The existing deep-sea sediment plume tests are mostly under small-scale static water and rarely under large-scale flowing water conditions.In this study,large-scale tank experiments of flowing water were designed and ...The existing deep-sea sediment plume tests are mostly under small-scale static water and rarely under large-scale flowing water conditions.In this study,large-scale tank experiments of flowing water were designed and conducted to investigate the morphological characteristics and concentration evolution of the sediment plumes under different discharge rates(Q)and initial sediment concentrations(c).Viscosity tests,resuspension tests and free settling tests of the sediment solution with different c values were performed to reveal the settling mechanism of the plume diffusion process.The results show that the plume diffusion morphology variation in flowing water has four stages and the plume concentration evolution has three stages.The larger the Q,the smaller the initial incidence angle at the discharge outlet,the larger the diffusion range,the poorer the stability and the more complicated the diffusion morphology.The larger the c,the larger the settling velocity,the faster the formation of high-concentration accumulation zone,the better the stability and the clearer the diffusion boundary.The research results could provide experimental data for assessing the impact of deep-sea mining on the ocean environment.展开更多
Water tank experiments were carried out to investigate the thermal convection due to the bottom heating in an asymmetrical valley under neutral and stably stratified approach flows with the Particle Image Velometry (P...Water tank experiments were carried out to investigate the thermal convection due to the bottom heating in an asymmetrical valley under neutral and stably stratified approach flows with the Particle Image Velometry (PIV) visualization technique. In the neutral stratification approach flow, the ascending draft induced by bottom heating is mainly located in the center of the valley in calm ambient wind. However, with ambient wind flow, the thermal convection is shifted leeward, and the descending draft is located on the leeward side of the valley, while the ascending draft is located on the windward side. The descending draft is minorly turbulent and organized, while the ascending draft is highly turbulent. With the increase of the towing speed, the descending and ascending drafts induced by the mechanical elevation begin to play a more dominant role in the valley flow, while the role of the thermal convection in the valley airflow becomes limited. In the stable stratification approach flow, the thermal convection is limited by the stable stratification and no distinct circulation is formed in calm ambient wind. With ambient wind, agravity wave appears in the upper layer in the valley. With the increase of the ambient wind speed, a gravity wave plays an important role in the valley flow, and the location and intensity of the thermal convection are also modulated by the gravity internal waves. The thermal convection has difficulty penetrating the upper stable layer. Its exchange is limited between the air in the upper layer and that in the lower layer in the valley, and it is adverse to the diffusion of pollutants in the valley.展开更多
Water tank and channel experiments have been widely utilized in indoor and outdoor airflow studies for their ability to adjust variables and boundary conditions in a controlled environment.This study reviews the exper...Water tank and channel experiments have been widely utilized in indoor and outdoor airflow studies for their ability to adjust variables and boundary conditions in a controlled environment.This study reviews the experimental setup of water tanks and channels,measurement techniques,and their applications in multi-scale airflow modeling,in particular indoor airflow,street-canyon flow,city-scale urban heat circulation and meso-scale boundary-layer flows.Water tanks are mainly adopted for thermally-dominated airflow studies without considering the background wind,while water channels are applied to dynamic-thermal interacting airflow researches.The advantages and disadvantages of commonly adopted measurement techniques in water tank and water channel experiments are summarized in terms of particle image velocimetry(PIV),acoustic Doppler velocimeter(ADV),laser Doppler velocimeter(LDV),and magnetic resonance imaging(MRI).Based on the water tank and channel measurements,the exhaled airflow and natural ventilations are major concerns in indoor environments.Wind-and buoyancy-driven flow,ventilation and pollutant dispersion are investigated within and above the street canyons.The urban heat island circulation and the convective boundary layer are intensively studied under different thermal and stratification conditions.Current limitations include the oversimplification of building models,the inability to ensure strict flow field similarity,and the neglect of specific dimensionless numbers.Water tank and channel experiments serve as important tools for parametric experiments,allowing for the validation of numerical simulations and comparisons with full scale measurements.In the future,water tank and water channel experiments should more closely align with real atmospheric conditions,such as using more realistic physical models,accounting for actual atmospheric background wind circulations,and considering the non-uniform distribution of heat fluxes in urban areas.展开更多
