NUMERICAL STUDIES ON THE NATURAL SMOKE VENTING OF ATRIA

K e y w o r d s : FDS; Natural venting; Atrium. 4/2019 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 135 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 4/2019 d o i : 1 0 . 2 1 3 0 7 / A C E E 2 0 1 9 0 5 9 K . Ż y d e k , M . K r ó l 136 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 4/2019 program, particularly commonly used in these circumstances is FDS (Fire Dynamics Simulator) [4]. The use of CFD programs always raises doubts about the reliability of the results obtained. When making calculations using the CFD program, many choices must be made. Among other things, it is necessary to decide on the choice of boundary conditions, the choice of turbulence model or the choice of the size of the calculation grid. All these parameters have an impact on the quality of the results obtained. To reduce or even eliminate the uncertainty of the results obtained, there are many works aimed at the validation and verification of the FDS program [5–13]. The numerical analysis of a smoke removal system involves testing the influence of the factors which disturb the system’s efficiency. The wind influence is considered above all [14–16]. Although FDS has undergone many validation analyzes, after building a new building model it is beneficial to subject it to validation based on real measurements. The paper presents numerical analyzes made using the FDS program. The aim of the analysis was to match the numerical model to the results obtained in the real atrium building. For the validation of the numerical model, the results of the temperature distribution in the atrium located in Murcia, Spain were used. The atrium is in the laboratory of Technological Metal Centre. Many studies were carried out in the atrium and all of them were widely described [17–21]. High compliance of the temperature distribution was obtained at selected points in the numerical model compared to tests in the real object. The least compliance occurs in the vicinity of the fire source. 2. DESCRIPTION OF THE NUMERICAL TESTS 2.1. Numerical model of the atrium To build the appropriate numerical model of the atrium, research presented by Gutierrez-Montes was used [21]. Fire test simulations were carried out using a program Fire Dynamics Simulator (FDS). FDS numerically solves equations describing the phenomena of heat flow and transport in space where fire occurs. Using the FDS program the model of the atrium was built. The model of the atrium consists of a prismatic structure of 19.5 19.5 17.5 m and a pyramidal roof raised 4.5 m at the centre. Total dimensions are 19.5 19.5 22 m. The numerical model of the atrium was the same as the real atrium described by Gutierrez-Montes [21]. In the model, the natural ventilation was designed. There are four square exhaust vents on the roof, each of the dimensions of 0.5 m. There are also four open vents at the lower parts of the walls. Two on the wall A and two on the wall C. Each vent has dimensions of 4.75 2.25 m. The model with its dimensions is shown in Fig. 1. Figure 1. Layout and main dimensions of the model N U M E R I C A L S T U D I E S O N T H E N A T U R A L S M O K E V E N T I N G O F A T R I A E N V I R O N M E N T 4 /2019 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 137 The pyramidal roof of the atrium was designed using nine steps. Each step was 0.5 m high. The construction of the roof is shown in Fig. 2. The roof and walls were modelled as 6 mm thick steel with a density of 7800 kg/m3, specific heat of 0.46 kJ/kg K and conductivity of 45 W/K m. The floor was modelled as concrete with density of 1860 kg/m3, specific heat of 0.78 kJ/kg K and conductivity of 0.72 W/K m. In the model of the atrium, square (1 1 m) pool fire was designed. The fire source was located in the centre of the atrium floor. The burning fuel in combustion process was heptane. Three different cases of the fire test simulation have been conducted. Each of 2.3 MW heat release rate fire. In all three cases, the same ambient conditions of the weather were adopted. The ambient air temperature of 16°C, pressure of 997 mbar and humidity of 49%. The default division of solid angles has been used. Other parameters have been left as the default values. In the simulations, the ongoing 900 seconds fire was investigated. 2.2. Computational domain The computational domain includes the atrium space, the roof, the walls and additional space around the model of the atrium. In this paper, three cases of fire simulation are shown. Each case consists of different mesh sizes and different positions of the atrium model in the computational domain. In each case, different dimensions of the mesh cells were used. To achieve optimal simulation accuracy, mesh cells that are approximately the same size in all three directions were used. Table 1. shows the meshes used. In case 1 and 2 regular meshes were used. In these two cases, the main differences are dimensions of the mesh cells and the location of the model in the computational domain. In the first case, mesh with main dimensions of 25 25 25 m was used, while in the second case the main dimension of the mesh was 22 22 24 m. In the first case, the mesh had a dimension of the cell 0.25 m in each direction and in the second case that dimension was 0.2 m. Fig. 3 shows the position of the model in case 1. The model was Table 1. Summary of the three considered cases. Case Heat release rate Burning time Dimensions of the computational domain Dimensions of the mesh cells Number of cells in each direction