Experimental validation of a numerical coupling environment between FEM and CFD

Authors

Christopher Hartmann  - University of Stuttgart, Germany
Julia Schweikert - University of Stuttgart, Germany
Francois Cottier - MTU Aero Engines AG, Germany
Ute Israel - MTU Aero Engines AG, Germany
Jochen Gier - MTU Aero Engines AG, Germany
Jens von Wolfersdorf - University of Stuttgart, Germany

Abstract

In modern aero engines, cooling of the thermally high-stressed components is an essential task in engine development. For optimum design, transient processes and solid-fluid interaction as well as the thermal time disparity of solid and fluid must take into account. The conjugate situation of thermal loading of the hot gas flow on the solid side, their time-dependent thermal conduction behavior, and the flow conditions on the cooling side significantly influence the individual engine components. Depending on the engine operating conditions strong interactions arise when the operating point changes with time, which cannot be adequately described by considering quasi-stationary conditions at individual operating points. Under this aspect, an external Python-based coupling interface, developed at the ITLR, controls the communication between a thermal FEM solver for the solid and a FVM solver for the fluid. The FEM solver CalculiX runs in transient mode, while a steady-state CFD simulation is applied for the fluid using ANSYS CFX. The results of both solvers are coupled only at specific points in time at the solid-fluid interface, where thermal boundary conditions are exchanged, i.e., the temperature for the CFD and the heat flux for the FEM. Results of the coupling environment are thereby compared with results of a fully-transient conjugate heat transfer (CHT) simulation in ANSYS CFX. The boundary conditions for the numerical simulations of both CHT and coupling environment are taken directly from the corresponding experiments. The experimental setup involves a channel flow over a flat plate and is suitable for fundamental studies of heat transfer characteristics in turbulent boundary layers. The experimental setup allows the independent setting of time-variable temperature and velocity boundary conditions with simultaneous spatially and temporally high-resolution determination of wall temperatures using IR thermography and wall heat fluxes at the interface between solid and fluid. Transient experiments like generic test cases and transient cycles, as they occur during a flight mission, are conducted to validate the numerical simulations. By means of the performed experiments on a flat plate with various solid-state materials, consideration of transient-conjugate effects as a function of Biot number as well as numerical stability investigations are presented. Moreover, transient experiments on an arrangement of five periodic V-ribs validate the results of the numerical studies transferred to a more complex flow geometry. The aim of this paper is therefore to demonstrate the capabilities of the experimental facility as validation for both CHT simulations and a coupling environment at different Biot numbers, different geometries, and different time-dependent boundary conditions.