Hypersonic flight is expected to be achieved with dual-mode-Ramjet (Ramjet under Mach 6 and Scramjet beyond) because of its high specific impulse and its capability to be reusable (especially interesting for space transportation)1, but one of the main issues at these flight conditions is the thermal management of the engine and the vehicle. Different cooling strategies have been evaluated by MBDA-France (calculations, material tests). Metallic panels have been tested as CMC composite ones (C/SiC for instance)2, which seem to be promising. But even CMC materials could not withstand such large heat loads (for example, total temperature of external air reaches 2000 K at Mach 7 and combustion add more energy as the inner part of the engine cannot be radiatively cooled). Consequently an active cooling system has to be used but not a dedicated one because it would increase the vehicle weight. Furthermore, another issue occurs under theses flight conditions. The time allocated to mix the injected fuel with inlet air, to ignite the combustion and to complete it before the chamber outlet is about 1 ms. These two points lead to the so-called "regenerative cooling" solution : using the fuel to cool down the engine's wall and then burning it in the engine. The fuel is injected in a composite channel (which surrounds the engine) near the outlet of the combustion chamber, it flows to the injection on the opposite way of the burned gases. For "moderate" hypersonic flight Mach numbers (below Mach 8), a heavy hydrocarbon fuel is often chosen here because of its high density compared to cryogenic fuels (800 kg.m-3 instead of 70/80 kg.m-3 for cryogenic hydrogen, with a specific impulse of liquid hydrocarbon halved)3. When heated and pyrolysed, it produces lighter hydrocarbons species that are considered as more energetic and easier to ignite. This point allows responding to rapid phenomenon in the combustion chamber.

Time-series analyses were used to investigate the relationships between barometric pressure changes, earth tides, and water-level fluctuations in a confined aquifer. The method was applied to data from the fractured aquifer at the Hydrogeological Experimental Site in Poitiers (France) and used to yield estimates of the aquifer’s storage capacity, porosity and barometric efficiency. The aim is to address relevance of these analyses for an aquifer showing both fracture draining and confined karstic flow in thin strata. Cross-correlation and spectral analysis are used to compare water-level head and atmospheric-pressure fluctuations. Porosity and storage capacity are calculated using this method and compared to results from petrophysical measurements and hydraulic pumping tests, respectively. The storage coefficients calculated by the time-series analyses are in agreement with those obtained by interpretation of the interference pumping tests. Conversely, porosity values calculated by time-series analyses are underestimated compared to those obtained by other methods.

Hydraulic interference pumping tests are widely used for identifying mid-to large-scale aquifer hydraulic parameters. Fractured reservoirs often behave as fractal media for which classical interpretations may fail because of the decrease in permeability and fracture porosity (or, equivalently, transmissivity and storage capacity) with the pumping time and the extent over which the pumping stress has propagated. A solution to hydraulic interference tests in fractal media is developed in dimensional variables, which allows for a very rapid and unique fitting to data. Hydraulic parameters, their scale exponents and the fractal dimension of the medium can be determined for each pressure draw-down curve without any prior information or other calculation. The method is applied to a large series of tests completed on the calcareous fractured aquifer of the experimental site in Poitiers (France). Even though data of pressure draw-downs are various and show a fractal behavior, permeability seems to rapidly homogenize for distances of 100–200m. On the other hand, the fracture porosity shows a much progressive decrease with distance and homogenization is reached for scales beyond 300–500m. It is also shown that the classical Cooper–Jacob interpretation of pressure draw-downs may yield artifacts in the identification of permeability and fracture porosity. Orders of magnitude are comparable to that from fractal interpretation but their evolution with respect to time or distance (scaling laws) may strongly differ.

The Time Domain Random Walk (TDRW) method has been recently developed by Delay and Bodin [Delay, F. and Bodin, J., 2001. Time domain random walk method to simulate transport by advection–dispersion and matrix diffusion in fracture networks. Geophys. Res. Lett., 28(21): 4051–4054.] and Bodin et al. [Bodin, J., Porel, G. and Delay, F., 2003c. Simulation of solute transport in discrete fracture networks using the time domain random walk method. Earth Planet. Sci. Lett., 6566: 1–8.] for simulating solute transport in discrete fracture networks. It is assumed that the fracture network can reasonably be represented by a network of interconnected one-dimensional pipes (i.e. flow channels). Processes accounted for are: (1) advection and hydrodynamic dispersion in the channels, (2) matrix diffusion, (3) diffusion into stagnant zones within the fracture planes, (4) sorption reactions onto the fracture walls and in the matrix, (5) linear decay, and (6) mass sharing at fracture intersections. The TDRW method is handy and very efficient in terms of computation costs since it allows for the one-step calculation of the particle residence time in each bond of the network. This method has been programmed in C++, and efforts have been made to develop an efficient and user-friendly software, called SOLFRAC. This program is freely downloadable at the URL http://labo.univ-poitiers.fr/hydrasa/intranet/telechargement.htm. It calculates solute transport into 2D pipe networks, while considering different types of injections and different concepts of local dispersion within each flow channel. Post-simulation analyses are also available, such as the mean velocity or the macroscopic dispersion at the scale of the entire network. The program may be used to evaluate how a given transport mechanism influences the macroscopic transport behaviour of fracture networks. It may also be used, as is the case, e.g., with analytical solutions, to interpret laboratory or field tracer test experiments performed in single fractures.