## 3aNS13. Sound radiation from a centrifugal blower in a free field.

### Session: Wednesday Morning, May 15

### Time: 11:50

**Author: Shigong Su**

**Location: Dept. of Mech. Eng., Wayne State Univ., Detroit, MI 48202**

**Author: Sean F. Wu**

**Location: Wayne State Univ., Detroit, MI 48202**

**Author: Morris Y. Hsi**

**Location: Ford Motor Co., Dearborn, MI 48120**

**Abstract:**

A new formulation for predicting sound radiation from a centrifugal blower
in a free field is derived. The fundamental difference between the present
formula and the previously derived ones is that the former considers a new
monopole, while the latter assumes the dipole as the primary source. For an
axial flow fan or a rotor blade under steady flow condition, the usual monopole
source proportional to ((rho)[inf o](cursive beta)v[inf n]/(cursive beta)t) is
negligible [Siddon, J. Acoust. Soc. Am. 53, 616--633 (1973)]. However, for a
centrifugal blower the monopole source induced by Coliolis acceleration
((omega)xv[inf t]) cannot be neglected because of a large inclination angle of
the impeller. With the inclusion of this monopole source term, the formula
yields a dependence of the radiated sound power on the fourth power of the
azimuthal speed, which agrees with the experimental data [Maling, J. Acoust.
Soc. Am. 35, 1556--1564 (1963); Neise, J. Sound Vib. 43, 61--75 (1975)]. The
resulting formula can be used to derive the radiated sound power spectrum using
the turbulence correlation curve. The spectra thus obtained are compared with
the measured ones from a centrifugal blower mounted in a free field. A favorable
agreement is obtained in all test cases.

from ASA 131st Meeting, Indianapolis, May 1996