Ferruccio Serraglia

MODELING OF SOLID MOTOR START-UP

An unsteady quasi- ID numerical simulation model has been developed in order to predict the behavior of large solid motors during the ignition transient. In particular, this model is finalized to be used as a numerical tool during the preliminary design phase, when no information about the future behavior of the motor is available. An Euler flow model has been adopted coupled with suitable semi-empirical models that take into account the main phenomena affecting the ignition transient. Special attention has been devoted to simulate the effects of the impingement of the igniter jets on the grain propellant surface (heating, ignition and combustion of the impingement region). A radiation model is also proposed. The simulation model has been extensively tested and the numerical results have been compared with the experimental results obtained for largely different motor concepts and configurations. Significant information about the role of some phenomena affecting the ignition transient has been also deduced from the critical analysis of these results.

Ignition Transient Pressure Oscillations in Solid Rocket Motors

In the static fire test of Zefiro 16, a solid rocket motor with a finocyl region in the rear, pressure oscillations have been detected during the first phase of the ignition transient. By analysing the results of the numerical simulations performed with an unsteady quasi-one-dimensional model, called SPIT, a possible explanation about the origin of these pressure fluctuations has been proposed. By means of the same simulation model, a parametric analysis of the motor behaviour, by changing some of its design parameters, has been also performed. This analysis seems to confirm the hypothesis about the concurring events that generate the pressure oscillations. In fact, on the contrary of what it could be expected, some design modification have no significant effects on these fluctuations. On the contrary, a simple solution, with a low impact on both design and operative procedures, is proposed and numerically tested for eliminating the pressure oscillations. The internal flow field of the motor has been simulated also with an inviscid axisymmetric model, called ALIAS, in order to validate the previous quasi-1D results. The results obtained by these two simulation models are in good agreement and, notwithstanding the increasing complexity of a multidimensional flowfield analysis, the same phenomena evidenced by the quasi-1D analysis can be qualitatively recognized in the axisymmetric numerical simulations.

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.

Vega Solid Rocket Motors Development and Qualification

This paper presents a technical and programmatic overview of the Vega Launcher achieved during last year with a particular focus on solid rocket propulsion. The propulsion system of the Vega LV at solid rocket motors level is composed of AP-based monolithic boosters, namely P80 (1 st stage), Zefiro 23 (2 nd stage) and Zefiro 9 (3 rd stage). The Vega development had a significant boost in 2008-2010 and major milestones providing essential results in terms of test data and design consolidation have been achieved successfully. Vega has reached an advanced and mature status and is preparing its maiden flight. Concerning propulsion, between 2008 and early 2010 all the three SRMs successfully went through their Ground Qualification Reviews and the Flight Unit models manufacturing is going to be completed by Fall 2010: in particular, for the P80 SRM, after the successfully development and qualification firing tests in December 2006 and December 2007, the mechanical qualification tests on Insulated Motor Case have been successfully performed in the first part of 2009 and were completed by the burst test at the end of 2009. For Z9 SRM, in its new improved version Z9A, with nozzle and grain redesign, three firing tests have been successfully performed in October 2008, April 2009 and May 2010.

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

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.

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.

3D Simulations of Pre-Ignition Transient of P80 SRM

The first three stages of the new small European launcher Vega are solid rocket motors characterized by a star-shaped finocyl region (close to the propulsive nozzle). Zefiro 16 (a prototype developed as a precursor of the three stages of Vega) static fire tests have evidenced pressure oscillations during ignition startup. This phenomenon has been analyzed by means of quasi-1D and 3D numerical models. The numerical results of both models have very good agreement with experimental data and they have allowed a complete explanation of pressure oscillation phenomenology. These studies have suggested that the use helium instead nitrogen as pressurizing gas could eliminate pressure oscillations. Instead the subsequent static fire tests of P80, Zefiro 23 and Zefiro 9 have been done with helium showing no pressure oscillations during ignition transient as numerical simulations have predicted. On the contrary a second firing of P80, made with nitrogen as pressurizing gas, has exhibited pressure oscillations [ref.]. Therefore we have done numerical simulations of P80 ignition transient using nitrogen: because of their differences the comparison between Zefiro 16 and P80 is interesting.