Called island-crossing tunnels,some specific underwater tunneling projects face constraints imposed by geological and water conditions,necessitating their passage through artificial or natural islands.The longitudinal...Called island-crossing tunnels,some specific underwater tunneling projects face constraints imposed by geological and water conditions,necessitating their passage through artificial or natural islands.The longitudinal of the tunnel follows aW-shaped distribution.The congestion situation does not allowfor immediate longitudinal smoke exhaust at the early stage of the fire,and the natural spread of smoke is complicated.An exhaustive investigation was carried out to analyze the smoke behaviors during a fire incident,employing the fire dynamics software FDS,considering five slopes and four fire locations.The simulation results reveal that the layer of high-temperature smoke becomes thicker as one gets closer to the fire source.The thermal pressure difference significantly impacts the temperature distribution within the tunnel and the distance of smoke spread.The value of the thermal pressure difference is significantly affected by changes in slope.It reaches a maximum of 157 Pa at a 5%slope,while it is only 41 Pa at a 1%slope when the fire occurs at the V-point.Fire hazards vary across locations within the W-shaped tunnel,necessitating separate consideration of the V-point and inverted V-point fire characteristics.The mass flow rate in small and large slope tunnels shows different decay rates due to variations in the main forces acting on the movement.Hence,two equations have been developed to predict the smoke mass flow rate,indicating a nonlinear relationship with the tunnel slope and the distance fromthe fire source.The tunnel slope inversely affects the smoke mass flowrate at the same location.The results can be utilized as a reference for conducting evacuation operations and aiding rescues during aW-shaped tunnel fire.展开更多
This study investigates the effects of a novel passive flow control mechanism,a flexible leading edge(LE),on the aerodynamic performance of a NACA 0018 airfoil and a scaled vertical axis wind turbine(VAWT)model.Wind t...This study investigates the effects of a novel passive flow control mechanism,a flexible leading edge(LE),on the aerodynamic performance of a NACA 0018 airfoil and a scaled vertical axis wind turbine(VAWT)model.Wind tunnel experiments were conducted on 2D airfoil sections under steady flow and dynamic pitching conditions,and a scaled VAWT model was tested in an open-field environment.The flexible LE airfoil demonstrated significant improvements in delaying static stall angles and enhancing lift generation during dynamic pitching by inducing earlier and prolonged high suction pressures.The scaled VAWT model with flexible LE blades showed increased rotational speeds and higher voltage outputs compared with the rigid blade VAWT,particularly at higher wind speeds.Both rotational speed and electrical voltage data suggest that the flexible LE structure enhances the aerodynamic efficiency of the VAWT.The findings suggest that the flexible LE structure is an efficient and cost-effective method to improve VAWT aerodynamic efficiency.展开更多
文摘Called island-crossing tunnels,some specific underwater tunneling projects face constraints imposed by geological and water conditions,necessitating their passage through artificial or natural islands.The longitudinal of the tunnel follows aW-shaped distribution.The congestion situation does not allowfor immediate longitudinal smoke exhaust at the early stage of the fire,and the natural spread of smoke is complicated.An exhaustive investigation was carried out to analyze the smoke behaviors during a fire incident,employing the fire dynamics software FDS,considering five slopes and four fire locations.The simulation results reveal that the layer of high-temperature smoke becomes thicker as one gets closer to the fire source.The thermal pressure difference significantly impacts the temperature distribution within the tunnel and the distance of smoke spread.The value of the thermal pressure difference is significantly affected by changes in slope.It reaches a maximum of 157 Pa at a 5%slope,while it is only 41 Pa at a 1%slope when the fire occurs at the V-point.Fire hazards vary across locations within the W-shaped tunnel,necessitating separate consideration of the V-point and inverted V-point fire characteristics.The mass flow rate in small and large slope tunnels shows different decay rates due to variations in the main forces acting on the movement.Hence,two equations have been developed to predict the smoke mass flow rate,indicating a nonlinear relationship with the tunnel slope and the distance fromthe fire source.The tunnel slope inversely affects the smoke mass flowrate at the same location.The results can be utilized as a reference for conducting evacuation operations and aiding rescues during aW-shaped tunnel fire.
文摘This study investigates the effects of a novel passive flow control mechanism,a flexible leading edge(LE),on the aerodynamic performance of a NACA 0018 airfoil and a scaled vertical axis wind turbine(VAWT)model.Wind tunnel experiments were conducted on 2D airfoil sections under steady flow and dynamic pitching conditions,and a scaled VAWT model was tested in an open-field environment.The flexible LE airfoil demonstrated significant improvements in delaying static stall angles and enhancing lift generation during dynamic pitching by inducing earlier and prolonged high suction pressures.The scaled VAWT model with flexible LE blades showed increased rotational speeds and higher voltage outputs compared with the rigid blade VAWT,particularly at higher wind speeds.Both rotational speed and electrical voltage data suggest that the flexible LE structure enhances the aerodynamic efficiency of the VAWT.The findings suggest that the flexible LE structure is an efficient and cost-effective method to improve VAWT aerodynamic efficiency.
