Study of a Multistage Canned Motor Pump: Simulation, Optimization and Validation

Abstract

This paper describes the detailed analysis of a multistage canned motor pump with an additional radial suction impeller by means of CFD simulations to determine the main losses and to establish optimization potential of the hydraulic parts. In addition to the main flow channels of the impeller, the degree of detail of the analysis also includes the front and rear impeller side spaces, relief holes, gaps, return sections and all hydraulically wetted surfaces of the canned motor. The model presented was successively generated and already at a very early stage it was obvious that the model has to contain all details mentioned in order to provide valuable simulation results. For the impeller, the gaps and the pressure relief holes primarily structured meshes were used with a final model of the existing pump consisting of more than 35 million nodes. The behavior of the main components was analyzed in detail and additionally the CFD simulations — stationary and transient — with scale resolving turbulence models were validated by means of model tests. Furthermore, a comprehensive loss analysis of the existing pump was performed to verify the optimization potential. The subsequent optimization was realized semi-automated. A tight corset of requirements, e.g. identical head curve, suction behavior and dimensions, has been defined to guarantee retrofit capability of the pump analyzed in order to fully satisfy the demand for a constant delivery head curve and at the same time to provide for a relative increase of the optimum efficiency by 25% and in a wide range of applications by at least 20%. The optimized model was manufactured based on rapid prototyping and tested in the laboratory. The results show a satisfying correlation between the numerically predicted and the measured results on the test rig and prove the high quality of the numerical simulations run.

Reverse engineering of pump as turbine for CFD analysis

“…The precise CFD evaluation of the cavitation pa- rameter σ s is quite problematic. Our procedure is based on a static evaluation of the given pressures on the runner blades [17,18]. This procedure proved successful in optimising Kaplan-type turbines [19].…”

Francis Type Turbine Runner Design and Comparison with Model Test Results

“…Navier-Stokes equations describe the partial differential equations of a viscous, incompressible fluid and are part of the principle of conservation of momentum, mass and energy. 4…”

“…Unlike the traditional Francis runner design, the leading edge of the x-blade runner blades was inverted and the trailing edge was crooked. Thanks to this design, a highly balanced flow area was created in the runner passageways and a homogeneous pressure distribution was achieved on the runner blades [4]. This process also helped to achieve a more even pressure distribution on the turbine runner [13].…”

“…Numerical analyses were accomplished with the help of Navier-Stokes equations in the CFX module of the ANSYS commercial software used during the studies. These equations allowed describing fluid motions in 3 dimensions and were used together with the RANS formulation [4].…”

“…Although the power plant mentioned in this study is one of the first power plants commissioned in Türkiye, it has not been the subject of a comprehensive rehabilitation study to date. The existing turbine runner blades in the power plant are conventional runner blades, and this type of blade causes cavitation damage, especially on the suction side of the runner blades [4]. There is also cavitation wear on the suction sides of the turbine runner blade surfaces in the power plant (Figure 1).…”