Unresolved lattice Boltzmann method-discrete bubble method coupling for turbulent cavitating flow in injector nozzles

The Euler–Lagrange method is an effective approach for simulating multiphase bubble flows, as it provides detailed bubble information. Many previous studies have used the computational fluid dynamics–discrete bubble model (CFD-DBM) for this purpose. Traditional CFD-based solvers often face limitations in parallel scalability and computational efficiency, particularly when dealing with transient cavitation dynamics. To address these challenges, an advanced lattice Boltzmann method–discrete bubble method (LBM-DBM) approach is proposed in this study for simulating liquid–bubble multiphase flows. The standard lattice Boltzmann equation is extended with mass and momentum source terms to recover the volume-averaged Navier–Stokes equations for unresolved simulations and is coupled with the DBM to capture complex bubble behaviors, including nucleation, growth, breakup, and coalescence. The proposed model is validated on cavitating flows in a fuel injector nozzle, where predictions of velocity fields and cavitation cloud shedding are compared with available experimental observations. The simulated outlet velocity matches the experiments across different inlet pressures, with relative errors typically <0.1%. The validation results demonstrate that the LBM-DBM framework achieves high accuracy in reproducing key cavitation features. Furthermore, transient simulations inside the nozzle are performed to investigate cavitation periodicity (characteristic period T ≈ 0.283 ms), the spatial distribution of cavitation regions, bubble velocity distributions, and the dynamic processes of bubble coalescence and breakup. These findings highlight the potential of the proposed method as a reliable and efficient tool for studying complex cavitating flows in engineering applications.