Model Design And Numerical Analysis Of Reversible Counter-rotating Axial Flow Pump

Compared with conventional single-stage axial flow pump, counter-rotating axialflow pump can be obtained by replacing the rear vanes of the traditional axial flowpump with the rear rotor blade and the front rotor and rear rotor rotates in the oppositedirection. Thus, the rear rotor can not only recover kinetic energy from the frontimpeller outlet, but also provide energy to the fluid, leading to counter-rotating axialflow pump with small size, high head, good cavitation performance characteristics. Thispaper aims to develop high efficient counter-rotating axial flow pump with methods ofmodel design and steady and unsteady numerical simulation to investigate the flexibilityof the application of counter-rotating axial flow pump in both directions occasions.The model design combined the linear circulation correction and streamline designmethod of axial flow pump, the design idea of reversible counter-rotating axial flowimpeller has been proposed on the basis of analyzing the inlet and outlet velocity triangleof the front and rear impeller, and the design process has been parameterized throughMATLAB7.0.Based on Fluent, the tangential component of absolute inlet velocity at the blades ofrear rotor and load distribution between stages are analyzed. To improve the reverseoperation performance of reversible counter-rotating axial flow pump, bidirectionalsymmetrical oval airfoil NACA0009-ellipse was obtained by the modified NACA0009airfoil, and comparative analysis of its performance was done on the circular arc andlinear airfoil. To investigate the problem of matching between the impeller stages, theimpact of axial gap and radial clearance on reversible counter-rotating axial flow pumpwas discussed preliminarily. The results show that the effective operating range of thepump narrows although the flow pattern within the pump is better under the jointassumptions; load distribution between the front and rear rotor has a smaller effect on synthetic performance and the cavitation performance of the rear impeller in reverseoperation can be improved by increasing the load ratio; in reverse operation, thickbidirectional symmetrical and linear airfoil can effectively reduce the back-flow loss ofthe suction side of the blade and improve operating performance of pump at reversibleoperation; it has a fine hydraulic performance that axial gaps is determined by80%of thechord length of the rear impeller; the causes and propagation characteristics of blade tipleakage vortex are similar at front and rear impeller; the vortex forms at large pressuredifference of the head airfoil between the pressure side and suction side of the blade,rotating in opposite direction with the swirling strength weakening. The difference inpropagation characteristics is that the tip leakage vortex of the rear impeller movestowards the main flow direction.Three-dimensional unsteady numerical calculation of the whole flow path of thereversing rotating axial flow was executed by using the time marching method andsliding mesh on the base of solutions in steady computing and the dynamic propertieswas predicted. It was given that the internal flow field of full flow channel and theinterference plane between rotors in design flow and small flow operating conditions andthe transient interference was also analyzed. The results show that dynamic-dynamicinterface, vortex and pressure distribution on the counter-rotating base stage areapparently periodic, which can reflect the interference process between rotary impellers.