Title Procjena triplet kovarijanci turbulencije za buru Title (english) Evaluation of turbulent triplet covariances for bora flows Author Barbara Malečić Mentor Željko Večenaj (mentor)Committee member Željko Večenaj (predsjednik povjerenstva)Committee member Branko Grisogono (član povjerenstva)Committee member Ivica Sović (član povjerenstva)Committee member Maja Telišman Prtenjak (član povjerenstva)Committee member Josip Stipčević (član povjerenstva)Granter University of Zagreb Defense date and country 2019-03-01, Croatia Scientific / art field, NATURAL SCIENCES Abstract Bura je jak, relativno hladan i mahovit vjetar koji najčešće puše iz sjeveroistočnog kvadranta na istočnoj obali Jadranskog mora. U ovom radu analizirane su, po prvi puta, triplet kovarijance turbulencije bure.
Korišteni podaci su s mjernog tornja na Pometenom brdu u zaleđu Splita. Od travnja 2010. do lipnja 2011. godine mjerene su tri komponente brzine vjetra te sonična temperatura. Mjerenja su vršena na tri visine, 10, 22 i 40 m, frekvencijom uzorkovanja od 5 Hz. Tijekom promatranog razdoblja izdvojeno je 60 epizoda bure.
Glavni cilj ovog rada je analiza članova prognostičke jednadžbe za varijance turbulencije. Pritom je određena viskozna disipacija na dva načina: (i) standardnom inercijskom metodom (ɛIDM), i po prvi put (ii) izravnom metodom iz prognostičkih jednadžbi za varijance tubulencije (ɛEQ). Izravna metoda pokazala se uspješnom u smislu da može reproducirati oblik krivulje viskozne disipacije, ali su vrijednosti dobijene izravnom metodom za nekoliko redova veličine manje. Nadalje, dobijena je linearna veza između ɛIDMi i ɛEQ. Uz pomoć rezultata dobijenih izravnom metodom procijenjena je viskozna disipacija u longitudinalnom, transverzalnom i vertikalnom smjeru strujanja. Pokazalo se da viskozna disipacija najveći utjecaj ima upravo u longitudinalnom smjeru puhanja bure.
Glavni fokus ovog rada je na članu turbulentnog transporta koji sadrži triplet kovarijancu. Utvrđeno je da je turbulentni transport značajan po intenzitetu za buru. On može poprimiti i pozitivne i negativne vrijednosti. Na višim nivoima on je najčešće negativan, dok je na nižim pozitivan. Odnosno, turbulentni transport na višim nivoima najčešće odvodi turbulentnu varijancu te je dovodi na niže nivoe. To je ujedno i jedan od glavnih zaključaka ovog rada i doprinosi spoznaji zašto je bura tako poseban, svjetski poznat vjetar.
Abstract (english) Bora is a strong, relatively cold, gusty wind that usually blows from the northeastern quadrant on the east coast of the Adriatic Sea. In this study turbulence triplet covariances were analyzed, for the first time, for bora flows.
The measurements used were obtained from the measuring tower on Pometeno brdo, in the hinterland of Split, Croatia. From April 2010 until June 2011 three components of wind speed and sonic temperature were measured. The measurements were performed on three heights, 10, 22 and 40 m above the ground with the sampling frequency of 5 Hz. During the observed period, total of 60 bora episodes were isolated.
The main objective of this study is to analyze terms in prognostic equations for turbulence variances. In that respect the viscous dissipation term was calculated using two methods: (i) inertial dissipation method (ɛIDM), and for the first time (ii) direct by the prognostic equations for variances of turbulence (ɛEQ). It has been determined that direct method can successfully reproduce the shape of the curve, but the values were for several orders of magnitudes smaller. Further, linear relationship between ɛIDM and ɛEQ was obtained. Using the results for viscous dissipation in longitudinal, transversal and vertical direction was determined. It has been shown that viscous dissipation has the greatest impact in bora’s longitudinal direction.
The main focus is on the turbulent transport term, in other words, the triplet covariance term. It has been found that turbulent transport is significant for intensity for bora flows. Furthermore, turbulent transport can be both positive and negative. It is mostly negative at the upper levels and positive at the lower levels. Therefore, turbulent transport, in most cases, takes away turbulent variance from the upper levels and brings it down to the lower ones. This is one of the main findings of this study; it adds to the understanding of peculiarities of bora wind.
Keywords
triplet kovarijanca turbulencije
bura
turbulentni trasnport
viskozna disipacija
Keywords (english)
turbulence triplet covariance
bora
turbulent transport
viscous dissipation
Language croatian URN:NBN urn:nbn:hr:217:537269 Study programme Title: Graduate university study pf Physics - Geophysics; specializations in: Seismology and Physics of the Earth's Interior, Meteorology and Physical Oceanography Type of resource Text File origin Born digital Access conditions Open access Terms of use Created on 2019-03-06 12:25:10
