Influence of Thermal Boundary Conditions in a Numerical Simulation of a Small-Scale Tunnel Fire

 

Mirko Kozić

 

The influence of different thermal boundary conditions, i.e. adiabatic and constant wall temperature is examined using the CFD simulation of a small-scale tunnel fire. The obtained temperature profiles along the vertical line in the plane of symmetry at three stations along the tunnel are compared with available experimental and numerical ones. Simple volumetric heat sources are used in modeling combustion due to little effect of different combustion models on the region of temperature field that is not too close to the fire source. In cases of natural convection and forced convection with low ventilation velocity, the turbulent flow of heated air and smoke is primarily affected by the buoyant force caused by changes in volume which are connected with the temperature gradient. The numerical results show that different thermal boundary conditions give considerable differences in temperature distribution in the tunnel, affecting the intensity of the buoyant force that influences the velocity field and the smoke spreading region. This fact must be taken into account in a fire simulation inside a real traffic tunnel, because the wall heat transfer coefficients may not be fully known.

Key words: fluid dynamics, numerical simulation, fire, tunnel, boundary conditions, thermal conditions.