Analysis of High Amplitude Acoustic Pressure Field Dynamics in a LOX/H2 rocket combustor

High frequency combustion instabilities present a serious problem for liquid propellant rocket engines. These interactions between combustion chamber acoustics and variations of the heat release rate are difficult to predict, because the underlying coupling mechanisms are still not fully understood. For this reason self-excited combustion instabilities are investigated with a cryogenic research combustor at DLR Lampoldshausen. In order to get a better understanding of the coupling mechanisms the acoustic pressure field inside the combustion chamber needs to be described precisely. Due to the highly turbulent nature of the processes in a rocket combustor it can be expected that also the acoustic pressure field shows some variation during unstable combustion. The framework of this report new methods with high time resolution were applied to experimental data to analyze the dynamics of the pressure field for different types of instability. The results reveal that the applied methods give further insight into the excited pressure field and may help to identify the coupling mechanisms in the future

Berührbarkeit und Generationenbildung. Überlegungen zu einem Bildungsbegriff in Zeiten demografischer Veränderungen

Gröning K. Berührbarkeit und Generationenbildung. Überlegungen zu einem Bildungsbegriff in Zeiten demografischer Veränderungen. In: Andresen S, Pinhard I, Weyers S, eds. Erziehung - Ethik - Erinnerung. Basel: Beltz-Verlag; 2007: 60-74

EFFECTS OF EDGE GEOMETRY ON FLOW PAST THE DEEP, CIRCULAR, AXISYMMETRIC CAVITY: ANALYSIS OF THE FIRST DIAMETRAL ACOUSTIC MODE

In this paper, the phenomenon of aeroacoustic resonance due to the flow past a deep, circular, axisymmetric cavity with a depth much larger than its width or length is investigated. Several representative cases of the internal cavity geometry that involved chamfers of various lengths of the upstream and the downstream edges of the cavity, as well as a reference case with sharp, 90° edges were analyzed. The acoustic mode shapes, as well as the distribution of acoustic particle velocity, were reconstructed using the dynamic pressure data while the flow velocity in the vicinity of the cavity opening and distribution of the turbulent intensities, as well as shear stress over the cavity length, were measured using digital particle image velocimetry (PIV). This combined approach allowed to determine the effect of chamfered edges on acoustic response of the system, evolution of the cavity free shear layers, and on the azimuthal characteristics of the first acoustic diametral mode of the cavity

Large-Eddy Simulations of a sub-scale liquid rocket combustor: influence of fuel injection temperature on thermo-acoustic stability

International audienceThe present work aims at the prediction of high frequency combustion instabilities in cryogenic rocket engines using Large Eddy Simulation (LES). The sub-scale rocket combustor BKD from DLR has 42 coaxial injectors fed with liquid oxygen and gaseous hydrogen operating at conditions representative of full-scale engines. The combustor is found to be stable for low hydrogen injection temperatures and unstable for higher ones. The LES solver is first validated on the Mascotte test-bench from ONERA. Two BKD cases are then simulated, corresponding to naturally stable and unstable regimes in the experiment. The recent progresses and results are described and analyzed

Joint experimental, LES and Helmholtz analysis of self-excited combustion instabilities in a hydrogen-oxygen rocket combustor

Self-excited combustion instabilities of the first tangential mode have been observed in a research combustor operated with hydrogen and oxygen in cryogenic state as propellants. A detailed analysis of this unstable mode is conducted and the experimental observations are compared with numerical simulations. A high fidelity Large-Eddy Simulation together with an acoustic eigenmode computation performed with a Helmholtz solver give complementary information on the mechanisms driving the instability. A methodology for the 3D reconstruction of the acoustic field is presented