The effect of micro-bubbles on the turbulent boundary layer in the channel flow with Reynolds numbers (Re) ranging from 0.87 × 105 to 1.23 × 105 is experimentally studied by using particle image velocimetry ...The effect of micro-bubbles on the turbulent boundary layer in the channel flow with Reynolds numbers (Re) ranging from 0.87 × 105 to 1.23 × 105 is experimentally studied by using particle image velocimetry (PIV) measurements.The microbubbles are produced by water electrolysis.The velocity profiles,Reynolds stress and instantaneous structures of the boundary layer,with and without micro-bubbles,are measured and analyzed.The presence of micro-bubbles changes the streamwise mean velocity of the fluid and increases the wall shear stress.The results show that micro-bubbles have two effects,buoyancy and extrusion,which dominate the flow behavior of the mixed fluid in the turbulent boundary layer.The buoyancy effect leads to upward motion that drives the fluid motion in the same direction and,therefore,enhances the turbulence intense of the boundary layer.While for the extrusion effect,the presence of accumulated micro-bubbles pushes the flow structures in the turbulent boundary layer away from the near-wall region.The interaction between these two effects causes the vorticity structures and turbulence activity to be in the region far away from the wall.The buoyancy effect is dominant when the Re is relatively small,while the extrusion effect plays a more important role when Re rises.展开更多
In order to optimize plastic viscosity of 18 mPa·s circulating micro-bubble drilling fluid formula,orthogonal and uniform experimental design methods were applied,and the plastic viscosities of 36 and 24 groups o...In order to optimize plastic viscosity of 18 mPa·s circulating micro-bubble drilling fluid formula,orthogonal and uniform experimental design methods were applied,and the plastic viscosities of 36 and 24 groups of agent were tested,respectively.It is found that these two experimental design methods show drawbacks,that is,the amount of agent is difficult to determine,and the results are not fully optimized.Therefore,multiple regression experimental method was used to design experimental formula.By randomly selecting arbitrary agent with the amount within the recommended range,17 groups of drilling fluid formula were designed,and the plastic viscosity of each experiment formula was measured.Set plastic viscosity as the objective function,through multiple regressions,then quadratic regression model is obtained,whose correlation coefficient meets the requirement.Set target values of plastic viscosity to be 18,20 and 22 mPa·s,respectively,with the trial method,5 drilling fluid formulas are obtained with accuracy of 0.000 3,0.000 1 and 0.000 3.Arbitrarily select target value of each of the two groups under the formula for experimental verification of drilling fluid,then the measurement errors between theoretical and tested plastic viscosity are less than 5%,confirming that regression model can be applied to optimizing the circulating of plastic-foam drilling fluid viscosity.In accordance with the precision of different formulations of drilling fluid for other constraints,the methods result in the optimization of the circulating micro-bubble drilling fluid parameters.展开更多
基金the National Natural Science Foundation of China(Grant 51609115)the Foundation of National Key Laboratory of Transient Physics(Grant9140C300206150C30143).
文摘The effect of micro-bubbles on the turbulent boundary layer in the channel flow with Reynolds numbers (Re) ranging from 0.87 × 105 to 1.23 × 105 is experimentally studied by using particle image velocimetry (PIV) measurements.The microbubbles are produced by water electrolysis.The velocity profiles,Reynolds stress and instantaneous structures of the boundary layer,with and without micro-bubbles,are measured and analyzed.The presence of micro-bubbles changes the streamwise mean velocity of the fluid and increases the wall shear stress.The results show that micro-bubbles have two effects,buoyancy and extrusion,which dominate the flow behavior of the mixed fluid in the turbulent boundary layer.The buoyancy effect leads to upward motion that drives the fluid motion in the same direction and,therefore,enhances the turbulence intense of the boundary layer.While for the extrusion effect,the presence of accumulated micro-bubbles pushes the flow structures in the turbulent boundary layer away from the near-wall region.The interaction between these two effects causes the vorticity structures and turbulence activity to be in the region far away from the wall.The buoyancy effect is dominant when the Re is relatively small,while the extrusion effect plays a more important role when Re rises.
基金Project(50304010) supported by the National Natural Science Foundation of China
文摘In order to optimize plastic viscosity of 18 mPa·s circulating micro-bubble drilling fluid formula,orthogonal and uniform experimental design methods were applied,and the plastic viscosities of 36 and 24 groups of agent were tested,respectively.It is found that these two experimental design methods show drawbacks,that is,the amount of agent is difficult to determine,and the results are not fully optimized.Therefore,multiple regression experimental method was used to design experimental formula.By randomly selecting arbitrary agent with the amount within the recommended range,17 groups of drilling fluid formula were designed,and the plastic viscosity of each experiment formula was measured.Set plastic viscosity as the objective function,through multiple regressions,then quadratic regression model is obtained,whose correlation coefficient meets the requirement.Set target values of plastic viscosity to be 18,20 and 22 mPa·s,respectively,with the trial method,5 drilling fluid formulas are obtained with accuracy of 0.000 3,0.000 1 and 0.000 3.Arbitrarily select target value of each of the two groups under the formula for experimental verification of drilling fluid,then the measurement errors between theoretical and tested plastic viscosity are less than 5%,confirming that regression model can be applied to optimizing the circulating of plastic-foam drilling fluid viscosity.In accordance with the precision of different formulations of drilling fluid for other constraints,the methods result in the optimization of the circulating micro-bubble drilling fluid parameters.
