Rapid predictions of pressure and velocity fields in a 5 × 5 bending fuel assembly based on a POD-based black-box model

•The impact of varying bending scales on flow behaviors of 5 × 5 fuel rod bundles is researched.•The POD black-box model is proposed and used to predict the flow fields of 5 × 5 fuel rod bundles.•The POD black-box model offers a rapid and accurate method for predicting flow fields of 5 × 5 fuel rod bundles. The fuel assembly is crucial in pressurized water reactors (PWRs) as it can undergo bending deformation due to flow-induced vibrations (FIVs), impacting its flow characteristics. To evaluate the effect of different bending scales on flow behaviors, the Computational Fluid Dynamics (CFD) model of 5 × 5 fuel assembly is developed. This configuration considers common beam-like deformations: 1st-order C-shape, 2nd-order S-shape, and 3rd-order W-shape. The flow characteristics of the 5 × 5 bending fuel assembly with bending scales of 1 mm and 2 mm are studied, aiming to explore how variations in deformation scales impact these flow characteristics. Subsequently, CFD simulations are conducted for various flow velocities, bending shapes, and scales, with the simulation results organized into a snapshot matrix. Through the Proper Orthogonal Decomposition (POD) method, both the POD coefficients and modes of the snapshot matrix are determined. A black-box model is subsequently utilized to predict the POD coefficients of non-sample cases. The research enables rapid predictions of pressure and velocity fields within a 5 × 5 fuel assembly for any given flow velocity, bending shape, and scale by integrating the predicted POD coefficients and modes. Relative to comprehensive CFD simulations, the POD-based black-box model presented in this study provides a rapid and precise approach for pressure and velocity fields prediction, demonstrating its effectiveness and accuracy.