Hybrid diffuser performance analysis for a gas turbine combustion chamber

Gas turbine engines, widely used in aviation, are expected to be powerful, lightweight, and efficient given their tasks and operating conditions. In optimization studies aimed at meeting these requirements, the aerodynamic compatibility between the compressor and the combustion chamber, a key component of the engine, is of critical importance. The high-speed air exiting the compressor needs to be slowed down and its pressure increased in a widening cross-section (diffuser) to improve combustion efficiency; however, this process is prone to aerodynamic losses and flow separation. This study investigates the aerodynamic performance of a "hybrid diffuser" concept, which aims to reduce engine weight by shortening the diffuser length. Computational Fluid Dynamics (CFD) models, validated using experimental data from the literature (Stieglmeier vd., 1989), were used to perform analyses with the 𝑘−𝜔 𝑆𝑆𝑇 turbulence model. In parametric analyses conducted with a constant 5% discharge rate, the effects of discharge gap geometry, discharge distance, and in-flow obstruction elements were investigated. As a result of the analyses, the geometry with a second diffuser angle of 45° and a passage distance of 2 mm (Case 4) was determined as the optimum design with a static pressure recovery coefficient (𝐶𝑝) of 0.4718 and a total pressure loss coefficient (K) of 0.1473 at the laboratory scale. When the study was adapted to real engine conditions (Re=20*10^4), the performance coefficient (𝐶𝑝) reached a value of 0.8461. In addition, it was determined that conical guides prevent flow separation more effectively compared to spherical geometries in in-flow obstruction analyses. The findings show that the proposed hybrid diffuser design offers a compact and highly efficient solution by allowing high expansion angles over short distances.