26th International Symposium on BALLISTICS, September 12-16, 2011 - Miami, Florida, USA

Abstract Category: Interior Ballistics - Presentation Format: Oral Presentation

Internal Ballistics Simulation of a NAWC Tactical SRM

E. Cavallini∗, B. Favini †and M. Di Giacinto‡

Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy

F. Serraglia§

ESA ESRIN, VEGA/IPT Via Galileo Galilei 00044 Frascati (Rome), Italy

In the design and development of solid propellant rocket motors, the use of numerical tools able to predict thebehavior of a SRM in all its operational conditions is particularly important in order to decrease all the planning timesand costs.

This work is devoted to present the results of the internal ballistics numerical simulation of the NAWC tacticalmotor n. 6 for its entire combustion time (from ignition to burn-out) by means of a Q1D unsteady numerical simulationmodel (SPINBALL1–6).

SPINBALL core model is a quasi-1D unsteady gasdynamics model with source terms accounting for the contri-butions due to igniter, grain propellant and cavities. The flow is assumed as a non-reacting mixture of perfect gaseswith space and time varying thermophysical properties. The governing equations are discretized by a Godunov-typescheme, first or second order. This main model is completed by several sub-models: igniter model, heat transfer modelfor convection and radiation, propellant ignition criterion, cavity model (floaters, submergence and slot regions), graincombustion model (APN model + Lenoir-Robillard model) and grain burnback model, some of them coming from theSPIT code (Ref. 7–14).

The grain burning surface evolution model is a 3D numerical grain regression model (GREG3–5), based on a levelset15 approach. The Hamilton-Jacobi type equation, for normal direction regression, is discretized by means of afirst or second order numerical scheme. GREG can handle 3D complex geometries directly from madrel design CADtools output, building up its initial condition from STL (stereolithography) files16 of grain propellant and thermalprotections3,5.

Comparisons between the results obtained with a 0D quasi steady model and SPINBALL are, hence, made and theeffects of the increased detail level of the internal ballistic simulation are discussed for NAWC motor n. 6, widely studiedduring last years17–23. NAWC n. 6 is a high length-to-diameter SRM, with a six-points finocyl grain (see Fig. 1) anda low port-to-throat area value, constituted by a reduced smoke propellant with additives. The numerical simulationyielded with SPINBALL shows a good agreement with the experimental pressure (see Fig. 2(a)), considering that notuning on the model is made. The effects on the internal ballistics of erosive burning and total pressure variationsare highlighted comparing the numerical results of a 0D quasi steady model and the Q1D model (see Fig. 2(a) and2(b)). A code validation is also made comparing the experimental pressure published in Ref. 17–20 and some previousnumerical results published in Ref. 19, 23 (see Fig. 2(a) and 2(b)), further characterizing the analysis/simulationcapabilities of the SRMs internal ballistics model proposed.

A complete analysis of the results will be presented in the full paper.

References

1Cavallini, E., Favini, B., Di Giacinto, M., and Serraglia, F., “Internal Ballistics Simulation of NAWC Tactical Motors with SPINBALL Model,”July 2010, 46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 25-28 July 2010, Nashville, TN.

2Cavallini, E., Favini, B., Di Giacinto, M., and Serraglia, F., “SRM Q1D unsteady Internal Ballistics Simulation using 3D Grain Burnback,”Space Propulsion 2010 , 2010, 3-6 May, San Sebastian, Spain.

3Cavallini, E., Modelling and Numerical Simulation of Solid Rocket Motors Internal Ballistics, Ph.D. thesis, Sapienza University of Rome,2009.

4Cavallini, E., Favini, B., Di Giacinto, M., and Serraglia, F., “SRM Internal Ballistic Numerical Simulation by SPINBALL Model,” AIAAPaper 2009-5512, Aug. 2009, 45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2-5 August 2009, Denver, Colorado.

5Favini, B., Cavallini, E., Di Giacinto, M., and Serraglia, F., “An Ignition-to-Burn Out Analysis of SRM Internal Ballistic and Performances,”44th AIAA/ASME/SAE/SEE Joint Propulsion Conference & Exhibit , 21-23 July 2008, Hartford, Connecticut.

6Cavallini, E., Di Giacinto, M., Favini, B., and Serraglia, F., “An Ignition-to-Burn Out Analysis of Solid Rocket Motors Internal Ballistic,”Space Propulsion 2008 - 2nd International Symposium on Propulsion for Space Transportation, 5-8 May 2008, Heraklion - Crete, Greece.

7Di Giacinto, M. and Serraglia, F., “Modeling of Solid Motor Start-up,” AIAA Paper 2001-3448, July 2001, 37th Joint Propulsion Conference,Salt Lake City, UT.

8Favini, B., Serraglia, F., and Di Giacinto, M., “Modeling of Flowfield Features During Ignition of Solid Rocket Motors,” AIAA Paper 2002-3753,July 2002, 38th Joint Propulsion Conference, Indianapolis, Indiana.

9Favini, B., Di Giacinto, M., and Serraglia, F., “Solid Rocket Motor Ignition Transient Revisited,” Proc. of the 8th Int. Workshop on Combustionand Propulsion, June 2002, Pozzuoli, Italy.

10Di Giacinto, M. and Serraglia, F., “Modeling of SRM Ignition Transient: Role of the Main Phenomena,” AIDAA, September 2001, XV ICongresso Nazionale AIDAA, Palermo, Italy.

∗Ph.D., Research Fellow, Department of Mechanics and Aerospace Engineering, Email: enrico.cavallini@uniroma1.it†Associate professor, Department of Mechanics and Aerospace Engineering, Email: bernardo.favini@uniroma1.it‡Full professor, Department of Mechanics and Aerospace Engineering, Email: maurizio.digiacinto@uniroma1.it§Ph.D., Propulsion and System Engineer VEGA-IPT ESA-ESRIN, Email: ferruccio.serraglia@esa.int

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(a) web = 0 mm (b) web = 4.412 mm

(c) web = 13.236 mm (d) web = 35.296 mm

Figure 1. NAWC Motor n. 6 grain burning surface evolution

(a) Experimental-numerical Q1D model, Rocbal-list1D23 and SPP19

(b) Experimental-numerical 0D quasi steadymodel and Rocballist0D23

Figure 2. HEP experimental and code-to-code comparison

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