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Zhukov V.P.,German Aerospace Center | Zhukov V.P.,German Institute of Space Propulsion
Journal of Propulsion and Power | Year: 2015

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.


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 | Year: 2011

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.


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 | Year: 2016

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.


Stark R.,German Aerospace Center | Stark R.,German Institute of Space Propulsion | Genin C.,German Aerospace Center | Genin C.,German Institute of Space Propulsion
48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit 2012 | Year: 2012

The flow during transient startup and shutdown in all rocket engines operated on sea level under ambient conditions will separate inside the supersonic part of the nozzle. A separated nozzle flow is circumferential asymmetric distributed and induces high side loads. DLR carried out a cold flow subscale test campaign to study devices that can reduce the side loads during transient operation of a thrust optimised parabolic nozzle. A detailed parametrical study was performed and experimental data demonstrate the potential of the device to reduce the side loads. © 2012 by German Aerospace Center.


Stark R.H.,German Aerospace Center | Stark R.H.,German Institute of Space Propulsion | Genin C.,German Aerospace Center | Genin C.,German Institute of Space Propulsion
Journal of Propulsion and Power | Year: 2012

The flow in all rocket engines operated on sea level under ambient conditions will separate inside the supersonic part of the nozzle during transient startup and shutdown. A separated nozzle flow has an asymmetrical distribution in the circumferential direction and therefore induces high side loads. The German Aerospace Center of Lampoldshausen carried outacold flow subscale test campaigntostudy devices that can reduce the side loads during transient engine operation. These devices can be installed on either ground test facilities or launch pads. A detailed parametric study was performed, and experimental data demonstrate the potential of the device for side load reduction. © 2011 by the American Institute of Aeronautics and Astronautics, Inc.


Madlener K.,German Aerospace Center | Madlener K.,German Institute of Space Propulsion | Ciezki H.K.,German Aerospace Center | Ciezki H.K.,German Institute of Space Propulsion
Journal of Propulsion and Power | Year: 2012

Gelled fuels and propellants are shear-thinning non-Newtonian fluids. Their dependency of the shear viscosity from the shear rate can be described with sufficient accuracy by an extended version of the Herschel-Bulkley equation in the whole rocket and ramjet propulsion-relevant shear-rate range. Additionally to the analytically determined generalized Reynolds number for fluids, which follow the extended Herschel-Bulkley equation, a method for the estimation of critical Reynolds numbers (as a phenomenological approach) is presented. Both dimensionless numbers are useful for the characterization of the flow and partially also of the spray processes of gel fluids. The results show furthermore that both the shear-thinning property and the yield stress tend to stabilize the laminar flow and thus shift the critical Reynolds number to higher values when compared to Newtonian liquids. Copyright © 2011 by K. Madlener and H.K. Ciezki.


Chloe N.-G.,German Aerospace Center | Chloe N.-G.,German Institute of Space Propulsion | Stark R.,German Aerospace Center | Stark R.,German Institute of Space Propulsion
Journal of Propulsion and Power | Year: 2010

The dual bell nozzle is a concept of altitude-adaptive nozzles. The flow adapts to the altitude by separating at the wall inflection at low altitude and flowing full at high altitude. To understand the phenomenology of the flow by the transition from sea-level to high-altitude mode, a series of tests have been made under subscale cold flow conditions. Three nozzles with different geometries have been tested. Two of them were successively shortened and driven under the same conditions for each extension length. This study yields the influence of the geometric parameters of the base and extension on the transition conditions. Furthermore, a prediction of the transition conditions is given. © 2010 by the American Institute of Aeronautics and Astronautics, Inc.


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 | Year: 2010

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.


Jack S.,German Institute of Aerodynamics and Flow Technology | Genin C.,German Institute of Space Propulsion
51st AIAA/SAE/ASEE Joint Propulsion Conference | Year: 2015

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.


Webster S.,German Institute of Space Propulsion | Hardi J.,German Institute of Space Propulsion | Oschwald M.,German Institute of Space Propulsion
Proceedings of the 19th Australasian Fluid Mechanics Conference, AFMC 2014 | Year: 2014

Experimental investigations into combustion instability were undertaken using a rectangular subscale combustion chamber. High speed optical diagnostics were used to observe flame-acoustic interactions. A sector wheel was used to produce an acoustic field with time varying amplitude. The acoustic field under investigation is the first transverse mode with a velocity anti node located in the central combustion zone under observation by high speed optical diagnostics. Increased combustion product emission was observed near to the face plate for periods of high amplitude excitation. Combustion zones with high emission were convected downstream as excitation amplitudes decreased. During phases of increasing amplitude an increase in emission intensity at the mixing border between dense oxygen and cryogenic hydrogen was observed. This provides visual confirmation of increased mixing efficiency due to high amplitude transverse velocities in the vicinity of the injection plane.

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