The characteristics of a vapor bubble within the thermal boundary layer were theoretically analyzed.The physical models accounting for the variation of ioterfacial tension and nuid density with tempera-ture were propo...The characteristics of a vapor bubble within the thermal boundary layer were theoretically analyzed.The physical models accounting for the variation of ioterfacial tension and nuid density with tempera-ture were proposed to investigate bubble interfaCe aspects and the fluid flow around the bubble. The analyses demonstrated that the variation in interfacial tension results in variations in the liquid-vapor interface shape and bubble dynamics, which may play a significant role in the departure process of a vapor bubble from a heated wall surface. Increasing temperature gradients in the boundary layer and the gravitational field induce a contact line contraction and correspondingly promotes bubble depar-ture. The simulation of liquid now around the bubble shows that natural convection dominates the flow for earth conditions; however, the thermocapillary forces provide the principal catalyst for bubble departure in a microgravity environment. The results indicate that both the vapor bubble contraction and the Marangoni flow may increase the heat transfer around the vapor bubble and may cause the bubble to mov away from the heating surface, further increasing heat transfer.展开更多
This study demonstrates the potential for shock wave-boundary layer interaction control in air by plasma aerodynamic actuation.Experimental investigations on shock wave-boundary layer interactions control by plasma ae...This study demonstrates the potential for shock wave-boundary layer interaction control in air by plasma aerodynamic actuation.Experimental investigations on shock wave-boundary layer interactions control by plasma aerodynamic actuation are conducted in a Mach 3 in-draft air tunnel.Schlieren imaging shows that the discharges cause the oblique shock to move forward.Schlieren imaging and static pressure probes also show that separation phenomenon shifts backward and the size of separation is enlarged when plasma aerodynamic actuation is applied.The intensity of shock wave is weakened through wall pressure probe.Furthermore,numerical investigations on shock wave-boundary layer interactions control are conducted with plasma aerodynamic actuation.The discharge is modeled as a steady volumetric heat source which is integrated into the energy equation.The input energy level is about 7 kW through discharge process.Results show that the separation phenomenon shifts backward and the intensity of shock is reduced with plasma actuation.These numerical results are consistent with the experimental results.展开更多
Horseshoe vortex topological structure has been studied extensively in the past,traditional"saddle of separation"and new"attachment saddle point"topologies found in literature both have theoretical...Horseshoe vortex topological structure has been studied extensively in the past,traditional"saddle of separation"and new"attachment saddle point"topologies found in literature both have theoretical basis and experimental and computational evidences for support.The laminar incompressible juncture flows at low Reynolds numbers especially are observed to have new topology.Studies concerning the existence of the new topology though found in literature,the topological evolution and its dependency on various critical flow parameters require further investigation.A Particle Image Velocimetry based analysis is carried out to observe the effect of aspect ratio,?*/D and shape of the obstacle on laminar horseshoe vortex topology for small obstacles.Rise in aspect ratio evolves the topology from the traditional to new for all the cases observed.The circular cross section obstacles are found more apt to having the new topology compared to square cross sections.It is noted that the sweeping effect of the fluid above the vortex system in which horseshoe vortex is immersed plays a critical role in this evolution.Topological evolution is observed not only in the most upstream singular point region of horseshoe vortex system but also in the corner region.The corner vortex topology evolves from the traditional type to new one before the topological evolution of the most upstream singular point,resulting in a new topological pattern of the laminar juncture flows"separation-attachment combination".The study may help extend the understanding of the three-dimensional boundary layer separation phenomenon.展开更多
文摘The characteristics of a vapor bubble within the thermal boundary layer were theoretically analyzed.The physical models accounting for the variation of ioterfacial tension and nuid density with tempera-ture were proposed to investigate bubble interfaCe aspects and the fluid flow around the bubble. The analyses demonstrated that the variation in interfacial tension results in variations in the liquid-vapor interface shape and bubble dynamics, which may play a significant role in the departure process of a vapor bubble from a heated wall surface. Increasing temperature gradients in the boundary layer and the gravitational field induce a contact line contraction and correspondingly promotes bubble depar-ture. The simulation of liquid now around the bubble shows that natural convection dominates the flow for earth conditions; however, the thermocapillary forces provide the principal catalyst for bubble departure in a microgravity environment. The results indicate that both the vapor bubble contraction and the Marangoni flow may increase the heat transfer around the vapor bubble and may cause the bubble to mov away from the heating surface, further increasing heat transfer.
基金supported by the National Natural Science Foundation of China(Grant Nos.51276197,51207169,11372352)
文摘This study demonstrates the potential for shock wave-boundary layer interaction control in air by plasma aerodynamic actuation.Experimental investigations on shock wave-boundary layer interactions control by plasma aerodynamic actuation are conducted in a Mach 3 in-draft air tunnel.Schlieren imaging shows that the discharges cause the oblique shock to move forward.Schlieren imaging and static pressure probes also show that separation phenomenon shifts backward and the size of separation is enlarged when plasma aerodynamic actuation is applied.The intensity of shock wave is weakened through wall pressure probe.Furthermore,numerical investigations on shock wave-boundary layer interactions control are conducted with plasma aerodynamic actuation.The discharge is modeled as a steady volumetric heat source which is integrated into the energy equation.The input energy level is about 7 kW through discharge process.Results show that the separation phenomenon shifts backward and the intensity of shock is reduced with plasma actuation.These numerical results are consistent with the experimental results.
基金supported by the National Natural Science Foundation of China(Grant No.11372027)
文摘Horseshoe vortex topological structure has been studied extensively in the past,traditional"saddle of separation"and new"attachment saddle point"topologies found in literature both have theoretical basis and experimental and computational evidences for support.The laminar incompressible juncture flows at low Reynolds numbers especially are observed to have new topology.Studies concerning the existence of the new topology though found in literature,the topological evolution and its dependency on various critical flow parameters require further investigation.A Particle Image Velocimetry based analysis is carried out to observe the effect of aspect ratio,?*/D and shape of the obstacle on laminar horseshoe vortex topology for small obstacles.Rise in aspect ratio evolves the topology from the traditional to new for all the cases observed.The circular cross section obstacles are found more apt to having the new topology compared to square cross sections.It is noted that the sweeping effect of the fluid above the vortex system in which horseshoe vortex is immersed plays a critical role in this evolution.Topological evolution is observed not only in the most upstream singular point region of horseshoe vortex system but also in the corner region.The corner vortex topology evolves from the traditional type to new one before the topological evolution of the most upstream singular point,resulting in a new topological pattern of the laminar juncture flows"separation-attachment combination".The study may help extend the understanding of the three-dimensional boundary layer separation phenomenon.
