ECN Spray C injector simulation: Internal flow with complete needle motion

The complete needle motion, including both opening and closing phases, is modelled with a robust mesh-to-mesh topology change strategy employing spherical linear interpolation (SLERP) using OpenFOAM. The Schnerr–Sauer mass-transfer model is utilised and validated to simulate phase change. Two representative fuels, n-dodecane and iso-octane, are investigated to assess the physical property impact on void fraction dynamics, vortex formation, and flow separation. Furthermore, the influence of turbulence modelling is evaluated for both fuels by comparing Reynolds averaged Navier–Stokes (RANS) and large-eddy simulation (LES) approaches under identical operating conditions in capturing transient flow features, including phase change phenomena. The simulation results are validated against previously conducted X-ray and CT measurements. Results show that (a) complete needle motion in OpenFOAM is feasible but requires topology-aware numerics; (b) resolving full opening/closing is necessary to reproduce transient in-nozzle structures; (c) while LES is resolving cavitation strings and near-wall unsteadiness, RANS provides comparable accuracy in predicted void fraction trends, making it a more computationally efficient choice for the present validation metrics; (d) a reduced liquid–vapour formulation demonstrates good agreement with experimental measurements while avoiding the additional modelling overhead of explicitly resolving ambient and non-condensable gases (NCGs), though the resulting void fraction must be interpreted as an effective quantity. Fuel effects are consistent with thermodynamics: n-dodecane exhibits stronger hydraulic flip, while iso-octane sustains a thicker cavitation core.