| The high specific speed centrifugal pump is considered that whose ns is between 150 and 300,and it is widely used in nuclear power,aerospace,precision chemical industry and some other fields.Under the background of the purpose of designing and optimizing a certain type high specific speed centrifugal pump by an enterprise,some related work is organized by this thesis,which supported by the Training of Innovative Talents Collaborative Projects(XTPY201618).The importance of chemical process pump can not be ignored,not only is it the pivotal infrastructure in the chemical production unit,but also the maximum dosage rotating equipment,which plays a key role in the chemical process.In recent years,with the further reform of economic development,the stereotypical chemical process pump whose type is single,and the running stability is poor,and the energy consumption is high,can not satisfy the future industrial 4.0 requirements.As known to all,the operation efficiency of centrifugal pump depends largely on the critical flow components especially the design of the impeller.Currently,the investigation of blade main geometric parameters affected on the flow characteristics inside the pump and the structural dynamic characteristics is not enough in-depth and comprehensive.Considering the profit maximization,the blade needs to be redesigned under the premise of without changing the main structure parameters.Therefore,the critical parameters of blade outlet angle is focused on by this thesis,in order to reveal its mechanism from multiple perspectives,not only the performance but also the structural dynamic characteristics are researched.The main research contents and conclusions of this thesis are as follows:1.A chemical process centrifugal pump with high specific speed was selected to be researched,and 4 impellers with different blade outlet angle were redesigned based on the prototype pump,which ensure that other geometrical parameters unchanged.Meanwhile,doing the numerical simulation of different schemes under different conditions.The comparison of performance simulated for different schemes was acquired and analyzed.It shows that with the increase of blade outlet angle,the head increases under the design condition.Because the outlet circumferential velocity increases with the increase of blade outlet angle,combing with the basic equation of pump,it is not difficult to find that the head of pump can increases with the increase of outlet circumferential velocity.But if the outlet blade angle is too big,it will cause that blade bending is serious,the sigmoid will be generated,and the flow passage between the two adjacent blades will be shorten.Besides,the diffusion angle will be bigger,which resulted in that hydraulic loss increases and the efficiency will be significantly lower especially under the overload conditions.The comparison of performance curve on experimental data and simulated prediction on value of prototype pump was analyzed,it can verify that the fluid domain for this model is reasonable,and the numerical simulation method used is reliable.2.In order to present a more clear comparison results and give a direct intuitive understanding of the influence of blade outlet angle on the internal flow in this chemical process pump,the 4 impellers newly designed are analyzed from the aspect of static pressure distribution,turbulent kinetic energy and velocity vector distribution,distribution of Hn on the medium section of impellers with different schemes under different conditions,and the reflux characteristics under part load condition.The results illustrate that with the increase of the blade outlet angle,the low energy fluid region around the inlet of the impeller gradually spread to the outlet.Besides,there was an adverse pressure gradient near the pressure side,the unstable low energy fluid gathered,which can bring the flow separation easily.When the outlet blade angle is too bigger,the turbulent kinetic energy is larger,and the axial vortex is enlarged,it nearly expands to the entire passage under the overload condition.The value of Hn is biggest under the partload condition,means that can bring flow instability easily and will produce unstable flow structure.It is found that the reflux phenomenon is increased with the increase of the outlet blade angle,and it mainly appeared near the front / rear cover board.This phenomenon is consistent with the instability characteristics of the Hn prediction.What is more,there is turbulence phenomena appeared in the distribution of Hn for the impeller whose ?2 is equal to 47°,and not only positive vortex but also reverse vortex have been generated,whose strength is higher.This may be due to increase of the impeller wake caused by the increase of blade outlet angle.3.Through comparing and analyzing distribution of the pressure fluctuation and the radial force on the impellers of the 4 schemes under multiple loading conditions,the effect of the blade outlet angle on the unsteady flow characteristics in the pump was revealed.The results show that the pressure fluctuation amplitude increases with the increasing of the blade outlet angle,but the main fluctuation frequency does not change,and it means the pressure fluctuation is mainly caused by the rotor-stator interaction mechanism between blades and the baffle tongue.In addition,the pressure fluctuation is more intense under the overload condition than the part load condition,and its amplitude is larger.Furthermore,there is a trend that the subdominant frequency moves to the low frequency when the blade outlet angle increases,and it shows the flow structure and the pressure are effected by the blade outlet angle.Through the simulation of the radial force,it is found that the radial force on the impeller is minimum under the designed condition,and it is most affected under part load condition.The distribution of radial force on the impellers can be improved through reducing the blade outlet angle.4.The numerical calculation is applied for each scheme under design condition based on the two-way coupled fluid-structure interaction(FSI)simulations to reveal the effect of the blade outlet angle on the structural behavior of the pump.Through simulation,the head after the fluidsolid coupling is lower than before,but the error is reduced.Comparing the distribution of equivalent stress at intersection boundary,it shows that the places from 0.6 times to 0.8 times at the outlet at the intersection boundary of stress side and shroud are greatly affected by blade outlet angle,and the places from 0.8 times at the outlet to the outlet at the intersection boundary of stress side and shroud are also greatly affected by blade outlet angle.In addition,the equivalent stress increases with the increasing of blade outlet angle,and the place near the outlet all tend to have the phenomena of stress concentration.Moreover,the total deformation shows that the deformation can be reduced through reducing the blade outlet angle.Also,the structural behavior of the impeller indicates that the first-order inherent frequency is much higher than the blade frequency,and it avoids the second harmonic frequency and the third harmonic frequency.The inherent frequency can be improved when the blade outlet angle is relatively bigger,but if it is oversize,it may cause swing and twist,and if it is lesser,the total deformation can be uniform. |
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