Unsteady Flow and Wake Transport in a Low-Speed Axial Fan With Inlet Guide Vanes

[+] Author and Article Information
Jesús Manuel Fernández Oro

Área de Mecánica de Fluidos, Universidad de Oviedo, Campus de Viesques, 33271, Gijón (Asturias), Spainjesusfo@uniovi.es

Katia María Argüelles Díaz, Carlos Santolaria Morros, Eduardo Blanco Marigorta

Área de Mecánica de Fluidos, Universidad de Oviedo, Campus de Viesques, 33271, Gijón (Asturias), Spain

J. Fluids Eng 129(8), 1015-1029 (Mar 15, 2007) (15 pages) doi:10.1115/1.2746920 History: Received December 05, 2006; Revised March 15, 2007

The present study is focused on the analysis of the dynamic and periodic interaction between both fixed and rotating blade rows in a single stage, low-speed axial fan with inlet guide vanes. The main goal is placed on the characterization of the unsteady flow structures involved in an axial flow fan of high reaction degree, relating them to working point variations and axial gap modifications. For that purpose, an experimental open-loop facility has been developed to obtain a physical description of the flow across the turbomachine. Using hot-wire anemometry, measurements of axial and tangential velocities were carried out in two transversal sectors: one between the rows and the other downstream of the rotor, covering the whole span of the stage for a complete stator pitch. Ensemble- and time-averaging techniques were introduced to extract deterministic fluctuations from raw data, both of which are essential to understand flow mechanisms related to the blade passing frequency. An exhaustive analysis of the measured wakes has provided a comprehensive description of the underlying mechanisms in both wake-transport phenomena and stator-rotor interaction. In addition, unmixed stator wakes, observed at the rotor exit, have been treated in terms of dispersion and angular displacement to indicate the influence of the blades loading on the transport of the stator wake fluid. The final aim of the paper is to highlight a complete picture of the unsteady flow patterns inside industrial axial fans.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 15

Radial distribution of the rotor wakes’ displacement thickness

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Figure 16

Radial distribution of the rotor wakes’ shape and energy factors

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Figure 17

Vorticity structure of boundary layers: casing viscous regions and wakes’ shear layers at rotor exit

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Figure 18

Unsteady flow patterns in axial and tangential velocity distributions at rotor exit

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Figure 19

Unsteady flow patterns at rotor exit as a function of the operating point in the case of reduced axial gap

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Figure 14

Identification of the rotor wakes’ shear layers

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Figure 13

Radial evolution of the rotor wake structure

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Figure 12

Influence of the axial gap in the dispersion of stator wakes at different operating conditions for the midspan

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Figure 11

Influence of the operating conditions on the radial migration of the stator wake-rotor blockage interaction

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Figure 10

Influence of the rotor blockage on the time-averaged flow at different operating conditions

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Figure 9

Sketch of streamlines in the throughflow

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Figure 8

Throughflow at rotor exit

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Figure 7

Throughflow incidence

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Figure 6

Throughflow at stator exit

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Figure 5

Measuring sectors D (at stator exit) and R (at rotor exit)

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Figure 4

Sketch of the dual hot-wire probe. Measurement chain.

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Figure 3

Fan performance curves

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Figure 2

Characteristics of vanes and blades

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Figure 20

Temporal pitchwise distribution of axial velocity at the rotor exit for nominal conditions

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Figure 21

Sketch of the transport and convection of an IGV wake through a rotor passage

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Figure 22

Influence of the operating conditions in the wake transport at midspan

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Figure 23

Three-dimensional view of the stator wake transport downstream of the rotor

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Figure 24

Dispersion and angular displacement of unmixed stator wakes




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