This study investigated numerically the characteristics of laminar flow around two identical circular cylinders placed in tandem, with slits of the same width through their respective axis. The center to center distan...This study investigated numerically the characteristics of laminar flow around two identical circular cylinders placed in tandem, with slits of the same width through their respective axis. The center to center distance between the cylinders and the slit orientation were varied to study their effects on the flow structure, lift and drag, and vortex shedding characteristics. It was found that three flow regimes could be distinguished, the transitions between which could be indicated by the sudden changes in drag and lift. Asymmetrically, configured slits destabilized the stagnant region between cylinders;whereas in-line slits connect the two cylinders to act as a single elongated bluff body, even at large cylinder separation, by stabilizing the stagnant region in between. These in turn strongly modified the transition between flow regimes. Vortex shedding was also strongly influenced by both slit configuration and cylinder separation.展开更多
Temporal evolutions of scour at submerged circular cylinders were investigated.Flow visualization was carried out around the cylinders over plane,under developed and equilibrium scour holes.Video analysis technique wa...Temporal evolutions of scour at submerged circular cylinders were investigated.Flow visualization was carried out around the cylinders over plane,under developed and equilibrium scour holes.Video analysis technique was used to formulate the equations for determining the diameter of the horseshoe vortex around the submerged cylinders,which is also verified from the vector diagrams drawn using the velocity measurements.The scour process similar to live bed scour was noticed around the downstream cylinder.The diameter of the horseshoe vortex is found to depend on the diameter of respective cylinder,submergence ratio,spacing between the cylinders and skew angle.This formulation along with the dislodgement and transportation of a single sediment particle is further incorporated in the proposed model for determining the time variation of scour around the submerged cylinders.It is evident from the results that the upstream cylinder shelters the downstream cylinder and thereby reduces the scour at the downstream cylinder.Proposed model is further extended to incorporate the effect of non-uniformity of the sediment particles on the time variation of scour depth.The results indicate significant reduction of scour depth of around 6%and 35%for upstream and downstream cylinders respectively due to the formation of the armor layer.The model is also compared with the local scour component of field data around cylindrical bridge piers to establish the differences in the scour process around a partially submerged cylinder and fully submerged tandem and skewed cylinders.展开更多
A numerical investigation is carried out for the different orientations of a circular cylinder where the upstream cylinder moves with varying anglesα=0˚,30˚,45˚,60˚,90˚with respect to the downstream cylinder in a fix...A numerical investigation is carried out for the different orientations of a circular cylinder where the upstream cylinder moves with varying anglesα=0˚,30˚,45˚,60˚,90˚with respect to the downstream cylinder in a fixed position at a gap ratio(L/D)of 3 where L is the distance from centre to centre between cylinders and D is the diameter of the cylinder.Reynolds number(Re),is based on cylinder diameter,is kept constant at 200 for all the cases with air as the working medium.The vortex shedding formation is analysed when the vortices from the upwind cylinder interact with the downwind cylinder and give impressive flow patterns.It is observed that the drag and lift coefficients increase for both the cylinders with change in angular position.Strouhal number is calculated with the help of Fast Fourier transformation(FFT)of vorticity magnitude and evaluated for each case.It is observed that the effect of upwind cylinder on downwind cylinder is significant forα=30˚,45˚,60˚orientation cases and vortex shedding frequency increases for these cases.Further,the investigation is extending on the laminar forced convection heat transfer performance and variation of Nusselt number for the cylinders.Maximum heat transfer is observed for the downwind cylinder atα=45˚.In contrast,the local Nusselt number does not vary much for the cylinders except for the downwind cylinder atα=0˚.展开更多
基金Project(51576213) supported by the National Natural Science Foundation of ChinaProject(2017JJ1031) supported by Hunan Provincial Natural Science Foundation of China+1 种基金Project(CSUZC201921) supported by the Open Sharing Fund for the Large-scale Instruments and Equipments of Central South University,ChinaProject(2019zzts536) supported by the Fundamental Research Funds for the Central Universities,China
文摘This study investigated numerically the characteristics of laminar flow around two identical circular cylinders placed in tandem, with slits of the same width through their respective axis. The center to center distance between the cylinders and the slit orientation were varied to study their effects on the flow structure, lift and drag, and vortex shedding characteristics. It was found that three flow regimes could be distinguished, the transitions between which could be indicated by the sudden changes in drag and lift. Asymmetrically, configured slits destabilized the stagnant region between cylinders;whereas in-line slits connect the two cylinders to act as a single elongated bluff body, even at large cylinder separation, by stabilizing the stagnant region in between. These in turn strongly modified the transition between flow regimes. Vortex shedding was also strongly influenced by both slit configuration and cylinder separation.
基金This study is funded by the Department of Science and Technology,Government of India(Grant No:SR/S3/MERC/0029)。
文摘Temporal evolutions of scour at submerged circular cylinders were investigated.Flow visualization was carried out around the cylinders over plane,under developed and equilibrium scour holes.Video analysis technique was used to formulate the equations for determining the diameter of the horseshoe vortex around the submerged cylinders,which is also verified from the vector diagrams drawn using the velocity measurements.The scour process similar to live bed scour was noticed around the downstream cylinder.The diameter of the horseshoe vortex is found to depend on the diameter of respective cylinder,submergence ratio,spacing between the cylinders and skew angle.This formulation along with the dislodgement and transportation of a single sediment particle is further incorporated in the proposed model for determining the time variation of scour around the submerged cylinders.It is evident from the results that the upstream cylinder shelters the downstream cylinder and thereby reduces the scour at the downstream cylinder.Proposed model is further extended to incorporate the effect of non-uniformity of the sediment particles on the time variation of scour depth.The results indicate significant reduction of scour depth of around 6%and 35%for upstream and downstream cylinders respectively due to the formation of the armor layer.The model is also compared with the local scour component of field data around cylindrical bridge piers to establish the differences in the scour process around a partially submerged cylinder and fully submerged tandem and skewed cylinders.
文摘A numerical investigation is carried out for the different orientations of a circular cylinder where the upstream cylinder moves with varying anglesα=0˚,30˚,45˚,60˚,90˚with respect to the downstream cylinder in a fixed position at a gap ratio(L/D)of 3 where L is the distance from centre to centre between cylinders and D is the diameter of the cylinder.Reynolds number(Re),is based on cylinder diameter,is kept constant at 200 for all the cases with air as the working medium.The vortex shedding formation is analysed when the vortices from the upwind cylinder interact with the downwind cylinder and give impressive flow patterns.It is observed that the drag and lift coefficients increase for both the cylinders with change in angular position.Strouhal number is calculated with the help of Fast Fourier transformation(FFT)of vorticity magnitude and evaluated for each case.It is observed that the effect of upwind cylinder on downwind cylinder is significant forα=30˚,45˚,60˚orientation cases and vortex shedding frequency increases for these cases.Further,the investigation is extending on the laminar forced convection heat transfer performance and variation of Nusselt number for the cylinders.Maximum heat transfer is observed for the downwind cylinder atα=45˚.In contrast,the local Nusselt number does not vary much for the cylinders except for the downwind cylinder atα=0˚.
