摘要
围绕双流道污水泵叶轮的三维设计方法、基于Pro/Engineer二次开发的双流道叶轮三维参数化设计程序,和双流道污水泵内部主要过流部件叶轮与蜗壳耦合的全通道数值模拟,本文展开了较为广泛而深入的研究,取得了以下研究成果:
1.对常用的双流道污水泵叶轮图纸的表达方法进行了研究,发现存在平面图上与轴面图中的流道断面投影结果不一致的问题。断面形状为沿对称轴对折的椭圆,此对称轴始终垂直于轴截面,则其方向与平面图上的流道中线无关。因此,传统中认为其垂直于平面图上的流道中线而确定的截面尺寸并不符合实际的投影关系。这就是传统设计中经常出现的双流道叶轮平面图、断面面积与叶轮木模三者不一致的主要原因。建议在双流道污水泵叶轮设计时,平面绘型应作为初步设计,然后在三维造型中确定其余参数,由三维造型来生成平面绘型,以保证设计与木模一致。
2.双流道污水泵叶轮形状比较特殊,不同于一般离心泵,造型方法尚有待探讨。在Pro/ENGINEER中进行双流道叶轮三维造型的方法如下:用投影方法生成空间流道中线,并作为内流道的原始轨迹,各断面形状作为混合用截面,使用扫描混合命令形成内流道;按内流道中线规律,延长内流道中线到叶轮外径,用投影得到的空间曲线作为外流道原始轨迹,按外流道截线位置放置适当截面,由扫描混合命令形成外流道。叶轮在二维绘型图转化为三维造型时,可能会出现无法形成有效内流道的问题,本文分析了其中的原因,并给出了调整措施。
3.研究了在Pro/E中直接进行叶轮的三维设计方法。
4.双流道叶轮设计中,平面流道中线普遍使用变异阿基米德螺线。推导了平面流道中线采用变异阿基米德螺线时,流道中线出口角与包角、变异系数之间的关系式,为设计中控制流道中线出口角提供了依据,解决了传统设计法中采用变异阿基米德螺线作为平面流道中线时,无法事先确定流道中线出口角的难题。
5.推导了变异阿基米德螺线法线方向到叶轮外圆距离的变化规律,在此基础上给出了确定内流道出口点的解析方法。
6.使用所提出的叶轮三维设计方法,编写了基于Pro/E二次开发的双流道污水泵叶轮三维参数化设计程序。用户可直接输入参数得到叶轮流道的三维造型,为叶轮的CFD数值模拟和NC(Numerical Control简称数控)制造提供了基础。在造型前可预览轴面图和平面图,初步筛选设计方案;在外流道造型前,可检查有效内流道是否形成,并提供了修改模块以改善内流道造型。该程序还可交互地修改截面积变化规律曲线以及外流道壁厚规律,能够灵活地控制叶轮流道造型。并采用该程序设计了双流道污水泵叶轮QW950-15-55。
7.基于有限体积法,采用SIMPLEC算法及标准κ-ε两方程湍流模型,对双流道污水泵QW950-15-55的主要过流部件内部流场,作了全通道定常流动数值模拟。模拟了包括设计工况在内的11个工况,捕捉到双流道叶轮及蜗壳内部流动的一些典型特征,重现了一些重要的流动现象,提出了进一步改进的办法。
8.由山东双轮集团股份有限公司制造的样机,经过试验测定,额定效率达到85.33%,而目前国产泵的各种叶轮形式的污水泵,排出口径为300mm的,效率在74%～83%之间。
9.数值模拟得到的预测特性与样机试验结果比较表明,两者吻合较好,说明CFD计算结果是可靠的,可作为进一步完善设计提高性能的依据。
Research was carried out focusing on Three-Dimensional design methods of Double Channel Sewage Pump' s impeller and developing programs based on redevelopment of Pro/E for parametric design of impeller and CFD computation of impeller and volute,the whole flow passage of Double Channel Sewage Pump.Some achievements as follows were obtained.
