Low-frequency acoustic radiation from a flanged circular pipe at an inclined angle.

Jialin Su,Aimee S Morgans,Dong Yang

doi:10.1121/10.0009586

Jialin Su, Aimee S Morgans + Show 1 more

Open Access

https://doi.org/10.1121/10.0009586

Copy DOI

Abstract

The generic problem of low-frequency acoustic radiation through quiescent air from a circular pipe that is inclined with respect to its exit flange is studied in this work. The exit flange is taken to extend as an infinite plane away from the pipe opening. The analysis implements a hybrid method that combines modal expansions with the boundary element method. The reflection coefficient and pipe end correction for Helmholtz numbers (based on the pipe radius) less than 2.5 are calculated for various inclination angles up to 75°. Calculations are validated using simulations from the finite-element solver of the commercial software package COMSOL. The reflection coefficient and end correction predictions agree closely with the validation simulations yet differ notably from the results available in the literature. The solution obtained from the hybrid method is subsequently used to analyse the acoustic field at the pipe exit and in the downstream space. The key aspects of the governing physics pertaining to practical engineering applications at low frequencies are captured in a low-order approximation, which significantly reduces the degrees of freedom of the problem and provides generally good estimates of the reflection coefficient and end correction, as well as the downstream acoustic field.

Highlights

Analogous to the unflanged pipe with a scarfed exit, the corresponding problem for a flanged pipe is the acoustic radiation from a circular pipe at an inclined angle to the infinite flange at the pipe exit
The key aspects of the governing physics pertaining to practical engineering applications at low frequencies are captured in a low-order approximation, which significantly reduces the degrees of freedom of the problem and provides generally good estimates of the reflection coefficient and end correction, as well as the downstream acoustic field
Similar to the previous work by Norris and Sheng[3] and by Selamet et al.,[7] the acoustic response of the inclined flanged pipe with respect to a planar incident wave from the upstream side is characterised by the complex reflection coefficient, R 1⁄4 ÀjRjeÀi2kL, where L is the end correction

Summary

Introduction

Analogous to the unflanged pipe with a scarfed exit, the corresponding problem for a flanged pipe is the acoustic radiation from a circular pipe at an inclined angle to the infinite flange at the pipe exit. The acoustics of a circular pipe normal to its exit flange have been thoroughly studied, the literature on the generic extension to circular pipes with an inclination to the exit flange is rather limited. Such a canonical configuration is of relevance to general engineering applications concerned with noise reduction or propagation. Of fundamental interest to gain further insights into the underlying physics

Methods

Results

Conclusion