导叶式离心泵透平工况下固液两相流动特性分析

发布时间：2018-06-21 23:41

本文选题：导叶式离心泵 + 液力透平　；参考：《兰州理工大学》2017年硕士论文

【摘要】：液体余压能的高效回收利用对节能降耗,促进可持续发展具有重要意义。采用离心泵反转作液力透平工况运行,以达到液流余能转化为其他形式能量是行业内正积极探索,大力推广的方向。本文在自主设计的导叶式离心泵基础上,尝试以其反转运行工况为研究对象,采用大涡模拟与Mixture多相流模型相结合的数值计算方法,对液力透平运行在不同流量工况下,分别过流清水介质和含沙水介质的外特性和内流场特性展开研究。首先,采用标准k-ε两方程模型和Mixture多相流模型对清水介质和固液两相介质进行定常计算,得到了液力透平0.7~1.4QBEP(QBEP为最优效率流量)工况下的外特性曲线。分别对清水介质和含沙水介质在0.7 QBEP、1.0QBEP、1.3QBEP三种不同流量工况流道内压力、速度、涡量和流线等物理量和固相颗粒分布情况进行了对比分析。定常计算结果表明:在流量较小的情况下,固液两相介质下的压头高于清水时的压头,而当流量增大至1.0QBEP左右时,固液两相介质下的压头开始低于清水时的压头;固液两相介质下的效率始终明显低于清水介质,且最高点并未出现在清水介质下1.0QBEP处,而是向大流量处偏移。沿透平工况的液流方向,压力和速度均呈阶梯式递减规律分布,固液两相介质时流道内整体压降较清水介质大。小流量时,颗粒的存在对流场紊乱程度的影响较大,大流量时,颗粒存在对流场紊乱程度的影响较小。其次,采用大涡模拟和Mixture多相流模型分别对清水介质和含沙水介质进行了非定常计算,对0.7 QBEP、1.0QBEP、1.3QBEP三种流量工况下流道内压力脉动情况进行了对比分析,对1.0QBEP工况下动静叶栅流道内涡量分布的变化情况进行了追踪。非定常计算结果表明:动静叶栅交界面处和导叶内监测点压力脉动时域周期性受到叶轮内压力梯度的交替变化影响明显,且与叶片通过周期一致。各监测点的压力系数随着流量的增大而逐渐增大,脉动幅度随流量增大而逐渐减小。流道内越靠近干涉区域,压力脉动幅度越大,且脉动高频成分越多。不同工况压力脉动的主频均为叶片通过频率,谐频为叶频的倍数,其脉动幅值呈指数形式衰减。在小流量工况下,叶轮内部涡流诱导了明显的二次谐波,颗粒的存在增强了动静叶栅附近的高频压力脉动。大流量工况下,颗粒的存在削弱了动静叶栅附近的高频压力脉动。随着叶轮叶片逐渐接近导叶叶片出口,叶轮叶片背面生成大量涡旋,沿水流方向出现拉伸、合并等多种复杂演化形式后逐渐耗散。固液两相流体粘性更大,加速了流场中大尺度涡的破裂和小尺度涡的消亡。
[Abstract]:The efficient recovery and utilization of liquid residual pressure energy is of great significance for energy saving and sustainable development. It is an active exploration and popularizing direction in the industry to use the centrifugal pump to reverse the hydraulic turbine working condition so as to convert the residual energy of liquid flow into other forms of energy. On the basis of the self-designed guide vane centrifugal pump, this paper attempts to take its reverse operation condition as the research object, and adopts the numerical calculation method combining the large eddy simulation and the mix multiphase flow model to calculate the hydraulic turbine operating under different flow conditions. The external characteristics and internal flow field characteristics of overflowing water medium and sand bearing water medium are studied respectively. Firstly, the standard k- 蔚 two-equation model and Mixture multiphase flow model are used to calculate the steady state of clear water medium and solid-liquid two-phase medium, and the external characteristic curve of hydraulic turbine 0.7 ~ 1.4QBEP (QBEP is the optimal efficiency flow rate) is obtained. The distribution of solid particles and pressure, velocity, vorticity and streamlines in the flow channel of 0.7 QBEPU 1.0QBEPU 1.3QBEP in clear water medium and sand bearing water medium were compared and analyzed respectively. The steady calculation results show that when the flow rate is small, the pressure head in solid-liquid two-phase medium is higher than that in clear water, but when the flow rate increases to about 1.0 QBEP, the pressure head in solid-liquid two-phase medium is lower than that in clear water. The efficiency of the solid-liquid two-phase medium is always lower than that of the clear water medium, and the highest point does not appear at 1.0QBEP under the clear water medium, but deviates to the high flow rate. Along the flow direction of turbine, the pressure and velocity are all distributed in step decreasing law, and the whole pressure drop in the channel is larger than that in the clear water medium in the solid-liquid two-phase medium. When the flow rate is small, the influence of the disturbance degree of the flow field is greater than that of the large flow rate. Secondly, the unsteady calculation of clear water medium and sand bearing water medium is carried out by using large eddy simulation and mix multiphase flow model, and the pressure pulsation in flow channel under 0.7 QBEPU 1.0 QBEPU 1.3 QBEP flow condition is compared and analyzed. The variation of vorticity distribution in static and static cascade flow channels under 1.0 QBEP condition was tracked. The unsteady calculation results show that the time domain pressure pulsation at the interface between the static and static cascades and the monitoring points in the guide vane is obviously influenced by the alternating variation of the pressure gradient in the impeller and is consistent with the passing period of the blade. The pressure coefficient of each monitoring point increases gradually with the increase of flow rate, and the amplitude of pulsation decreases with the increase of flow rate. The closer the channel is to the interference region, the greater the pressure fluctuation amplitude is and the more the high frequency components of the pulsation are. The main frequency of pressure pulsation in different working conditions is the blade passing frequency, the harmonic frequency is the multiple of the leaf frequency, and its pulsation amplitude is exponentially attenuated. Under the condition of small flow rate, the eddy current in the impeller induces obvious second harmonic waves, and the presence of particles enhances the high frequency pressure fluctuation near the stator and stator cascades. Under large flow conditions, the presence of particles weakens the high frequency pressure pulsation near the dynamic and static cascades. With the impeller blade approaching the outlet of the guide blade, a large number of vortices are formed on the back of the impeller blade, stretching along the direction of the water flow and gradually dissipating after merging various complex evolution forms such as the impeller blade. The viscosity of solid-liquid two-phase fluids is stronger, which accelerates the rupture of large-scale vortices and the extinction of small-scale vortices in the flow field.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH311

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