Title Razvoj matematičkog modela za ocjenu toplinske ugodnosti u spojenom mlazu Title (english) Development of the mathematical model for evaluation of the thermal comfort in the merged jet Author Darko Smoljan Mentor Igor Balen (mentor)Committee member Zdravko Virag (predsjednik povjerenstva)Committee member Igor Balen (član povjerenstva)Committee member Davor Zvizdić (član povjerenstva)Committee member Miroslav Ruševljan (član povjerenstva)Committee member Bernard Franković (član povjerenstva)Granter University of Zagreb Defense date and country 2011-09-28, Croatia Scientific / art field, TECHNICAL SCIENCES Universal decimal classificationUDC ) 53 - Physics Abstract Spojeni mlaz je fenomen turbulentnog strujanja koji u sustavima ventilacije nastaje meñusobnom interakcijom dvaju nasuprotnih zračnih mlazova iz susjednih istrujnih otvora te mu je, iako predstavlja važan čimbenik toplinske ugodnosti u zoni boravka, u dosadašnjim istraživanjima u ventilaciji posvećeno vrlo malo pozornosti. Cilj istraživanja je temeljem teorije samosličnosti strujanja u razvijenoj zoni turbulentnog mlaza razviti bezdimenzijski matematički model koji bi omogućio procjenu brzine i intenziteta turbulencije zraka kao veličina o kojima ovisi osjećaj propuha u zoni spojenog mlaza, a koji bi u primjeni bio znatno jeftiniji i jednostavniji od složenih CFD proračuna koji još uvijek ne daju pouzdane rezultate kod ovakvih strujanja. Razvoj modela temelji se na eksperimentalnim mjerenjima brzine i intenziteta turbulencije CTA anemometrom te na teorijskoj analizi strujanja uz primjenu analitičkih i jednostavnih numeričkih metoda. Obzirom na oskudna istraživanja vrtložnog ventilacijskog difuzora za proizvodnju mlaza, odabran je vrtložni radijalni stropni difuzor. Mjerenja su vršena u zoni izotermnog priljubljenog stropnog radijalnog mlaza i u zoni izotermnog spojenog mlaza koji nastaje interakcijom te koji se takoñer, na temelju dokaza drugih autora, smatra radijalnim mlazom te se opisuje modelom strujanja slobodnog radijalnog mlaza usmjerenog prema zoni boravka. \Nalaženje rješenja osrednjenog strujanja radijalnog mlaza, kao unaprjeñenje dosadašnjih rješenja, temelji se na pretpostavci o razdiobi brzine u glavnom smjeru strujanja u obliku Gaussove funkcije, te uzimajući u obzir da turbulentna viskoznost u zoni mlaza nije konstantna. S obzirom da eksperimentalni rezultati govore da spojeni mlaz ima više nego dvostruko veći koeficijent širenja od klasičnog radijalnog mlaza, provedena je analiza primjenjivosti Prandtlovih pretpostavki graničnog sloja te su rješenja osrednjenog strujanja donesena uz primjenu i bez primjene pojednostavljenja graničnog sloja. Uz primjenu ovih pretpostavki došlo se do analitičkog rješenja za razdiobu turbulentne viskoznosti, srednje brzine i turbulentnog naprezanja dok je bez primjene ovih pretpostavki bilo potrebno primijeniti jednostavne numeričke metode. Kinetička energija turbulencije odnosno intenzitet turbulencije dobiven je numeričkim rješenjem transportne jednadžbe kinetičke energije turbulencije pri čemu su, kao modeli turbulencije, korištena rješenja \Navier-Stokesove jednadžbe odnosno turbulentne viskoznosti dobivene uz i bez primjene pretpostavki graničnog sloja. Usporedba razvijenog modela s eksperimentalnim rezultatima govori o dobrom slaganju rezultata srednje brzine, turbulentnog naprezanja i kinetičke energije turbulencije u usporedbi s rezultatima klasičnog mlaza drugih autora. Slaganje teorijskog modela s eksperimentalnim rezultatima intenziteta turbulencije u spojenom mlazu je bolje u slučaju bez primjene pretpostavki graničnog sloja nego u slučaju primjene ovih pretpostavki.
Abstract (english) Merged jet is a turbulent flow phenomenon which is formed by interaction of two opposed air jets from adjacent ventilation diffusers. Regarding its significant influence on thermal comfort conditions in occupied spaces it received very little attention in former studies. The research in this work aims at developing non-dimensional mathematical model for the assessment of air velocity and turbulence intensity as the parameters of sensation of draught in merged jet. This model is intended to be cheaper and simpler than more complex CFD calculations that still do not provide good results for this kind of flow. Development of the model is based on CTA (constant temperature anemometry) measurements of velocity (speed) and turbulence intensity and on theoretical analysis of the flow using analytical and simple numerical methods. Regarding limited research on vortex diffusers found in literature ceiling vortex ventilation diffuser is used for the production of the jet. Measurements are performed in the zone of isothermal attached ceiling radial jet and in the zone of isothermal merged jet that is formed by the interaction of ceiling jets. Merged jet is considered to be a free radial jet flowing towards the occupied zone. Integral solution for the mean flow profiles of the turbulent radial jet, as the improvement of former solutions, is found with the assumption of Gaussian functional form for the streamwise velocity distribution and the assumption of non-constant turbulent viscosity distribution in the zone of the jet. As the experimental data shows that coefficient of spread for the merged jet is more than twice higher than the coefficient for the classical free radial jet the analysis of applicability of Prandtl shear flow approximations is performed and solutions of the mean flow were derived with and without these approximations. Using these approximations enables derivation of algebraic equations for turbulent viscosity, mean velocity and turbulent shear stress. Solutions without these approximations are numerical and demand use of simple numerical methods. Turbulence kinetic energy and turbulence intensity are obtained by numerical solution of transport equation for turbulent kinetic energy by using solutions of Navier-Stokes equation, that are turbulence viscosity solutions with and without shear flow approximations, as the turbulence models. Agreement of mean velocity, turbulent shear stress and turbulent kinetic energy data of the developed theoretical model with the experimental data of classical jet found in literature is good. Agreement of the developed theoretical model with experimental data for mean velocity of the merged jet is good and agreement with experimental data for turbulence intensity is better in the case of not using approximations of shear flow than in the case of using them.
Keywords
turbulentni radijalni mlaz
spojeni mlaz
stropni vrtložni difuzor
turbulentna viskoznost
Keywords (english)
turbulent radial jet
merged jet
ceiling vortex diffuser
turbulent viscosity
air velocity
Language croatian URN:NBN urn:nbn:hr:235:992373 Study programme Title: Mechanical Engineering and Naval Architecture Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2020-05-15 18:05:15
