Changes in Fluctuation Waves in Coherent Airflow Structures with Input Perturbation

TL;DR

This study models how input perturbations at different frequencies influence fluctuation waves in an air jet, revealing ways to control wave propagation and reduce noise in airflow structures.

Contribution

It introduces a method to predict fluctuation development in perturbed airflow using linearized Euler equations, highlighting the impact of perturbation frequency on wave behavior.

Findings

Perturbation frequency affects wave propagation patterns.

Frequency modulation can mitigate noise levels.

Coherent structures synchronize with input frequency.

Abstract

We predict the development and propagation of the fluctuations in a perturbed ideally-expanded air jet. A non-propagating harmonic perturbation in the density, axial velocity, and pressure is introduced at the inflow with different frequencies to produce coherent structures in the airflow, which are synchronized with the applied frequency. Then, the fluctuations and acoustic fields are predicted for each frequency by integrating the axisymmetric linearized Euler equations. We investigate the effect of the perturbation frequency on different characteristics of the pressure and velocity waves. The perturbation frequency can be used to alter the propagation pattern and intensity of the waves and mitigate the noise levels at certain zones.