The internal flow field of an axial-flow pump under low flow rate conditions is extremely turbulent. The unstable flow region is formed due to the tip leakage and the rotating stall, and is distinguished by a saddle p...The internal flow field of an axial-flow pump under low flow rate conditions is extremely turbulent. The unstable flow region is formed due to the tip leakage and the rotating stall, and is distinguished by a saddle patterned zone in its flow-head curve that demonstrates restrictions in its workable flow range. It is therefore important to understand and improve the operational characteristics of an axial-flow pump under low flow rate conditions. In this study, experiments are performed for the performances of an axial-flow pump at the flow rate in a range between 0.8Qd and 1.2Qd, with the internal flow field measured by the particle image velocimetry (PIV), and with the pump performances and the internal flow field simulated by the Ansys CFX. The simulation results agree well with the experimental results. From the predicted heads at the flow rate in the range between 0.1Qd and 0.7Qd by the numerical simulation, the complete flow-head curves are obtained. The streamlines and the velocity contours in the region in front of the impeller leading edge under different flow conditions are analyzed. By adopting the double-inlet structures, the flow-head characteristics are studied by varying the values of δ and σ respectively, where δ denotes the gap between the inner cylinder end and the impeller leading edge, and σ denotes the gap between the inner cylinder and the outer cylinder. The findings indicate that with the double-inlet design, the velocity distribution can be effectively improved in the region in front of the impeller leading edge, as well as the head performance under the low flow rate conditions, and the positive slope value of the head curve is reduced in the unstable flow range. The optimal δ and σ values are determined.展开更多
Hull form of a high-speed shallow-water craft used in fresh water is presented in this paper.Model tests for this hull lines are conducted at different water depth in towing tank, and the effect of shallow water on cr...Hull form of a high-speed shallow-water craft used in fresh water is presented in this paper.Model tests for this hull lines are conducted at different water depth in towing tank, and the effect of shallow water on craft performance is investigated.Test resalts show that powering performance of this craft is superior to other representativeplanningboat, no matter in deep or shallow water.Concept of double-inlet water-jet system is designed with one inlet in side and the other in bottom.This craft,combined with the double-inlet water-jet system, can run in deep water with high speed and safely run in shallow water.The critical water depth can almost be the same as the draft of this craft.展开更多
A 23-year-old, lean, scoliotic female presented to our hospital with a history of shortness of breath and cyanosis on exertion. Her 2D echocardiography revealed single left ventricle with both atrio-ventricular valves...A 23-year-old, lean, scoliotic female presented to our hospital with a history of shortness of breath and cyanosis on exertion. Her 2D echocardiography revealed single left ventricle with both atrio-ventricular valves opening in it. She had normally related great arteries, with severe pulmonary artery hypertension, without pulmonary stenosis. Her blood tests indicated that she was reactive to human immunodeficiency virus (HIV-1). The patients died within 2 months despite treatments with anti-retroviral therapy and decongestive therapy.展开更多
基金This work was supported by the Fundamental Research Fund for Central Universities(Grant No.JZ2015HGBZ0129)the Open End Fund of Jiangsu University(Grant No.NRCP201603).
文摘The internal flow field of an axial-flow pump under low flow rate conditions is extremely turbulent. The unstable flow region is formed due to the tip leakage and the rotating stall, and is distinguished by a saddle patterned zone in its flow-head curve that demonstrates restrictions in its workable flow range. It is therefore important to understand and improve the operational characteristics of an axial-flow pump under low flow rate conditions. In this study, experiments are performed for the performances of an axial-flow pump at the flow rate in a range between 0.8Qd and 1.2Qd, with the internal flow field measured by the particle image velocimetry (PIV), and with the pump performances and the internal flow field simulated by the Ansys CFX. The simulation results agree well with the experimental results. From the predicted heads at the flow rate in the range between 0.1Qd and 0.7Qd by the numerical simulation, the complete flow-head curves are obtained. The streamlines and the velocity contours in the region in front of the impeller leading edge under different flow conditions are analyzed. By adopting the double-inlet structures, the flow-head characteristics are studied by varying the values of δ and σ respectively, where δ denotes the gap between the inner cylinder end and the impeller leading edge, and σ denotes the gap between the inner cylinder and the outer cylinder. The findings indicate that with the double-inlet design, the velocity distribution can be effectively improved in the region in front of the impeller leading edge, as well as the head performance under the low flow rate conditions, and the positive slope value of the head curve is reduced in the unstable flow range. The optimal δ and σ values are determined.
文摘Hull form of a high-speed shallow-water craft used in fresh water is presented in this paper.Model tests for this hull lines are conducted at different water depth in towing tank, and the effect of shallow water on craft performance is investigated.Test resalts show that powering performance of this craft is superior to other representativeplanningboat, no matter in deep or shallow water.Concept of double-inlet water-jet system is designed with one inlet in side and the other in bottom.This craft,combined with the double-inlet water-jet system, can run in deep water with high speed and safely run in shallow water.The critical water depth can almost be the same as the draft of this craft.
文摘A 23-year-old, lean, scoliotic female presented to our hospital with a history of shortness of breath and cyanosis on exertion. Her 2D echocardiography revealed single left ventricle with both atrio-ventricular valves opening in it. She had normally related great arteries, with severe pulmonary artery hypertension, without pulmonary stenosis. Her blood tests indicated that she was reactive to human immunodeficiency virus (HIV-1). The patients died within 2 months despite treatments with anti-retroviral therapy and decongestive therapy.
