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To address the problem of flow aggregation caused by gas phase aggregation in a helical axial gas-liquid pump under high gas void fraction (IGVF≥30%), this study, based on the Euler multiphase flow model and SST k-ω investigates the quantitative correlation between clearance dimensions and performance characteristics as well as internal flow patterns in multiphase pumps operating under varying inlet gas volume fractions. The findings reveal that gas phase aggregation, induced by radial pressure gradients, stemming from the density difference between gas and liquid phases, is the dominant mechanism governing gas accumulation within the flow passages. Implementing the slotted configuration with an optimal gap width coefficient ξ=21.4% resulted in a 3.38% enhancement in multiphase pump efficiency compared to the baseline model, with only a marginal head reduction, achieving significant overall performance optimization. Mechanistic analysis demonstrates that the slotted configuration establishes a fluid dynamic coupling between the pressure and suction surfaces, allows high-momentum flux to transfer from the pressure-side boundary layer, replenishing energy to the low-velocity region on the suction side, thereby effectively suppressing the axial adverse pressure gradient effect.