Lowcost life assessment of liquid rocket engines by replacing full-scale engine tests with TMF panel tests

Liquid rocket engines are still key components of many space transportation systems. The combustion chamber of the engine itself is one of the most critical parts as it has to withstand severe temperatures, extreme temperature gradients and high pressures. Reusability and therefore cyclic loading can lead to failure due to rupture of the cooling channelsin the inner liner of the combustion chamber. Those failures are induced by a progressing failure mechanism called doghouse effect. The doghouse effect causes thinning of the cooling channels until rupture. For the development of new engines numerical methods are used. In order to save costs for obtaining experimental data to validate numerical analysis methods, a Thermo-Mechanical Fatigue (TMF) test bench was set up at the Lampoldshausen site of German Aerospace Center (DLR) to reduce the need for expensive full scale rocket engine tests. The test bench uses so-called thermomechanical fatigue panels representing a small section of the geometry (5 - 7 cooling channels) of the hot gas wall. To simulate the heat load, a diode laser can provide thermal loading with heat fluxes up to q = 25 MW/m² applied to an area of 10 mm x 34 mm. Supercritical Nitrogen at a temperature of T = 160 K and a pressure of p = 50 bar serves as coolant. The laser is cyclically powered on for typically 200 s until rupture is visible. The heat distribution on the laser-loaded surface of the TMF panel is measured with an infrared camera. The fatigue life is assessed by counting the number of laser cycles. With this method the appropriateness and response of different copper based alloys can be predicted for different use-cases like liquid core stage engines, liquid booster engines or liquid upper stage engines regarding thermomechanical fatigue by utilizing a cost-saving alternative to full scale rocket engine tests. This paper presents the detailed capabilities and potential of the TMF panel test bench at DLR Lampoldshausen as well as the recent results of a TMF panel made of CuCrZr alloy

Low cost life assessment of liquid rocket engines by replacing full scale engine tests by TMF panel tests

Liquid rocket engines are still key components of many space transportation systems. The combustion chamber of the engine itself is one of the most critical parts as it has to withstand severe temperatures, extreme temperature gradients and high pressures. Reusability and therefore cyclic loading can lead to failure due to rupture of the cooling channelsin the inner liner of the combustion chamber. Those failures are induced by a progressing failure mechanism called doghouse effect. The doghouse effect causes thinning of the cooling channels until rupture. For the development of new engines numerical methods are used. In order to save costs for obtaining experimental data to validate numerical analysis methods, a Thermo-Mechanical Fatigue (TMF) test bench was set up at the Lampoldshausen site of German Aerospace Center (DLR) to reduce the need for expensive full scale rocket engine tests. The test bench uses so-called thermomechanical fatigue panels representing a small section of the geometry (5 - 7 cooling channels) of the hot gas wall. To simulate the heat load, a diode laser can provide thermal loading with heat fluxes up to q = 25 MW/m² applied to an area of 10 mm x 34 mm. Supercritical Nitrogen at a temperature of T = 160 K and a pressure of p = 50 bar serves as coolant. The laser is cyclically powered on for typically 200 s until rupture is visible. The heat distribution on the laser-loaded surface of the TMF panel is measured with an infrared camera. The fatigue life is assessed by counting the number of laser cycles. With this method the appropriateness and response of different copper based alloys can be predicted for different use-cases like liquid core stage engines, liquid booster engines or liquid upper stage engines regarding thermomechanical fatigue by utilizing a cost-saving alternative to full scale rocket engine tests. This paper presents the detailed capabilities and potential of the TMF panel test bench at DLR Lampoldshausen as well as the recent results of a TMF panel made of CuCrZr alloy

Longitudinal Stability Measurements of a Winged Biconic Configuration in Supersonic Flow

In the present manuscript a biconic re-entry model was investigated in a blow down wind tunnel at Mach 1.5, 2, 3, and 4. The main focus was on studying the longitudinal stability and aerodynamic efficiency in this flying regime. In particular, the influence of wings near the rear part of the model, their wing dihedral, and of additional body flaps was investigated. While the purely biconic configuration was unstable, it could be stabilized with wings at a 20 deg downward pitch and with the additional body flaps. In general a larger dihedral angle improved static longitudinal stability

Dependency of Surface Temperature on Coolant Mass Flow and Heat Flux in Rocket Combustion Chambers

This paper presents the simulation and experimental results of the dependency of the surface temperature of a heat transfer test (HTT) panel representing liquid rocket engine combustion chamber geometry on the coolant mass flow rate and heat flow rate. The HTT panel is made of a high-conductivity copper material. This material is appropriate for the inner liner of lowly loaded regeneratively cooled combustion chambers like upper stages. In the experimental setup the HTT panel uses only a small section of the actual combustion chamber geometry, typically five cooling channels. The panel is heated by a high power diode laser providing realistic amounts of heat flux. For safety and cost reasons supercritical nitrogen is used as coolant instead of hydrogen or methane. Within the experiment differ ent combinations of surface temperature, heat flux and mass flow rate were examined, in total 24 different test conditions. Subsequently a coupled steady state thermal fluid-structureinteraction analysis was conducted in ANSYS and validated with the experimental data. ANSYS CFX was used to analyze the nitrogen coolant fluid flow with a Shear Stress Turbulence (SST) model. ANSYS Mechanical was used for the thermal finite element analysis. The relevant thermophysical parameters like heat conductivity, diffusivity and heat capacity were measured for temperatures above 273 K. For lower temperatures these parameters were determined theoretically. The results gained in this study will be used for the accurate modeling of the heat transfer in a thermomechanical fatigue life analysis by adding a dedicated structural Finite Element (FE) Analysis in ANSYS Mechanical. The accurate modeling of thermomechanical fatigue is particularly important for reusability of rocket engines. Furthermore the results of the validated numerical simulation are useful for the estimation of heat transfer in new developments of liquid rocket engines, particularly upper stages