Fast-bränsle-raketer (SRM) har funnit sin plats i en stor mängd tillämpningar sedan deras framkomst mer än 2000 år sedan. En SRMs prestanda är förutbestämd av geometrin av drivmedelskrutet och är begränsad av gjutningsmetoden, som idag främst används i produktion. Forskning inom 3D-skrivning av drivmedelskrut har undersökt nya komplexa geometrier som kan öka prestandan. Studier kring 3D-skrivning med UV-härdning är få till antalet och undersöks i detta projekt. Ett bindemedel av polyuretandiakrylat (PUDA) har syntetiserats och därefter karakteriserats, med och utan diverse monomerer genom dragprovsmätningar och differentialkalorimetri (DSC). Tillsats av tvärbindarna 1,6-hexandioldiakrylat (HDDA) samt trimetylolpropantriakrylat (TMPTA) till PUDA producerade ett mer sprött material. Denna skillnaden var mer påtaglig för TMPTA än HDDA, vilket tillskrivs den högre akrylatfunktionaliteten i den förstnämnda. Den kommersiella produkten Ebecryl 113 har karakteriserats med inerta fyllmedel. Härddjupet (DOC) undersöktes med Ebecryl 113 i ett experiment, vilket påvisade en minskning av härddjupet med ökande mängder aluminium. Orsaken är troligen de reflektiva egenskaperna för UV-ljus som aluminium innehar. Reologiska studier utfördes, från vilka en minskning i viskositet påvisades till följd av en ökad polydispersitet i partikelstorlekarna. 3D-skrivning med kolvextrudering och påföljande härdning med UV-strålning utforskades. Detta visade utmaningar med tekniken som behövs bemästras. I synnerhet uppmärksammades fasseparation och residuell härdning från reflekterat UV-ljus som begränsande faktorer för fortsatt arbete. / Solid rocket motors (SRMs) have found their place in many applications since their conception more than 2000 years ago. The performance of SRMs is determined by the geometry of the propellant grain and is limited by the cast-and-mould production method typically used today. Research has been made on 3D printing propellant grains to explore new complex geometries, which may increase performance. Studies on 3D printing techniques using UV curing are limited and are in this work investigated. A polyurethane diacrylate (PUDA) binder was synthesized and then characterized, with and without various monomers by tensile testing and differential scanning calorimetry. Additions of the crosslinkers 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA) to PUDA rendered the final product more brittle. This change was more noticeable for TMPTA than HDDA, as the former has a higher acrylate functionality. The commercial product Ebecryl 113 was also characterized with inert fillers added. A depth of cure (DOC) study with Ebecryl 113 was conducted, which showed a decrease in DOC with increasing amounts of aluminium. This is attributed to the reflective properties of aluminium in the UV spectrum. Rheological studies were conducted and a decrease in viscosity could be seen as a result of increasing the polydispersity of particle sizes. A 3D printing technique using plunger extrusion followed by UV curing was explored, which highlighted challenges which need to be overcome. Most notably, phase separation and residual curing from scattered UV rays are limiting factors for future work.

Cette thèse vise à modéliser les instabilités hydrodynamiques générant des détachements tourbillonnaires pariétaux (ou VSP) responsables des Oscillations De Pression dans les moteurs à propergol solide longs et segmentés par interaction avec l’acoustique du moteur. Ces instabilités sont modélisées en tant que modes de stabilité linéaire globaux de l’écoulement d’un conduit à parois débitantes. En supposant que les structures pariétales émergent d’une perturbation de l’écoulement de base, des modes discrets et indépendants du maillage utilisé sont calculés. Dans ce but, une discrétisation par collocation spectrale multi-domaine est implémentée dans un solveur parallèle afin de s’affranchir de la croissance polynomiale des fonctions propres et de la présence de couches limites. Les valeurs propres ainsi calculées dépendent explicitement des frontières du domaine, à savoir la position de la perturbation et celle de la sortie, et sont ensuite validées par simulation numérique directe. On montre alors qu’elles permettent bien de décrire la réponse à une perturbation initiale de l’écoulement modifié par une rupture de débit pariétale. Ensuite, la simulation d’une réponse forcée par l’acoustique se fait sous forme de structures tourbillonnaires dont les fréquences discrètes sont en accord avec celles des modes de stabilité. Ces structures sont réfléchies en ondes de pression de même fréquences remontant l’écoulement. Finalement, la simulation numérique et la théorie de la stabilité permettent de montrer que le VSP, dont la réponse est linéaire vis-à-vis d’un forçage compressible comme l’acoustique, est le phénomène moteur des Oscillations De Pression. / The current work deals with the modeling of the hydrodynamic instabilities that play a major role in the triggering of the Pressure Oscillations occurring in large segmented solid rocket motors. These instabilities are responsible for the emergence of Parietal Vortex Shedding (PVS) and they interact with the boosters acoustics. They are first modeled as eigenmodes of the internal steady flowfield of a cylindrical duct with sidewall injection within the global linear stability theory framework. Assuming that the related parietal structures emerge from a baseflow disturbance, discrete meshindependant eigenmodes are computed. In this purpose, a multi-domain spectral collocation technique is implemented in a parallel solver to tackle numerical issues such as the eigenfunctions polynomial axial amplification and the existence of boundary layers. The resulting eigenvalues explicitly depend on the location of the boundaries, namely those of the baseflow disturbance and the duct exit, and are then validated by performing Direct Numerical Simulations. First, they successfully describe flow response to an initial disturbance with sidewall velocity injection break. Then, the simulated forced response to acoustics consists in vortical structures wihich discrete frequencies that are in good agreement with those of the eigenmodes. These structures are reflected into upstream pressure waves with identical frequencies. Finally, the PVS, which response to a compressible forcing such as the acoustic one is linear, is understood as the driving phenomenon of the Pressure Oscillations thanks to both numerical simulation and stability theory.

