Numerical Modeling of Heat Exchangers in Gas Turbines Using CFD Computations and Thermodynamic Cycle Analysis Tools

The optimization of energy systems such as gas turbines presents a continuous technological challenge both for economic and environmental reasons. The use of heat exchangers in gas turbines for exhaust gas waste heat recovery can strongly contribute in this direction since it can lead to significant improvement of gas turbine performance and reduction of fuel consumption and pollutant emissions. For proper implementation of a heat exchanger in gas turbines and the maximization of its benefits, engineers should be in the position to assess the most important operational characteristics such as the inner and outer pressure losses and the effectiveness. For this purpose, validated numerical tools are developed since they can provide time-and cost-efficient methods to assess the performance of various heat exchanger designs for gas turbine applications. The current work deals with the modeling of a state-of-the-art heat exchanger for gas turbine aero engine applications with the use of high-fidelity 2D and 3D CFD computations. The derived numerical results were validated against experimental measurements and the heat exchanger characteristics were integrated into the thermodynamic cycle model of the gas turbine/aero engine. In this paper the analysis was performed in the following steps: 1. Creation of a 2D CFD model of the heat exchanger core outer flow and its validation using experimental measurements 2. Creation of a 3D CFD model of the heat exchanger for both flows (inner/outer) including the effect of heat exchanger material. 3. Computations using the 3D CFD model were performed for a wide range of operational conditions leading to the derivation of heat exchanger characteristics, inner and outer pressure losses and thermal effectiveness as functions of its operating conditions. 4. Development of a 0D thermodynamic cycle model of the gas turbine aero engine application and incorporation of the previously derived heat exchanger operational characteristics. 5. Parametric analysis and performance assessment of the gas turbine thermodynamic cycle with the incorporated heat exchanger characteristics and further optimization of the thermodynamic cycle. This analysis is based on a heat exchanger design which was developed by MTU Aero Engines AG. The results demonstrate the potentials of the heat exchanger integration in a gas turbine/aero engine for significant performance improvement and fuel consumption reduction.