Transient flow analysis in axial-flow pump system during stoppage

Abstract

Axial-flow pumps with siphon outlet are widely used in South-to-North Water Transfer Project of China for the excellent characteristics and good performance in stopping period. The reverse rotational speed and the head of impeller are the key parameters for the system's safety in stoppage. In this article, the computational fluid dynamics method was used for three-dimensional unsteady numerical simulations. The method based on volume of fluid model was executed on geometrical model of the whole flow system to get the variation laws of internal and external characteristic parameters. Through numerical calculation, the variation laws of the parameters were got in the pump operating condition, braking condition, and turbine condition, and the maximum reverse speed of the impeller was 203.0 r/min (20.947 times the rated speed). Compared with the designed mode, when the air valve was opened in advance, the pump system would go through the weir flow state first, and a higher head of impeller would be got as a result. When the air valve refused to open, the pump system would get into runaway state. Comparisons of the calculated and measured results indicate the proposed computational fluid dynamics method is reliable in the simulation of the transient flow in axial-flow pump system.

Numerical Investigations of Transient Flow Characteristic in Axial Flow Pump and Pressure Fluctuation Analysis Based on the CFD Technique

“…Validation results are the most important stage in numerical analysis to verify accurately computational physical model in actual flow system [16][17][18][19][20]. The experimental work carried out by Mostafa, N. H. was used to validate the numerical model in the current study [15].…”

“…The impeller diameter of 101 mm, the blade angle was 60. The boundary condition simulation is set at the inlet part with variety of inlet velocity, and the outflow is set as outlet condition [16][17][18][19][20]. The pump experimental data are got from Mostafa, N. H. [15] as mentioned earlier.…”

Study on a Horizontal Axial Flow Pump during Runaway Process with Bidirectional Operating Conditions

“…The finite volume method (FVM) with pressure-based solver was adopted to discretize the governing equations. The semi-implicit method for pressure-linked equations-consistent (SIMPLEC) method was applied to the coupling solution of pressure and velocity [23]. A second-order upwind scheme is selected to discretize the convection and diffusion terms.…”

“…Simultaneously, CFX and Fluent became the most widely used CFD components in 3D simulation during transient process owing to their strong adaptability and flexible programmability. To close the control equations with low computational cost and reasonable accuracy, a variety of turbulence models have been widely used in simulations, such as two-equation turbulence models [19][20][21][22][23][24][25], four-equation turbulence model [17,18,26], and the SST based Scale-Adaptive Simulation (SAS) model [15,16,[27][28][29]. Additionally, the compressibility of water is not considered for most studies, however, few scholars still adopted the user-defined density function with pressure as an independent variable in their investigations [17,18,21].…”

“…Thus, the VOF model is suitable for tracking free surface and calculating the volume fraction of water phase. The governing equations of the VOF formulations on multiphase flow are defined as [23]:…”