In this paper we argue that the predominant flat rate billing in conjunction with the practice of overbooking and its associated mismatch between actual costs and billed posts results in a substantial misalignment between the interests of providers and customers that stands in the way of trustworthy and sustainable cloud computing. On these grounds, we propose a hybrid IaaS pricing model that aims to avoid these problems in a non-technical fashion by shifting to consumption based billing on top of credible minimum performance.

FEARLESS (Fluid mEchanics with Adaptively Refined Large Eddy SimulationS) is a new numerical scheme arising from the combined use of subgrid scale (SGS) model for turbulence at the unresolved length scales and adaptive mesh refinement (AMR) for resolving the large scales. This tool is especially suitable for the study of turbulent flows in strongly clumped media. In this contribution, the main features of FEARLESS are briefly outlined. We then summarize the main results of FEARLESS cosmological simulations of galaxy cluster evolution. In clusters, the production of turbulence is closely correlated with merger events; for minor mergers, we find that turbulent dissipation affects the cluster energy budget only locally. The level of entropy in the cluster core is enhanced in FEARLESS simulations, in accord with a better modeling of the unresolved flow, and with its feedback on the resolved mixing in the ICM.

We present a numerical scheme for modeling unresolved turbulence in cosmological adaptive mesh refinement codes. As a first application, we study the evolution of turbulence in the intracluster medium (ICM) and in the core of a galaxy cluster. Simulations with and without subgrid scale (SGS) model are compared in detail. Since the flow in the ICM is subsonic, the global turbulent energy contribution at the unresolved length scales is smaller than 1% of the internal energy. We find that the production of turbulence is closely correlated with merger events occurring in the cluster environment, and its dissipation locally affects the cluster energy budget. Because of this additional source of dissipation, the core temperature is larger and the density is smaller in the presence of SGS turbulence than in the standard adiabatic run, resulting in a higher entropy core value.

In the context of explosion models for Type Ia Supernovae, we present one- and two-dimensional simulations of fully resolved detonation fronts in degenerate C+O White Dwarf matter including clumps of previously burned material. The ability of detonations to survive the passage through sheets of nuclear ashes is tested as a function of the width and composition of the ash region. We show that detonation fronts are quenched by microscopically thin obstacles with little sensitivity to the exact ash composition. Front-tracking models for detonations in macroscopic explosion simulations need to include this effect in order to predict the amount of unburned material in delayed detonation scenarios.