Research On The Variable Rotation Speed And Transient Process Of Centrifugal Pump As Turbine System

Energy development is faced with the challenge of large demand pressure, energy supply constraints, ecological environment damage caused by energy production and consumption, low level of energy technology and so on. Currently, the globe experiences a new round of energy technology revolution. Guided by the green and low carbon pricinples, energy saving and efficient energy technology have risen to the strategic height of national development and security. The energy recovery device of pump as turbine(PAT) is applied to petroleum chemical industry, metallurgy, coal, waste water treatment and other industries. It recycles pressure energy of fluid and achieves the effect of saving and reducing energy consumption. At present, in the key areas of the aforementioned industries, almost all turbine applications are imported units to recycle liquid pressure energy, while domestic equipments are faced with the problem that the recovery efficiency and the reliability is not satisfiying. In terms of industrial applications, the issue of device running security, especially the transient effect of system including the transition process of variable speed, is a valuable problem with a view to the turbine system. On this basis, this paper studies the characteristics of variable speed and transient process of pump as turbine system. The focused objects contain the performance selection, theoretical prediction of turbine working point, and the behaviors in the various processes include the constant rotation, the variable speed mode and the coherent transient condition. Therefore, this paper studies the three processes by theoretical analysis, numerical calculation and experiment researches. The main work and innovative results are as follows:1. The application status of industrial test and laboratory measurement on the characteristics of pump as turbine was summarized in this paper. Then, the test ring and control system were estanbilished for the transient process. The experiment sessions contained the performance of pump as turbine in steady state, transient operations and vibration test, etc.2. With reference to the classic one-dimensional matching theory of centrifugal pump impeller and volute, the characteristics of the rotor and the volute under the reverse working condition were studied through theoretical analysis. A new method predicting turbine performance was proposed and validated by test which considered the limited blades effect and the vortex in rotor vanes, therefore it was of significant importance for engineering usage.3. The flow field and external characteristic of PAT at the design speed were numerically and experimentally investigated. The unsteady flow and flow profile in PAT domain were focued, the flow rate distributeon and hydraulic load were paid attation in additional. The flow rate strategy was proposed to reveal the complicated flow issues in a direct way. In this paper, the reason of huge error when ignoring the bilateral chambers in CFD was explored using the above method. Besides, the hydraulic loss distribution of the flowing components, the pressure fluctuation and the characteristics of axial force and radial force were investingated respectively.4. The hydraulic stability under different speed conditions was discussed in the thesis. PAT speed characteristic curves were obtained by test and the flow fields of different BEP points were compared by CFD. Three typical BEP points were selected to be the objects; the comprehensive behaviors of PAT were researched, including the hydraulic fluctuation, and the mechanical properties of rotor. In the end the conclusions on the hydraulic stability were validated by vibriation test indirectly.5. The application of generalized Euler equation was analysed and elaborated in this paper. Meanwhile, the integral rotation analysis of rotor of PAT system was carried out, through which the general strategy for transient calculation of transient flow field in transient process was established. Both the acceleration and deceleration of PAT transient flow field in constant pressure and constant flow rate were calcultaed. The transient performance and flow field evolution of PAT during this period were numerically analyzed. The predicted result was coinciding well with the experiment, it was optimised by nonlinear rotational speed function and the calculation accuracy was promoted accordingly. Significant cavitation effect was discovered by adding a cavitation model to the transition model and the results proved the relevance between these two processes.