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Milne A.,Fluid Gravity Engineering Ltd. | Milne A.,University of St. Andrews | Longbottom A.,Fluid Gravity Engineering Ltd. | Frost D.L.,McGill University | And 3 more authors.
Shock Waves | Year: 2016

Rapid acceleration of a spherical shell of liquid following central detonation of a high explosive causes the liquid to form fine jets that are similar in appearance to the particle jets that are formed during explosive dispersal of a packed layer of solid particles. Of particular interest is determining the dependence of the scale of the jet-like structures on the physical parameters of the system, including the fluid properties (e.g., density, viscosity, and surface tension) and the ratio of the mass of the liquid to that of the explosive. The present paper presents computational results from a multi-material hydrocode describing the dynamics of the explosive dispersal process. The computations are used to track the overall features of the early stages of dispersal of the liquid layer, including the wave dynamics, and motion of the spall and accretion layers. The results are compared with new experimental results of spherical charges surrounded by a variety of different fluids, including water, glycerol, ethanol, and vegetable oil, which together encompass a significant range of fluid properties. The results show that the number of jet structures is not sensitive to the fluid properties, but primarily dependent on the mass ratio. Above a certain mass ratio of liquid fill-to-explosive burster (F / B), the number of jets is approximately constant and consistent with an empirical model based on the maximum thickness of the accretion layer. For small values of F / B, the number of liquid jets is reduced, in contrast with explosive powder dispersal, where small F / B yields a larger number of particle jets. A hypothetical explanation of these features based on the nucleation of cavitation is explored numerically. © 2016 The Author(s)


Grant
Agency: Cordis | Branch: FP7 | Program: CP-FP | Phase: SPA.2012.2.2-02 | Award Amount: 2.74M | Year: 2013

As mentioned in the FP7 space call for Europe to be active in space in the long term, be it in earth-orbit or across the solar system, it is essential that space technologies with key capabilities are at its disposal. This goal requires developments by radical innovation which may then lead to disruptive technologies. In this frame new thermal shielding and low risk return strategies are defined as European key activities in the future. In Europe the design of spacecraft for high-energetic interplanetary or sample return flights is still performed with big safety margins, which means high mass. This again leads to higher costs and a reduction in scientific payloads or instrumentation. Ablative thermal protection materials are a key technology for current and future space exploration missions. However, the mission feasibility is determined by the materials available, and the development of new materials is performed, essentially, by an iterative trial-and-error process. This is due to the absence of validated predictive models for ablative material behaviour models are tuned to bulk material properties from tests. For each new material, this tuning has to be redone because the models are not of sufficiently high fidelity to be able to make even small extrapolations. This means that materials cannot be designed to a specification to fulfil the needs of a particular mission. The aim of this project is to make a substantial step towards a predictive model of an ablative thermal protection system by incorporating aspects of high fidelity mesoscale ablator physics within a modular framework. In order to successfully develop such physics modules, the understanding of the fundamental processes occurring within the ablative materials must be improved. To this end, existing ablative materials will be tested in the most powerful European long duration high enthalpy facilities using both standard instrumentation and advanced measurement techniques. From the data obtained, and the state-of-the-art knowledge of ablator physical processes, modules for the specific processes of internal gas flow, internal radiation and gas-surface interaction will be developed to fit inside an overall multi-scale ablator modelling scheme. The improvements made in the representation of an ablative material will be validated against the ground testing, and this advanced ablator model will be applied to realistic flight configurations to demonstrate the impact of the enhanced physics on the understanding of real ablator performance. The existence of this capability will allow improvements in the efficiency and cost of developing advanced new ablative materials which are tailored to meet the specifications of Europes future mission needs. In order to reach this objective, the ABLAMOD project brings substantial expertise from across Europe in ablator materials, thermochemistry, microfluidics, entry systems and instrumentation.


