Acoustic nonlinearities in a quasi 1-D duct with arbitrary mean properties and mean flow. (23rd June 2022)

• Record Type: Journal Article
• Authors: Basu, Sattik; Rani, Sarma L.
• Is Part Of: Journal of sound and vibration. Volume 528(2022)
• Publication Date: 2022-06-23
• Subjects: Limit cycle -- Van der Pol oscillator -- Lindstedt–Poincaré method -- Method of averaging; Sound -- Periodicals; Vibration -- Periodicals; Son -- Périodiques; Vibration -- Périodiques; Sound; Vibration; Periodicals; Electronic journals; 620.205
• DOI: 10.1016/j.jsv.2022.116862
• Languages: English
• ISSNs: 0022-460X

Abstract

Abstract: Nonlinear temporal dynamics of acoustic oscillations in a quasi one-dimensional (1-D) duct are investigated using both numerical and analytical methods. The spatiotemporal nonlinear wave equation is derived for pressure oscillations in a quasi 1-D duct with axially varying cross-section and spatially inhomogeneous mean properties such as the velocity, temperature, density and pressure. Using the finite element method with quadratic interpolation functions, the linear Helmholtz equation is solved for the modal shapes and frequencies. With the modal shape as the weighting function, the standard Galerkin method is applied to transform the spatiotemporal wave equation into a second-order nonlinear ordinary differential equation (ODE) governing the time evolution of modal amplitudes. The limit-cycle amplitude and frequency of pressure oscillations are quantified analytically using the Lindstedt–Poincaré perturbation method. Furthermore, to capture the transient evolution to the limit cycle, the method of averaging is applied to the nonlinear temporal ODE for the modal amplitude. From the Lindstedt–Poincaré method, it is seen that a limit cycle exists when the linear damping coefficient μ in the nonlinear ODE is of the opposite sign as the quantity S that is a function of the coefficients of the quadratic and cubic terms in the ODE. For a given S, limit cycle is created or destroyed as μ changes sign, a scenario referred to as the "Hopf bifurcation." The phase portraits and limit-cycle amplitudes obtained from numerical solution are in excellent agreement with those derived from the analytical techniques. Highlights: Nonlinear temporal dynamics of acoustic oscillations are investigated. Modal shapes and frequencies were obtained using Finite Element Method. Governing temporal equation was derived, and solved numerically and analytically. Limit cycle oscillations were obtained.