Large-Eddy Simulation of an Integrated High-Pressure Compressor and Combustion Chamber of a Typical Turbine Engine Architecture

The design optimisation of aviation propulsion systems by means of computational-fluid dynamics is key to increase their efficiency and reduce pollutant and noise emissions. The growth of computing power allows nowadays to perform unsteady high-fidelity computations of the different components of a gas turbine. However, these simulations are often made independently of each other and they only share average quantities at interfaces.  In this work, the methodology and first results for a sectorial large-eddy simulation (LES) of an integrated high-pressure compressor and combustion chamber of a typical turbine engine architecture is proposed. The compressor is composed of one main blade and one splitter blade, two radial diffuser vanes and six axial diffuser vanes. The combustion chamber is composed of the contouring casing, the flame tube and a T-shaped vaporizer. The integrated computation considers the best trade-off between accuracy of the simulation and affordable CPU cost. A law-of-the-wall boundary condition is used to reduce the mesh size. The liners of the flame tube are represented by perforated plates and film cooling using the ‘thickened-hole model’ [1] for the micro-perforations but actual meshed holes for the primary and dilution holes. In addition, combustion is simulated using the thickened-flame model with a reduced chemistry of 6 species and 2 reactions. The outline of the methodology is described as follows. The simulation of a stand-alone compressor [2] and combustion chamber are performed independently, and then coupled together. The compressor is initialised from the flow at rest to the converged point increasing progressively the outlet pressure. The combustion chamber is initialised from uniform conditions and a mono-species non-reactive flow to converge the aerodynamics and design point. Then the solution is transformed to 6 species and reactive flow. Once combustion stabilises, both final solutions are interpolated into an integrated compressor-combustion chamber mesh. The flow overcomes a short transient in order to adapt the outlet conditions of the compressor to the inlet conditions of the combustion chamber. Results are compared between the stand-alone combustion chamber simulation and the integrated one in terms of global, integral and local instantaneous and average quantities. Preliminary results show that pressure perturbations generated by the interaction of the impeller blades with the diffuser vanes are propagated through the axial diffuser and enter the combustion chamber through the dilution holes and the vaporizer. Due to the high amplitude of the pressure perturbations, the mass-flow on the injection system and outlet plane of the combustion chamber are perturbed at the blade-passing frequency (BPF) and multiples. This is also reflected on combustion where a broadband peak appears for the global heat release.

[1] R. Bizzari et al., A Thickened-Hole Model for Large Eddy Simulations over Multiperforated Liners, FTAC 2018
[2] J. Dombard et al. Large Eddy Simulations in a Transonic Centrifugal Compressor. In ASME Turbo Expo 2018