On the simultaneous 3-D measurements of turbulent velocity and vorticity vectors by hot-wire probes

Abstract

Flow measurement tests of HVAC installations and their elements, with dominant presence of turbulent flows characterized by fluctuations of velocity and vorticity fields, mainly assume measurements of time-averaged velocity fields of applied fluids. These classical methods enabled significant advancing the modern HVAC technique. However, further development in this area, primarily relating to increased efficiency, environment protection, noise control etc., especially in non-stationary conditions, demands a detailed insight in the turbulence structure, among others. This can be achieved by applying the contemporary methods of turbulence modeling, as well as the measuring methods based on laser-Doppler and hot-wire anemometer. In the paper are presented the latest sophisticated techniques that have become operationally available in the previous decade, specified for simultaneous 3-D measurements of turbulent velocity, velocity gradients and vorticity vector fields by the probes containing 9 or 12 sensors within the measuring volumes of about 2.2 mm in diameter. Fundamental role of vorticity and importance of researching its dynamics are also explained.

Strujno-tehnička ispitivanja instalacija KGH i njihovih elemenata, u kojima dominiraju turbulentna strujanja karakterisana fluktuacijama brzine i vrtložnosti fluida, uglavnom obuhvataju merenja vremenski osrednjenih polja brzine radnih fluida. Ove klasične merne metode su tehniku KGH dovele na zavidan nivo. Ipak, dalji razvoj ove oblasti, prvenstveno sa gledišta poboljšanja efikasnosti sistema KGH, očuvanja okoline, kontrole buke itd., posebno u izrazito nestacionarnim režimima rada, pored ostalog zahteva i detaljan uvid u strukturu odgovarajućih strujnih procesa. To je moguće postići primenom savremenih metoda matematičkog modeliranja turbulencije sa jedne i mernih metoda zasnovanih na primeni laserskog i anemometra sa zagrejanim vlaknima, sa druge strane. U radu su prikazane najsavremenije tehnike mehanike fluida, koje su postale operativne tek u prošloj deceniji, namenjene preciznom simultanom 3-D merenju trenutnih vrednosti fluktuacija brzine, njenih gradijenata i vrtložnosti fluida pomoću minijaturnih sondi sa 9 i 12 zagrejanih vlakana smeštenih u mernoj zapremini prečnika oko 2,2 mm. Objašnjena je i uloga vrtložnosti i značaj istraživanja njene dinamike.