Eksperimentalno modeliranje udara bure na cestovna vozila

The Bora is a very strong and gusty downslope wind that blows from the northeast across the coastal mountain ranges on the eastern coast of the Adriatic Sea. It creates substantial difficulties for engineering infrastructure, traffic, and life in general. While the effects of the quasi-steady turbulent atmospheric boundary layer flow on road vehicles are currently fairly well known, the Bora wind also creates unsteady aerodynamic loads on these vehicles, which are still not fully understood. These gust effects on road vehicles have thus been experimentally examined here. This study was conducted on a small-scale road vehicle model, which to our knowledge is the first study of this type. Particular emphasis was placed on the aerodynamic forces and moments experienced by the road vehicle related to the strength and frequency of the Bora wind gusts, the vertical wind incidence angle, and the vehicle position on the bridge. In the experiments regarding the wind gust strength and frequency, the road vehicle model was placed in the upwind traffic lane at zero horizontal and vertical flow incidence angles. The effect of the vertical wind incidence angle and vehicle position was analyzed for the road vehicle model placed in the upwind, middle, and downwind traffic lanes of the bridge-deck section model, where the horizontal flow incidence angle was zero, while the vertical flow incidence angle was studied from 0° to 50°. The experiments were carried out in the Transient Flow Field Simulator of the NatHaz Modeling Laboratory at the University of Notre Dame, USA. The results reveal some important findings. Regarding the wind gust strength and frequency experiments, the aerodynamic loads rose linearly with increasing gust strength and were concurrently affected by vortex shedding and wind gusting phenomena. The steady aerodynamic loads were generally higher for a road vehicle closer to the upwind edge of the bridge decks. The wind gusting of the Bora can cause difficulties for the maneuvering of road vehicles and for their stability in the upwind traffic lane, while the risk for road vehicles in the downwind traffic lanes was predominantly a consequence of the impinging shed vortices unique to bridge architecture and the aerodynamic form of vehicles.Bura je vrlo jak i mahovit zavjetrinski vjetar koji puše iz smjera sjeveroistoka preko obalnih planinskih lanaca na istočnoj obali Jadranskog mora. Pričinjava značajne poteškoće za inženjersku infrastrukturu, promet i život općenito. Dok su učinci kvazistacionarnog turbulentnog atmosferskog graničnog sloja na cestovna vozila trenutno prilično poznati, bura stvara nestacionarna aerodinamička opterećenja na vozila, koja još uvijek nisu u potpunosti shvaćena. Stoga su utjecaji udara bure na cestovna vozila eksperimentalno ispitani. Istraživanje je provedeno na modelu cestovnog vozila, što je prema našim saznanjima prva analiza ove vrste. Poseban je naglasak na aerodinamičnim silama i momentima vozila ovisno o jačini i učestalosti udara bure, kutu nastrujavanja vjetra i položaju vozila na mostu. U eksperimentima koji se odnose na jačinu i frekvenciju udara bure, model vozila je postavljen u prometnu traku neposredno uz naletni rub sekcije mosta, pri čemu su horizontalni i vertikalni kutovi nastrujavanja jednaki nuli. Utjecaj vertikalnog kuta nastrujavanja i položaja vozila je analiziran za model vozila postavljen uz vjetar, niz vjetar i u srednjoj prometnoj traci. Pritom je horizontalni kut nastrujavanja jednak nuli, dok je utjecaj vertikalnog kuta nastrujavanja proučavan od 0° do 50°. Eksperimenti su provedeni u simulatoru polja nestacionarnog strujanja zraka u sklopu NatHaz laboratorija Sveučilišta Notre Dame u SAD-u. Rezultati su otkrili neka važna saznanja. S obzirom na jačinu i frekvenciju udara bure, aerodinamička opterećenja se linearno povećavaju s povećanjem jačine udara bure i na njih istodobno utječu pojave odvajanja vrtloga od sekcije mosta i udara vjetra. Osrednjena aerodinamička opterećenja su općenito veća kod vozila smještenih bliže naletnom bridu sekcije mosta. Udari bure mogu stvoriti poteškoće kod upravljanja vozilom i njegovom stabilnosti u prometnom traku uz naletni brid sekcije mosta, dok je rizik za vozila u drugim prometnim trakama uglavnom posljedica odvajanja vrtloga od naletnog ruba sekcije mosta, što je karakteristično za aerodinamičke oblike mosta i vozila

An alternative approach to experimental simulation of wind characteristics in urban environments

AbstractThe classical Counihan vortex generators for wind-tunnel simulations of the atmospheric boundary layer (ABL) flow were redesigned to experimentally simulate natural wind characteristics in urban environments. Three redesigned (truncated) vortex generators, a castellated barrier wall and a fetch of roughness elements were employed to reproduce a lower portion of the neutrally stratified ABL developing above an urban type terrain. A hot-wire anemometry system was used to measure mean velocity and velocity fluctuations. Investigated parameters were mean velocity, turbulence intensity, integral length scale of turbulence, and power spectral density of velocity fluctuations. Experimental results indicate that the truncated vortex generators developed for this study can be successfully employed in urban ABL part-depth wind-tunnel simulations, as they compare well with commonly applied empirical models and wind specifications for urban type terrain given in the ESDU 74031 data sheets

