Influence of invert channel height and floor slope on the hydraulic performance of manholes

Urban flooding is an increasingly frequent and disruptive phenomenon, often driven by stormwater infrastructure exceeding its design capacity. Manholes’ hydraulic performance remains poorly characterised. This study numerically investigates the influence of guided channels height and lateral floor slope, on the hydraulic performance. An open-source CFD framework was adopted, combining Salome for geometry and meshing, OpenFOAM for flow simulation, and ParaView for post-processing. Model validation against 1:6-scale laboratory experiment data showed good agreement, with velocity field comparisons yielding NRMSE ≈20% normalised by the peak velocity, and r2 > 0.89. Four manhole geometries were evaluated by combining two guided channel heights (half-section and full-section) with two floor-slope configurations and testing them under three flow-regime heights. Results indicate that full-section guides and sloped floors significantly reduce head loss (by up to 49%) and suppress turbulence near the outlet. The study was further extended to assess the effect of pipe curvature. Sharper angles led to increased flow distortion, recirculation, and energy dissipation, with head loss coefficients rising by up to 179%.