0 With the rapid development of new technologies such as computer technology and computational fluid dynamics, it is possible to calculate the internal flow field of fluid machinery. CFD analysis replaces a large number.
3.2 Computation method and boundary condition calculation The segregated method is used. The turbulence model is a standard k-e model. The coefficients in the model are all default values. The calculation uses multiple rotating coordinate systems.
Import conditions are speed imports, and export conditions are pressure exports. The wall surface function is used in the area near the solid wall, and the non-slip boundary condition is used for the solid wall surface.
In the difference grid, the pressure terms are in the standard format, the velocity term, the turbulent kinetic energy term, and the turbulent viscosity coefficient term all adopt the first-order upwind difference scheme. The coupling algorithm between pressure and velocity is the relaxation factor in the SIMPLE solution process: the pressure term is 0.3. , Velocity term 0.7, turbulent kinetic energy term and turbulent viscous coefficient term 0.5, turbulent dissipation factor term 0.3. 3.3 CFD calculation results and analysis The calculation was performed on 10 working conditions, and calculated on the basis of the simulation of the 3D viscous flow field. The difference between the ring volume of the inlet and outlet surfaces of the impeller and the energy of the inlet and outlet surfaces is used to derive the shaft power and the actual head, and then the hydraulic efficiency of the pump is obtained. The operating conditions for each operating condition are shown in Table 1. The hydraulic efficiency and head for each operating condition are shown in Table 2 and Table 3, respectively. The calculations show that when operating condition 7, that is, the flow rate is 1.989m1/s, the efficiency reaches the maximum value, and the efficiency is 90.2%; In condition 1, that is, the flow rate is 1.683m3/s, the head | max is 50.0m. The wheel is used to achieve energy conversion. Therefore, the flow condition of the moving impeller has a decisive influence on the performance of the pump. The pressure distribution map of the suction surface of the moving blade is shown as the low pressure area appears near the impeller head. This is due to the effect of the head detachment, and it can clearly see the flow near the impeller head. . Obviously, the head detachment is more serious with increasing radius, because the blade circumferential velocity increases with the radius. The back side of the inlet side of the impeller is the dangerous part of the axial water pump where airfoil cavitation damage occurs.
Flow table working condition table 2 working condition-efficiency table working condition efficiency,% table 3 working condition-head express working condition head, m 4 conclusion and experimental result comparison proves that using 3D fluid calculation software Fluent can get enough accurate flow field Distribution, calculation of the interaction between the various components, a more accurate estimate of its performance, and then optimize the design, save a lot of experimental costs, with a small cost to design a good fluid machinery.
Relative velocity distribution near the moving impeller's head (R = Simultaneously, it should be noted that the flow conditions inside the fluid machine are very complicated. In order to further understand the internal flow conditions, non-stationary simulation calculations and analysis should also be performed. Moreover, the three-dimensional fluid software is used to close the turbulent flow. The equations also introduce a series of assumptions that make the numerical calculation of the flow field possible while also reducing the credibility of the calculation results, so the flow field calculation can not be complete parameters; (2) determine the speed and specific speed; (4) The selected flow pattern, axial flow pump usually uses equal circulation flow pattern, at this time, the axial surface velocity is evenly distributed, if other flow types are selected, the circulation amount (head) and axial surface should be determined according to radial equilibrium conditions. The distribution of speed; (5) to determine the calculation of cross-section and make each section of the speed triangle, usually can take five sections for the calculation of leaf Shan, calculated section can be evenly divided in the radial direction to determine the pump's main structural parameters, such as hub ratio, Impeller outer diameter, number of blades;
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