Multiphase Flow Modelling Project

José Moral, EcosimPro/PROOSIS

The ESPSS (European Space Propulsion System Simulation) library that has been developed and validated for ESA by EAI in collaboration with other industrial and R&D centers and university partners, constitutes a shared and standard software for performing analysis and simulation of space propulsion systems, including chemical and electrical propulsion cycles, ground support equipment & operations, and ground/qualification tests.

To explore and develop new ESPSS’s capabilities ESA has recently launched the project “Multiphase Flow Modeling” where Empresarios Agrupados will lead the project in collaboration with ONERA, Von Karman Institute (VKI), Roma Sapienza University and KopooS as subcontractors. The project aims to enhance the ESPSS libraries, which will be extended to improve the simulation of solid and hybrid propulsion engines and the coupling of propulsion systems with vehicle dynamics. Furthermore the robustness and accuracy of the 1D fluid simulation will be improved by implementing new discretization methods and updating the existing ones allowing for multi-species aspects, and extending the physical formulation for two-phase and multi-component flow.

Simulation of New Advanced Propulsion Systems

Satellite manufacturers are presently evaluating hybrid chemical propulsion as an alternative thrust unit for the GEO transfer, between the usual chemical propulsion (bi-liquid) and the new trend of electrical propulsion (ACS-engine). This hybrid chemical propulsion is in line with the CleanSpace objectives, i.e. use of green propellants, and has a simpler design compared to the bi-liquid engine, still allowing for re-ignitability within a wide operational range and having a throttling capability. It guarantees shorter transfer time and reduced cost of operations compared to the all-electrical propulsion.


The development of these technologies require fast and accurate simulation tools. Therefore, the extension of the fluid/solid properties database, the development of analytical correlations for the 1D simulation of the heat and mass exchange between the grain and the fluid, as well as the grain regression will be needed.

Coupled Simulation of the Propulsion System and Vehicle Dynamics

In order to evaluate the performances of the propulsion system being designed under different operating conditions along the mission, or under failure modes, the coupling of the propulsion system dynamics with the motion of the vehicle is needed.

A first prototype of the SATELLITE library, for the coupled simulation of the propulsion system and the integration trajectory and attitude motion of the space vehicle  has been already developed, showing the capability of the tool for such kind of simulations. In this workpackage, it is proposed to extend and validate this version of the library to allow different scenarios (ascent, re-entry, Earth orbit, solar orbit, etc..) and different levels of perturbation accuracy, from Keplerian orbits to medium accuracy orbit propagation, allowing the ESPSS-user a fast evaluation of the modelled propulsion system linked to the motion of the spacecraft.

Advanced Numerical Schemes for Robustness Improvement

In the current formulation of the ESPSS libraries, two different methods were used for the discretization of the 1D partial derivative equations; a centered scheme and the Roe scheme (the user can select which method to use for the simulation). The Roe splitting has been commonly accepted as one of the most accurate techniques available today. It is less dissipative than the centered scheme and then is preferable in some applications, however the related drawback is represented by an increase in the computational cost. Additionally, the Roe scheme cannot be extended with new physical effects or equations without changing the entire structure of the scheme itself. Since one of the points of the ESPSS libraries is their flexibility to be extended for the simulation of new propulsion concepts, these drawbacks of the Roe scheme becomes quite important. The present activity will explore different approaches to improve the robustness and efficiency of the simulations with ESPSS while reducing the risk of wrong model input/options.

Extension of Two-Phase Physical Formulation

The formulation used so far in the libraries is based on the homogenous equilibrium hypothesis, where the liquid, vapour and non-condensable gas coexist at the same temperature and pressure in each node. Recently, a new formulation has been proposed, where different temperatures for each phase of the fluid are considered. In the present activity it is proposed to extend this new formulation taking into account the different flow regimes (annular flow, bubble flow, slug flow, etc) in the formulation of the library, as well as the validation of the new formulation with test cases