Integration of a Gas Model into Computational Fluid Dynamics Analysis for the Simulation of Turbine Exhaust Flows With High Steam Loads

Kurzfassung

The water-enhanced turbofan (WET) is a promising future propulsion concept to reduce aero engine emissions. In the WET-engine, a heat exchanger uses turbine exhaust heat in order to generate superheated steam out of liquid water. For evaporator design, computational fluid dynamics (CFD) simulations are necessary since correlation-based predictions have a high uncertainty during preliminary design. A common way of modeling steam loaded flows is the integration of gas models into CFD analysis. However, to the author's knowledge, there is no gas model published that accounts for the exact gas composition of turbine exhaust flows with high steam loads and is commonly used by low- and high-fidelity methods. Therefore, a gas model predicting the thermodynamic behavior of the turbine exhaust flow considering high steam loads is presented and integrated into an existing CFD solver. The approach is able to incorporate the implemented gas model into the CFD simulation by two methods: runtime and offline. The offline method has a computational advantage in iteration time compared to the runtime integration. As demonstration case, a single two-dimensional cylinder is considered. A variation of the steam loading of the flow shows a significant effect on local properties and therefore on local and average heat transfer. Increasing the steam loading up to 40% results in an increase of the average Nusselt number of 17%.