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Jack S.,German Institute of Aerodynamics and Flow Technology | Genin C.,German Institute of Space Propulsion
51st AIAA/SAE/ASEE Joint Propulsion Conference

During the transient startup and shutdown process of a rocket engine high side loads occur, due to unsymmetrical flow patterns. The resulting deformation, and its retroactive effect onto the internal flow, excite the nozzle structure and can lead to its fatal damage. Flow separation at the nozzle wall amplifies the deformation. To investigate and predict the effects as well as the underlying mechanism that cause these phenomena, the flow characteristics in ovalized nozzles are investigated in the DLR project ProTAU. In this paper CFD results of ovalized TIC nozzles are presented and compared to experimental data, to validate the used numerical method. The presented results show good overall agreement for the relevant regimes, with a tendency to slightly overpredict the separation position. In the consecutive step the method will be extended to simulate the coupled problem of ow structure interaction. © 2015 American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Source

Hardi J.S.,German Aerospace Center | Hardi J.S.,German Institute of Space Propulsion | Hallum W.Z.,Purdue University | Huang C.,Purdue University | Anderson W.E.,Purdue University
Journal of Propulsion and Power

Combustion dynamics are controlled by the coupling between heat addition and gas dynamic modes, and their direct measurement and comparisons with prediction are key to improving computational tools, as well as our fundamental understanding of the problem. This paper demonstrates several methods for characterizing and comparing dynamic combustion response from experiment and simulation. A model rocket combustor that exhibits self-excited instabilities is used for the study. Comparisons are made for two configurations: one stable and one unstable. High-speed chemiluminescence imaging from the experiment was first phase averaged, then treated with an Abel inversion routine to produce a dynamic two-dimensional distribution of heat addition. The distribution before inversion could be compared with line-integrated calculations of the heat release rate from three-dimensional largeeddy simulations, and after inversion to azimuthally averaged cross sections from simulations. Modal decomposition of the two-dimensional distributions was performed and compared. The applicability and limitations of each comparison approach are assessed. © 2015 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Source

Arnold R.,German Aerospace Center | Arnold R.,Purdue University | Suslov D.I.,German Aerospace Center | Suslov D.I.,German Institute of Space Propulsion | And 2 more authors.
Journal of Propulsion and Power

By the application of film cooling in addition to regenerative cooling, a considerable reduction in thermal and structural loads of rocket combustion-chamber walls can be reached. This paper discusses important influence parameters on film cooling in terms of efficiency of the injected film and wall temperature reduction. For the experimental investigations a high-pressure subscale combustion chamber operated with the cryogenic propellant combination LOX=GH2 was used. A gaseous film with ambient tempered hydrogen was injected in the axial direction at the face plate. Typical film-cooling parameters such as film blowing rate, velocity ratio between film injection velocity and hot-gas velocity, circumferential slot positioning, and film injection slot height were investigated systematically at the European Research and Technology Test Facility P8. © 2010 by the American Institute of Aeronautics and Astronautics, Inc. Source

Zhukov V.P.,German Aerospace Center | Zhukov V.P.,German Institute of Space Propulsion
Journal of Propulsion and Power

A single-element combustor known as the "Penn State preburner combustor" is modeled numerically using the commercial computational fluid dynamics codeANSYSCFX. The aim of computational fluid dynamics modeling is to simulate the wall heat flux, which has been measured experimentally. The simulated combustion chamber has a single shear coaxial injector and operates with gaseous oxygen and hydrogen in a staged combustion configuration. The turbulent flow in the combustion chamber is modeled using the Favre-averaged Navier-Stokes equations and the shear-stress transport turbulence model. The turbulent non-premixed flame is modeled using an extended eddy dissipation model. The developed turbulent combustion model shows good agreement with the experimental data, good convergence, and a short computational time.Amesh convergence study is performed, and a mesh-independent solution is obtained on a mesh with 1.5 million nodes. The complexity of the model is gradually increased until the model is capable of predicting the wall heat flux. The analysis of numerical results shows a significant effect of boundary conditions on wall heat flux predictions. The comparison of the Reynolds-averaged Navier-Stokes simulations with the experimental data demonstrates the capability of Reynolds-averaged Navier-Stokes simulations to predict wall heat fluxes in a rocket combustion chamber. © 2015 by V. P. Zhukov. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Source

Genin C.,German Aerospace Center | Genin C.,German Institute of Space Propulsion | Stark R.H.,German Aerospace Center | Stark R.H.,German Institute of Space Propulsion
Journal of Propulsion and Power

The contour inflection of the dual bell nozzle forces the flow to a symmetrical and controlled separation in sea level mode. At a certain altitude, the transition to high-altitude mode takes place: the flow attaches rapidly to the nozzle extension wall, down to the exit plane. During this transition the separation point moves in the extension, generating potential high side load peaks duetoits asymmetrical position.Acoldflow subscale test campaign has been conducted on three nozzle models at the German Aerospace Center to evaluate the generation of side loads in dual bell nozzles. The phenomenology is given for the different nozzle flow regimes. Both operating modes are related to very low side loads. Transition and retransition induce a strong short time peak. The phaseof sneak transition, corresponding to a flow separation within the inflection region before the start of the actual transition, generates comparable side loads to separated conventional nozzles. The influence of the various geometrical parameters on flow behavior and side load generation was also investigated in this study. The extension length is shown to bethe critical parameter for flow stability, transition duration, and side load generation, leadingtothe necessity of a tradeoff for the optimization of the dual bell concept in rocket applications. Copyright © 2011 by DLR, German Aerospace Center. Source

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