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