Establishment of the Function for the Stiffness in a Special Model GRAL Dealing with Air Pollution Dispersion from Roadway Tunnel Portals

摘要

There is an urgent need in models dealing with the dispersion of pollutants from roadway tunnel portals, since the air quality around portals is getting worse. In this paper, a specialized model called as GRAL (Grazer Lagrangian model) has been studied. During the use of GRAL, proper values for an important intermediate parameter called as stiffness has to be decided after pilot calculations, since there is still no definitive expression for it. To simplify this process and popularize this model, an expression is tried to be established. At first, through comparing the calculated and observed NO2 concentrations at a national air quality monitoring site under different combinations of stiffness, the one of 90.5% in non-head winds plus 20% in head winds for a studied tunnel jet flow has been selected finally. And then a semi-empirical piecewise function of the stiffness has been derived on the basis of these pilot calculations.