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A numerical study was conducted at the German Aerospace Center in Lampoldshausen, to investigate the impact of various chemical models on reactive nozzle flow. Therefore, a chemical reaction mechanism for oxygen/methane combustion was implemented into DLR's flow solver TAU. Ignition delay simulations were conducted to demonstrate the validity of th...

## Contexts in source publication

**Context 1**

... increase of engine performance yields a potential payload gain. 11 The principle of the dual bell nozzle concept is illustrated in figure 1. Sea-level mode (top) and altitude mode (bottom) are both well known stable operation conditions and are of lesser interest in scientific research. ...

**Context 2**

... the approximation of a frozen nozzle flow seems not to be valid in the case of a LOX/CH4 combustion and expansion. In addition the not valid assumption Figure 10. Comparison of the mass fraction distribution along the generic nozzle center line between the frozen nozzle flow and the nozzle flow in chemical non-equilibrium. ...

**Context 3**

... be observed in figure 10. Here, for both cases the mass fraction development of the three major species in the combustion gas water, carbon dioxide and carbon monoxide is illustrated. ...

**Context 4**

... impact of an chemical equilibrium approach compared to the non-equilibrium approach is illustrated in the figures 11-13. Figure 11 depicts the temperature distribution for the two different chemical reaction models. A higher temperature level in the flow field of the chemical equilibrium approach can be observed. ...

**Context 5**

... the chemical equilibrium state emits more heat, because of the ongoing reactions in the flow field after reaching the non-equilibrium condition of the baseline simulation. The dedicated Mach number distribution of the generic equilibrium flow field is illustrated in figure 12. It can be observed, that the Mach numbers of the chemical equilibrium simulations are significantly lower than in the chemical non-equilibrium flow field. ...

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... obtained results were compared to the chemical non-equilibrium simu- lation results. Figure 14 illustrates the comparison of the temperature distributions. A good agreement of the temperature field can be observed. ...

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... good agreement of the temperature field can be observed. Figure 15 depicts the comparison of the Mach number distribution. Compared to the results of the frozen and the chemical equilibrium approach, the Mach number distribu- tion of the 7-step simulation agrees well with the 66-step simulation results. ...

**Context 8**

... In downstream direction with increasing flow expansion the deviation from the 66-step simulation increases slightly. Figure 16 illustrates the mass fraction development along the nozzle center line for the three major species water, carbon dioxide and carbon monoxide. These three species together account more than 90 % of the total combustion gas mass. ...

**Context 9**

... agreement of the 66-step and 7-step RANS simulations is satisfying along the entire generic nozzle. Figure 17 depicts the mass fraction development along the nozzle wall for the three major species. The combustion gas composition near the wall would be important, if a reliable estimation of the heat flux inside the wall is requested. ...

**Context 10**

... a dual-bell nozzle model was designed using a DLR in-house code based on the method of characteristics (MOC). 27 The contour of the base nozzle was designed as a truncated ideal contour (TIC) Figure 18. Construction plot of the tested dual-bell nozzle model. ...

**Context 11**

... dual bell nozzle model was made of copper alloy due to the high thermal conductivity and therefore good cooling properties. Figure 18 illustrates a sketch of the dual-bell nozzle model. For the regenera- tive water cooling, the nozzle model was equipped with forty cooling channels. ...

**Context 12**

... complex configuration was chosen, in order to realize realistic flow conditions at the nozzle exit area without flow disturbance by a manifold. Figure 19 depicts the dual-bell nozzle model mounted at DLR's test facility P6.1 in Lampoldshausen. ...

**Context 13**

... transition and retransition ROF had to be determined based on the experimental mass flow rate data of the liquid oxygen and the methane, because of the fluctuating ROF during the test. Figure 21 illustrates the transition and retransition NPRs as a function of ROF for all conducted test runs. A clear impact of the mixture ratio on the transition and retransition NPR can be observed. ...

## Similar publications

A numerical study is conducted to investigate the impact of different chemical reaction mechanisms on the behavior of reactive nozzle flow. Therefore, a 66-step chemical reaction mechanism for oxygen/methane combustion is implemented into German Aerospace Center’s flow solver TAU. Ignition delay simulations are conducted and compared to experimenta...

A numerical study was conducted at the German Aerospace Center in Lampoldshausen, to investigate the impact of various chemical models on reactive nozzle flow. Therefore, a chemical reaction mechanism for oxygen/methane combustion was implemented into DLR's flow solver TAU. Ignition delay simulations were conducted to demonstrate the validity of th...

## Citations

... Previous investigations revealed that flow separation transition can be influenced not only by the variation of total propellant mass-flow rate but by a variation of the propellant mixture ratio r of as well. While its increase yielded in a reduction of the transition pressure ratio, lowering of r of produces an opposite result [59,60]. However, these effects are accompanied by a reduction of the width of the hysteresis, the pressure ratio gap between transition ...