Neeb D.,German Aerospace Center | Gulhan A.,German Aerospace Center | Merrifield J.A.,Fluid Gravity Engineering Ltd.
Journal of Spacecraft and Rockets | Year: 2016

Surface roughness, especially if enhanced due to ablative form change, increases skin friction drag and convective heat transfer over reentry vehicles. Although the corresponding heat flux augmentation is usually lower compared to increased friction, careful consideration in the prediction of the resulting heat load levels is required. Within the European Mars mission ExoMars, the potential roughness impact on the thermal protection system of the descent module has been analyzed based on analytical predictions, numerical calculations, and dedicated experimental campaigns. This paper describes the experimental efforts in the compressible flow regime to study the impact of roughness at representative conditions. The data are discussed based on comparisons with prediction methods and results of other investigators. Based on these data, the numerical predictive capabilities within the ExoMars program are characterized and validated. Copyright © 2015 by German Aerospace Center (DLR).


Neeb D.,German Aerospace Center | Gulhan A.,German Aerospace Center | Merrifield J.A.,Fluid Gravity Engineering Ltd
AIAA AVIATION 2014 -11th AIAA/ASME Joint Thermophysics and Heat Transfer Conference | Year: 2014

Surface roughness, especially if enhanced due to ablative form change, increases skin friction drag and convective heat transfer over re-entry vehicles. Although the corresponding heat flux augmentation is usually lower compared to increased friction, careful consideration in the prediction of the resulting heat load levels is required. Within the European Mars mission ExoMars, the potential roughness impact on the thermal protection system of the descent module has been analyzed based on analytical predictions, numerical calculations and dedicated experimental campaigns. This paper describes the experimental efforts in the compressible flow regime to study the impact of roughness at representative conditions. The data is discussed based on comparisons with prediction methods and results of other investigators. Based on this data the numerical predictive capabilities within the ExoMars program is characterized and validated.


Grant
Agency: Cordis | Branch: FP7 | Program: CP-FP | Phase: SPA.2012.2.2-02 | Award Amount: 2.72M | Year: 2013

There are key space technologies existing at European level and during the last space calls many European projects are framed on space re-entry, but none of them dealing with radically new technologies, able to compete with technologies from other leading countries or allowing collaboration with them. The THOR project will provide knowledge in key space technologies for accessing space, through the design and development of disruptive technologies based on novel thermal management concepts which are specifically targeted to atmospheric entries of future space vehicles and hypersonic transport vehicles. This project, including the participation of several SMEs and relevant end-users, aims at the collaboration among them to strengthen the European space sector and enable international cooperation. The technical approach is focused non-local concepts for thermal management including active cooling as well as passive cooling technologies, in order to extent the capabilities of re-usable Thermal Protection Systems (TPS) towards the requirement of future space flight including hypersonic transport. To achieve this technical target radically new thermal management solutions will be implemented in a new concept of TPS together with innovative materials and unique ceramic structures, reaching a TRL 2-3 at the end of the project. The passive systems will be based on thermal equilibration establishing an efficient heat transfer from highly loaded areas to regions with less loading. New ceramic matrix composites incorporating a new generation of highly thermal conductive fibres will be applied. In addition, active cooling will be implemented by passing a fluid through a ceramic porous structure. The project includes a strong effort on design, modelling and simulation in order to fulfil the technical requirements before integrating the complete TPS. Finally the concepts will be verified by ground tests under realistic entry conditions in high enthalpy facilities.


Joiner N.,University of Saskatchewan | Joiner N.,Fluid Gravity Engineering Ltd. | Dorland W.,University of Maryland University College
Physics of Plasmas | Year: 2010

Advanced tokamak schemes which may offer significant improvement to plasma confinement on the usual large aspect ratio Dee-shaped flux surface configuration are of great interest to the fusion community. One possibility is to introduce square shaping to the flux surfaces. The gyrokinetic code GS2 [Kotschenreuther, Comput. Phys. Commun. 88, 128 (1996)] is used to study linear stability and the resulting nonlinear thermal transport of the ion temperature gradient driven (ITG) mode in tokamak equilibria with square shaping. The maximum linear growth rate of ITG modes is increased by negative squareness (diamond shaping) and reduced by positive values (square shaping). The dependence of thermal transport produced by saturated ITG instabilities on squareness is not as clear. The overall trend follows that of the linear instability, heat and particle fluxes increase with negative squareness and decrease with positive squareness. This is contradictory to recent experimental results [Holcomb, Phys. Plasmas 16, 056116 (2009)] which show a reduction in transport with negative squareness. This may be reconciled as a reduction in transport (consistent with the experiment) is observed at small negative values of the squareness parameter. © 2010 American Institute of Physics.


