| The cross-flow fan is widely used in the field of air conditioning and ventilation,fully understanding the flow field characteristics of the cross-flow fan is of great significance for energy saving and noise reduction.Eccentric vortex is the most typical characteristic of the cross-flow fan,and the formation mechanism has not yet reached a consensus.Meanwhile,the general design criterion of the cross flow fan has not yet been formed.Based on two-dimensional numerical simulation,the paper focuses on clarifying the flow details of the cross-flow fan for air conditioning,the essential factors of the cross-flow fan with forward curved impeller,the formation process of the eccentric vortex and the control principle of housing geometry to the eccentric vortex,and the effect of blade parameters on the flow field and the performance of the fan.Combined with the simulation results and Rankine vortex theory,the vorticity,angular velocity and vortex core pressure of the eccentric vortex are calculated.The characteristics of eccentric vortex is consistent with that of Rankie vortex.On the other hand,the vortex,whose direction of rotation is opposite to that of the impeller and near the inlet of the volute,is mainly caused by the diffusion and merging of the vortex on the suction surface of the upstream blade.Compared the flow field of forward-bent,backward-bent and radial impellers,it is found that the inner circle area of the three impellers can form a low pressure vortex which controls the distribution of the whole flow field.Unlike those of other two impellers,the vortex generated by the forward-bent impeller has larger negative pressure,and the position of the vortex is located at the blade tip.Therefore,only the forward-bent impeller can generate the eccentric vortex with great attraction force and stable position after adding volute tongue,which provides the theoretical basis for the application of the forward-bent impeller.Combined with the free flow field of three kinds of impeller and the flow filed after adding different housing geometry,it is observed that the eccentric vortex is mainly produced by the merging of vortex,whose direction of rotation is the same as that of the impeller.In the inner edge of the impeller,the energy of the eccentric vortex is mainly supplied by a large number of shedding vortices on the blade pressure surface near the vortex nucleus.The position of eccentric vortex is mainly determined by the flow incidence angle of blades downstream the vortex nucleus.The addition of the volute tongue changes the incidence angle distribution downstream the vortex nucleus,and reduces the vortex shedding of the blade pressure surface.Thus,the volute tongue can control the position of the eccentric vortex,while the volute mainly plays the role of guiding and expanding.The simulation results of blade parameters show that,blade leading radius R_i and rear edge radius R_o,tilt angle?and camber angle?have different effect on the flow field and performance of the fan.The fundamental mechanism of these influences is that the parameters can change the distribution of the flow incidence angle around the blade,resulting in the variations of vorticity distribution of the eccentric vortex region and inlet impeller area.The research achievements of this paper can provide theoretical guidance for the design of the cross flow fan. |
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