Implementation of a Reduced Order Model for rotating seal annular leakage flow inside a centrifugal pump

Abstract

Sustainability and net zero emissions targets drive the importance of turbomachinery design, optimisation, and efficient operation in modern geoenergy systems. To further enable integration of advanced large-scale technologies, accurate and resource-efficient simulations of complex equipment and systems need to be completed readily. An approach to simulate internal leakage flows of centrifugal pumps is presented, an important factor that influences equipment operation efficiency. One significant challenge when internal leakage flow is investigated is achieving sufficient simulation detail in the flow regions separating rotating and stationary components where close-running clearances are present. Computational fluid dynamics (CFD) meshes typically require excessively fine resolutions of node points in these situations for accuracy. For example, the typical annular suction wear ring clearance ranges between 0.1–0.5 mm, whilst impeller diameters and other geometric properties have length scales from 600–1200 mm or even larger. A reduced order model (ROM) of an annular seal configuration was developed that allows for analytical calculation of the leakage flow by implementing user scripting in the CFD solver setup. The ROM implementa tion has a low symbol count and does not require any type of logic and/or recursive and iterative functionality. Thus, fine and resource-intensive meshing can be robustly eliminated and replaced by a sufficiently detailed ROM that contributes leakage flow effects to the overall simulation. Leakage flow through the suction wear ring of a high differential head (𝛥𝐻), high flow rate, double suction centrifugal pump with water as working fluid was used as a case study for ROM development. The calibrated model was verified against a commercial fluid dynamics software package and achieved a level of precision of 2.4% with 𝜎 = 0.0118 in a wide operating range of 10m ⩽ 𝛥𝐻 ⩽ 350m and fluid temperature (𝑇) of 283.15K ⩽ 𝑇 ⩽ 353.15K. The leakage flow calculated by the ROM was proven to be accurate and therefore capable of accounting for a range of pressure heads, incorporating surface roughness effects and temperature variations, and adaptable for various fluids. Guidance for the implementation of the ROM in the Ansys CFX solver environment is also provided to aid future work.