The Research On The Turbulence Flow Structure And Heat Transfer In Rotating Curvilinear Pipes

Rotating curvilinear pipes have a wide application in engineering practice. The characteristics of fluid flow and convective heat transfer in curvilinear pipes are important factors that influence the performance of various rotating machinery, such as fluid transportation system, controlling pipe system and cooling pipe system. Almost all flows are turbulent in engineering applications. The studies in the characteristics of flow and heat transfer in rotating curvilinear pipes are scarce when the flow is in turbulent state. However, it is an urgent problem which needs solving in application. Meanwhile, solving this problem will help the progress of biological fluid mechanics. Because, the blood flow in the blood vessel is a typical problem of curvilinear pipes. From this point of view, this study is significant and has a broad application future.In this dissertation, research findings of nearly latest one hundred years on fluid flow and convective heat transfer in curvilinear pipes are reviewed and analyzed. Then, the RANS equations,κ-εturbulent model equations and energy equation in rotating curvilinear coordinate system are derived based on a multi-parameters helical pipe model. The numerical method is then applied to study the fluid flow and heat transfer in curvilinear pipes, which are stationary or rotating, with various parameters and different cross-sections. The effects of different parameters and cross-sections on axial velocity, the distribution of secondary flow, temperature field, turbulent kinetic energy, wall friction coefficient and wall Nusselt number are analyzed in detail.The contributions and innovations of the paper lie on the following: the turbulence RANS equations and the two parametersκ-εturbulence model equations in rotating helical coordinates are deduced and simulated numerically. The effects of different parameters on the turbulence flow and heat transfer are analyzed. The most important findings are:(1) The region of high axial velocity of helical pipe in the turbulence flow is larger than the corresponding laminar region. In the condition of same flow flux, the maximum axial velocity in the turbulence flow is smaller than laminar one.(2) There are two secondary vortices in the helical pipe with circular cross-section when the flow is turbulent. The vortex on the upper half rotates clockwise and is restricted on a very limited region. Comparing with the flow in laminar state, this region is rather small. When the fluid flows in a planar curved pipe with rectangular cross-section and the aspect ration is smaller than a certain value, the flow will become instability. The distinct difference from laminar flow is that the vortices in the cross-section are always no more than 4. The flow will restore to stable state if the aspect ration decreases further.(3) For the rotation number considered in this paper ([-2, 1]), the axial velocity firstly increases with the increasing of rotation number. When rotation number is near -0.25, it reaches the maximum. Then it decreases with the increasing of rotation number. The secondary flow, dimensionless temperature, friction coefficient and Nusselt number firstly decreases as the rotation number increases and then increases when rotation number is larger than -1.(4) The magnitudes of wall friction coefficient and Nusselt number of turbulence flow in rotating helical pipe are larger than laminar ones. In the developing region, there are evident oscillations of the friction coefficient and Nusselt number along the axis. The friction coefficient and Nusselt number reach their minimum values when the rotation number is near -1. However, these minimums are still larger than corresponding ones of the straight pipe with same parameter.(5) The influence of inlet turbulence intensity on the velocity, temperature, turbulence kinetic, friction coefficient and Nusselt number is limited on a limited region which is smaller than 30d. In the inlet turbulence intensity influenced region, the larger the inlet turbulence intensity is, the larger the turbulence kinetic, friction coefficient and Nusselt number is.