Numerical method and software package for prediction of pressure pulsation in centrifugal ventilators

Abstract

A numerical method and software package was developed for designers and researchers in the field of vibration and noise problems in centrifugal ventilators. The numerical procedure is based on a representation of unsteady compressible liquid flow as a form of vortex (pseudo-sound) and acoustic mode superposition. It gives a possibility to determine absolute amplitudes of pressure pulsation in the ventilator casing induced by unsteady interaction between nonuniform flow outgoing from a centrifugal impeller volute tongue or diffuser vanes, so-called blade passing tones. Inupt data includes 2-D ventilator geometry and operation mode. Acoustic impedance boundary conditions can be defined with a circuit specification or by direct inlet and outlet specific complex impedance definition. It is possible to take into account local wall-specific complex impedance to study a coating effect on reduction of pressure pulsation. Output data represents: unsteady pressure map in the ventilator casing; amplitude distribution map for any selected harmonic; pressure versus time curves with accompanied spectrum information at any point selected by user; total vibration load vectors acting on the ventilator volute casing; and static pressure, velocity, and vorticity distribution in the centrifugal impeller. Validation of the software was completed on the centrifugal pump air model with more than 400 measuring points for two different radial gaps. The mismatch with experimental data is mostly 1.5–2.0 dB of unsteady pressure amplitude. Effects of radial clearance, number and form of impeller blades, exit and wall impedance are considered as well. The successful validation of the numerical method shows a good prospect in optimizing centrifugal ventilator geometry with improving vibration and noise characteristics at the draft stage and reducing refinement costs.

Numerical 2-D and 3-D methods for computation of internal unsteady pressure field and near-field noise of fans

“…Then the source function of the wave equation is defined from the unsteady velocity field of the vortex mode. The computational procedure is the same as for centrifugal ventilators [17][18][19] and pumps 20,21 .…”