Study of the mixing characteristics of a multibypass combustor of a turbine-based combined cycle

Abstract

When the multimode and multibypass turbine-based combined cycle (TBCC) engine performs mode transition, it involves switching between multiple bypasses. During the transition process, the flow field of the combustor is adjusted rapidly, and the mixing performance is affected. However, superior mixing is the premise of the superior combustion performance of the combustor. In this paper, the mixing characteristics of the TBCC triple-bypass combustor during the mode transition process are studied by numerical simulation. Different structural and aerodynamic parameters, including equivalent expansion angle (5.5°, 9.2°, 12.8°), lobe mixer width (20, 25, 30 mm), bypass ratio (0.44, 0.56, 0.66) and inlet temperature, were studied to discuss the trending of flow field, vorticity field, temperature field, and oxygen content distribution. The results show that the performance of triple-bypass combustor is worse than that of double-bypass combustor under the condition of turbo core inlet Mach number 0.3. The total pressure loss is increased by 0.3% and the thermal mixing efficiency is decreased by 12.4%. The increase in the equivalent expansion angle reduces the mixing efficiency (12.5%) and improves the total pressure recovery coefficient (1%). However, increases in lobe width, bypass ratio, and ram inlet temperature increased mixing characteristics but increased flow losses. The increase in turbo bypass inlet temperature (300–500 K) improved the total pressure recovery coefficient by 0.17% and the thermal mixing efficiency by 7.0%. Conversely, the increase of the turbo core inlet temperature (800–1200 K) not only reduces the total pressure recovery coefficient, but also reduces the mixing performance. In addition, the studies show that the mixing performance of the lobe mixer is mainly affected by the velocity difference between the primary and secondary flow. Besides the streamwise vortex and normal vortex, the normal vortex dissipation rate controlled by the velocity difference is also one of the factors affecting the mixing performance.