The prometheus combustor design system aims to reduce the complexity of evaluating combustor designs by automatically defining preprocessing, simulation, and postprocessing tasks based on the automatic identification of combustor features within the computer-aided design (CAD) environment. This system enables best practice to be codified and topological changes to a combustor's design to be more easily considered within an automated design process. The following paper presents the prometheus combustor design system and its application to the multiobjective isothermal optimization of a combustor prediffuser and the multifidelity isothermal optimization of a fuel injector feed arm in combination with a surrogate modeling strategy accelerated via a high-performance graphical processing unit (GPU).

The following paper presents an overview of the Prometheus design system and its applications to gas turbine combustor design. Unlike a traditional “optimizer-centric” method, Prometheus aims to reduce both the level of workflow complexity and rework by taking a more “geometry-centric” approach to design optimization by shifting the control of script generation away from the optimization program to the computer aided design (CAD) package. Prometheus therefore enables significant geometry changes to be automatically reflected in all subsequent scripts necessary for the analysis of a combustor. Prometheus’ current capabilities include automatic fluid volume generation and aero-thermal and thermo-acoustic network generation as well as automatic mesh and computational fluid dynamics (CFD) script generation.

The persistent release of gas at basaltic volcanoes where there is a low magma eruption rate can be driven by an exchange flow of magma in the conduit, in which gas-rich magma ascends, degasses and crystallises and then sinks back down the conduit. The driving force of the flow is provided by the density difference between the buoyant bubble-rich magma at depth and the dense degassed crystallised magma at shallow levels. In this study we attempt to constrain the physical and chemical processes driving an exchange flow of magma at Stromboli, Aeolian Archipelago, Italy. The model uses a simple, cylindrical geometry. We define degassing and crystallisation paths of the ascending and descending magmas, constrained by gas flux and melt inclusion data given in the literature, to produce a three-phase model of ascending and descending magmas driving persistent gas fluxes. We calculate the viscosity of the three-phase magma using end-member rheological models for bubble and crystal suspensions. Combining our modelled magma properties with analogue exchange flow experiments we can relate the regime of magma flow driving persistent degassing to pressure. At pressures ≲ 90 MPa (≲ 3 km) the viscosity ratio is ≲ 100 and the regime is predicted to be side by side flow with both ascending and descending magmas adjacent to a portion of the conduit wall. At pressures ≳ 90 MPa (≳ 3 km) the viscosity ratio between the ascending and descending magma is ≳ 100 and the flow is predicted to be core annular flow, with the ascending vesiculating magma in the inner core and the more crystalline degassed magma flowing down along the conduit wall. By analogy, we hypothesise that degassed magma would flow down along the walls in dike-like plumbing geometries that have been proposed for the deeper Strombolian system. Analogue experiments suggest that exchange flows do not overturn under conditions of maximum volume flux; we use an empirical relationship to characterise the volume flux of the exchange flow and show that the radius of a cylindrical conduit required to account for the observed persistent gas flux at Stromboli at 0.1 MPa is ~ 1 m.

Strain dilatometers have been operated on the volcanic island of Montserrat (West Indies) for more than a decade and have proven to be a powerful technique to approach short‐term dynamics in the deformational field in response to pressure changes in the magmatic system of the andesitic dome‐building Soufrière Hills Volcano (SHV). We here demonstrate that magmatic activity in each of the different segments of the SHV magmatic system (shallow dyke‐conduit, upper and lower magma chambers) generates a characteristic strain pattern that allows the identification of operating sources in the plumbing system based on a simple scheme of amplitude ratios. We use this method to evaluate strain data from selected Vulcanian explosions and gas emission events that occurred at SHV between 2003 and 2012. Our results show that the events were initiated by a short phase of contraction of either one or both magma chambers and a simultaneous inflation of the shallow feeder system. The initial phase of the events usually lasted only tens to hundreds of seconds before the explosion/gas emission started and the system recovered. The short duration of this process points at rapid transport of fluids rather than magma ascent to generate the pressure changes. We suggest the propagation of tensile hydraulic fractures as viable mechanism to provide a pathway for fluid migration in the magmatic system at the observed time scale. Fluid mobilization was initiated by a sudden destabilization of large pockets of already segregated fluid in the magma chambers. Our study demonstrates that geodetic observables can provide unprecedented insights into complex dynamic processes within a magmatic system commonly assessed by theoretical modeling and petrologic observations.

