Abstract
The current paper studies the influence of annular seal flow on the transient response of centrifugal pump rotors during the start‐up period. A single rotor system and three states of annular seal flow were modeled. These models were solved using numerical integration and finite difference methods. A fluid‐structure interaction method was developed. In each time step one of the three annular seal models was chosen to simulate the annular seal flow according to the state of rotor systems. The objective was to obtain a transient response of rotor systems under the influence of fluid‐induced forces generated by annular seal flow. This method overcomes some shortcomings of the traditional FSI method by improving the data transfer process between two domains. Calculated results were in good agreement with the experimental results. The annular seal was shown to have a supportive effect on rotor systems. Furthermore, decreasing the seal clearance would enhance this supportive effect. In the transient process, vibration amplitude and critical speed largely changed when the acceleration of the rotor system increased.
Highlights
In multistage centrifugal pumps, annular seal passages, such as sealing rings and balance drums, can provide fluid-induced forces, which play an important role in determining the rotor dynamic stability of a centrifugal pump 1, 2
The current paper studies the influence of annular seal flow on the transient response of centrifugal pump rotors during the start-up period
The peak value increases with the acceleration of the rotating speed, indicating that the backwards whirling motion may occur when rotor systems pass through the critical speed
Summary
Annular seal passages, such as sealing rings and balance drums, can provide fluid-induced forces, which play an important role in determining the rotor dynamic stability of a centrifugal pump 1, 2. The dynamic coefficients method cannot consider nonlinear characteristics of fluid-induced forces and inertia effects of rotor systems due to its linear simplification 5 Given these disadvantages of the traditional methods, studying the influence of the annular seal on rotor systems in the quick-start process using other methods is beneficial. The reason is that in centrifugal pumps, the annular seal flow is not maintained in the laminar state but grows from a laminar state to transition regime state and a turbulent state with the increase of the rotor rotating speed. Because only the radial displacement and the deflection angle of the impeller are useful in the rotor dynamic analysis and the deformation of the impeller is usually not necessary in FSI calculation, this simplification is accurate enough This simplification can overcome problems on missing data and remarkably reduce computing time by replacing the impeller with a node. The results can be helpful in the improvement of the vibration characteristics of the centrifugal pump during the start-up period
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