Numerical evaluation of aerodynamic performances of vertical-axis wind turbine rotor with flow concentrator

Abstract

With wind energy extraction constantly increasing, the interest in small-scale urban wind turbines is also expanding. Given that these machines often work in adverse operating conditions (Earth’s boundary layer, vortex trails of surrounding objects, small and changeable wind speeds), additional elements that locally augment wind velocity and facilitate turbine start may be installed. This paper investigates possible benefits of adding an optimized flow concentrator to a vertical-axis wind turbine (VAWT) rotor. Three-dimensional, unsteady, turbulent, incompressible flow simulations of both isolated rotor consisting of three straight blades and a rotor with flow concentrator have been performed in ANSYS FLUENT by finite volume method for several different operational regimes. This type of flow simulations is challenging since flow angles are high, numerous flow phenomena and instabilities are present and the interaction between the blades and detached vortices can be significant. The rotational motion of the blades is solved by the unsteady Sliding Mesh (SM) approach. Flow field is modeled by Unsteady Reynolds Averaged Navier-Stokes (URANS) equations with k-ω SST turbulence model used for closure. Both quantitative and qualitative examinations of the obtained numerical results are presented. In particular, the two computed power coefficient curves are compared and the advantages of installing a flow concentrator are accentuated.

Usled stalnog porasta iskorišćenja energije vetra, interesovanje za male vetroturbine za urbane sredine se takođe širi. Kako ovakve mašine često funkcionišu u nepovoljnim radnim uslovima (Zemljinom graničnom sloju, vrtložnom tragu okolnih objekata, pri maloj i promenljivoj brzini vetra), moguće je instalirati dodatne elemente čija uloga je da lokalno povećaju brzinu kroz rotor i olakšaju pokretanje vetroturbine. Ovaj rad istražuje prednosti dodavanja optimizovanog koncentratora struje vazduha rotoru vetroturbine sa vertikalnom osom obrtanja. Prostorne, nestacionarne simulacije turbulentnog, nestišljivog opstrujavanja izolovanog rotora koji sadrži tri prave lopatice kao i rotora sa koncentratorom izvedene su u softverskom paketu ANSYS FLUENT metodom konačnih zapremina za nekoliko različitih radnih režima. Ova vrsta proračuna je izazovna jer su napadni uglovi visoki, javljaju se brojni strujni fenomeni i nestabilnosti dok interakcija između lopatica i odvojenih vrtloga može biti značajna.Obrtno kretanje lopatica rešeno je pristupom klizajućih mreža. Strujno polje modelovano je nestacionarnim Navije-Stoksovim jednačinama osrednjenim Rejnoldsovom statistikom (URANS) koje su zatvorene k-ω SST turbulentnim modelom. Prikazane su i kvantitativne i kvalitativne analize dobijenih numeričkih rezultata. Naročito je izvršeno poređenje dve krive koeficijenta snage i naglašene su prednosti instaliranja koncentratora struje vazduha.