Modeliranje atmosferskog graničnog sloja u zračnom tunelu

Tema rada je modeliranje atmosferskog graničnog sloja unaprijed određenih karakteristika u zračnom tunelu. Modelirani granični sloj odgovara graničnom sloju u atmosferi, koji nastaje uslijed strujanja zraka iznad predgrađa s niskim obiteljskim kućama. U radu je prikazan princip nastajanja atmosferskog graničnog sloja, prikaz njegove strukture i zakonitosti kojih se treba pridržavati prilikom modeliranja u zračnom tunelu. Ispitivanja su izvršena u zračnom tunelu C Katedre za Mehaniku fluida Tehničkog Sveučilišta u Miinchenu. Atmosferski granični sloj je u zračnom tunelu modeliran prema Counihanovoj metodi, uz korištenje barijere, generatora vrtloga i podne hrapavosti. Istražen je utjecaj promjene visine barijere, visine ispupčenja na barijeri, te visine i gustoće razdiobe podne hrapavosti na strukturu generiranog graničnog sloja, kao i promjene strukture graničnog sloja u uzdužnom i poprečnom smjeru, te u odnosu na pojedinačne elemente podne hrapavosti i generatore vrtloga. Također je ispitan i utjecaj nagiba stropa mjerne sekcije na profil statičkog tlaka uzduž mjerne sekcije pri različitim konfiguracijama podne hrapavosti. Istraživanja potvrđuju mogućnost modeliranja atmosferskog graničnog sloja u zračnom tunelu i predstavljaju dobar temelj za buduća istraživanja

Utjecaj mjerila na strukturu modeliranog atmosferskog graničnog sloja

Eksperimentalno je istražen utjecaj mjerila na strukturu modeliranog atmosferskog graničnog sloja i promjene strukture strujanja u određenom mjerilu za različite modele atmosferskog graničnog sloja. U zračnom tunelu su Counihanovom metodom generirani modeli atmosferskog graničnog sloja karakterizirani eksponentom zakona potencije 0.17, 0.21 i 0.35 u mjerilima 1:500, 1:333 i 1:250. Razmatrane su vrijednosti najvažnijih parametara koji definiraju strukturu strujanja: osrednjene vrijednosti brzine, intenziteti turbulencije, tangencijalno Reynoldsovo naprezanje, integralna duljinska mjera turbulencije i spektar turbulentnih pulzacija. Potvrđena je osnovna hipoteza rada da mjerilo simulacije ima utjecaja na strukturu modela atmosferskog graničnog sloja. U gornjem dijelu graničnog sloja s povećanjem mjerila dolazi do smanjenja osrednjenih vrijednosti brzine zbog utjecaja sekundarnog graničnog sloja, a intenzitet turbulencije brže opada s povećanjem visine. Iznosi Reynoldsovog naprezanja u gornjem dijelu modela atmosferskog graničnog sloja se smanjuju s povećanjem mjerila. U donjem dijelu graničnog sloja razlike vremenski osrednjenih struktura strujanja u različitim mjerilima su relativno male. Vrijednosti intenziteta turbulencije i Reynoldsovog naprezanja su veće u mjerilu u kojem je postignuta veća hrapavost podloge. Integralna duljinska mjera turbulencije se na određenoj visini unutar graničnog sloja povećava sa smanjenjem mjerila. Razlike u profilima spektara energije turbulentnih pulzacija uslijed promjene mjerila se mogu zanemariti

Advances in Gas Flow Measurement using Weighing Method

The transfer gas flow standard ROMBACH NB2 was calibrated in the Zagreb Gasworks using two different balances incorporated into the basic calibration system. The basic difference between these balances was in their resolution, i.e. 1 g for the SARTORIUS IS64FG and 0,1 g for the SARTORIUS LA64001. Before measurements with the SARTORIUS IS64FG balance, absolute pressure sensors HBM P3MBA were calibrated using the digital barometer VAISALA PTB 220. The deadweight tester PRESSUREMENTS 6100-1L was employed for HBM P3MBA calibration before tests with the SARTORIUS LA64001 balance. In all tests, experiments were carried out for flow rates from 0,02 m3/s to 1,4 m3/s. Experimental results compare well with experiments previously performed in the Baden-Württemberg Office of Legal Metrology, Germany. The spread of obtained experimental values was within 0,25% for the total range of flow rates. The measurement repeatability was within 0,1%. The highest contributions to measurement uncertainty result from the air temperature and humidity in the tested gas flow meter and in the container. The measurement uncertainty in tests with the SARTORIUS LA64001 was smaller than in tests with the SARTORIUS IS64FG. Total measurement uncertainty was reduced when absolute pressure sensors HBM P3MBA were calibrated using the deadweight tester PRESSUREMENTS 6100-1L compared to results obtained with the VAISALA PTB 220 digital barometer

Utjecaj hrapavosti terena na dimenzije recirkulacijske zone vjetra nizvodno od zgrade

