Numerical Simulation Of Turbulent Swirling Flow In Pipes And Investigation Into Its Flow Characteristics

Turbulent swirling flow is a kind of flow widespread in nature and engineering practice with the example of tornado for the former while cyclone separator,heat transfer enhancement tube and hydrocyclone for the latter,which also plays a good role in sand flushing,oncomelania sweeping,energy dissipation and so on in hydraulic engineering.A study on the flow characteristics of turbulent swirling flow not only has high engineering value,but also can lead to better understanding of fluid dynamics.Due to the complexity of the turbulent swirling flow,numerical simulations method to which are in the majority of simplified two-dimensional axisymmetric model and the inlet conditions are reliable on experimental results nowadays.Furthermore,the research mainly centers on the flow field characteristics and resistance characteristics of the turbulent swirling flow while the results of energy loss is relatively rare.In view of this,numerical simulation and theoretical analysis are adopted to gain an insight into the special flow phenomenon on the basis of previous research in this paper,thus the following results can be obtained:(1)The method on three-dimensional numerical simulation of turbulent swirling flow in pipes is discussed.From the point of turbulence closure mode,Reynolds stress model is more qualified for the simulation of middle high intensity swirling flow.Non-equilibrium wall function has more advantages over the standard wall function for near wall treatment in complex flows such as swirl flow.A numerical swirl generator is developed to gain a swirl of high quality at the inlet of pipes automatically.Targeted Grid layout requires taking both the flow characteristics of the swirl and the structure of the device characteristics into consideration.Results calculated for validation are in good agreement with experimental data.(2)Based on the theory of total flow,a calculation expression of total energy loss of turbulent swirling flow in pipes is proposed.In contrast to the empirical expressions established in terms of experimental or prototype observations,this one can directly consider the effects of turbulence and can implement a uniform description of the total flow characteristics and flow field characteristics of the turbulent swirling flow.On the basis of the three-dimensional numerical simulation results,the total flow energy loss can be calculated immediately.(3)A series of schemes were calculated and the kinematic characteristics of the swirl were explored,the results show that:1)The swirling intensity decays along the streamwise exponentially,while the decay rate is dependent on the experiment.2)Reversal flow appears at the head of pipes when the swirling flow is of middle high intensity.3)When the swirl number is larger than a critical value,the radial distribution of the tangential velocity can be well summarized by the velocity distribution characteristic of the combined vortex,whereas the maximum velocity and its position given by empirical formula are bit of different those from the numerical results.4)The pressure has a large gradient along the radial direction and declines streamwise with the speed related to swirl numbers closely.(4)The resistance characteristics and energy characteristics of the turbulent swirl flow are studied.The results show that:1)The axial and tangential components of the time mean wall shear stress are positively correlated with the swirl number and the Reynolds number.When it comes to a fixed Reynolds number,the axial shear stress varies exponentially with the of swirl number.2)Based on the results of flow field calculation and the expression of total flow characteristic obtained by theoretical analysis,the energy loss character can be uncovered.Compared with the uniform pipe flow,the energy loss coefficient of the turbulent swirling flow is much larger and increases with the increase of the swirl intensity even reaches several times of the former.