Section: Application Domains

Multiphase flows with mass transfer

Another domain of application is the simuation of multiphase flows. Here, the system (1 ) need to be supplemented by at least a PDE describing the phase volume changes, and the equation of states of the phases. The system is in most case written in a non-conservative form, so that additional difficulties need to be handled.

Multiphase fows occur in many applications: for petroleum industry, nuclear industry (accident management), engines, pipes, etc.

An adding difficulty is given by the presence of mass transfer between the phases. Cavitation consists in a local pressure drop below the vapor pressure at the liquid temperature, thus creating a phase change and vapor bubbles formation. Their collapse in high-pressure region can dramatically lead to failure, erosion and other undesirable effects. For this reason, there is a strong effort devoted to develop predictive numerical tools for cavitating flows in industrial applications. Unfortunately, an accurate description of interactions between the vapour and liquid phases requires accurate physical models and a way to take into account the dynamics of the interface. Moreover, multiscale effects, turbulence and thermodynamics should be also considered. Cavitation models are typically dependent on two types of parameters: first, on some physical parameters, such as for example the number of bubbles, that is not usually well measured; secondly, on some empiric parameters, useful for fitting and calibration procedures with respect to the experimental data. Therefore, model parameters represent an important source of uncertainty. Moreover, it is not an easy task to well define boundary and initial conditions, because of difficulties encountered in order to control accurately experiments in cavitating flows. As a result, conditions imposed for the setting of a numerical simulation, are affected by a dramatic randomness.

We performed a systematic study for considering the probabilistic properties of the input parameters permitting to capture non-linearities in uncertainty propagation. Moreover, the DEM method has been modified to take into account exotic phenomena with real-gas effects.