Abstract
Centrifugal pumps as turbines (PATs) are widely used in chemical engineering for recycling the abundant energy from high-pressure fluid. The operation of PATs is significantly affected by their upstream conditions, which are not steady (i.e., with a constant flow rate) in reality, thus, research on the flow mechanism of PATs under transient conditions should be considered of higher importance. In this study, a numerical model of a PAT was developed by employing the sliding mesh method to describe turbine rotation, and a user-defined function (UDF) for characterizing transient flow conditions. Corresponding experiments were also conducted to provide validation results for the simulation, and the simulation results agreed well with the experimental outcomes. The instantaneous characteristic curves under the current working conditions were obtained for different transient flow rates. The results show that the turbine’s efficiency is significantly affected by transient flow conditions. In particular, a rapid increase (large time derivative) of flow rate results in a large energy dissipation at the turbine outlet, and therefore, the turbine efficiency decreases. In addition, as the flow rate increases, the hydrodynamic force on the impeller, and the pressure fluctuation amplitude in the volute first decrease and then increase, reaching the minimum near the design flow rate. The current study provides a reliable and precise approach for the estimation of hydrodynamic performance of fluid machinery under transient flow conditions.
Highlights
Chapallaz et al, and Buono et al found that pumps as turbines (PATs) can be widely used in the chemical engineering industry, for small water conservancy, and in hydropower resources owing to their simple structure, low cost, stable operation, and convenient maintenance [1,2,3]
The difference between the performance characteristic curves of transient and steady-state operating conditions, and the change in the PAT’s working state due to increases in flow rate were studied by analyzing internal flow fields and stability characteristics
The PAT’s working conditions were not steady during its operation, and the flow conversion efficiency was constantly changing under the unsteady working condirate and pressure conditions continued to change over time
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Yang et al applied precise numerical simulations to predict the best efficiency point (BEP) of a turbine for a centrifugal pump’s positive and negative working conditions [8,9]. PATs are often subject to upstream traffic; in this situation, their flow rates increase or decrease over time. The existing research concerning PATs should be supplemented with an analysis of the impact of variable working conditions on PATs (in terms of turbine operation). Processes 2022, 10, 408 to simulate the inlet conditions with different increasing rates of flow, and the sliding mesh method was used to simulate the rotational motion of the rotor. The difference between the performance characteristic curves of transient and steady-state operating conditions, and the change in the PAT’s working state due to increases in flow rate were studied by analyzing internal flow fields and stability characteristics
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