Change of temperature field in the depending mixing chamber on the bypass ratio

Abstract

The mixing chamber of a turbofan jet engine with an additional turbofan unit is the object of this study. The subject of the research is the influence of the bypass ratio on the formation of the temperature field in the mixing chamber before the turbofan unit turbine. This study investigates how the bypass ratio affects the temperature distribution in a turbofan engine’s mixing chamber. Modern aircraft engines’ three-stream architecture improves thrust-specific fuel consumption by combining a powerful gas generator with a turbofan attachment. A critical stage in the operation of such an engine is the mixing process of the hot gas flow after the gas generator turbine with the cold airflow of the second stream, which passes through the fan. The mixed flow is formed and directed to the turbine of the turbofan unit in the mixing chamber, and its thermal uniformity is crucial for ensuring reliable blade operation. Non-uniformity of the temperature field before the turbine leads to significant thermal gradients along the height of the turbofan blades. High-temperature gradients cause additional thermal stresses in the blade material, reducing its mechanical strength. The calculations show that the use of a mixing chamber significantly reduces the gas temperature at the turbofan inlet to the turbine section. This study aims to determine the optimal bypass ratio for different thermal conditions at which the mixing chamber achieves the best temperature field uniformity. To achieve this goal, the numerical simulation method was used. A series of simulations was performed in ANSYS Fluent using the Reynolds Stress Model (RSM) turbulence model. Under constant total pressure, the temperature parameters at the inlets of both streams were varied, allowing a comprehensive analysis of the influence of thermal boundary conditions on mixing efficiency. The dependence of temperature non-uniformity on the optimal bypass ratio was established. The practical value of this study lies in the possibility of optimizing the design of turbofan engine mixers by selecting the optimal bypass ratio (m) and minimizing temperature non-uniformity (σ₁), which ensures reduced thermal loads, improved fuel efficiency, increased thermal efficiency, and extended engine life while maintaining environmental standards.