Experimental Investigations On The Flow Structure In An Annulus Space Between Two Coaxial Rotating Conical Cylinders

This thesis work deals with the the flow in an the annulus space between two coaxial rotating conical cylinders,which is a further investigation of the Taylor-Couette flow in the classical two coaxial rotating cylindrical spaces.As the rotational speed increases,the laminar flow loses stability and forms the Taylor vortices of various styles and finally develops to turbulence.This research on the detailed process has important academic significance for studying turbulence,and could be widely used for efficient mixing in industrial application.The more complex flow within the annulus space is a strong three-dimensional flow due to the changes in radius.There are less publicly available research.In this paper,the internal flow field is visualized and quantified by the display experiment with colorful flow and the particle image velocity measurement technique.The periodic law of vortices motion is analyzed,and the influence of different factors on the flow field is discussed,including the speed,water level,the free surface and no-slip wall above.The differences between the flow field of the wide annulus(d = 16.5mm)and narrow annulus(d<= 10mm)were found.The helical vortices in the wide gap can be a single helical structure or multi-helical structure,while the scroll in the narrow annulus is only a single helix structure.When the width of the gap is increased,the ratio of the helical vortices' speed to the inner conical cylinder'speed decreases due to the helical vortices following slowlier,which is also different from that stable ratio of the narrow annulus.The most important found is in the dynamic mechanism.In addition to centrifugal force,as well as static pressure can from the dominant role.There are two kinds of flow pattern in the time-averaged flow field through the midline of the gap.One is the convex outward flow,the other is concave inward flow.It is concluded that the difference of the flow patterns is because the directions of the centrifugal force and the static pressure are opposite,so the convex outward flow exists when centrifugal force is dominated and the concave inward flow appears when inward static pressure is dominated.Although centrifugal force and static pressure are both able to produce positive vortices,with no difference in apperance,but according to most time-averaged flow field of concave inward flow,and the calculation that the static pressure is bigger than the centrifugal force,it is indicated that static pressure can play a leading role.The radial normal stress and shear stress of the Reynolds are mainly concentrated in the middle of the radial central section,while the axial shear stress is mainly concentrated near the inner and outer wall surfaces.Radial normal stress accounts for the main part.The large-scale vorticity contributes greatly to the Reynolds stress,while the small-scale vorticity contribution in the turbulence is small.So the Reynolds stress is at the peak on the eve of the helical vortices to change into turbulent vortices.