分布式能源终端接入,智慧园区中爆炸式增长的业务对队列积压、误码率、吞吐量等服务质量(quality of service,QoS)需求差异性大,现有的路由优化与差异化业务需求适配性差、时间同步与路由优化存在耦合性、链路与网络拥塞信息的...随着大量分布式能源终端接入,智慧园区中爆炸式增长的业务对队列积压、误码率、吞吐量等服务质量(quality of service,QoS)需求差异性大,现有的路由优化与差异化业务需求适配性差、时间同步与路由优化存在耦合性、链路与网络拥塞信息的不确定性等挑战,影响园区网络路由性能。针对上述挑战,提出了一种联合背压和Q学习的时间同步感知多态路由协议(backprEssure and Q-Learning based timE synChronizaTion-aware polymoRphic routIng protoCol,ELECTRIC)算法。首先,建立时间同步感知多态路由协议架构,实现园区终端的集中管理和数据传输优化;其次,根据背压算法,将队列积压最小化问题转化为队列积压差最大化问题,避免网络拥塞;然后,利用时间偏差阈值的概念对时间同步进行感知,使延迟唤醒的休眠态终端变为活跃态,并基于本地和历史信息进一步学习最优路由选择策略;最后,通过仿真结果验证,相较于基于Q学习的路由选择(Q-learning based route selection,QLRS)算法和基于队列积压的背压路由选择(queue backlog based backpressure route selection,QBBRS)算法,所提算法可分别提高平均吞吐量17.39%和56.52%,降低平均队列积压33.86%和44.07%,降低误码率31.58%和58.06%,保障智慧园区不同业务差异化的QoS需求。展开更多
文摘从理论分析和数值计算两方面研究不同背压下的液体离心喷嘴内液膜厚度.在经典理论的基础上建立的包含气液界面摩擦作用的损失系数理论模型并不足以体现背压对液膜厚度的改变;通过使用旋转轴对称模型在自适应网格中求解耦合VOF(volume of fluid)方程的Navier-Stokes方程组的数值模拟表明,随气体密度增加而减小的气液界面附近过渡区域中的平均速度分布是导致液膜厚度增加的原因.
文摘直接空冷凝汽器积灰和迎面风速降低是影响机组背压上升的主要因素,机组背压升高会影响机组出力。以某330 MW直接空冷机组为例,分析了积灰和迎面风速对传热系数和机组背压的影响规律,并提出了防治措施。结果表明:当积灰厚度达到1.0 mm时,机组背压由设计值34.0 k Pa升高到49.0 k Pa,机组功率降低了8.6 MW;迎面风速由设计值2.2 m/s降低到1.6 m/s,机组背压由设计值34.0 k Pa升高到50.1 k Pa,机组功率减小了9.4 MW。
基金The National Key Basic Research Program of China(No.2012CB026000)the National Natural Science Foundation of China(No.51776155)
文摘In this paper,a correlation model between centrifugal compressor and its piping system is built based on plenum chamber model and throttle valve model.This model could be used to conduct numerical analysis of compressor systems from steady to surge operating points.Three dimensional unsteady numerical simulations were performed to predict the performance of a centrifugal compressor.The flow structures in blade passage and diffuser were plotted and analyzed.The fluctuations of pressure and mass flow rate over time at the outlet of diffuser are obtained at surge condition.The characteristic changes of compressor-pipe network under the surge condition were carried out,and the effects of model characteristics including valve coefficient and backpressure on surge were analyzed.
基金co-supported by the China Postdoctoral Science Foundation (No. 2017M612059)the Fundamental Research Funds for the Central Universities of China (JZ2015HGBZ0471)the National Natural Science Foundation of China (Nos. 11402263 and 11132010)
文摘Experimental investigations are conducted on an axisymmetric hypersonic inlet to evaluate the effects of trips on oscillatory flows. The model exit is throttled with a fixed block to generate oscillatory flows at a freestream Mach number of 6 in a conventional wind tunnel and a shock tunnel. Schlieren imaging and pressure measurements are adopted to record unsteady flow features.Results indicate that trips with a 1 mm thickness prominently suppress external separations, shorten oscillatory cycles, and modify pressure magnitudes. Trips can reduce the upstream movement ranges of separated shocks from nose regions to locations axially 142 mm downstream. The oscillatory cycles are shortened from 3.75 ms to 3.25 ms and from 4 ms to 3.13 ms in two facilities.Tripped cases generally exhibit higher pressure magnitudes than those of untripped cases, of which the increment is up to 21 times the freestream static pressure for the farthest downstream transducer in the shock tunnel. The effects of trips are related to the streamwise vortexes in wake flows, in which interactions between external separations modify the separated flow patterns and enhance the sustainment of the forebody boundary layers to backpressure. Flow processes causing increments of oscillatory frequencies and pressure magnitudes are analyzed, while the flow mechanisms dominating the processes still need to be clarified in the future.
基金Supported by National Natural Science Foundation of China(Grant Nos.51205366,51205367,51377147)Zhejiang Provincial Natural Science Foundation of China(Grant No.LQ13E050007)
文摘Due to the limited output capability of piezoelectric diaphragm pumps, the driving voltage is frequently increased to obtain the desired output. However, the excessive voltage application may lead to a large deformation in the piezoelectric ceramics, which could cause it to breakdown or become damaged. Therefore, increasing the number of chambers to obtain the desired output is proposed. Using a check-valve quintuple-chamber pump with quintuple piezoelectric actuators, the characteristics of the pump under different driving modes are investigated through experiments. By changing the number and connection mode of working actuators, pump performances in terms of flow rate and backpressure are tested at a voltage of 150 V with a frequency range of 60 Hz -400 Hz. Experiment results indicate that the properties of the multiple-chamber pump change significantly with distinct working chambers even though the number of pumping chambers is the same. Pump performance declines as the distance between the working actuators increases. Moreover, pump performance declines dramatically when the working piezoelectric actuator closest to the outlet is involved. The maximum backpressures of the pump with triple, quadruple, and quintuple actuators are increased by 39%, 83%, and 128%, respectively, compared with the pump with double working actuators; the corresponding maximum flow rates of the pumps are simply increased by 25.9%, 49.2%, and 67.8%, respectively. The proposed research offers practical guidance for the effective utilization of the multiple-chamber pumps under different driving modes.
文摘随着大量分布式能源终端接入,智慧园区中爆炸式增长的业务对队列积压、误码率、吞吐量等服务质量(quality of service,QoS)需求差异性大,现有的路由优化与差异化业务需求适配性差、时间同步与路由优化存在耦合性、链路与网络拥塞信息的不确定性等挑战,影响园区网络路由性能。针对上述挑战,提出了一种联合背压和Q学习的时间同步感知多态路由协议(backprEssure and Q-Learning based timE synChronizaTion-aware polymoRphic routIng protoCol,ELECTRIC)算法。首先,建立时间同步感知多态路由协议架构,实现园区终端的集中管理和数据传输优化;其次,根据背压算法,将队列积压最小化问题转化为队列积压差最大化问题,避免网络拥塞;然后,利用时间偏差阈值的概念对时间同步进行感知,使延迟唤醒的休眠态终端变为活跃态,并基于本地和历史信息进一步学习最优路由选择策略;最后,通过仿真结果验证,相较于基于Q学习的路由选择(Q-learning based route selection,QLRS)算法和基于队列积压的背压路由选择(queue backlog based backpressure route selection,QBBRS)算法,所提算法可分别提高平均吞吐量17.39%和56.52%,降低平均队列积压33.86%和44.07%,降低误码率31.58%和58.06%,保障智慧园区不同业务差异化的QoS需求。
