【作者】 孙波；

【导师】 马文星；

【作者基本信息】 吉林大学 ， 机械设计及理论， 2011， 博士

【摘要】 作为一种液力传动元件液力偶合器具有很多优点。尤其是调速型液力偶合器应用在风机、水泵等耗能设备上调速节能效果明显。当液力偶合器工作时,会产生较大的轴向力,加速轴承的疲劳和磨损,缩短轴承的使用寿命,进而影响整机的使用寿命。液力偶合器叶轮本身不存在磨损,其可靠性和寿命主要是由轴承和密封决定的。因此,研究轴向力对提高液力偶合器的寿命和可靠性具有重要意义。本文结合国家高技术研究发展计划(863计划)专题课题“大型泵与风机液力调速节能关键技术研究”(2007AA05Z256),采用计算流体动力学数值计算方法,对液力偶合器的流场和轴向力进行计算分析,找出其变化规律,并对轴向力进行试验研究。探讨液力偶合器轴向力的影响因素,并分析减小液力偶合器轴向力的措施。本文主要研究内容和结论如下:1、液力偶合器轴向力理论分析液力偶合器轴向力包括泵轮轴向力和涡轮轴向力,它们均由工作腔轴向力和辅腔轴向力两部分组成。工作腔轴向力产生原因有两个,一是由于工作腔内流体受离心力作用产生的静压力所致;二是由于工作腔内流体循环流动,速度方向改变导致动量变化而产生的轴向力。辅腔轴向力主要是离心力产生的静压力所致。要准确计算轴向力,关键是获得工作腔和辅腔内准确的流场分布。通过对调速型液力偶合器结构和工作特点分析知,辅腔内流体对泵轮和涡轮的轴向作用力是一对大小相等方向相反的力;同理,工作腔内流体对泵轮和涡轮的轴向作用力也是一对大小相等方向相反的力。那么泵轮轴向力合力与涡轮轴向力合力必然也是一对大小相等方向相反的力。在计算轴向力时只计算其中一个即可。2、液力偶合器气液两相流计算计算调速型液力偶合器轴向力的关键是计算内流场。液力偶合器工作时,其工作腔内是非定常、三维、不可压缩、粘性气液两相流动。为此采用将气液两相流视为连续流体的Mixture多相流模型来描述其流动;对湍流计算采用计算量小、注重反映流场综合效果的雷诺时均法和基于Boussinesq涡粘假设理论的Relizable k -ε湍流模型;考虑到涡轮和泵轮叶片间的耦合影响,采用将泵轮和涡轮一起计算的整体流道计算域,泵轮和涡轮两计算域间边界采用滑移网格技术进行处理;叶片和流道表面设置为无滑移壁面条件;基于有限体积法对控制方程离散,空间离散格式选用稳定性好、精度较高的二阶迎风离散格式;对两相流离散方程采用分离式解法,速度—压力耦合采用PISO算法。并以YOCQz465调速型液力偶合器为例给出计算过程。同时对液力偶合器辅腔流场也采用同样的方法进行计算。3、调速型液力偶合器轴向力及流场分析为得到液力偶合器轴向力的大小和变化规律,以YOCQz465调速型液力偶合器为例,对各充液率、不同转速比条件下的流场和轴向力进行计算。并对制动工况、典型牵引工况和额定工况下液力偶合器工作腔、辅腔流场和轴向力进行分析。在此基础上获得液力偶合器轴向力合力。通过分析得出以下结论:在充液率一定的情况下,液力偶合器轴向力随转速比的增大而减小;在制动工况下轴向力最大,在额定工况下最小。轴向力的变化规律是由工作腔内和辅腔内流场压力这一对矛盾决定的。工作腔内的压力随转速比增大而减小,因为随转速比增大,工作腔环流量减小,由于速度方向改变而产生的动反力减小;辅腔内压力随转速比增大而增大,是由于转速增大,离心力增大的缘故。但各工况下,工作腔内压力均大于辅腔内压力,对轴向力起主导作用,决定轴向力的方向,所以液力偶合器泵轮和涡轮的轴向力都是向外的,即有使泵轮和涡轮分开的趋势。4、调速型液力偶合器轴向力试验研究理论分析与计算的结果是否正确只能通过试验来验证。为此在大连液力机械有限公司对YOCQz465调速型液力偶合器轴向力进行试验测试。首次提出并采用通过测量推力盘轴向应变来测量液力偶合器轴向力的方法。该方法不需要对原液力偶合器结构进行改造,对原液力偶合器结构和性能影响小,简单、方便,适用于具有推力盘的大功率液力偶合器。对试验结果进行分析表明,工作时液力偶合器轴向力脉动较大,对液力偶合器轴承和结构都有较大影响,但其平均值较稳定。将理论计算结果与试验结果进行对比分析表明,理论计算值比试验值略大一些,平均误差为8%,最大误差22%。实验测试和理论计算的轴向力方向是一致的。说明基于CFD的轴向力计算方法是可行的。5、液力偶合器轴向力影响因素分析液力偶合器轴向力影响因素很多也很复杂,为控制液力偶合器轴向力过大,分析了减小轴向力的措施。本文采用对比的方法,从理论计算和流场分析的角度,对液力偶合器的充液率、腔型、循环圆直径、输入转速等参数对轴向力的影响进行了分析。分析结果表明:液力偶合器充液率大,轴向力大,并近似成正比关系;液力偶合器腔型对轴向力影响较大,并且桃形腔轴向力明显大于圆形腔;循环圆直径增大,轴向力迅速增大,轴向力与循环圆直径四次方近似成正比;输入转速增大,轴向力增大,轴向力与转速平方近似成正比。在此基础上分析了减小轴向力措施。一是在涡轮壳体上开卸荷孔,可减小工作腔与辅腔间压力差,从而减小轴向力;二是采用双腔结构,对称结构可使轴向力相互抵消。更多还原

【Abstract】 Hydrodynamic coupling is a hydrodynamic transmission component with many advantages. Especially variable speed hydrodynamic coupling is a better reliable and economical speed regulator, which is widely used for fans and pumps because of its obvious energy-saving effect. However, greater axial force will be produced during its running, which will accelerates the bearing fatigue and wearing, shortening bearing’s life cycle and the coupling’s life cycle. In fact, hydrodynamic coupling itself doesn’t exist wearing owing to its hydrodynamic transmission, the lifespan and reliability of hydrodynamic coupling is mainly depended on bearing and its sealing. In a word, axial force has a significant impact on hydrodynamic coupling’s reliability.Aiming at the axial force calculation of variable speed high-power hydrodynamic coupling, an indispensable part of the special subject“Key Technological Research on Hydrodynamic Variable Speed and Energy Saving of Large Pump and Fan”from the National High Technology Research and Development Plan (863) (2007AA05Z256), in the paper, multi-phase CFD method is effectively made use of to carry out the flow field calculation and analysis of hydrodynamic coupling and reveal its flow law, and axial force exeperimental measuring is carried on. Based on this, the