<p>The volcanology community is systematically testing numerical models for pyroclastic density currents (PDCs) against datasets from that are defined through large-scale experiments. Here, we present the results of a three-dimensional Large Eddy Simulation (LES) mixture model for the case of a partially channel-confined, fully dilute, fully turbulent experimental PDC. Our LES model is based on solving the three-dimensional Navier–Stokes equations using a finite-difference method, the Constrained Interpolation Profile-Combined Unified Procedure (CIP-CUP) scheme. The model results are compared to the experimental dataset and to the results of a previous validation of a one-dimensional depth-averaged model. To better understand the effect of three-dimensionality of the flow and entrainment of ambient air on flow evolution, we contrast two scenarios: (1) a fully channel-confined simulation, limiting lateral entrainment of air; and (2) a partially confined simulation following the setup geometry of the experiment. For the first case, the modelling results are similar to those obtained in the depth-averaged simulation, with a close agreement of the position of the flow front against time but showing a more prominent head shape and body height than the physical experiment. In the second case, the front velocity is slightly overpredicted. However, the front height of the gravity current head, the body thickness, and the vertical velocity profiles closely mimic those measured experimentally. The downstream dilution of the PDCs is significantly enhanced in the partially confined scenario due to the formation of vortexes that laterally spill over the sidewalls, which is also observed in the large-scale experiment.</p>