VPH-Tank
The VPH-Tank project is dedicated to developing a simulation chain to couple thermodynamic and thermomechanical effects during the filling of cryogenic liquid hydrogen tanks. The aim is to assess the structural effects of fuelling at the level of the carbon-fibre-reinforced plastic (CFRP) plies. In addition, optimised refuelling strategies for hydrogen-powered aircraft and rockets are being identified. The project involves Technia (framework), TOPAS (optimisation), the DLR Institute of Space Systems (thermodynamics) and the DLR Institute of Lightweight Structures (thermomechanics).
The project will run from 1 November 2025 to 31 October 2027. The organisations involved are Technia (ECOMAT Bremen), TOPAS Industrial Mathematics, the DLR Institute of Space Systems and the DLR Institute of Lightweight Structures.
The project focuses on developing a simulation chain to assess structural effects during the filling of cryogenic CFRP tanks for hydrogen-powered aircraft and rockets. The research centres on CFRP tanks manufactured using the ‘Automated Fibre Placement’ (AFP) method, which is relatively new for tank production. During filling, the tanks cool down relatively quickly. The CFRP material contracts as a result of the cooling, thereby generating thermomechanical stresses.
At its core, the simulation chain consists of a thermodynamic model and a thermomechanical model, which are coupled together. The thermodynamic model can be used to simulate processes that occur during filling, such as the evaporation and condensation of hydrogen. A key result is the locally discretised heat flux density through the tank wall.
The heat flux serves as an input parameter for the thermomechanical model. Within this model, a temperature distribution at the ply level is calculated based on the heat flux, from which the resulting stress state at the ply level can be derived. As the simulation chain is designed to be transient (time-dependent), stress states are calculated continuously throughout the refuelling process. These stress states enable an optimiser to specifically adjust the mass flow rate during refuelling. A typical objective is to fill the tank as quickly as possible – subject to the constraint that the tank structure does not sustain any long-term damage. This is relevant for optimising the refuelling time between the arrival and departure of a hydrogen-powered aircraft.
The DLR’s contribution lies, on the one hand, in providing the thermomechanical structural model of an AFP-manufactured tank. Preliminary work has already been carried out in this area: a model generator was developed to automatically create structural models of AFP-manufactured tanks. These models are now being adapted and expanded for VPH tanks. A key enhancement involves the capability for transient heat conduction at the ply level.
The DLR is also developing a model for the thermodynamic simulation of fuel tank filling. In doing so, it can draw on extensive experience in the field of cryogenic rocket tanks. Building on this expertise, the project is developing thermodynamic fuelling models specifically for hydrogen aircraft tanks. In addition to its technical responsibilities, the DLR is also in charge of project management.