Using thermoelectric generators (TEG), engine waste heat can be directly converted to electricity, hence reducing the fuel consumption. This topic has been addressed by the TERA-project (Thermoelectric Energy Recuperation for Aviation), conducted in the framework of Germanys fifth Aeronautical Research Program (LuFo-V). As a part of TERA-project, the present work investigates the impact of TEG's heat redistribution from the core flow to the bypass flow at thrust and efficiency of a turbofan engine. Both, the internal and external boundary layers of the exhaust section are strongly influenced by this heat redistribution, the former in a negative and the latter in a positive way. RANS simulations have been applied to quantify and assess the corresponding viscous losses and blockage effects. These parameters show high sensitivity to transferred heat rates, due to high Mach numbers in the nozzle. The temperature and density inhomogeneities, caused by the local heat flux of TEG contact surface, are adequately captured by the numerical simulations. Three different flight conditions have been investigated: take-off, top of climb and cruise.