influencing factors to hydrodynamic coupling axial force are discussed so as to find the measures of reducing hydrodynamic coupling axial force. The research method, content and conclusions are as follows:1.Theoretical analysis of axial force in Hydrodynamic couplingHydrodynamic couplings axial force includs the pump axial force and turbine axial force. Both consist of working chamber axial force and secondary chamber axial force. Working chamber axial force can be attributed to two aspects, on the one hand, it is resulted from the static pressure initiated from centrifugal force due to flow in the working chamber, on the other hand, it is produced by the circulated flow with direction variation of velocity and variation of momentum. But, secondary chamber axial force is mainly resulted from static pressure owing to centrifugal force. To accurately calculate the axial force, the key is to get the accurate flow field in both the working chamber and the secondary chamber.It can be seen that from the structural and working characteristics of hydrodynamic coupling that there exists an action and reaction axial force pair between the pump and turbine in the secondary chamber; it is same situation as in the working chamber. Therefore, the resultant force of pump and turbine is an force pair; they are the same in size and opposite in direction. In calculating the axial force, anyone calculation of these two forces will be enough.2.Numerical Calculation of Gas-liquid Two-phase Flow in Variable Speed Hydrodynamic CouplingThe inner flow field calculation of hydrodynamic coupling is the key to decide the axial force, which is unsteady, incompressible and viscous two-phase flow. In solving this complex flow, a multi-phase model Mixture is adopted to describe the gas-liquid continuous flow; for turbulent calculation, a Relizable k-εturbulent model based on Boussinesq eddy viscosity assumption is chosen to characterize the turbulent flow by using Reynolds time-averaged method at the result of shorter calculation time and better calculation results; taking into account the hydrodynamic coupling effect between the pump and turbine, the computational domain of pump and turbine is integrated, while the interface of the pump and turbine is dealt with sliding mesh theory; boundary conditions of blade and wall surfaces are set as non-slip wall condition; the N-S equation based on finite volume method is differentiated by a more stable and accurate second-order upwind scheme; PISO algorithm is used in velocity-pressure hydrodynamic coupling algorithm; the two-phase differentiation equation is solved by variable separation method. Finally, YOCQz465 variable speed hydrodynamic coupling is taken for example to show the complete simulation process. For hydrodynamic coupling secondary chamber flow field calculation, the above method validates. 3.Axial Force and Flow Field Analysis in Variable Speed High-power Hydrodynamic couplingTo identify the value and variation law of hydrodynamic coupling axial force, taking YOCQz465 variable speed hydrodynamic coupling for example, flow field and axial force are respectively calculated at different filling rate and speed ratio, further, the flow field and axial force in working chamber and secondary chamber are analyzed under braking condition, traction condition and rated condition to finally obtain the resultant force of hydrodynamic coupling axial force. The following conclusions can