Enrico Cavallini

SRM Internal Ballistic Numerical Simulation by SPINBALL Model

In the design and development of solid propellant rocket motors (SRMs), the use of numerical tools able to simulate, predict and reconstruct the behavior of a given motor, in all its operative conditions, is particularly important in order to decrease all the planning times and costs. This paper is devoted to propose and present an approach to the numerical simulation of SRM internal ballistics, during the entire combustion time, by means of dierent own made models. The core of this procedure is represented by the SPINBALL model and numerical code. SPINBALL considers a Q1D unsteady modeling of the SRM internal ballistics, with many dierent sub-models able to represents all the driving phenomena that characterize the bore chamber oweld conditions during the SRM timelife, from the motor start-up to burn-out. In particular, the grain burning surface evolution is accomplished by means of a 3D numerical grain regression model, named GREG. This model is based on a full matrix level set approach, on rectangular or cylindrical structured grids. GREG gives to the SPINBALL gasdynamical model the evolution in time of the port area, wet perimeter and burn perimeter along the motor axis and, in case, within the submergence zone. The nal objective is, hence, to develop an analysis/simulation capability of SRM internal ballistics, for the entire combustion time, with simplied physical models, in order to reduce the computational cost required, but ensuring, in the meanwhile, an accuracy of the simulation greater than the one usually given by 0D quasi steady models, during quasi steady state and tail o. Notwithstanding, a 0D quasi steady model of SRM internal ballistic has been developed to reconstruct the experimental data coming from static ring tests (SFTs), in order to evaluate non-ideal behaviour parameters, like combustion eciency, hump law and nozzle eciency and the nozzle throat area evolution. These parameters are used in the SPINBALL model as inputs. The results of the internal ballistics numerical simulation, from motor start-up to burnout yielded with the SPINBALL model, will be shown for Zero23, second solid rocket motor stage developed in the ESA (European Space Agency) project of the new European small launcher Vega.

Internal Ballistics Simulation of a NAWC Tactical SRM

In the design and development of solid propellant rocket motors, the use of numerical tools able to predict the behavior of a given motor is particularly important in order to decrease the planning times and costs. This paper is devoted to present the results of the internal ballistics numerical simulation of the NAWC tactical motor n. 6, from ignition to burn-out, by means of a quasi-one-dimensional unsteady numerical simulation model, SPINBALL, coupled with a three-dimensional grain burnback model, GREG. In particular, the attention is focused on the effects on the SRM behavior of the erosive burning, total pressure drops and the cause of the pressure overpeak occurring during the last part of the ignition transient. The final objective is to develop an analysis/simulation capability of SRM internal ballistics for the entire combustion time with simplified physical models, in order to have reduced the computational costs, but ensuring an accuracy greater than the one usually given by zero-dimensional models. The results of the simulations indicate a very good agreement with the experimental data, as no attempt of submodels calibration is made, enforcing the ability of the proposed approach to predict the SRMs internal flow-field conditions. The numerical simulations show that NAWC n. 6 internal ballistics is completely led by the erosive burning, that is the root cause of the pressure peak occurring immediately after the SRM start-up.

Numerical simulations of acoustic resonance of Solid Rocket Motor

Low amplitude but sustained pressure and thrust oscillations can characterize the quasisteady condition of solid rocket motor; notwithstanding they are not threatening for motor life, coupling to the structural modes, they can damage the payload. These oscillations are due to uid dynamics instabilities and acoustic coupling. To correctly predict the oscillatory level, a numerical model has to include ad hoc model for: two-phase

Propellant trade-off analysis for upper stage solid rocket motors performance

Aim of this paper is to perform a propellant trade-off analysis in order to determine the propellant formulation able to maximize solid rocket motor performance for upper stage solid rocket motors (SRMs). The study is performed with the use of a 0D quasi-steady model of SRM internal ballistics developed on this purpose, which assumes the chemicalequilibrium in the combustion chamber up to the nozzle throat, frozen flow conditions in the nozzle divergent, and takes into account the nozzle throat erosion using a validated semi-empirical correlation of the throat recession rate. Three different upper stage SRM configurations are selected for the propellant trade-off analysis. The SRM configurations are inspired in terms of design to the available data in the open literature of three Zefiro family SRMs: Zefiro 23 and Zefiro 9A, second and third stage of VEGA launcher, and Zefiro 40, candidate for the evolution of Zefiro 23. Results indicate that, with respect to the baseline propellant HTPB 1912 (19 % aluminum 12 % HTPB), a gain in the performance can be obtained for propellant formulation with a higher aluminum loading and roughly the same HTPB mass fraction. The optimum aluminum loading increases with respect to the baseline formulation for SRM configurations characterized by high nozzle throat erosion.

Pressure Oscillations Numerical Simulation in Solid Rocket Motors

Large solid rocket motors can be a ected by sustained pressure and thrust oscillations during the quasi-steady state. The root cause of this phenomenon is represented by the coupling between the vortices generation, shedding, advection and interaction with the SRM chamber geometry and the acoustic chamber modes excitement, which may act together, in a feedback coupled loop. In the present work, a Q1D model for the simulation of the pressure oscillations in solid rocket motors, named AGAR (Aerodynamically Generated Acoustic Resonance), is described, discussing a new formulation of the Q1D vorticity equation and of the closure terms for modeling the vortex sound generation. The results of the pressure oscillations simulation yielded with the new model formulation are discussed for the P80 solid rocket motor, rst stage of the European launcher VEGA.