In this study numerical simulations and water tank experiments were used to investigate the flow and pollutant dispersion in an urban street canyon. Two types of canyon geometry were tested. The studies indicate that ...In this study numerical simulations and water tank experiments were used to investigate the flow and pollutant dispersion in an urban street canyon. Two types of canyon geometry were tested. The studies indicate that in a step-up notch canyon （higher buildings on the downstream side of the canyon）, the height and shape of the upstream lower buildings plays an important role in flow pattern and pollutant dispersion, while in a step-down notch canyon （lower buildings on the downstream side）, the downstream lower buildings have little influence. The studies also show that the substitution of tall towers for parailelepiped buildings on one side of the canyon may enhance the street ventilation and decrease the pollutant concentration emitted by motor vehicles.展开更多
In this study, the effect of the free surface on the cloud cavitating flow around a blunt body is investigated based on the water tank experiment and the CFD method. Numerical results are in good agreement with experi...In this study, the effect of the free surface on the cloud cavitating flow around a blunt body is investigated based on the water tank experiment and the CFD method. Numerical results are in good agreement with experimental data, and the mesh independence of the methods is verified. The cavity evolution process includes the cavity growth, the re-entrant jet, the cavity shedding, and the collapse, which can all be observed from the water tank experiment. The effects of the free surface on the cavity length, the thickness, and the cavity evolution period are analyzed by comparing the difference between the cavitating flows on the upper and lower sides of the body. This study also examines the effect of the distance between the free surface and the model through a series of water tank experiments and numerical simulations. The cavity stability and asymmetry, as well as the thickness and the velocity of the re-entrant jet inside the cavity, which varies with the submerged depth, are discussed with consideration of the effect of the free surface. The effect of the free surface on the cavitating flow around the blunt body is enhanced with the decrease of the submerged depth.展开更多
基金supported by the Major Project of Hunan Natural Science Foundation,China(No.2021JC0010)the National Natural Science Foundation of China(No.51274251)。
文摘The existing deep-sea sediment plume tests are mostly under small-scale static water and rarely under large-scale flowing water conditions.In this study,large-scale tank experiments of flowing water were designed and conducted to investigate the morphological characteristics and concentration evolution of the sediment plumes under different discharge rates(Q)and initial sediment concentrations(c).Viscosity tests,resuspension tests and free settling tests of the sediment solution with different c values were performed to reveal the settling mechanism of the plume diffusion process.The results show that the plume diffusion morphology variation in flowing water has four stages and the plume concentration evolution has three stages.The larger the Q,the smaller the initial incidence angle at the discharge outlet,the larger the diffusion range,the poorer the stability and the more complicated the diffusion morphology.The larger the c,the larger the settling velocity,the faster the formation of high-concentration accumulation zone,the better the stability and the clearer the diffusion boundary.The research results could provide experimental data for assessing the impact of deep-sea mining on the ocean environment.
基金This research was supported by the National Natural Science Foundation of China under Grant Nos.40105003 and 4001161948partly supported by the Chinese Academny of Sciences Projct KZCX-201.
文摘Water tank experiments were carried out to investigate the thermal convection due to the bottom heating in an asymmetrical valley under neutral and stably stratified approach flows with the Particle Image Velometry (PIV) visualization technique. In the neutral stratification approach flow, the ascending draft induced by bottom heating is mainly located in the center of the valley in calm ambient wind. However, with ambient wind flow, the thermal convection is shifted leeward, and the descending draft is located on the leeward side of the valley, while the ascending draft is located on the windward side. The descending draft is minorly turbulent and organized, while the ascending draft is highly turbulent. With the increase of the towing speed, the descending and ascending drafts induced by the mechanical elevation begin to play a more dominant role in the valley flow, while the role of the thermal convection in the valley airflow becomes limited. In the stable stratification approach flow, the thermal convection is limited by the stable stratification and no distinct circulation is formed in calm ambient wind. With ambient wind, agravity wave appears in the upper layer in the valley. With the increase of the ambient wind speed, a gravity wave plays an important role in the valley flow, and the location and intensity of the thermal convection are also modulated by the gravity internal waves. The thermal convection has difficulty penetrating the upper stable layer. Its exchange is limited between the air in the upper layer and that in the lower layer in the valley, and it is adverse to the diffusion of pollutants in the valley.
