| Snow throwing remover is one kind of modern and efficient snow-removingmachine which generally has the function of cutting,concentrating,moving andthrowing,and is applied widely. The thickness of snow removing is big and thedistance of snow throwing is far. The function of centrifugal fan is to cause pressuredifference and form strong flow so as to throwing snow. With the loader goingforward and the snow collection's self-rotating,the snow is collected and concentratedto the intermediate from two ends,then enters into the centrifugal fan due to thedouble effects of different inner-outer velocity pressure caused by high speed rotatingblade and the continue moving of loader. Centrifugal force caused by centrifugalblade rotating makes snow move to the tip of blade,and snow arrives at the arcsurface in centrifugal fan,then snow rotates with blade and is threw out when itarriving at projectile outlet. The aim to deeply understand the snow throwingmechanism is to reduce the power consumption and improve the throwing efficiencyin the premise of guaranteeing no clogging in the process of throwing snow,and toprovide reference for the actual design and production of centrifugal fan. It hasimportant practical value for the snow coverage country and city to have a goodtransportation and hygienic environment in winter. In this paper,three-dimensionalnumerical simulation and analysis are conducted to the internal gas-solid two-phaseflow field of centrifugal fan by using the method of Computational FluidDynamics(CFD),and its flow phenomenon is studied,which preliminarily reveals t hespeed and pressure distribution. Then the optimization analysis is carried out on itsstructure.This paper mainly studies several aspects as the followings:(1) Physical and mechanical properties of snow as well as the method and theoryof snow clearing are described,according to the design requirement of snow remover,the structural parameters of centrifugal fan are analyzed and calculated,thenthe theoretical productivity and power as well as the maximum distance of throwingsnow are determined.(2) The definition and basic characteristics of two-phase flow are introduced,then the method to numerical simulation of gas-solid two-phase flow and the model ofmulti-phase flow as well as turbulence model in CFD are analyzed and chosen. Threekinds of multi-phase flow models are provided in CFD such as VOF model,Mixturemodel and Eulerian model. According to the method of choosing multi- phase flowmodel,Eulerian model is used to calculate the gas-solid two-phase flow incentrifugal fan,and standard two-equation model is selected to the turbulenck -εemodel .(3) In order to simplify the process of modeling and meshing,some hypothesesare made to the structure and working status as well as flow field of the centrifugalfan,and also some subsidiary elements are ignored. Meshing model of the flow fieldis built with meshing built tool. On this basis,the solvers and speed-pressurecoupling algorithm as well as discretization scheme are analyzed contrastively,andthen separated solver is adopted；to speed-pressure coupling algorithm,PC-SIMPLEis chosen；Second Order Upwind method is used to accomplish the spacediscretization. Then the model is numerical simulated by using unsteady flowmethod,and sliding mesh model theory is adopted to define the interface betweenimpeller area and shell area. With the help of the CFD software,the gas-solid twophaseflow flied characteristics of distribution in centrifugal fan are achieved afternumerical simulation.(4) Based on the numerical simulation results,the flow flied characteristics ofcentrifugal fan is analyzed in this paper. For the whole pressure distribution ofcentrifugal fan,the pressure increases gradually in radial direction,which is mainlycaused by the swirling flow of fluids in the channel of fan,comprehensive effect ofthe coriolis force and centrifugal force caused by rotating makes the pressure riseradically. For the whole velocity distribution of centrifugal fan,the velocity of lateral fluid is higher than the blade inside,and the fluid velocity in right side ishigher than left side in shell outlet. This is mainly because that the tip of the highspeed revolving fan blade closes to right side in shell outlet. It forms the backflowphenomenon because of the effect of the pressure differential in centrifugal fan outletarea,there is whirlpool and secondary flow in the impeller channel,the flow iscomplex.(5) In the condition of keeping other parameters invariant,the optimizationanalysis is carried out respectively on different numbers of fan blade and differentinclination angle of fan blade. The result shows that when the number of fan blade is4 and the inclination angle is 10°retroversion. The average velocity is more higher,and it is more advantageous to throw the snow,reduce the power consumption andimprove the throwing efficiency,which provides reference for the actual design andproduction of impeller blowers.
|
PDF Full Text Request