19 October AME Graduate Student Conference Flow Induced Oscillations of a Helmholtz Resonator Paul E. Slaboch Advisor: Scott C. Morris

20 November AME Graduate Student Conference Motivation Interior pressure oscillations are a problem for both the automotive and aerospace communities. In automotive vehicles, the very low frequency (~ Hz) high amplitude pressure oscillations can exceed 120 dB, which can be painful to both drivers and passengers. The goal of this study is to determine the underlying flow physics of the problem and to generate design guidelines for future vehicles to minimize buffeting.

20 November AME Graduate Student Conference Introduction Helmholtz resonators occur when flow passes over an orifice, through a neck and into a volume. The resonator can be modeled as a spring- mass system. U onset occurs when f n =f R

20 November AME Graduate Student Conference Previous Work

20 November AME Graduate Student Conference Previous Work

20 November AME Graduate Student Conference Experimental Setup PIV Cameras Cavity Open Orifice

20 November AME Graduate Student Conference Pressure Measurements

20 November AME Graduate Student Conference Pressure Measurements

20 November AME Graduate Student Conference Pressure Measurements

20 November AME Graduate Student Conference PIV Flow Visualization

20 November AME Graduate Student Conference PIV Measurements

20 November AME Graduate Student Conference Effect of Free Stream Velocity

20 November AME Graduate Student Conference Effect of BL Thickness

20 November AME Graduate Student Conference Future Work

20 November AME Graduate Student Conference Future Work

20 November AME Graduate Student Conference Conclusions A series of experiments has been performed to determine the underlying flow physics of a flow induced Helmholtz resonator. The actual mechanism of the oscillations is neither the roll up of discrete vortices nor a flag flapping shear layer instability. Rather, it appears to be a combination of the two. The effect of free stream velocity is to spread the vorticity into a more continuous stream while the effect of the boundary layer thickness is to alter the location of the formation of a vortex. This study, combined with future work, will provide design guidelines for automotive designers.

20 November AME Graduate Student Conference Thank you for your attention. Questions?