Simultaneous CFD Analysis of the Hot Gas and the Coolant Flow in Effusion Cooled Combustion Chambers

Kurzfassung

In order to increase the efficiency of currently available 10 MPa combustion chambers, hot gas pressures of up to 25 MPa are desirable. As such high pressures lead to an increased heat transfer from the hot gas into the combustion chamber wall, alternative cooling methods to the conventional regenerative cooling are required. One of the most promising alternative cooling approaches is effusion cooling. DLR has been working for the last few years in the field of effusion technology. Experiments performed at DLR Lampoldshausen have demonstrated the capability of carbon fibre / carbon matrix (C/C) composite materials to perform well in model combustion chambers [4],[6]. For previous analyses with the CFD-program ANSYS/FLOTRAN [5],[7], the -kε turbulence model was chosen. These analyses were restricted to the usage of a globally specified value for the specific heat capacity for all the involved species. In this contribution, improved analyses of effusion cooled combustion chambers with the CFD-program ANSYS/CFX are shown, taking into account the correct values of the specific heat capacity for each of the involved species. These analyses are based on the following principles: (1) 1-degree 3D model (quasi 2D axisymmetric) (2) solution of the Reynolds Averaged Navier Stokes equations (3) coupled analysis of the hot gas and the coolant flow („multi species“) (4) compressible flow (5) SST turbulence model (with different parameter settings in the hot gas area and the porous chamber wall) (6) „distributed resistance“ model according to Forchheimer inside the porous chamber wall The CFD analysis of the stationary hot run of the engine simultaneously models the hot gas flow in the combustion chamber and the coolant flow in the porous chamber wall. The detailed analysis of the combustion itself is avoided by defining the injector plate of the combustion chamber as an inlet of the hot by-product of the combustion (steam). A good comparison between the experimentally and the numerically obtained mass flow rates can be obtained by fitting the turbulence parameters in the area of the porous medium.