Advanced Numerical Simulation of Mixing Hot Core and Cold Bypass Flow in Modern Propulsion Systems with Internal Lobed Forced Mixer

摘要

The development of more efficient and environmentally friendly powerplants for air transportation is getting more and more challenging. Therefore a deep understanding of all components of an aeroengine is necessary to fulfill the increasing requirements. One of these components is the exhaust system, which is the focus in this study. The flow through the nozzle system with installed lobed forced mixer with complex scarfing is performed using the Favre-averaged Navier-Stokes equations, to investigate the mixing of the hot core and cold bypass streams behind the mixer. Simulating such highly anisothermal flows requires good heat-flux prediction. The widely used Eddy Diffusivity Model to close the turbulent heat-flux term in the energy equation requires the definition of a turbulent Prandtl number, which is commonly assumed to be constant. However, the turbulent Prandtl number is not constant in such flows and therefore the prediction of the turbulent heat-flux might be calculated incorrectly in some regions. Therefore, a differential model has been utilized to overcome the dilemma defining a turbulent Prandtl number and to directly solve for the turbulent heat-flux. The model has been implemented in the open source software OpenFOAM and the results are compared to simulations using the Eddy Diffusivity Model with different turbulent Prandtl numbers. The resulting total temperature contours at the nozzle exit are compared to experimental temperature measurements. Furthermore, nozzle performance parameters are calculated to quantify the influence of the models.