NUMERICAL SIMULATIONS OF PRESSURE OSCILLATIONS IN VEGA FIRST STAGE - P80 SRM
- Paper number
IAC-08.C4.2.13
- Author
Mr. Fabio Paglia, Italy
- Coauthor
Dr. Marino Fragnito, Italy
- Coauthor
Mr. Emanuele Lambiase, Italy
- Year
2008
- Abstract
VEGA is the new European small 4 stages launch vehicle dedicated to the scientific/commercial market of small satellites (300 ÷ 1500 kg) into Low Earth Orbits, with inclinations ranging from 5.2° up to Sun Synchronous Orbits and with altitude ranging from 300 to 1500 km. In the framework of the development of the VEGA Launch vehicle a great effort has been spent by EUROPROPULSION (AVIO-SNECMA company) and AVIO itself in the development of all the three SRMs powering the LV. Even if this development is really challenging on the other hand a great amount of experimental data coming from SRM firing tests is available. Taking benefit of the up to date CFD methodology and of the existence of experimental data a verification/validation activity has been performed by AVIO on all the aspects regarding the SRMs. This paper presents a part of the activities performed by AVIO S.p.A., aimed to the estimation of pressure oscillations occurred in VEGA first stage P80 SRM firing test. Pressure oscillations is a well-known problem of large solid rocket motors (SRMs). In this kind of motors pressure oscillations lead to thrust oscillations and to important dynamic loads that usually cause the need of dampers on payload, reducing payload mass capability and launcher usability. This problem has attracted the attention of several researcher during last decades and, although the control of pressure oscillations is not yet completely obtained, the physics of the mechanism leading to pressure oscillations in SRM is well-known. The origin of pressure oscillations in SRM has been individuated in the presence of vortices in the combustion chamber of SRM. These vortices can be produced in three different ways: 1)by the tip of frontal thermal protections (Obstacle Vortex Shedding) 2)by the propellant surface (Parietal Vortex Shedding) 3)by propellant grain angles (Angle Vortex Shedding) The third of the over-mentioned causes is, in the authors opinion, the most important one in P80 SRM. The basic mechanism of this process can be described as a feedback loop consisting of the following steps: 1)the hydrodynamic instability of the shear layer region that develops near a geometric discontinuity; 2)the roll – up and advection of a vortex structure; 3)the impingement of the vortex on a surface located downstream (such as the nozzle head); 4)acoustic propagation from the downstream source; 5)the acoustical triggering and generation of a new vortex structure. When the vortex-shedding frequency is close to a natural frequency of the chamber, pressure oscillations reach a maximum. Numerical simulation of such complex phenomenon is quite a challenging task, since every one of these effects have to be properly numerically simulated. In the past devoted codes for pressure oscillations prediction have been developed and extensively applied. One of the goals of the present work is to use a commercial tool such as “FLUENT” for the estimation of pressure oscillation frequencies and amplitudes in P80 SRM. Several different tests have been conducted on simpler geometry, ranging from cold flow tests to small scale SRM up to ARIANE 5 P230 booster in order to validate the numerical adopted approach. All performed analyses share the same idea in approaching the problem, i.e. pressure oscillation is basically a fluid dynamic phenomenon and therefore it can be adequately reproduced using a pure CFD approach. Basically the adopted approach consists in the use of the MILES (Monotonically Integrated Large Eddy Simulation) model. Generally speaking the idea of MILES is to substitute the Subgrid-Scale (SGS) dissipation model that is explicitly included in Large Eddy Simulation with the dissipative error that is naturally introduced with up-wind schemes. Flow and geometrical conditions relative to the initial instants of the combustion time for P80 SRM has been chosen. Validation of the adopted approach has been conducted by means of a mesh sensitivity analysis and comparison with experimental data.
- Abstract document
- Manuscript document
IAC-08.C4.2.13.pdf (🔒 authorized access only).
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