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Study of the Characteristics of Unsteady Flow in A Cross-flow Fan with Porous Stabilizers

Author: YaoJin
Tutor: LaiHuanXin
School: East China University of Science and Technology
Course: Fluid Machinery and Engineering
Keywords: cross-flow fan porous stabilizer experimental measurement numerical simulation
CLC: TH432
Type: Master's thesis
Year: 2012
Downloads: 53
Quote: 0
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Abstract


The aerodynamic characteristics and aeroacoustics of the cross-flow fans have attracted more and more attentions of researchers in recent years. In this paper, experimental measurements and numerical simulations are carried out to study the internal flow and the noise of a cross-flow fan which has porous stabilizers.The unsteady pressure fluctuations at four locations in the inflow zone are measured using a four-channel testing system, which has high frequency pressure transducers. Fast Fourier transform (FFT) technology is employed to analyse the data of the pressure fluctuations. The results show that the amplitude of pressure fluctuation is large in the outflow zone and near the stabilizer, so they are the main source of noise. The porous stabilizers are verified of attenuating the noise of the CFF in the frequency range of 500-2500Hz.Large-eddy simulations are carried out to study the internal flows of the fan as well as in the porous stabilizers. Both two-dimensional and three-dimensional numerical simulations reveal that large scale vortical motions can be identified in the inflow of the impeller and outflow zone of the CFF. The periodical generation of large scale vortices at the rear wall in the outflow zone, which have a opposite direction with the fan. Besides, the spectra at the measure points show that the pressure fluctuations are basically in broadband. The calculated pressure fluctuations are in good agreements with the experiments.In order to study the effects of porous media on vortex sound, a modified form of Powell’s vortex sound equation is proposed. The effects of porous media on the generation of flow induced sound are taken into consideration. Powell’s original vortex sound equation can be regarded as a special case of porous media with the porosityε=1. The FW-H equation is employed to predict the farfield noise of the cross-flow fan.A design of deflector for regulating the non-uniform outflow field is proposed for a sirocco fan. Feasibility of the design is checked.

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CLC: > Industrial Technology > Machinery and Instrument Industry > Gas compression and transportation machinery > Fan > Centrifugal ( radial flow )
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