The present research project is carried out at the von Karman Institute for Fluid Dynamics (Rhode-Saint-Genèse, Belgium) with the financial support of the European Space Agency.<p><p>The first stage of spacecrafts (e.g. Ariane 5, Vega, Shuttle) generally consists of large solid propellant rocket motors (SRM), which often consist of segmented structure and incorporate a submerged nozzle. During the combustion, the regression of the solid propellant surrounding the nozzle integration part leads to the formation of a cavity around the nozzle lip. The propellant combustion generates liquefied alumina droplets coming from chemical reaction of the aluminum composing the propellant grain. The alumina droplets being carried away by the hot burnt gases are flowing towards the nozzle. Meanwhile the droplets may interact with the internal flow. As a consequence, some of the droplets are entrapped in the cavity forming an alumina puddle (slag) instead of being exhausted through the throat. This slag reduces the performances.<p><p>The aim of the present study is to characterize the slag accumulation process in a simplified model of the MPS P230 motor using primarily optical experimental techniques. Therefore, a 2D-like cold-gas model is designed, which represents the main geometrical features of the real motor (presence of an inhibitor, nozzle and cavity) and allows to approximate non-dimensional parameters of the internal two-phase flow (e.g. Stokes number, volume fraction). The model is attached to a wind-tunnel that provides quasi-axial flow (air) injection. A water spray device in the stagnation chamber realizes the models of the alumina droplets, which are accumulating in the aft-end cavity of the motor.<p><p>To be able to carry out experimental investigation, at first the the VKI Level Detection and Recording(LeDaR) and Particle Image Velocimetry (PIV) measurement techniques had to be adapted to the two-phase flow condition of the facility.<p><p>A parametric liquid accumulation assessment is performed experimentally using the LeDaR technique to identify the influence of various parameters on the liquid deposition rate. The obstacle tip to nozzle tip distance (OT2NT) is identified to be the most relevant, which indicates how much a droplet passing just at the inhibitor tip should deviate transversally to leave through the nozzle and not to be entrapped in the cavity.<p><p>As LeDaR gives no indication of the driving mechanisms, the flow field is analysed experimentally, which is supported by numerical simulations to understand the main driving forces of the accumulation process. A single-phase PIV measurement campaign provides detailed information about the statistical and instantaneous flow structures. The flow quantities are successfully compared to an equivalent 3D unsteady LES numerical model.<p><p>Two-phase flow CFD simulations suggest the importance of the droplet diameter on the accumulation rate. This observation is confirmed by two-phase flow PIV experiments as well. Accordingly, the droplet entrapment process is described by two mechanisms. The smaller droplets (representing a short characteristic time) appear to follow closely the air-phase. Thus, they may mix with the air-phase of the recirculation region downstream the inhibitor and can be carried into the cavity. On the other hand, the large droplets (representing a long characteristic time) are not able to follow the air-phase motion. Consequently, a large mean velocity difference is found between the droplets and the air-phase using the two-phase flow measurement data. Therefore, due to the inertia of the large droplets, they may fall into the cavity in function of the OT2NT and their velocity vector at the level of the inhibitor tip.<p><p>Finally, a third mechanism, dripping is identified as a contributor to the accumulation process. In the current quasi axial 2D-like set-up large drops are dripping from the inhibitor. In this configuration they are the main source of the accumulation process. Therefore, additional numerical simulations are performed to estimate the importance of dripping in more realistic configurations. The preliminary results suggest that dripping is not the main mechanism in the real slag accumulation process. However, it may still lead to a considerable contribution to the final amount of slag.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

<p>This work investigated the effects of varying the crystal sizes of ammonium perchlorate (AP) when embedded with a polymeric binder, hydroxyl-terminated polybutadiene (HTPB) on impact-induced temperature behavior.  AP and HTPB are the most used oxidizers and fuel binders in the aerospace solid rocket design industry. In this study, samples of 200 µm and 400µm coarse AP crystals in HTPB were constructed using a conventional hand-mixing method. Using a parametric optimization technique such as the Taguchi method, direct-ink-writing as the additive manufacturing process was used for achieving the required shape fidelity in printing HTPB and by introducing ultraviolet polymers to decrease the curing time.</p> <p>A drop hammer experiment in conjunction with an infrared camera was used to study the impact-induced behavior in the conventionally made AP-HTPB samples. The thermal images obtained from the camera at millisecond resolution are invaluable and provide information about distribution across the sample surface, and the evolution of temperature rise observed in the samples which are complex and not easily understood otherwise and therefore help in improving and attaining desired propellant performance. A two-sample t-Test has been utilized to infer the results and statistical nonsignificance has been observed in the highest temperature rises among 200 µm and 400 µm AP-HTPB sample conditions but a difference in temperature distribution has been observed. A much uniform distribution of temperature over the sample surface on impact is observed in thermal images of 200 µm AP-HTPB sample condition compared to 400 µm AP-HTPB sample condition.</p>