Physics

Impeller

Mechanics

Vortex

Dissipation

Enstrophy

Turbulence

Vorticity

Turbine

Flow (mathematics)

Draft tube

Thermodynamics

Journal of Hydrodynamics

Hydraulic loss and vorticity are two most common methods in analyzing the flow characteristics in hydro-machine, i.e., centrifugal pump, Francis turbine, etc. While the relationship and correlation between hydraulic loss and vortex evolution are not uncovered yet. In this study, hydraulic loss is regarded as the combination of dissipation effect and transportation effect in flow domains. Meanwhile, vorticity ω can be decomposed into two parts, namely the Liutex part ωR, the shear part ωs, of which ωR is regarded as the third-generation vortex identification method for its precise and rigorous definition of local rigid rotation part of fluid. Based on the dimensional analysis, two new physical quantities related to vorticity (ω, ωR and ωS), namely enstrophy Ω, vorticity transport intensity T are adopted to express the energy characteristic in vortex evolution process. Finally, operating points at pump mode of an ultra-high head reversible pump-turbine are selected as the research object and the numerical results calculated using SST k-ω turbulence model are consistent well with the experimental data. Pearson correlation coefficient is adopted to evaluate the correlation between hydraulic loss and vortex evolution in main flow regions. Results show that apart from the spiral casing domain, the enstrophy of shear part Ωs has very strong correlation with dissipation effect and Liutex transport intensity TR has stronger correlation with transportation effect when compared with other forms of vorticity. The correlation between Liutex transport intensity TR and transportation effect is strong in stay/guide vanes (SGVs) while reduce to medium level in runner and draft tube domains. In spiral casing domain, all forms of vorticity show weak or very weak correlation with transportation effect. Based on the proposed method, we believe that the relationship and correlation between hydraulic loss and vortex evolution in other hydraulic machineries can also be clearly investigated.

Investigation on the relationship between hydraulic loss and vortex evolution in pump mode of a pump-turbine