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

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,vorticityωcan be decomposed into two parts,namely the Liutex partω_(R),the shear partωs,of whichω_(R)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,ω_(R)andωS),namely enstrophyΩ,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-ωturbulence 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 partΩs 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.

Entropy production by dissipation effects and characteristic vortex evolution in a rocket turbopump

The relationship between entropy production and vortex evolution affects the efficiency and stability of rotating machinery.This study investigated the energy characteristics of a rocket turbopump and revealed the correlated mechanisms of the entropy production rate using the dissipation effects and characteristic vortex evolution.For the first time,direct and turbulent dissipation and rigid and shear vorticity decomposition methods were utilized to analyze the correlation between flow loss and characteristic vorticities in rotating machinery.With an increase in the flow rate,the hydraulic losses of the dissipation effects and wall decreased by 60%and 38.3%,respectively,and the proportions of the input energy decreased(from 13%to 8%)and remained stable(8%),respectively.The local direct dissipative entropy production(DDEP)in the inducer-impeller is strongly related to shear entropy,and the correlated effect of total enstrophy on DDEP is weaker than that of shear vorticity,indicating that rigid enstrophy suppresses direct dissipation.The correlation between turbulent dissipation and rigid enstrophy was significantly weaker in the static flow passage of the turbopump owing to the weak rigid rotational effect.The correlation between the rigid entropy and local turbulent dissipative entropy production(TDEP)gradually increased with increasing flow rate,reaching a medium correlation(the maximal correlated degree in the turbopump)and exhibiting rigid rotation effects on the hydraulic loss.Moreover,the flow rate significantly affected the correlation(except for the diffuser),and the two characteristic vorticities reached a maximum at the designed flow rate owing to optimal efficiency and minimum hydraulic loss.