Embedded Files
During the summer of 2017 I studied abroad at the Technische Universität Berlin. I participated in a wind tunnel lab, where with a partner, I researched aerodynamic properties to successfully perform experiments and alter the design of a 1:18 scaled down model car to reduce the coefficient of drag. The results were presented to a large group of peers and professors.
Motivation
Motivation
Learning about aerodynamic automotive modeling is crucial for the automotive industry. Understanding fluid dynamics can reduce gas consumption and increase the maximum velocity of the vehicle. By optimizing the aerodynamics of the BMW model using putty one can directly see the results of aerodynamic optimization.
Procedure
Procedure
In the first experiment, pressure taps placed along the centerline and underside of the car were used to measure the local pressure at those points. The second experiment measured the wake of the original model and modified model by changing the height of a pitot static tube at two distances downstream of the model. These pressure measurements were used to calculate drag and lift coefficients. The last experiment used flow visualization to model the streak lines along the centerline of the original and modified model.
Results
Results
From the first experiment the models lift and drag coefficient were calculated to be 0.15 and 0.59 respectively, compared to the real BMW drag coefficient of 0.33.
In the second experiment, the pressure and velocity profiles of the unmodified and modified model car were developed and can be seen in the figures above. From the pressure figure, there is slightly less of a difference in pressure for nearly all corresponding heights with the modified model car as opposed to the unmodified car. This suggests that the wake of the modified car may have been smaller than that of the unmodified car. Additionally, from the velocity figure it can be observed that the flow velocity was greater than the free stream velocity of 20m/s at higher heights for the modified model versus the unmodified model.
The corresponding coefficients of drag for the unmodified car at the near and far wake location were 0.44 and 0.42, respectively compared to 0.18 and 0.10 for the near wake location. The constants are lower because of the smoother curvature and subsequent reduction in flow separation and stagnation.
Discussion
Discussion
The model had many sources of error that altered the measurements compared to an actual BMW M5. The wind tunnel blockage causes the airflow to accelerate around the model, which in turn underestimates pressure. The open windows and plastic tubes of the original model increase turbulence and reduce pressure. A loose pitot static tube and taps could have underestimated the pressure.
This aerodynamics lab supplemented my knowledge of aerodynamic properties by having me work on a hands on group project. The results are not realistic because of the modifications to the length and safety of the car, but it was a valuable learning experience.
Page updated
Google Sites
Report abuse