The forces applied on a wing depend partly on its angle of attack. The goal of this report was to analyze the drag and lift coefficients of a NACA 2412 airfoil for various angles of attack. To get a diversity of results, three methods were used : experimental with a wind tunnel, theoretical with XFOIL code and numerical with ANSYS Fluent, where various models of the RANS turbulence-viscosity models are used and compared. The results obtained by each methods are compared, with the aim to understand the reasons behind the differences. An improvement proposition concludes this report.
Global behavior of the flow in the tunnel Globally, the flow goes from left to right (from the train station towards the tunnel where the train is located). The pressure is the highest on the side of the train station and decreases along the tunnel. This observation is consistent with the direction of the flow, the pressure gradient along the tunnel is indeed pushing the air and the smoke away from the train station (high pressure point). In terms of velocity, the main component is the x-component, the flow being close to a unidirectional flow in the main section of the tunnel. However, around the train station and the train itself, the changes in geometry alter the flow and the magnitudes of the y and z components are of the same order as the magnitude of the x component. At the front of the train, there is a sharp increase for the x-velocity as the cross flow area is reduced by the presence of the train. In order to respect the principle of mass conservation, the velocity needs to increase. The smoke stems from the middle of the train and this is logically where the largest concentration of smoke is to be found. It is mainly concentrated at the top of the tunnel as it tends to rise. The smoke is flowing in the right direction, pushed by the air flow. Nevertheless, there is a small amount of smoke that can be found in front of the train. These conclusions for the smoke concentration field hold as well for the temperature field as they are very similar. Effect of the security ventilation system on the global flowThe purpose of the security ventilation system is to move the smoke and heat in the opposite direction of the train station and therefore creating a security area. The ventilation creates a high pressure zone, which makes the air moving in the tunnel. The airflow only propagates laminar in one direction, towards the fire. In the opposite direction there is a turbulent(?) flow, this may indicate that it is blocked. The blocking creates an even higher pressure. The velocity of the airflow in the train station is next to zero. As the airflow leaves the station the velocity increases and become constant in the rest of the tunnel, except around the train and at the exit of the station, where the velocity is increased due to differences in area. Due to the constant velocity it may seem like the model has not taken friction into consideration. Another possibly it that the model is too small to see the difference along the tunnel. Analysis of the effect of the security ventilation system on the evacuation of passengersIn order to assist the evacuation of passengers, the security ventilation system needs to slow down the progression of the smoke and to contain it in a restricted area near the fire. Indeed, once the passengers are out of the train, they need to rejoin a safety place as soon as possible. By blowing some fresh air at the train station, it guarantees to maintain a safety zone there, where the passengers could gather while waiting for the security orders. Moreover, as the smoke stays mainly at the top of the tunnel, the passengers, once they are off the train, can easily rejoin the train station without being asphyxiated. To improve this security ventilation system, we could imagine some exhaust pipes in the tunnel to remove, as soon as possible the smoke present in the tunnel, in order to ease the evacuation of the train and possibly let the emergency services act in good conditions without risking their lives.
When humans have to cope with a problem, they often handle the problem by several tasks, in a more or less random way. The goal of the computational thinking concept is to help people to solve large ranges of problems, by setting systematical methods. These methods have to be numerical inspired, such that the problem can be solved by computers. Decomposition, pattern recognition, abstraction and algorithms design are the base concepts of computational thinking.In our case, to produce a picture, we use a lot the principle of decomposition. Using Paraview was a new experience for all of us, so we proceed step by step into producing the final image. First discovering the software's environment and the basic numerical model. Then in a second step we deal with streamlines generation and featuring, to make it larger, to change colors and to choose the number of streamlines that we want to generate. Then the next step was to rebuild all the train's environment, such as the train, the tunnel or the station, and to set appropriate colors to show the different key elements in this situation. It was important to make the situation clear for those will see the picture, and to make them understand the behavior of the flow represented by streamlines. The last step was to highlight the presence of smoke in the shuttle, what is the main danger for passengers. Finally, we set some text to complete information. Thus producing the picture by a step-by-step method, by focusing on each challenge separately ,help us to progress faster Pattern recognition was also useful to understand the software behavior. For many different items (fields, geometries, streamlines), the individual treatment procedures contain some similarities, for example the choice of colors which use the same menus and offers the same possibilities. It let us to gain time by understanding how the software work, by knowing how to set the objects properties, only by knowing how to do with some of its. In conclusion, computational thinking provides us a strong way of thinking, in order to avoid wasting time in complex problems solving, and to build a safer way to progress in achieving our goals. References : "Computational Thinking for Educators", Google, read the 10.10.2017, https://computationalthinkingcourse.withgoogle.com/unit"Introduction to computational thinking", BBC Bitesize, read the 10.10.2017, https://www.bbc.co.uk/education/guides/zp92mp3/revision/1