Columnar jointing in basaltic lava flows on the island of Staffa, NW Scotland, was studied using a combination of field mapping and measurement of column dimensions, sample petrology and measurements of plagioclase crystal size distributions (CSDs) interpreted using theoretical models of cooling. Four different lava flow units were measured, and column ordering was assessed using the hexagonality index and relative standard deviations of column side length, top area and internal angle. Upper and lower colonnades consist of dominantly 5-, 6- and 7-sided columns, with a hexagonality index value very similar to that of Giant’s Causeway and other basaltic columnar jointed localities. CSDs from samples at different heights within one colonnade were used to infer the propagation of the solidus isotherm, which was consistent with a convective cooling mechanism within the colonnade interior. Sample petrology and CSD measurements suggest that entablature can form both by the interaction of propagating joint sets and flooding of the flow surface by water, and the most widely exposed unit on Staffa shows evidence of both mechanisms operating on the same flow. Crystal size distribution measurements can provide a useful tool for field interpretation of lava flow cooling mechanisms.

We present a software application, SolEx, to calculate basaltic melt and coexisting vapour compositions in the system C–O–H–S–Cl. Such a model has great utility in interpreting emitted gas and melt inclusion compositions, especially through the incorporation of sulphur and chlorine, the most commonly measured volcanic gas species. We assume that the behaviour of the fluid phase is controlled by the volumetrically dominant volatile species, H2Oand CO2, whereas sulphur and chlorine partition between the melt and fluid phases. Melt–fluid partition coefficients for S and Cl were parameterised from measurements by Lesne et al. (2011a, p. 1737). The model of Churakov and Gottschalk (2003a, p. 2415) was applied to calculate fugacity coefficients and the equilibrium constants for the reaction imelt→ifluid were thereby deduced. SO2dominates at oxidation states of ΔNNO>0.5 (Jugo et al., 2010, p. 5926), where this model is applicable.In the forward model, total volatile inventories and melt composition are specified by the user. The parameterisation of Dixon (1997, p. 368) is used to predict the partitioning of CO2and H2Obetween vapour and melt phases. An iterative procedure is employed to predict the partitioning of S and Cl components between fluid and melt phases. Melt and gas compositions and gas volume fraction are thereby modelled over pressures in the range 5–4000bar. This approach satisfactorily reproduces independent literature data on S and Cl behaviour in basalt. SolEx is a user-friendly software package available for OS X and Windows, facilitating modelling of closed- and open-system C–O–H–S–Cl degassing in basalts.

We present an experimental study of a buoyancy-driven, low-Reynolds-number (Re < 1) exchange flow of two Newtonian fluids in a vertical cylindrical pipe (length 1 m and diameter 38.4 mm) connecting two fluid reservoirs. The denser, more viscous fluid was golden syrup and the less dense, less viscous fluid was a golden syrup–water solution; the ratio of the viscosities of the two fluids (β) ranged from 2 to 1180. Flows were initiated by removing a bung in the base of the upper reservoir or sliding out a gate positioned at the top, middle or bottom of the pipe. We observe the flows over long time durations (up to 356 h), and define the development of the flow with reference to a non-dimensional time (τ). The initial transient development of the flow was dependent on which of the two fluids initially filled the pipe, but this did not systematically affect the flow regime observed at τ ≫ 1. Two distinct flow regimes were observed: axisymmetric core-annular flow (CAF), in which the less viscous fluid occupies a cylindrical core and the denser fluid flows downwards in an annulus, and side-by-side (SBS) flow where both fluids are in contact with the pipe and there is a single interface between them. CAF formed at β ≥ 75 and SBS flow at β ≤ 117. In several experiments, for 5 ≤ β ≤ 59, a slowly developing transitional SBS (TSBS) flow was observed where SBS flow and CAF occurred simultaneously with SBS in the lower portion of the pipe; SBS existed throughout most of the pipe and in one case grew with time to entirely fill the pipe. Velocity profiles determined by tracking tracer particles show that the observed CAFs are adequately described by the formulation of Huppert & Hallworth (J. Fluid Mech., vol. 578, 2007, pp. 95–112). Experimental SBS velocity profiles are not well produced by the formulation of Kerswell (J. Fluid Mech., 10.1017/jfm.2011.190), possibly because the latter is restricted to flows whose cross-section has an interface of constant curvature. Despite the variations in flow regime, volume fluxes can be described by a power-law function of β, Q1 = 0.059 β−0.74. A comparison of experimental data with the theoretical approaches of Huppert Hallworth (2007) and Kerswell (2011) indicates that fluids are not arranged in the regime that maximises volume flux (e.g. SBS or CAF), nor do they adopt the geometry that maximises volume flux within that particular regime.