Some problems of usual drawing manner of the Vane of Double Channel Impeller were found.It is the inconformity between the dimensions of plane-view and pinacoid-view of fluid cross-section.The shape of cross-section is an ellipse folded in half through one symmetry axis.And the axis keeps perpendicular with pinacoid-view.Thus the direction of the cross-section is unrelated with center channel curve in plane-view.Traditionally,it is assumed that the cross-section is perpendicular with center-channel curve.This is not the fact.It is considered the major cause resulted in the disagreement among plane view,dimension of cross-section and actual wood former of double channel impeller.The more reasonable design process suggested is drawing design first,then three-dimension design second,and three-dimension achieved finally can be use to create the drawing so as to secure the agreement of the three.Design experience proves the rationality of the design process.
The impeller of Double Channel Sewage pump is deferent from common centrifugal pump,its shape is special.So the method of building 3-D model still needs to be explored further.Research of modeling 3-D shape of the impeller in Pro/E was carried out.3-D passage center-line is generated by projection,and then it is made the original trajectory to produce inner passage by command sweep and blend,with passage cross-sections as sections. Inner passage center-line is extended to the outer diameter of the impeller with its rule formula,the curve resulted is regarded as an original trajectory,and sections is placed in proper position through outer passage profile line.Then the outer passage can be made by command sweep and blend. A failure to form Double-Inner-Channel most possibly is encountered during the procedure to transform 2-D drawing to 3-D model of Double-Channel impeller,and analysis was available for the potential causes,the measures was presented to improve such condition.By practice,the method presented proves correct and efficient.
Problem of disagreement between 2-D drawing and actual wood former of Double-Channel impeller of sewage pump most possibly encountered if the design is from traditional 2-D manner.Research was carried out for the method of 3-D design directly in Pro/ENGINEER,so 2-D drawing can be produced by projecting through 3-D impeller designed.The procedure can secure the agreement between 2-D drawing and actual wood former. Additionally,a formula was deuced,which shows the relation between the outlet angle of center line of channel and wrap angle,variant coefficient, if Archimedes spiral is assumed as the curve of center line of plate plane. It is the basis for controlling outlet angle of channel.
Another formula was present for the calculation of normal distance from points on the center line to outer diameter and formula of cross-section area is also available.They provide convenience for CAD of Double-Channel impeller.Based on it,a analytic method was developed for finding out the outlet point.
Based on the three-dimension design method,program for parametric design of the impeller of Double-Channel Sewage Pump was developed.It was redeveloped in Pro/E with VC++.The program can be use to create passages of the impeller of Double-Channel Sewage Pump directly by inputting some required parameters.Resulted passages of impeller can be a proper base for further CFD computation and NC manufacture.It provides chance to preview the axial profile and plane profile,so user can decide proper plan at first after inputting parameters.Before the outer passage is created, user can check inner passages is successful or not,then decide whether to do something to make them better.The program also provide modules to modify the control curve of inner passage flow area and regulation of outer passage thickness,in order to control the shape of the impeller.And Double Channel Impeller QW950-15-55 was designed by the programme.
The internal flow in impeller and volute casing of QW950-15-55 double-channel passage pump was investigated.Based on the Reynolds averaging N-S Equations and standardκ-εtwo equation turbulent model, the simulations of turbulent flow between impellers are performed by using the flow computing software Fluent under 11 differentoperating conditions. Important flow information was obtained.
Model machine was manufactured by Shandong Shuanglun Pumps Co.,Ltd,and Characteristics experiment was carried out and the efficiency of design condition reach 85.33%.However,the efficency of current domestic sewage pumps of all types impeller,with outer discharge diameter 300mm,is between 74%～83%.
The experiment results comparing with CFD predicted characteristics shows a good identity.So CFD results can provide references for further design.
引文
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