Demonstration and validation of nonlinear acoustic shock wave formation in a renovated waveguide

When acoustic waves attain high enough pressure amplitudes, the wave speed becomes amplitude-dependent, causing the wave to steepen. If the amplitude is high enough, a shock is formed. Shock formation is commonly covered in nonlinear acoustics courses, but it is difficult to demonstrate experimentally in a classroom setting. Dr. Isadore Rudnick designed a nonlinear waveguide demonstration, as recalled by Dr. Robert Keolian [J. Acoust. Soc. Am. 145(3 Pt. 2), 1682 (2019)]. In his setup, a high amplitude driver inputs an acoustic plane wave into a long PVC pipe. At the Pennsylvania State University, a similar waveguide was built by Dr. Lauren Falco as part of her research on nonlinear jet noise. The waveguide was then used as part of an assignment in a laboratory class taught by Dr. Steven Garrett. However, the waveguide has not been used for almost 10 years. This demonstration apparatus has been restored to working order and was validated by measuring the nonlinear generation and decay of harmonics at three locations along the pipe by varying the peak pressure and frequency of the sinusoidal input. This paper will demonstrate the formation of shock waves using this apparatus.