Magma degassing processes are commonly elucidated by studies of melt inclusions in erupted phenocrysts and measurements of gas discharge at volcanic vents, allied to experimentally constrained models of volatile solubility. Here we develop an alternative experimental approach aimed at directly simulating decompression-driven, closed-system degassing of basaltic magma in equilibrium with an H-C-O-S-Cl fluid under oxidized conditions (f(O2) of 1 center dot 0-2 center dot 4 log units above the Ni-NiO buffer). Synthetic experimental starting materials were based on basaltic magmas erupted at the persistently degassing volcanoes of Stromboli (Italy) and Masaya (Nicaragua) with an initial volatile inventory matched to the most undegassed melt inclusions from each volcano. Experiments were run at 25-400 MPa under super-liquidus conditions (1150 degrees C). Run product glasses and starting materials were analysed by electron microprobe, secondary ion mass spectrometry, Fourier transform infrared spectroscopy, Karl-Fischer titration, Fe2+/Fe3+ colorimetry and CS analyser. The composition of the exsolved vapour in each run was determined by mass balance. Our results show that H2O/CO2 ratios increase systematically with decreasing pressure, whereas CO2/S ratios attain a maximum at pressures of 100-300 MPa. S is preferentially released over Cl at low pressures, leading to a sharp increase in vapour S/Cl ratios and a sharp drop in the S/Cl ratios of glasses. This accords with published measurements of volatile concentrations in melt inclusion and groundmass glasses at Stromboli (and Etna). Experiments with different S abundances show that the H2O and CO2 contents of the melt at fluid saturation are not affected. The CO2 solubility in experiments using both sets of starting materials is well matched to calculated solubilities using published models. Models consistently overestimate H2O solubilities for the Stromboli-like composition, leading to calculated vapour compositions that are more CO2-rich and calculated degassing trajectories that are more strongly curved than observed in experiments. The difference is less acute for the Masaya-like composition, emphasizing the important compositional dependence of solubility and melt-vapour partitioning. Our novel experimental method can be readily extended to other bulk compositions.

Magmas progressively exsolve volatiles as they ascend towards the Earth's surface, such that their volatile content is a function of pressure. Water and carbon dioxide concentrations measured in melt inclusions from degassing volcanoes rarely coincide with modelled degassing trends. I show that observed melt inclusion trends can be reproduced through mixing of magmas, either during convection within the volcanic conduit, or within a subterranean magma reservoir. No fluxing gas phase or post-entrapment loss of water need be invoked. A permeable network allowing gas transport is still required to avoid fragmentation of magma at shallow depths.

Gas loss from ascending magma controls the chemical and physical evolution of volcanic systems. Melt inclusions trapped in volcanic phenocrysts contain snapshots of volatile evolution, but are notoriously hard to interpret in terms of conventional degassing models because gas fluxing, diffusive re-equilibration and external sources can also contribute to the volatile budget. Here we supplement published melt inclusion volatile data from a wide range of volcanoes with new ion-microprobe data on H2O, CO2, Be, B, Li and Sc in melt inclusions from the 1980–1986 eruptions of Mount St. Helens. The new and published data demonstrate that suites of melt inclusions are typically displaced to higher CO2 contents than would be predicted from calculated open or closed-system degassing trends. We reconcile all CO2–H2O data into a coherent framework based on the ratio of gas to melt during eruption. Interaction of shallow-stored magmas with vapours released from deeper in the magma system displaces melts to CO2-rich compositions. Our observations require that arc magmas are significantly more CO2-rich than is estimated from melt inclusions alone because of the low probability of trapping high CO2 melts during magma ascent. We illustrate this process with calculations in the model system albite–H2O–CO2.

The Boiling Lake of Dominica has exhibited stable high‐temperature behavior for at least 150 a. This stability is punctuated by occasional crises involving rapid filling and draining of the lake and changes in water temperature. The most recent such crisis occurred in December 2004 to April 2005. Using the results of previous theoretical and experimental work on analogue models, we present a combined thermal, hydrological, and fluid mechanical model of the Boiling Lake. This reveals that the lake appears to be suspended above the local water table by a constant supply of rising steam bubbles sourced from the boiling of groundwater near an igneous intrusion. The bubbles condense in the Boiling Lake, maintaining the temperature at ∼90°C. The geometry of the lake‐conduit system provides a mechanism for instability, with a denser liquid lake overlying a bubbly fractured permeable conduit. Following a sufficiently large perturbation, the whole lake rapidly drains until the surface is at the local water table level. The persistent gas supply then reinitiates filling. We propose that local seismic activity may have caused shock nucleation of bubbles within the conduit and triggered the instability of the Boiling Lake.