Numerical investigation on the flow and heat transfer characteristics of tube-bundle precooler based on the multi-layer grid Superposition method

The investigation into compact tubular precoolers is vital for improving precooled air-breathing engines. This study introduces a novel three-dimensional numerical simulation method tailored for annular tube bundle precoolers, focusing on simplification while maintaining high accuracy. By leveraging circumferential and axial periodicity, the precooler is discretized into the minimal periodic heat transfer unit (MPHTU), which serves as the fundamental building block for the computational grid. The MPHTU is meshed once, then repeated and stacked to construct the full-scale grid, requiring adjustments only to spatial data. Validation of this method comes from its close agreement with experimental results from the precooler module. Simulations revealed that the wall boundary layer significantly intensifies heat transfer within the near-wall MPHTU by up to 50.7 %, accompanied by an increase in the flow resistance by 98.2 %. Yet, this effect is limited to the first three MPHTUs. Analysis showed that at least five stacked MPHTUs are needed to properly account for the wall boundary layer's influence on airflow and heat exchange. Moreover, increasing the air inlet Reynolds number reduces heat transfer non-uniformities caused by the wall boundary layer, decreasing the required number of stacked MPHTUs. Considering these findings, and in light of the overall flow and heat transfer characteristics of the heat exchanger, this study establishes an optimal grid construction and numerical simplification method for the annular tube bundle precooler. The method enhances the efficiency of multidimensional simulations for precooler heat exchangers under the constraints of constructing complex cross-scale grids and managing large computational loads.