离心泵叶片仿生非光滑结构的布置位置

为研究离心泵叶片上仿生非光滑减阻效果与仿生非光滑结构布置位置的关系及离心泵水力效率对仿生结构布置位置的敏感程度,将仿生非光滑结构分别均匀布置于离心泵叶片的6种不同位置上.利用ANSYS软件进行数值模拟,研究了目标流量下6种方案离心泵的性能参数及叶轮内部流动情况,将根据数值计算结果得到的仿生非光滑结构的最佳布置方案与常见布置方案在全流量下进行对比分析,并在应用相同仿生非光滑结构布置方式的前提下,分析了粗糙度的影响.结果表明:该离心泵模型在目标流量下,应用仿生叶片后,其水力效率变化有限,而叶片壁面上平均剪应力相较于光滑壁面情况下降最大约12.7%;布置于任意位置的仿生非光滑单元均能在一定范围内产生减阻效果,相邻仿生单元对于同一壁面位置的减阻效果不具有线性叠加关系;在全流量下,将仿生非光滑结构布置于叶片背面的中部,相比于将其布置于叶片背面的出口部分,增效率与减阻率均更为优秀,且2种方案的增效率与减阻率随流量变化的趋势较为相近;粗糙表面尽管能和仿生结构表面一样在近壁面形成低速层,但无法实现减阻效果.该研究表明,仿生结构对离心泵水力效率的影响与模型本身有关,在使用一定个数的仿生凹坑单元的前提下,应尽量将凹坑布置在剪应力大处.

Layout position of bionic non-smooth structure on blades of centrifugal pump

In order to explore the correlation between drag reduction rate and layout position of bionic non-smooth structure,and the sensitivity of hydraulic efficiency of centrifugal pump to the structure,bionic non-smooth structures were decorated on six different locations on blade two surfaces of a centri-fugal pump,respectively,and six design cases were obtained.The hydraulic characteristic parameters and internal flow of the centrifugal pumps with these designs were studied numerically by using ANSYS CFX software at a duty point.An optimal design was decided by comparing hydraulic efficiency and drag reduction rate among six designs.Then,the optimal layout design was compared and analyzed against the existing usual layout position of bionic non-smooth structure in the whole range of flow rate.Finally,the influence of roughness on the performance and flow in the pumps were clarified in terms of the same layout position of bionic non-smooth structure.The results show that the hydraulic efficiency of the pumps with bionic non-smooth structure is less or equal to the efficiency without the structure,but the average shear stress on the blade surfaces is lowered by about 12.7%.The bionic non-smooth stru-cture unit in any position can produce a drag reduction effect in some degree,however,the drag reduction effect produced by an adjacent bionic non-smooth unit does not show a linear relation of superposition in an intersected position.In the whole range of flow rate,the layout position of bionic non-smooth structure in the middle of blade suction side always leads to both higher hydraulic efficiency and larger drag reduction rate,compared with the layout arranged near the outlet on blade suction side.Additionally,the hydraulic efficiency change and drag reduction rates in two layouts show a similar trend versus flow rate.Unfortunately,the efficiency change rate is too tiny to be considered as a standard to evaluate the bionic non-smooth structure,while the drag reduction rate is substantial.It is suggested that the bionic non-smooth structure should be arranged in the position suffering from the largest shear stress for a better performance and pit elements in the structure should be apart with large enough spa-cing to increase the average drag reduction rate.The results demonstrate that even though a rough surface can form a low-velocity layer near a wall like a bionic surface,the drag reduction is unachievable because only macroscopic bionic units play a positive role in drag reduction.The results reveal that the layout position has limited influence on the hydraulic efficiency of centrifugal pump.For a fixed number of pits applied,the pits should be placed in the position as close as possible where the maximum shear stress is experienced.