Maurizio Di Giacinto

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.

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.

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.

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.

Post-Firing Analysis of Z23 SRM Ignition Transient

In the present work it is presented a detailed post-firing analysis of the ignition transient phase of Zefiro 23, the second stage solid rocket motor of ESA Vega launcher. The post-firing analysis is based on SRM ignition transient numerical simulation performed by the SPIT code (developed by DMA) and experimental data acquired by static firing test. Zefiro 23 static firing test available are the demonstration, Z23 DM, and the qualification, Z23 QM, static firing test. For both the firing test the head end pressure and thrust data are analysed while only for Z23 QM it is also available the aft end pressure data (seal nozzle transducer). Because the ignition transient data are strongly non-stationary and non-linear, the frequency analysis of both numerical and experimental data is performed using the Hilbert-Huang Transform (HHT). A comparison between the numerical simulation and the experimental data, an analysis of the data timing and a comparison between Z23 DM and Z23 QM static firing test data are also presented.

Comparison Between Different Pressurant Gases for Ignition Transient of P80 SRM

In the framework of the qualifying process of the new small European launcher Vega several experimental tests and numerical studies were done. Among them the qualification of P80 is particularly interesting: P80 is the only motor of the Zefiro-like family that was tested with different pressurizing gas both with nitrogen and helium. The static firing tests of P80 have shown that the pressure oscillations during ignition transient are more intense using nitrogen rather than helium. Several previous numerical studies 8 have pointed out that the pressurizing gas is fundamental for the behavior of the interaction between the hot igniter jets and combustion chamber geometry variations: it can favor or limit the generation of pressure oscillations depending on its compressibility. The present paper reports the numerical analysis of the P80 ignition transient both for nitrogen and helium and a comparison with the experimental date provided by the P80 static firing tests.

Shock detection and discontinuity tracking for unsteady flows

Abstract A method is presented for the numerical solution of inviscid flows with discontinuities in quasi-one-dimensional unsteady problems. The numerical technique, belonging to the family of the fitting techniques, is based on the method of characteristics for the calculation of discontinuity points, boundary points and, when required, of grid points close to them. The integration of the remaining grid points, enclosed between the discontinuities, is performed by a finite difference scheme following the “λ formulation”. The time step adopted for the numerical integration of the two different sets of points can be substantially decoupled. A simple and effective criterium for the unsteady shock detection is also proposed. Both the general philosophy and the details of the formulation of the method are illustrated and the efficiency of the numerical procedure is analyzed by means of suitable test cases involving shocks, contact and gradient discontinuities, and their interactions. Moreover, as applicative examples, the results of the simulation of complicated flow transients in convergent/divergent nozzles and in closed-end tubes are presented.