Abstract
The mechanism of flow separation in the impeller of a centrifugal pump with a low specific speed was explored by experimental, numerical, and theoretical methods. A novel delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm combined with a rotation and curvature correction method was developed to calculate the inner flow field of the original pump for the large friction loss in the centrifugal impeller, high adverse pressure gradient, and large blade curvature. Boundary vorticity flux theory was introduced for internal flow diagnosis, and the relative velocity vector near the surface of the blade and the distribution of the dimensionless pressure coefficient was analyzed. The validity of the numerical method was verified, and the location of the backflow area and its flow features were determined. Finally, based on flow diagnosis, the geometric parameters influencing the flow state of the impeller were specifically adjusted to obtain a new design impeller. The results showed that the distribution of the boundary vorticity flux peak values, the skin friction streamline, and near-wall relative velocities improved significantly after the design change. In addition, the flow separation was delayed, the force applied on the blade was improved, the head under the part-load condition was improved, and the hydraulic efficiency was improved over the global flow ranges. It was demonstrated that the delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm was capable to capture the separation flow in a centrifugal pump, and the boundary vorticity flux theory was suitable for the internal flow diagnosis of centrifugal pump.
Highlights
Centrifugal pumps are used in aerospace, nuclear power, petrochemistry, and ocean engineering areas.[1,2] these pumps suffer from operational instability and technical limitations that affect their design and restrict their application
The particle image velocity (PIV) test errors, pressure sensor calibration, motor speed, shaft power, and flow measurement uncertainty analyses for this pump are discussed in detail in literature.[26,27]
To explore the working conditions that lead to flow separation, the flow rate was decreased from 1.2QBEP to 0.1QBEP
Summary
Centrifugal pumps are used in aerospace, nuclear power, petrochemistry, and ocean engineering areas.[1,2] these pumps suffer from operational instability and technical limitations that affect their design and restrict their application. The position of flow separation generated within the centrifugal pump impeller is identified using BVF, the skin friction streamline, and the surface pressure distribution on a blade section at half span.
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