Aerodynamic Evaluation of Intermediate Compressor Ducts with Integrated Heat Exchangers

Abstract

The aviation industry is actively investigating hydrogen as a future aircraft fuel due to its potential to significantly reduce greenhouse gas emissions. One promising application is the use of cryogenic hydrogen for engine heat management through intercooling, where integrated heat exchangers can be placed within intermediate compressor ducts (ICDs) between compressor stages. The aerodynamic performance of such ducts is influenced by complex flow phenomena, including diffuser flow separation, swirl, three-dimensional flow structures, adverse pressure gradients and strong curvature. This thesis investigates the aerodynamic performance of two ICD geometries with integrated heat exchangers using computational fluid dynamics (CFD). The study compares conventional 2D axisymmetric simulations, 2D axisymmetric simulations with swirl modelling, and full 3D simulations in order to evaluate the importance of three-dimensional flow effects. Two diffuser configurations with different lengths and curvatures were analysed using steady-state Reynolds-Averaged Navier-Stokes (RANS) simulations with the k − ω SST turbulence model. The results show that the shorter and more aggressive diffuser geometry produces around 11% higher total pressure losses than the longer geometry. Full 3D simulations consistently predict higher pressure losses than the corresponding 2D models, indicating that three-dimensional flow effects contribute to additional aerodynamic losses that are not fully captured by axisymmetric approaches. Inlet swirl was found to provide an improvement in diffuser pressure recovery, although its influence on overall pressure losses was limited. The integrated heat exchanger was found to have a significant stabilizing effect on the flow by suppressing diffuser separation, allowing aggressive diffuser geometries to achieve a pressure recovery comparable to less aggressive designs. One important observation is that 2D simulations underpredict both the pressure recovery and total pressure losses by up to 2.5% compared to the performed 3D simulations. The findings suggests that two-dimensional CFD models can provide useful preliminary assessments at a low computational cost, while full three-dimensional simulations are recommended when accurate prediction of flow structures and pressure-loss mechanisms is required.