Assessment of transient flow behavior and sensitivity analysis in the Al-Hashimiyah water treatment pipeline system using an integrated method of characteristics

Sensitivity Analysis of Hydraulic Parameters on Contaminant Intrusion in Transient Conditions

Interdependence of Hydraulic Parameters in Transient Induced Contaminant Intrusion in a Pipeline

Numerical risk mitigation and modeling of pump sump system failures

ABSTRACT A three-dimensional CFD (Computational Fluid Dynamics) study was performed to evaluate the hydraulic performance of an existing flood‑protection pump sump designed for a discharge of 16.48 m3/s. The study aimed to assess flow uniformity at bell-mouth suction, quantify swirl angles, and identify subsurface vortex formation under operating conditions. A novel trident-shaped splitter combined with dividing walls is proposed to mitigate vortex-induced instabilities. The Reynolds-Averaged Navier–Stokes (RANS) equations combined with the realizable k–ε turbulence model and VOF (Volume of Fluid) approach were solved using STAR-CCM+. Results indicate that vortex intensity and flow separation observed in the original design are significantly reduced with the proposed modifications. Quantitative analysis shows swirl angles below 1.6°, well within Hydraulic Institute limits (5°). Mesh‑independence and pressure‑distribution analysis confirm improved hydraulic stability and reduced risk of mechanical damage.

Numerical Study of Culvert–Weir Operating Modes Under Steady and Unsteady Hydrographs: Stage Response, Regime Transition and Ventilation State

Culverts are widely used to provide crossings over small rivers and can strongly influence flood hydraulics by controlling upstream water levels. During high flows, insufficient conveyance may cause pressurization and overtopping, with important implications for flood hazard assessment. Although computational fluid dynamics (CFD) is increasingly applied to investigate these complex hydraulic processes, systematic evaluations of its performance remain limited. This study addresses this gap by validating a three-dimensional CFD model against previously published laboratory experiments for culvert-only, weir-only and combined culvert–weir configurations under both steady (rising and receding discharge sequences) and unsteady flow conditions. Beyond benchmark validation, diagnostic analyses examined inlet region mesh resolution, inflow ramp history and turbulence closure, together with the associated outlet ventilation and attachment mechanisms. The model reproduced upstream water levels with mean absolute relative error (MARE) values ranging from 0.90% to 5.42% and captured the main stage–discharge relationships across the tested configurations. However, the experimentally observed transition from partially full to pressurized flow in the combined culvert–weir configuration was not reproduced consistently. The diagnostic analyses showed that inlet resolution influences entrance losses and post-submergence headwater, inflow history alters outlet attachment and ventilation and turbulence closure affects barrel filling and air-pocket morphology. The results indicate that CFD can reproduce water level and overtopping responses well when carefully configured, while regime transition prediction remains more uncertain because of its sensitivity to ventilation and discharge history effects.

Numerical investigation for evaluating seepage and stability of zoned embankment dam

Investigation of Hydraulic Instability During the Transient Process from Synchronous Condenser Pumping Mode to Pumping Mode

The transition process from synchronous condenser pump (SCP) mode to pumping mode determines the response rapidity of the startup procedure and operational stability of pump-turbines; however, the complex gas–liquid interaction and transient hydraulic characteristics during this process remain insufficiently understood. To address this, this study develops a numerical framework for the SCP-to-pumping transition process, incorporating the full-passage system, a multiscale mesh strategy for coupling mainstream and clearance flow regions, and a gas–liquid two-phase flow model based on the Volume of Fluid (VOF) method. The reliability of the numerical model is verified through comparison with model experiments, demonstrating good agreement between simulations and experimental data. Based on the validated model, the transient evolution of hydraulic forces, pressure pulsations, and internal flow structures is systematically analyzed. Axial force analysis reveals a significant internal equilibrium; the crown bears a maximum instantaneous fluctuation of approximately 2800 kN. Conversely, the radial force is primarily dominated by blade hydraulic thrust (1294 kN), showing distinct anisotropic behavior. The runner blade channels and the upper draft tube region are identified as critical areas with intense pressure fluctuations, with peak-to-peak pressure amplitudes reaching 45~48 m and 54 m head, respectively. Furthermore, reducing the duration of the exhaust process constitutes the main strategy for accelerating the transition and mitigating prolonged high-amplitude force and pressure fluctuations. The findings provide new insights into the transient hydraulic mechanisms of SCP-to-pumping transitions and offer guidance for optimizing transition control strategies in pumped-storage units.