Slush is a two phase flow of solid particles (crystals) and liquid at the triple point temperature, and constitutes an appealing alternative to liquid propellants for space launchers. The crystals give to the mixture higher density and lower specific enthalpy than liquid, enabling reduced tank volume storage and larger fuel holding time. However, the presence of solid crystals significantly modifies the thermo-hydraulics of the fuel transport, and requires novel predictive tools and diagnostic techniques for efficiently exploiting slush propellants. This thesis contributes to both aspects. In particular, this work studied the flow pressure losses and the heat transfer of solid-liquid mixtures in pipelines, combining experimental and numerical methods. Hydraulic and thermal flow features were analyzed separately with substitute mixtures chosen to mimic the behavior of slush flows in engine fuel feed systems. A dedicated facility was designed and built. The pipeline mounted conventional probes for pressure, temperature and mass flow rate measurements. Moreover, a capacitance-based density meter was developed and validated to measure the mixture's solid content. Optical flow visualization and image processing routines were combined to retrieve particulate phase distribution and velocity fields. The experimental work was complemented with 3D Unsteady Reynolds Averaged Navier Stokes simulations in OpenFOAM. The simulations coupled the Euler-Euler approach with the granular kinetic theory for the treatment of the solid dispersed phase. The model was validated with the experimental results on the pressure drop, heat transfer and solid volume fraction.The resulting physical insights and the proposed empirical correlations on the pressure drop and heat transfer in solid-liquid flows contribute to move a step forward towards slush propelled space launchers. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

The ultimate goal of this research is to develop the capability of direct numerical simulation of a flow containing numerous rigid finite size particles. In order to reach this goal, we have implemented the smoothed profile method (SPM) in the University of Iowa in-house solver, pELAFINT3D and overcame several challenges related to the method. This includes a proposed formulation for the interface thickness and many validations and comparisons with experimental data as well as with a second-order accurate sharp interface method. As one of the issues related to low-density particles is the instability, SPM has been improved by developing to a fully implicit scheme. Moreover, use of higher order integration formulation and implementation of Euler parameters have been shown to be helpful in stabilization of the calculations. To preserve the efficiency when the number of the particles increases, local mesh refinement is shown to be a very effective tool. A revised version of SPM that has only one projection step is proposed to improve the efficiency of the method. A comprehensive efficiency study is performed and it has been shown that the new method is less expensive in problems with high added mass effect when strongly coupled fluid-structure interaction schemes are used. Moreover, the code is massively parallelized using MPI and PETSc libraries. The parallelization includes I/O, operations leading to construction of the linear solver as well as the solver itself. Simulation of a particle laden flow involves particles collisions. Two novel collision models are suggested which are able to avoid particle overlapping for arbitrary shape particles. The methods are efficient as they are not involved with extra grid refinement related to implementing lubrication forces. The issue of handling continuously changing number of particles in a particle laden flow is solved by implementation of a linked list data structure for the particles. By studying a flow over a constricted region we showed that the platelets’ activation is more likely to happen for the particles that pass from the middle of the upper bump region because those particles will have longer exposure time to the high shear flow behind the bump. PDF contour of particles’ presence show the more concentrated presence of the particles near the bump. Moreover, the interaction of RBCs and platelets pushes the platelets toward the wall after the bottom wall.

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Ce travail de thèse est consacré à l'étude des écoulements biphasiques grains-gaz dans un régime de blocage (jamming). Ce régime caractérisé par un écoulement interrompu en temps fini et fréquemment rencontré dans la nature ou les applications industrielles présente un caractère stochastique. Sa compréhension nécessite la mesure de son débit, de ses fluctuations et de la probabilité d'arrêt liée à la géométrie de confinement, à la microstructure granulaire et au gaz interstitiel. Une approche numérique discrète couplant la méthode de la dynamique des contacts non-régulière (Non Smooth Contact Dynamics) pour la dynamique des particules et une méthode mésoscopique de type homogène équivalente pour le gaz est développée. La statistique d'écoulement obtenue est en bon accord avec des résultats expérimentaux de la littérature : le débit vérifie une loi de puissance croissante en fonction de l'ouverture avec un débit moyen affecté par la présence du gaz. Ces résultats statistiques quantitatifs sont appliqués à l'estimation du taux de relocalisation du combustible nucléaire fragmenté et confiné dans son tube-gaine présentant un ballonnement local suite à une situation accidentelle de type Perte de Réfrigérant Primaire. / In this work, we investigate particle-gas two-phase flows in the jamming regime where the flow stops in finite time. In this regime, which occurs quite often in nature and industrial applications, the flow is stochastic and needs therefore to be characterized by the jamming probability as well as the flow rate and its fluctuations that depend on the confining geometry, granular microstructure and gas properties. We developped a numerical approach based on the coupling of the Non Smooth Contact Dynamics for the solid phase and a mesoscopic method for the gas phase. We find that the flow rate as a function of the opening is well fit by a power law in agreement with reported experimental data. The presence of a gas affects only the mean flow rate, the flow statistics being sensibly the same as in the absence of the gas. We apply our quantitative statistical results in order to estimate the relocation rate of fragmented nuclear fuel inside its cladding tube as a result of a local balloon caused by an accident (loss-of-refrigerent accident).