A computational model has been developed to determine wind characteristics in the wake of a rectangular building and validated against previous field-test results. Dimensions of the recirculation zone behind the building have been determined using the Reynolds-Averaged-Navier-Stokes (RANS) equations for two different wind incidence angles, i.e. for wind normal to the longer building side and for wind normal to the shorter building side. Obtained results show a decrease in the recirculation zone length for rougher terrains. Therefore, numerical results presented in this paper proved to be in good agreement with full-scale results indicating that the approach taken in this study can be successfully applied in calculating dimensions of recirculation zone in the wake of a rectangular building for various terrain types.U radu je postavljen model računalne simulacije strujanja vjetra oko zgrade pravokutnog presjeka s ciljem određivanja dimenzije zone recirkulacije iza zgrade u ovisnosti o hrapavosti terena na kojem se zgrada nalazi. Proračun je proveden računalnim paketom Fluent 6.2, a temelji se na rješavanju osrednjenih Navier-Stokesovih jednadžbi uz primjenu k-ε modela turbulencije, i to za dva različita kuta nastrujavanja vjetra na zgradu, tj. strujanje okomito na kraću i okomito na dulju stranicu zgrade. Određivanje dimenzije zone recirkulacije je provedeno za tri različite hrapavosti terena, pri čemu su karakteristike hrapavosti terena i strujanja vjetra u prirodi preuzete iz međunarodnog ESDU 85020 standarda. Postavljeni računalni model je validiran usporedbom s rezultatima mjerenja u prirodi za jedan tip hrapavosti terena. Dobiveni rezultati ukazuju na smanjenje duljine zone recirkulacije s povećanjem hrapavosti terena, pri čemu je postignuta zadovoljavajuća sličnost s rezultatima mjerenja u prirodi

The effect of parked wind turbines on wind flow and turbulence over a complex terrain

AbstractWind‐tunnel experiments were performed to study the wind characteristics on a parked wind turbine downwind of three types of hill and over a flat terrain. The focus of the study is on comparing wind characteristics on (a) a wind turbine standing alone and (b) this same type of wind turbine embedded in a wind farm. Particular emphasis is placed on the hill size and shape and the distance between the hill and the wind farm. The hill and wind‐farm models were subjected to an atmospheric boundary layer simulation to create realistic atmospheric conditions. Flow and turbulence were analyzed based on the measured mean flow velocity, Reynolds shear stress, turbulence intensity, and the power spectral density of velocity fluctuations. The experimental results reveal similar trends concerning (a) the wind characteristics obtained on a parked wind turbine embedded in a wind farm downwind of hills of various sizes and shapes and (b) the wind characteristics on this same type of parked wind turbine standing alone in the same position downwind of the same hills. In particular, the discrepancies in the mean flow velocity and turbulence intensity between these test cases are mostly below 5%, thus indicating that a complex terrain clearly has a dominant effect on the wind characteristics, while the effects of parked wind turbines on the wind characteristics are negligible. This important finding indicates that the structural loading of parked wind turbines situated on a complex terrain may be well calculated using the same procedures both for wind turbines standing alone and wind turbines embedded in wind farms if they are both placed at the same distance downwind of the same hills

Utjecaj hrapavosti terena na dimenzije recirkulacijske zone vjetra nizvodno od zgrade

A computational model has been developed to determine wind characteristics in the wake of a rectangular building and validated against previous field-test results. Dimensions of the recirculation zone behind the building have been determined using the Reynolds-Averaged-Navier-Stokes (RANS) equations for two different wind incidence angles, i.e. for wind normal to the longer building side and for wind normal to the shorter building side. Obtained results show a decrease in the recirculation zone length for rougher terrains. Therefore, numerical results presented in this paper proved to be in good agreement with full-scale results indicating that the approach taken in this study can be successfully applied in calculating dimensions of recirculation zone in the wake of a rectangular building for various terrain types.U radu je postavljen model računalne simulacije strujanja vjetra oko zgrade pravokutnog presjeka s ciljem određivanja dimenzije zone recirkulacije iza zgrade u ovisnosti o hrapavosti terena na kojem se zgrada nalazi. Proračun je proveden računalnim paketom Fluent 6.2, a temelji se na rješavanju osrednjenih Navier-Stokesovih jednadžbi uz primjenu k-ε modela turbulencije, i to za dva različita kuta nastrujavanja vjetra na zgradu, tj. strujanje okomito na kraću i okomito na dulju stranicu zgrade. Određivanje dimenzije zone recirkulacije je provedeno za tri različite hrapavosti terena, pri čemu su karakteristike hrapavosti terena i strujanja vjetra u prirodi preuzete iz međunarodnog ESDU 85020 standarda. Postavljeni računalni model je validiran usporedbom s rezultatima mjerenja u prirodi za jedan tip hrapavosti terena. Dobiveni rezultati ukazuju na smanjenje duljine zone recirkulacije s povećanjem hrapavosti terena, pri čemu je postignuta zadovoljavajuća sličnost s rezultatima mjerenja u prirodi