Pressure oscillations simulation in P80 SRM first stage VEGA launcher

Large solid rocket motors can exhibit sustained pressure and thrust oscillations during the quasi-steady operative condition. These uctuations are characterized by a frequency close to the rst acoustic mode, or one of its multiple, of the combustion chamber. The origin of this phenomenon is the coupling between shear layer instabilities, and acoustic feedback, resulting from the distruction of vorticity by some geometrical features of combustion chamber, as port area variations or nozzle walls. In the present work, a quasi-onedimensional model for the analysis of solid propellant rocket motor aero-acoustic phenomena is described. The proposed model is derived formally from the Euler conservation laws and it is implemented into a code named AGAR (Aerodynamically Generated Acoustic Resonance). AGAR model is here applied to the P80 SRM, rst stage of the European VEGA launcher. The demonstration test, P80 DM, exhibits four phases of pressure oscillations.

Analysis of Pressure Oscillations during Ignition Transient and Steady-State of an Overloaded VEGA First Stage

The dynamic environment of a solid rocket motor may bring about severe impacts on the launch vehicle performance suited to the payload requirements, and therefore, especially in the early phase of its design, it has to be carefully evaluated in order to correctly assess the design configuration of the SRM and the launcher. This paper provides a first assessment of the ignition transient phase and the steady state phase of a tentative configuration of the VEGA upgraded first stage SRM, with particular attention on the characterization of the onset of pressure oscillations that are responsible for the dynamic environment experienced by the SRM during its operative life. This tentative configuration has been designed as a P80 XL stretched SRM, waiting for the VECEP first state configuration that will be consolidated in the summer of 2014. This first assessment is performed with the use of numerical models of the ignition transient (SPIT) and of the aeroacoustic phenomena in solid rocket motors (AGAR), which set-up is consolidated and validated against the P80 firings (DM and QM) and flights (VV01 and VV02) data. Results of this first assessment indicate that, as for the VEGA solid stages, the use of helium as pressurizing gas is mandatory in order to control the dynamic environment generated during the motor start-up by the P80 XL. For the pressure oscillations during the steady state of the P80 XL stretched, the first numerical simulations indicate that, as the P80, this motor is characterized by the presence of pressure oscillation blows, which maximum amplitude is slightly higher than P80 ones. The occurrence of the pressure blows appears during the steady state in similar motor phases, when compared to the P80 ones, and related to the activation of the first longitudinal acoustic mode of the combustion chamber.

Propellant effects on SRM upper stage internal ballistics and performance with nozzle erosion characterization

Nozzle throat erosion is inherently present in high performance solid rocket motors because of high operative pressures and long combustion times. Whereas for large SRM boosters, operating in atmosphere, it does not represent a strong limit to obtain high performance, for upper stage SRMs it brings to relevant losses in the speci c impulse and, hence, less e cient design of the solid rocket motor due to the nozzle throat erosion e ects on both the operative pressure and speci c impulse. This paper discusses the e ects on the performance of an upper stage SRM of di erent kinds of aluminized propellants, compared to the baseline propellant HTPB 1912. The reference con guration is Ze ro 9A, third stage of the European launcher VEGA, recently quali ed with its rst maiden ight. The analysis is performed with the use of the complete coupling of the following models: a 3D grain burnback model, GREG, a full Navier-Stokes simulation of the nozzle throat erosion and a Q1D model of the SRM internal ballistic.

On the NDP onset in pre-ignition transient of high performance SRMs: VEGA Z9A experience

This paper discusses the early phase of the ignition transient of the VEGA Launchers third stage solid rocket motor, Zefiro 9A. During the first two firing tests of the Z9A SRM (QM2 and VT1) a peculiar unexpected negative force peak and a significant pressure unbalance in the motor chamber were measured during the very first phase of the ignition transient. In order to fix the unexpected negative force, out of the system specifications, a modification of the igniter re-design was decided for the Z9A SRM and a third static firing test was successfully carried out (VT2), with a reduction of the negative differential pressure of at least around a factor 3, followed by a reduction of the negative thrust by around the same factor. This paper wants to analyze the scenario outlined by the VT2 static firing test by means of three dimensional unsteady multi-component numerical simulations of the SRM pre-ignition transient.

Analysis and Performance Reconstruction of VEGA Solid Rocket Motors Qualification Flights

VEGA is the launch vehicle developed by the European Space Agency, qualified with its first two maiden flights on February, 13rd 2012 and on May, 7th 2013 and recently delivered to the commercial market with the third flight held on April, 30th 2014. During the launcher development, a total of eight static firing tests have been performed for the three solid stages, which compose the launcher: the first stage P80, the second stage Zefiro 23 and the third stage Z9. In this work, the analysis and performance reconstruction of the solid rocket motors of the VEGA launch vehicle for the two qualification flights is carried out with a post-firing reconstruction model, developed for the purpose. The aim is to use the measures acquired during the flights and the experience gained from the static firing tests analysis, in order to evaluate the actual behavior of the VEGA solid stages, through the non-ideal parameters: combustion efficiency, thrust efficiency, hump, scale factor and nozzle throat erosion law, which define the actual performance parameters of the solid rocket motors. The purpose of the work is to assess the SRMs performance parameters from the flight data, comparing the outcomes of the flight data analysis with the ones provided by the static firing test data analysis. The final aim is to consolidate the methodology for the analysis and reconstruction of the solid stage flight data, in order to define/characterize the scattering of the motor performance, reducing the uncertainties for the prediction methodologies in the upcoming and following VEGA flights.