Jörg Riccius

Thermomechanical Analysis and Optimization of Cryogenic Liquid Rocket Engines

A couplednite elementuid -structure interaction analysis of regeneratively cooled rocket combustion cham- bers, which allows the computation of the coolantow and the heat conduction between the coolant and the combustion chamber structure, is presented. Furthermore, the resulting elasto-plastic deformation of the combus- tion chamber under cyclic thermal and mechanical loading is analyzed. The developed solution strategy is applied to the prediction of the heat transfer and thermomechanical load-induced deformation process of the European rocket engine Vulcain. Based on the results, the failure mechanism of the combustion chamber and its governing parameters are identied. It is demonstrated that this mechanism signicantly reduces the lifetime of the rocket engine. Besides the conceptual design by the engineer, a mathematical optimization procedure based on thenite element model of the combustion chamber is investigated. This optimization method allows the improvement of an initial design with respect to anite number of design variables such that the stress, plastic strain, or temperature levels are decreased, and accordingly, the lifetime will be increased.

DETERMINATION OF LINEAR AND NONLINEAR PARAMETERS OF COMBUSTION CHAMBER WALL MATERIALS

A study for the determination of elastic elastoplastic parameters of a typical combustion chamber material (Cu alloy) with different test sample geometries is presented. Based on the experimental results of elastic and elasto-plastic tests of thre sample geometries the appropriate elasto-plastic parameters such as yield stress and hardening parameters are determined. Furthermore, details about the loading during the tests, the advantages and disadvantages of each of the sample geometries and of the appropriate range of testing are pointed out.

CFD Analysis of a Model Combustor Ignition and Comparison with Experimental Results

The ignition in a Micro Combustor, tested at the test facility M3 at DLR Lampoldshausen is modeled by the Eddy Dissipation Model (EDM). In order to avoid the EDM-typical over-prediction of the reaction rate in the wall boundary layers (flame “creeping” along walls), the reaction is disabled within 3 mm distance of the walls. Also, the reaction is disabled for temperatures of 400 K or lower, in order to reduce inaccuracies of burning velocities and possible flash backs. The SST turbulence model according to Menter (a blending of the k −e and the k −ω model with automatic choice of linear/logarithmic near wall profiles) is applied for the analysis of the pre-ignition cold flow as well as for the ignition. A hexahedron mesh on a 1° segment of the supply domes, the injector, the combustor and a small ambient exit area is used. Finally, the numerical results are compared with experimental results.

Comparison of 2d and 3d Structural FE-Analyses of LRE Combustion Chamber Walls

A coupled thermal and structural 3d quasi stationary Finite Element (FEM) analysis of a typical rocket combustion chamber wall during a full cycle including pre cooling, hot run, post cooling and relaxation is presented. The results of this 3d analysis are compared with the results of 2d plane strain and 2d generalized plane strain analyses. Finally, a post-processing method is applied in order to estimate the combustion chamber life time. This life time estimation method takes into account the standard Low Cycle Fatigue part as well as additional parts – accounting for the quasi static (or ratcheting) fatigue and the thermal degradation of the chamber wall material.

LRE Chamber Wall Optimization Using Plane Strain and Generalized Plane Strain Models

A method for the optimization of rocket combustion chamber walls with respect to the life time is presented. This method can be split into four main parts: P1) Determination of the thermal field within the combustion chamber wall and the cooling channel during the hot run phase by a steady state thermo-fluid mechanical analysis; P2) Analysis of the nonlinear deformation of the combustion chamber wall under cyclic thermal and mechanical loading using a 2d plane strain or a 2d generalized plane strain model; P3) Estimation of the life time of the combustion chamber wall by a post processing method and P4) Application of a mathematical optimization procedure (gradient free or Conjugate Gradient method). This strategy is used to analyse the thermal load induced deformation process and life time of a typical rocket combustion chamber and to optimise selected geometry parameters of the combustion chamber wall.