| Summary: | 碩士 === 逢甲大學 === 土木及水利工程研究所 === 88 === The fluid motion between two rotating cylinders is an important topic in classic fluid mechanics. There are several flow regimes existing in an incompressible viscous fluid between two concentric independently rotating cylinders. These flow regimes consist of laminar Couette flow, Taylor vortex, spiral vortex, transition to turbulent flows, depending on the angular velocity of cylinders. This study is carried out by both experimental investigation and numerical simulation to find the flow solution of the unsteady procedures, and it looks forward to utilizing in different kinds of engineering problems.
The experimental work in this study is carried out in the range of middle and low Reynolds numbers. For flow visualization, aluminum flakes were used as visible particle, laser sheet and searchlight were used as light source. The results show the different evolution processes of Taylor vortex flow. We found that the azimuthal flow between counter-rotating cylinders induce spiral flow. For modulated flow, the frequency of rotating velocity changes with time and space. The characteristic of flows fit our experimental results.
In this study, a numerical model to solve the three-dimensional Navier-Stokes equations is established to investigate the flow regimes in several different Reynolds numbers. The projection method is first employed to obtain the pressure Poisson equation such that the equation of continuity can be satisfied. Then the velocity is solved from the momentum equations by using a compound scheme. The Adams-Bashforth Scheme and the Crank-Nicolson scheme are used to release the restriction of small time step. The transient processes of the wavy vortex, modulated wavy flow and spiral vortex flow are vividly obtained from numerical simulations. The different gaps between two cylinders will generate the different flow patterns in the same inner and outer Reynolds numbers. Besides, different initial conditions (steady or unsteady state) also have large effects on the results of numerical computation.
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