Reducing Sound Pressure of an Aerodynamic Vehicle

The purpose of the experiment was to decrease the sound pressure of the resonance of a car driving with the windows down by changing the angle of the back of the window, while also keeping the drag force of the car the same. The resonance of the car causes an irritating noise, which is why the experiment involved decreasing the resonant sound pressure. A round-bottom flask was used to simulate a car because it was easier to experiment on and resonates more easily than a car. Three plastic models called “deresonators” at thirty, forty-five, and sixty degrees that deflect air; they were created to fit the round-bottom flask to alter the angle of the flask entrance. To find resonance, the flask was secured and an air current was blown perpendicular to the top of the flask and the sound pressure was recorded through a Vernier microphone.

For drag force, the flask was secured in a horizontal wind tunnel and attached to a force sensor which recorded the change in drag force. Two Analysis of Variance, ANOVA, tests were conducted to determine the significance of the experimental results. The lowest average sound pressure was produced by 60° at 2.758 dB compared to the sound pressure with no manipulation was 3.577 dB. The lowest drag force was produced from no deresonator at 0.049N.

The overall conclusion is that sound pressure was significantly reduced, but drag force significantly increased. Sound pressure decreased because the angle on the deresonator decreased the amplitude of the wave, therefore, decreasing the sound pressure. Also, the deresonator deflected the waves so a standing wave could not form. Drag force increased slightly because as the angle increased there was more perpendicular force needed to flatten the waves back to resting position.

Research Conducted By:

Ryan Gohlke
Sterling Heights High School

Alex Henry Warren
Warren Mott High School