Applications of different vortex identification methods in cavitation of a self-priming pump

To investigate the internal flow mechanisms during cavitation in self-priming pumps, this study employs numerical simulations based on the RNG k-ε turbulence model coupled with the Schnerr-Sauer cavitation model. The vapor-liquid two-phase flow characteristics at the critical cavitation condition are analyzed under various flow rates and rotational speeds. Based on the vorticity method, Q criterion, λ₂ criterion, Δ criterion, λ_ci criterion, and Ω criterion, predictions and comparative analyses of the vortex structures during cavitation in self-priming pumps have been conducted. Additionally, the energy loss in various regions of the pump before and after cavitation onset has been analyzed using the theory of entropy production. The results demonstrate that the Ω criterion, Q criterion, and λ₂ criterion yield consistent vortex identification outcomes across different regions. In contrast, the Δ criterion and λ_ci criterion produce more fragmented vortices, most notably in the gas-liquid separation chamber area, whereas the vorticity method is most susceptible to disturbances from strong shear layers; Energy losses are not directly related to vorticity but show a significant correlation with vortex intensity; Changes in flow rate and the onset of cavitation have the greatest impact on average entropy production in the reflux hole region, particularly under high flow conditions; The difference in energy loss of the impeller is the largest before and after cavitation occurs; When the cavitation coefficient is constant, the vapor volume fraction in the impeller region exhibits a positive correlation with both flow rate and rotational speed.