Alisandro Haouari

and 3 more

In this first mini-project, computational thinking has been used to help us analyze the results in a more rigorous and faster way. Since we did not perform the simulation ourselves, the first step was to understand the parameters at stake to be able to address these 3 requests:Description of the global behaviour of the flow in the tunnelDescription of the effect of the security ventilation system on the global flowAnalysis of whether the security ventilation system assists the evacuation of passengersOnce we had a good understanding of these questions, we have been able to produce a striking image summarizing the global situation.A simple and repeatable method, detailed below, has been applied to produce the image. This method was built with the goal to be applicable for any similar case, even with another post-processing software.1) Select areas of interest and key parameters based on the message we want to transmitIn our case, we chose to focus on the exit path and the area around the train, which are critical to evaluate the passenger safety. The key parameters selected were the temperature, the smoke concentration and the flow itself (velocity, shape, pressure).2) Define the optimal way of visualizing each parameter while ensuring the clarity of the messageKnowing the message we want to convey and the important parameters, we had figure out a way to display them in the image.In ParaView this is made using different filters that you can apply to one or many “block” (vehicle, fluid etc..) :Pressure: ContourTemperature:  SliceFlow: Stream Tracer, Tube and GlyphEtc.Because it was our first project on Paraview, there was also a part of “discovery” in the exercise so we tried methodically a maximum of filters to make sure not to miss a useful one, which would surely have happened if we had tried filters randomly.3) Iterate until the image provides the right information clearly and aesthetically
Figure 1

Manuel Deckart

and 3 more

The considered system consists of an underground train station and the tunnel in which a train is burning at rest, 80 meters from the station entry. The fire, situated in the center of the train acts as heat and smoke source. The station is equipped with a security ventilation system (SVS) which is supposed to guarantee a safe walk from the burning train to the station for any passengers. As a first step, the simulated temperature field has been considered, see Fig \ref{210101}. One can easily identify the heat source in the middle of the train, on the right of the figure.  The asymmetric distribution of the hot air (red) around the train shows that there is a flow away from the station. In order to study the properties of the air flow, streamlines are computed. As seen in Fig \ref{406758}, the flow of the air entering at the station mainly consists of a vortex around the axis of the tunnel. From the vortex, the air is then pushed towards the exits of the tunnels in both directions. Having a look at the velocity and smoke distribution along a slice of the tunnel in front of the train, one sees in Fig \ref{451589} that the smoke concentrated at the roof of the tunnel slows down the air. Note the no-slip condition, which assures that the velocity at the boundaries (tunnel walls) is zero.In Fig \ref{121525} and  \ref{934474} the velocity components orthogonal to the tunnel axis are shown. These components are two orders of magnitude smaller than the X-component. The flow is thus strongly directed parallel to the tunnel.The performance of the SVS, generating the air flow from the station to the exits of the tunnel, is studied by considering the region of the fire in the train. Fig \ref{995338} shows the temperature field in the region of the fire in the train.  It is remarkable that the temperature at the exit of the train, where the fire is, decreases this rapidly when leaving the train along the Z-direction. Once outside the train, passengers can walk to the station along the minus X-direction being exposed to temperatures of only 17°C. Note that the surface of the train is significantly hotter towards the exit of the tunnel. This asymmetry is obviously caused by the SVS.A crucial quantity regarding the safety of the passengers walking to the station is the smoke concentration. Fig \ref{430988} shows how the smoke is kept at the roof of the tunnel. The streamlines and the smoke concentration indicate that in the region  just behind the fire the smoke gets down to mid height of the train, which would still be sufficiently high for passengers to walk below the concentrated smoke. On the other side of the fire, towards the station, the smoke is only present on the roof as it has been shown in Fig \ref{451589}. The SVS is effectively transporting heat and smoke towards the exits of the tunnels. What still needs to be verified is that the air velocity in the tunnel is not too strong, so that it is possible for humans to walk against the air flow. The velocities reaching up to 2.2 m/s are well below the velocity of stronger winds having more than 8 m/s .As a conclusion the SVS is fulfilling its job satisfactory and assures a safe walk from the train to the station, at room temperature, low smoke concentration and sufficiently low air velocities.