be drawn from the analysis:The axial force of hydrodynamic coupling deceases with the increasing of speed ratio at a constant filling rate; the axial force reaches the maximum at braking condition while minimum at rated condition. Variation law of axial force lies in the contradiction between working chamber pressure and secondary chamber pressure. The pressure in working chamber decrease with the increase of speed ratio because the circulation flow reduces with the increase of speed ratio, which results in decreasing the reaction force due to direction alteration of velocity. However, the pressure in the secondary chamber increases with the rising of speed ratio because of the increment of centrifugal force. To sum up, pressure in working chamber is always greater than that in the secondary chamber, thus, the axial force of working chamber plays a dominant role in determining the direction of axial force, both axial forces of pump and turbine are opposite in direction, tending to disengage the pump and turbine.4.Axial Force Experimental Mmeasuring in Variable Speed High-power Hydrodynamic CouplingTheoretical analysis and calculation results must be verified before application, for this purpose, a series of proof tests are done on YOCQz465 in Dalian Hydrodynamic Machinery Company. An innovative method is proposed for measuring axial force of hydrodynamic coupling by virtue of measuring axial strain of thrust plate. This new method is simple and convenient, doesn’t need modification of the original hydrodynamic couplings, has little influence on the structure and properties of hydrodynamic coupling and is suitable for large-scale high-speed hydrodynamic coupling. Analysis of the test results shows that the axial force fluctuation is greater but the axial force average is stable during running, which has a greater impact on its structure and bearings. The comparison of the theoretical results with the experimental ones shows that the calculated values are slightly larger than the experimental ones.The mean error is 8%, and the maximum error is 22%; the direction of axial force is identical. Therefore, the calculation method based on CFD is feasible.5.Influencing Factors on Axial Force in Hydrodynamic CouplingFor the control of greater hydrodynamic coupling axial force, the influencing factors must be found. It is hard to decide the influencing factors, thus, a comparative method is used from the viewpoint of theoretical calculation and flow field analysis by focusing on filling rate, chamber shape, circulation diameter and input speed. The analytical results demonstrates that the greater the filling rate, the larger the axial force, existing approximate direct proportional relationship; chamber shape has a greater impact on the axial force, and the axial force of peach-type chamber is significantly greater than circle-type chamber; circulation diameter increasing brings about rapid increase of axial force, which is proportional to the fourth power of the circulation diameter; the greater input speed will produce greater axial force, being proportional to the square of input speed. Based on the above analysis, measures for decreasing axial force are as follows: the first is to open unloading holes in turbine housing so as to reduce the pressure difference between the working chamber and the secondary chamber; the second is the use of dual-chamber structure which can counterbalance the axial forces.更多还原