Variation of the drag coefficient with Reynolds number
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This is a Project Report of my 1month training as an intern
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J.W. Barlow - W.H. Rae - A. Pope: Wind Tunnel Testing 3rd edition, John Wiley & Sons, Inc.: 1999Description complète
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WIND TUNNEL LAB REPORT
Introduction Wind tunnel is use as a means of studying air flowing past the solid objects in aerodynamic studies. studies. The wind tunnel tunnel is made up of different different parts. They consist consist of Settling Chamber, Contraction cone, test section, diffuser and drive section as shown above. In Test Section, view ports are added in order to see the model inside. The air flow from the drive section and get into settli ng chamber. Then the air move into contraction cone where the velocity will be increase due to the shape of the cone due to the pressure difference. The high and constant velocity air will then enter the test section where the model is to be tested. After that the air will flow into the diffuser where they will be push into the drive section to circulate. Procedure
An experiment was conducted to test an aircraft model in order to evaluate the lift and drag forces under different angles of attack. The data were taken at different rpm and angles of attack of the model aircraft. The value of coefficient of lift, the coefficient of drag, lift and drag, and airspeed of the model can be obtained from the computer which is connected to the wind tunnel. By putting all the data into the table, series of graphs can be drawn. Using those data, stalling point of the plane can be calculated and also calculate the changes in drag and lift when the angle of attack increases.
The graph above shows the change in lift coefficient as the angle of incidence changes. The Angle of attack increases the C L (Coefficient of Lift) increase until a certain angle, ones the angle of attack reaches between 15-20 degrees then the coefficient of lift starts to decrease due to the plane starting the stalling phase. From
the point the plane would lose airspeed and soon enough reach a stall where the airspeed will decreases and the plane may start to spin.
According to the above graph, the coefficient of drag increases as the angle of attack increase due to the amount of plane exposed to the air passing the aircraft. Also there is induced drag because of the vortices are now a lot larger, the trend that is shown on the graph is that as the angle of attack increases with the coefficient of drag. But the coefficient of drag increases exponent.
According to the above graph, the lift and drag is increase gradually as angle of incidence increase up to a maximum point. From the maximum point, it‘s start to decrease because of the lift coefficient reduces. After 5˚ angle, the ratio will start to decrease due to passing the optimum level for maintaining lift and airspeed.
Considering above the two graphs, the coefficient of lift rises until the drag is at such a force that the plane goes into a stall. This i s highlighted very clearly in the second graph.