基金supported by the National Natural Science Foundation of China(No.U2442212,No.42175095,No.42205073&No.42475086)Natural Science Foundation of Guangdong Province(No.2023A1515012863)+1 种基金Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(No.311020001)Fundamental Research Funds for the Central Universities,Sun Yat-sen University(No.24xkjc004).
文摘Water tank and channel experiments have been widely utilized in indoor and outdoor airflow studies for their ability to adjust variables and boundary conditions in a controlled environment.This study reviews the experimental setup of water tanks and channels,measurement techniques,and their applications in multi-scale airflow modeling,in particular indoor airflow,street-canyon flow,city-scale urban heat circulation and meso-scale boundary-layer flows.Water tanks are mainly adopted for thermally-dominated airflow studies without considering the background wind,while water channels are applied to dynamic-thermal interacting airflow researches.The advantages and disadvantages of commonly adopted measurement techniques in water tank and water channel experiments are summarized in terms of particle image velocimetry(PIV),acoustic Doppler velocimeter(ADV),laser Doppler velocimeter(LDV),and magnetic resonance imaging(MRI).Based on the water tank and channel measurements,the exhaled airflow and natural ventilations are major concerns in indoor environments.Wind-and buoyancy-driven flow,ventilation and pollutant dispersion are investigated within and above the street canyons.The urban heat island circulation and the convective boundary layer are intensively studied under different thermal and stratification conditions.Current limitations include the oversimplification of building models,the inability to ensure strict flow field similarity,and the neglect of specific dimensionless numbers.Water tank and channel experiments serve as important tools for parametric experiments,allowing for the validation of numerical simulations and comparisons with full scale measurements.In the future,water tank and water channel experiments should more closely align with real atmospheric conditions,such as using more realistic physical models,accounting for actual atmospheric background wind circulations,and considering the non-uniform distribution of heat fluxes in urban areas.
基金This rearch was supported by the National Natural Science Foundation of China under Grant No.40575069.
文摘In this study numerical simulations and water tank experiments were used to investigate the flow and pollutant dispersion in an urban street canyon. Two types of canyon geometry were tested. The studies indicate that in a step-up notch canyon （higher buildings on the downstream side of the canyon）, the height and shape of the upstream lower buildings plays an important role in flow pattern and pollutant dispersion, while in a step-down notch canyon （lower buildings on the downstream side）, the downstream lower buildings have little influence. The studies also show that the substitution of tall towers for parailelepiped buildings on one side of the canyon may enhance the street ventilation and decrease the pollutant concentration emitted by motor vehicles.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11772340,11672315)the Youth Innovation Promotion Association of CAS(Grant No.2015015)
文摘In this study, the effect of the free surface on the cloud cavitating flow around a blunt body is investigated based on the water tank experiment and the CFD method. Numerical results are in good agreement with experimental data, and the mesh independence of the methods is verified. The cavity evolution process includes the cavity growth, the re-entrant jet, the cavity shedding, and the collapse, which can all be observed from the water tank experiment. The effects of the free surface on the cavity length, the thickness, and the cavity evolution period are analyzed by comparing the difference between the cavitating flows on the upper and lower sides of the body. This study also examines the effect of the distance between the free surface and the model through a series of water tank experiments and numerical simulations. The cavity stability and asymmetry, as well as the thickness and the velocity of the re-entrant jet inside the cavity, which varies with the submerged depth, are discussed with consideration of the effect of the free surface. The effect of the free surface on the cavitating flow around the blunt body is enhanced with the decrease of the submerged depth.
