Session: 01-01-01 Automotive Flows

Paper Number: 87902

87902 - Performance Analysis and Parametric Study of Vortex Whistle 

In a vortex whistle, air entering an inlet tube flows into a cylindrical cavity and begins to spiral in a vortex that eventually exits through an outlet terminator. As air exits the outlet tube, a series of sharp spectral peaks are produced with harmonic frequencies. In a simple analysis, the frequency of the lowest spectral peak (fundamental frequency) is proportional to the inlet flow rate. Recent investigations using vortex whistles have focused on the use of this relationship to quantify aspects of respiratory function. Despite promising results, there is a lack of understanding of the physical mechanisms underlying vortex whistle function. In the present study, the combined computational fluid dynamics (CFD) and computational aeroacoustics (CAA) method is applied to investigate the performance of the vortex whistle. A simplified vortex whistle model with a terminator is designed. The open-source CFD software, OpenFOAM is adopted as the solver. Large Eddy Simulation (LES) with Smagorinsky model is conducted to compute the flow field within and outside the whistle, and then Ffowcs-Williams and Hawkings analogy is used for aeroacoustic simulation to predict the acoustic response of the vortex whistle and the frequency and level of the signature tones. The simulation result is validated by the experimental data in Awan and Awan (2020). The result indicates that the harmonics are generated by the cylindrical cavity of the vortex whistle, and the outlet terminator increases the signal-to-noise ratio of the spectral peaks by increasing the pressure fluctuation within the cylindrical cavity. The whistles with different heights and diameters of the cylindrical cavity are also simulated to optimize the design. The results show that the height does not affect the harmonic frequency significantly; with the decrease of the diameter, the harmonic shifts to a higher frequency. It is beneficial for low flow rate cases; in addition, an optimal design exists which produces the largest signal-to-noise ratio. In general, based on CFD and CAA simulations, we 1) determine the precise range of expiratory flows to which the vortex whistle spirometer responds with distinct acoustic signatures, 2) use the computational model to investigate the effect and interaction of the whistle dimensions on the acoustic properties, and 3) develop design optimization of the vortex whistle as well as statistical analysis improvements to enhance the reliability of the vortex whistle analyses and enable additional spirometry measurements.

Presenting Author: Ang Li School of Mechanical Engineering, Purdue University