【作者】 史凤霞；

【导师】 杨军虎；

【作者基本信息】 兰州理工大学 ， 流体机械及工程， 2017， 博士

【摘要】 作为一种高压流体能量回收装置,离心泵反转作液力透平因其结构简单、成本低廉、检修方便等特点,被广泛应用于石油化工、煤化工、海水淡化等行业。液力透平对高压流体进行能量回收时,普遍存在效率不高和运转不稳定的问题。究其原因,一是没有为液力透平添加导叶,二是因为化工行业的高压流体大多属于气液两相介质,气体对液力透平的回收性能有很大影响,为此,论文以离心泵反转作液力透平为研究对象,在利用实验验证了本文数值计算策略的准确性和可靠性的基础上,采用数值计算首先在纯液体条件下为液力透平添加导叶,研究导叶对液力透平水力性能的影响,然后在气液两相条件下研究气体体积含量对液力透平的水力性能和液力透平内压力脉动分布规律的影响。通过数值计算和实验研究,取得主要成果如下:1.为液力透平添加导叶可以提高液力透平的效率和运转稳定性,导叶叶片数为Z+1、Z+3和Z+5(Z为液力透平转轮叶片数)时液力透平效率分别比无导叶的液力透平效率提高了0.58%,1.45%和2.00%。为液力透平添加导叶时,存在最佳的导叶叶片数可以使液力透平的效率提高,使透平转轮进口环量和叶片载荷分布更加均匀,增加流体对转轮的做功区域,并能增强大流量工况时的能量转换特性。当导叶叶片数为Z+3时,液力透平转轮上的瞬时径向力波动幅度和主频幅值均最小,且高频脉动最少,对液力透平的稳定运转有利。2.气液两相条件下液力透平的效率均低于纯液体条件下液力透平的效率,同一流量下,液力透平效率随着气体体积分数的增加而降低。最优工况时气体体积分数k?=0.05时液力透平的效率比k?=0.1,0.15和0.2时分别高0.8%、2.2%和2.8%。气液两相条件下液力透平内的总流动损失大于纯液体条件下的流动损失,流动损失随着气体体积分数的升高而增大,最优工况时气体体积分数k?=0.05时液力透平的总水力损失比k?=0.1,0.15和0.2时分别低5.1%、11.9%和16.3%。同一工况,不同气体体积分数下叶片载荷的分布趋势一致,气体体积分数越高,叶片载荷越小。大流量工况下叶片载荷分布曲线有明显的曲率变化,叶片载荷分布不均主要是由压力面的静压力变化引起的,流体对转轮做功的关键区域为转轮中部。低含气率大流量工况时径向力波动幅度和主频幅值最大。气液两相条件下,液力透平内气体分布不均,液力透平动静耦合面处存在尾迹效应,在转轮出口处有气体聚集现象。液力透平各过流部件内的压力脉动时域呈周期性变化,隔舌处存在二次压力脉动。一个转动周期内压力脉动数与转轮的叶片数相等,不同气体体积分数下液力透平内各点的主频都等于叶频,主频后无次主频出现。转轮内压力脉动最剧烈,蜗壳和导叶内次之,尾水管压力脉动最轻。气体体积分数大于0.05后其对液力透平内的压力脉动分布规律有影响,含气率越高,压力脉动最大脉动幅度和主频幅值越小。更多还原

【Abstract】 Centrifugal pump running in inverse mode(pump as turbine)is a kind of high pressure fluid energy recovery device.With the characteristic of simple structure,low cost and convenient maintenance,pump as turbine is widely used in petrochemical,coal chemical industry,seawater desalination industry and so on,but the pump as turbine generally has the problem of conversion efficiency is not high and working condition is not stable.In general there are two reasons: one is the guide vane is not added to pump as turbine,the other is that to the high pressure fluid in chemical industry,in addition to the liquid,a certain amount of gases are also contained.The gas has a great influence on the recovery performance of hydraulic turbine.In order to solve the above problems,based on the centrifugal pump as turbine,the external characteristics of the pump as turbine was studied by numerical calculation and experiment,and the accuracy of the numerical calculation method is verified by the experimental results.The guide vane is added to the pump as turbine,under the pure liquid working conditions,the effect of guide vane on the hydraulic performance in hydraulic turbine is studied,then under the gas-liquid two phase working conditions,the effect of gas volume fraction on the hydraulic performance and the distribution rules of pressure fluctuation in hydraulic turbine are studied,two main results in this paper are shown as follows:1.The efficiency and the running stability of pump as turbine can be improved by guide vane.When the guide vane numbers equal(Z+1),(Z+3)and(Z+5)(Z represents the impeller blade number),the efficiency of pump as turbine with guide vane respectively is improved 0.58%,1.45% and 2.00%.To the pump as turbine,an optimal guide vane number is existent,under which the effieciency of turbine is improved,the inlet circulation of impeller and the distribution of blade loading are the most uniform,the useful work areas of fluid are increased,the energy conversion characteristic in high flow rate is increased,the fluctuation amplitude and the dominant frequency amplitude are also the minimum,all of which is good to the performance of pump as tturbine.In this paper,the optimal guide vane number is(Z+3).2.Under the gas-liquid two phase conditions,the effieciency of pump as turine is higher than that of pure liquid conditions,to a same flow rate,with the gas volume fraction increases the efficiency of pump as turbine reduced.At the optimal flow rate,the efficiency of pump as turbine atk? =0.05 is respectively 0.8%,2.2% and 2.8% higher than that of k? =0.1,0.15 and 0.2.Under gas-liquid two phase conditions,the flow losses of pump as turine is higher than that of pure liquid conditions,to a same flow rate,with the gas volume fraction increases the flow losses in pump as turbine are also increased.At the optimal flow rate,the flow losses in pump as turbine at k? =0.05 is respectively 5.1%,11.9% and 16.3% lower than that of pure liquid conditions.To a same flow rate,under different gas volume fractions,the distribution trends are consistent,the higher the gas volume fraction,the smaller the blade loads.At high flow rate,the obvious curvature change of blade loads appeared,which is cased by the change of static pressure in pressure surface,the main working area is the impeller center.Under the low gas volume fraction and high flow rate,the radial force fluctuation amplitude and dominant frequency amplitude are the maximum.Under gas-liquid two phase conditions,the distribution of gas is not uniform,the wake effect appeared at the dynamic and static coupling interface,in the impeller outlet the gas gathered obviously.The time domain of pressure fluctuation in pump as turbine changes periodically,and near the volute tongue,the two times pressure fluctuation appeared.In one rotating circle the pressure fluctuation numbers equal the impeller blade numbers,and the dominant frequency equals the impeller blade frequency,and no subordinate appeared.The pressure fluctuation in impeller is the most intense,which in volute and guide vane is the second intense,and in draft tube is the lightest.When the gas volume fractionk? is greater than 0.05,the gas rate has obvious effect on the pressure fluctuation.The more the gas rate,the smaller the maximum fluctuation amplitude and the dominant frequency amplitude.更多还原