This chapter book summarizes the major achievements of the five topical focus areas, Structural Cooling, Aft-Body Flows, Combustion Chamber, Thrust Nozzle, and Thrust-Chamber Assembly of the Collaborative Research Center (Sonderforschungsbereich) Transregio 40. Obviously, only sample highlights of each of the more than twenty individual projects can be given here and thus the interested reader is invited to read their reports which again are only a summary of the entire achievements and much more information can be found in the referenced publications. The structural cooling focus area included results from experimental as well as numerical research on transpiration cooling of thrust chamber structures as well as film cooling supersonic nozzles. The topics of the aft-body flow group reached from studies of classical flow separation to interaction of rocket plumes with nozzle structures for sub-, trans-, and supersonic conditions both experimentally and numerically. Combustion instabilities, boundary layer heat transfer, injection, mixing and combustion under real gas conditions and in particular the investigation of the impact of trans-critical conditions on propellant jet disintegration and the behavior under trans-critical conditions were the subjects dealt with in the combustion chamber focus area. The thrust nozzle group worked on thermal barrier coatings and life prediction methods, investigated cooling channel flows and paid special attention to the clarification and description of fluid-structure-interaction phenomena I nozzle flows. The main emphasis of the focal area thrust-chamber assembly was combustion and heat transfer investigated in various model combustors, on dual-bell nozzle phenomena and on the definition and design of three demonstrations for which the individual projects have contributed according to their research field.

... A clear impact of the combustion chamber mixture ratio on the transition nozzle pressure ratio was observed. Based on this experimental work, Schneider et al. [43,44] developed a validated numerical method to predict the dual-bell transition and hysteresis behavior under LOX∕CH 4 hot-flow conditions. The clear impact of the combustion chamber mixture ratio on the transition nozzle pressure ratio was reproduced by these numerical simulations. ...

... The combustion chamber pressure is increased linearly with a gradient of dp∕dt 0.25 MPa∕ms. Former studies of Schneider and Génin [39] and Schneider et al. [43] have shown that this combustion chamber pressure gradient yields a good agreement with the experimental data of the operation mode transition process. The same pressure gradient was applied for the cooling film ramping. ...

... A dimensionless wall spacing of y O1 is applied to ensure a sufficient resolution of the laminar sublayer and the thermal boundary layer. The exact grid resolution inside the structured boundary layer is based on a detailed grid study of a cold-flow truncated ideal contour nozzle [71] performed by Schneider et al. [43,44]. For the following hot-flow simulations, the nozzle dimensions are in the same order of magnitude, and a turbulent Prandtl number of around one is applied. ...

A numerical study is conducted to investigate the impact of a film-cooled dual-bell nozzle extension on its operation mode transition behavior. Therefore, unsteady Reynolds-averaged Navier–Stokes simulations of the transition process between the sea level and altitude modes are carried out. The investigated dual-bell nozzle model is fed with hot gas by a combustion chamber using liquid oxygen as oxidizer and gaseous hydrogen as fuel. Upstream of the dual-bell nozzle contour inflection, gaseous hydrogen is injected as cooling fluid for the nozzle extension wall. The numerical studies yield a clear impact of the cooling fluid mass flow rate on the transition nozzle pressure ratio of the dual-bell nozzle. The increase of the cooling fluid mass flow rate leads to a shift of the dual-bell transition nozzle pressure ratio to lower values. Furthermore, the impact of the combustion chamber mixture ratio on the dual-bell operation mode transition is investigated. A clear shift to lower transition nozzle pressure ratio values due to higher propellant mixture ratios can be observed. A combination of the two effects is introduced for an active control of the dual-bell operation mode transition.

... A clear impact of the combustion chamber mixture ratio on the transition nozzle pressure ratio was observed. Based on this experimental work Schneider et al. 43,44 developed a validated numerical method to predict the dual-bell transition and hysteresis behavior under LOX/CH 4 hot-flow conditions. The clear impact of the combustion chamber mixture ratio on the transition nozzle pressure ratio was reproduced by these numerical simulations. ...

... The DLR TAU code is a finite volume, compressible flow solver for hybrid meshes. It has been applied for a wide variety of different flows such as steady and unsteady suband hypersonic applications with and without chemical reactions [8][9][10][11]. The Favre averaged Navier-Stokes equations are solved employing a Gudonov type finite-volume scheme. For the discretization of the inviscid flux terms an AUSMDV [12] upwind scheme in combination with a MUSCL-type [13] least square algorithm [14,15] for reconstruction of the second order spatial gradients is used. ...

... For combustion modelling a finite rate chemistry model is used. This model has successfully been applied for supersonic and hypersonic flows [10], reacting nozzle flows [11] and sub-scale rocket combustion chambers [18][19][20] using different kinetic schemes. The laminar viscosities for each individual species are spline fitted according to Blottner [21] based on thermodynamic data obtained from Gurvich tables [22]. ...

... The coaxial injector simulations were performed using the TAU code, a CFD solver developed in-house by DLR. It is a finite volume, compressible flow solver for hybrid meshes and has been applied for a wide variety of different flows, such as steady and unsteady sub-and hypersonic applications with and without chemical reactions [17,11,15,21]. ...

... The set of equations is closed, using the Spalart-Allmaras turbulence model [52]. The application of this turbulence model yielded reliable results for the prediction of the separation position in overexpanded nozzle flows [53] and of the dual-bell operation mode transition [47,[54][55][56]. Discretization of the inviscid flux terms is performed using the AUSMDV upwind scheme [57]. ...

The design of a film cooled dual-bell nozzle is presented. The nozzle is part of a thrust chamber assembly that adopts an existing LOX/GH2 thrust chamber. The dual-bell base nozzle, including the gaseous hydrogen cooling film injection, is a downscaled redesign of an already tested film cooled TIC nozzle. Future hot flow tests at the test facility P8 will study the impact of a ROF variation and a cooling film mass flow variation on the operation mode transition of the dual-bell. For this reason, a homogeneous hot flow and cooling film distribution are mandatory. To meet those demands, extensive numerical studies were performed and design optimizations were derived. The test specimen will be operated under sea level conditions.