Joiner N.,University of Saskatchewan | Joiner N.,Fluid Gravity Engineering Ltd. | Hirose A.,University of Saskatchewan | Dorland W.,University of Maryland University College
Physics of Plasmas | Year: 2010

At low Β it is common to neglect parallel magnetic field perturbations on the basis that they are of order Β2. This is only true if effects of order Β are canceled by a term in the ∇B drift also of order Β [H. L. Berk and R. R. Dominguez, J. Plasma Phys. 18, 31 (1977)]. To our knowledge this has not been rigorously tested with modern gyrokinetic codes. In this work we use the gyrokinetic code GS2 [Kotschenreuther, Comput. Phys. Commun. 88, 128 (1995)] to investigate whether the compressional magnetic field perturbation B is required for accurate gyrokinetic simulations at low Β for microinstabilities commonly found in tokamaks. The kinetic ballooning mode (KBM) demonstrates the principle described by Berk and Dominguez strongly, as does the trapped electron mode, in a less dramatic way. The ion and electron temperature gradient (ETG) driven modes do not typically exhibit this behavior; the effects of B are found to depend on the pressure gradients. The terms which are seen to cancel at long wavelength in KBM calculations can be cumulative in the ion temperature gradient case and increase with e. The effect of B on the ETG instability is shown to depend on the normalized pressure gradient Β′ at constant Β. © 2010 American Institute of Physics.


Frost D.L.,McGill University | Ruel J.-F.,McGill University | Zarei Z.,McGill University | Goroshin S.,McGill University | And 4 more authors.
Journal of Physics: Conference Series | Year: 2014

A coherent jet of particles may be generated by accelerating a conical volume of particles by detonating a layer of explosive lining the outside of the cone. Experiments have been carried out to determine the dependence of the velocity history and coherency of the jet on the particle properties and the ratio of the masses of the particles and explosive. Steel particles form thin, coherent jets, whereas lighter glass particles lead to more diffuse jets. For steel particles, the cone angle had little effect on the coherency of the jet. The efficiency of the conversion of chemical to kinetic energy is explored by comparing the experimental jet velocity with the velocity predicted from a formulation of the Gurney method for a conical geometry. The effect of particle density and cone angle on the jet formation and development was also investigated using a multimaterial hydrocode. The simulations give insight into the extent of the deformation of the particle bed in the early stages of explosive particle dispersal. © Published under licence by IOP Publishing Ltd.


Reynier P.,Ingenierie et Systmes Avances | Bugel M.,Ingenierie et Systmes Avances | Smith A.,Fluid Gravity Engineering Ltd.
International Journal of Aerospace Engineering | Year: 2011

In the frame of future sample return missions to Mars, asteroids, and comets, investigated by the European Space Agency, a review of the actual aerodynamics and aerothermodynamics capabilities in Europe for Mars entry of large vehicles and high-speed Earth reentry of sample return capsule has been undertaken. Additionally, capabilities in Canada and Australia for the assessment of dynamic stability, as well as major facilities for hypersonic flows available in ISC, have been included. This paper provides an overview of European current capabilities for aerothermodynamics and testing of thermal protection systems. This assessment has allowed the identification of the needs in new facilities or upgrade of existing ground tests for covering experimentally Mars entries and Earth high-speed reentries as far as aerodynamics, aerothermodynamics, and thermal protection system testing are concerned. © 2011 Mathilde Bugel et al.


Dunnett J.,Fluid Gravity Engineering Ltd.
Proceedings - 29th International Symposium on Ballistics, BALLISTICS 2016 | Year: 2016

The Holmquist-Johnson-Cook (HJC) concrete model has been implemented in the EDEN hydrocode and applied in studies investigating the normal impacts of simple projectiles against finite thickness concrete barriers. The results of these calculations have been used to investigate how the loading on the projectile and the residual velocity varies as a function of the projectile speed and barrier thickness. Results from the simulations are compared against predictions from cavity-expansion theory based engineering models for projectile penetration, such as those due to Li and Chen, and Forrestal. Special attention is paid to the roles that release waves from the barrier's back surface play in the process and further comparisons are made to investigate how well the extended model of Sjol and Teland is able to account for these effects. An empirically-derived release model is derived and applied to predict penetration data.

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