A spillway aerator should guarantee favorable flow conditions in the coupled water-air system even if the aerator is unconventionally wide. Eight air-vent configurations are devised and incorporated into a 35-m wide c...A spillway aerator should guarantee favorable flow conditions in the coupled water-air system even if the aerator is unconventionally wide. Eight air-vent configurations are devised and incorporated into a 35-m wide chute aerator for a generalized study. Computational fluid dynamics(CFD) simulations are performed to explore their effects on water-jet and air-cavity features. The Re-normalisation group(RNG) k-ε turbulence model and the two-fluid model are combined to predict the two-phase flow field. The results demonstrate appreciable influences of the vent layouts on the water-air flow. The air vents stir the air motion and re-distribute the cavity air pressure. Once the vent layout is modified, reciprocal adjustments exist between the jet behavior and air-pressure field in the cavity, thus leading to considerable differences in air-flow rate, jet-trajectory length, vent air-flow distribution across the chute, etc. The large width plays a discernable role in affecting the aerated flow. Telling differences exist between the near-wall region and the central part of the chute. To improve the duct pressure propagation, a gradual augment of the vent area should be assigned towards the chute center. Relative to single-slot vents across the flow, the layouts with segregated vents gain by comparison. A designer should see to it that a vented aerator operates satisfactorily for a given range of flow discharges.展开更多
The orthogonal experiments, which involves three factors： aeration intensity, suction time and suction suspended time, were designed to research membrane fouling of jet loop membrane bioreactor （JLMBR）. Experimenta...The orthogonal experiments, which involves three factors： aeration intensity, suction time and suction suspended time, were designed to research membrane fouling of jet loop membrane bioreactor （JLMBR）. Experimental results indicate that increasing aeration intensity, reducing suction time and increasing suction suspended time all could mitigate membrane fouling effectively. However excessive aeration intensity, too short suction time and excessive suction suspended time were bad for bioreactor running. The optimal aeration intensity, suction time and suction suspended time were 0.75 1.00 m3/（m2.h）, 8 -10 min and 4 -5 min, respectively. The three factors all had effect on membrane pollution rate, while the suction time was the most important one and followed by aeration intensity and suction suspended time. It also indicates that, comparing with traditional submerged membrane bioreactors, JLMBR had lower membrane pollution rate.展开更多
With the development of ski-jump energy dissipation for high and large discharge among the hydraulic projects,the effects of characteristics of water flow on energy dissipation are increasingly important.In the presen...With the development of ski-jump energy dissipation for high and large discharge among the hydraulic projects,the effects of characteristics of water flow on energy dissipation are increasingly important.In the present study,the effects of aeration and the initial water thickness on axial velocity attenuation of jet flow were analyzed,using variance analysis and numerical calculated methods.From the analysis of test data,both of the air concentration and initial water thickness are sensitive factors for the axial velocity attenuation of jet flow along the axial way,and there is no significant interaction effect between the aeration and initial water thickness.Aeration has a more significant effect on the axial velocity attenuation of jet flow.Decreasing the initial water thickness of jet flow can reduce the length of jet core,and make the initial position of axial velocity attenuation closer to the nozzle exit.The numerical calculation results show that aeration can contribute to the enhancement of entrainment ability of jet flow,which may improve the interaction between jet flow and surroundings.For ski-jump energy dissipation among the hydraulic projects,combining aeration with decreasing initial water thickness of jet flow is an effective way to enhance the rate of axial velocity attenuation.展开更多
基金part of research project "Hydraulic design of spillway aerators"funded in part by Swedish Hydropower Centre(SVC)+2 种基金Vattenfall R&DFortum GenerationUniper/Sweco have indirectly facilitated the study
文摘A spillway aerator should guarantee favorable flow conditions in the coupled water-air system even if the aerator is unconventionally wide. Eight air-vent configurations are devised and incorporated into a 35-m wide chute aerator for a generalized study. Computational fluid dynamics(CFD) simulations are performed to explore their effects on water-jet and air-cavity features. The Re-normalisation group(RNG) k-ε turbulence model and the two-fluid model are combined to predict the two-phase flow field. The results demonstrate appreciable influences of the vent layouts on the water-air flow. The air vents stir the air motion and re-distribute the cavity air pressure. Once the vent layout is modified, reciprocal adjustments exist between the jet behavior and air-pressure field in the cavity, thus leading to considerable differences in air-flow rate, jet-trajectory length, vent air-flow distribution across the chute, etc. The large width plays a discernable role in affecting the aerated flow. Telling differences exist between the near-wall region and the central part of the chute. To improve the duct pressure propagation, a gradual augment of the vent area should be assigned towards the chute center. Relative to single-slot vents across the flow, the layouts with segregated vents gain by comparison. A designer should see to it that a vented aerator operates satisfactorily for a given range of flow discharges.
基金Project supported by the Cooperation Program of China and Singapore(Grant No.042307013)
文摘The orthogonal experiments, which involves three factors： aeration intensity, suction time and suction suspended time, were designed to research membrane fouling of jet loop membrane bioreactor （JLMBR）. Experimental results indicate that increasing aeration intensity, reducing suction time and increasing suction suspended time all could mitigate membrane fouling effectively. However excessive aeration intensity, too short suction time and excessive suction suspended time were bad for bioreactor running. The optimal aeration intensity, suction time and suction suspended time were 0.75 1.00 m3/（m2.h）, 8 -10 min and 4 -5 min, respectively. The three factors all had effect on membrane pollution rate, while the suction time was the most important one and followed by aeration intensity and suction suspended time. It also indicates that, comparing with traditional submerged membrane bioreactors, JLMBR had lower membrane pollution rate.
基金Project supported by the National Natural Science Foundation of China (Nos. 51179113,51009102 and 50909067)the Program for the New Century Excellent Talents in University (No. NCET-10-0589),China
文摘With the development of ski-jump energy dissipation for high and large discharge among the hydraulic projects,the effects of characteristics of water flow on energy dissipation are increasingly important.In the present study,the effects of aeration and the initial water thickness on axial velocity attenuation of jet flow were analyzed,using variance analysis and numerical calculated methods.From the analysis of test data,both of the air concentration and initial water thickness are sensitive factors for the axial velocity attenuation of jet flow along the axial way,and there is no significant interaction effect between the aeration and initial water thickness.Aeration has a more significant effect on the axial velocity attenuation of jet flow.Decreasing the initial water thickness of jet flow can reduce the length of jet core,and make the initial position of axial velocity attenuation closer to the nozzle exit.The numerical calculation results show that aeration can contribute to the enhancement of entrainment ability of jet flow,which may improve the interaction between jet flow and surroundings.For ski-jump energy dissipation among the hydraulic projects,combining aeration with decreasing initial water thickness of jet flow is an effective way to enhance the rate of axial velocity attenuation.
