This paper analyzes the structure of turbulence and secondary flows at the exit of an axial flow fan with variable pitch blades. The influence of changing the blades’ pitch angle over the turbulent structures is assessed by means of turbulence intensity values and integral length scales, obtained by using hot-wire anemometry for several test conditions. Since total unsteadiness is composed of both periodic and random unsteadiness, it is necessary to filter deterministic unsteadiness from the raw velocity traces in order to obtain turbulence data. Consequently, coherent flow structures were decoupled and thus, levels of turbulence—rms values of random fluctuations—were determined using a filtering procedure that removes all the contributions stemming from the rotational frequency, the blade passing frequency, and its harmonics. The results, shown in terms of phase-averaged distributions in the relative frame of reference, revealed valuable information about the transport of the turbulent structures in the unsteady, deterministic flow patterns. The anisotropic turbulence generated at the shear layers of the blade wakes was identified as a major mechanism of turbulence generation, and significant links between the blade pitch angle and the wake turbulent intensity were established. In addition, the autocorrelation analysis of random fluctuations was also used to estimate integral length scales—larger eddy sizes—of turbulence, providing useful data for computational fluid dynamics applications based on large eddy simulation algorithms. Finally, contours of radial vorticity and helicity gave a detailed picture of the vortical characteristics of the flow patterns, and the definition of secondary flow as the deviation of the streamwise component from the inviscid kinematics was introduced to determine the efficiency of the blade design in the energy exchange of the rotor.
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April 2008
Research Papers
Turbulence and Secondary Flows in an Axial Flow Fan With Variable Pitch Blades
Jesús Manuel Fernández Oro,
Jesús Manuel Fernández Oro
Área de Mecánica de Fluidos,
e-mail: jesusfo@uniovi.es
Universidad de Oviedo
, Campus de Viesques, 33271 Gijón (Asturias), Spain
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Rafael Ballesteros-Tajadura,
Rafael Ballesteros-Tajadura
Área de Mecánica de Fluidos,
Universidad de Oviedo
, Campus de Viesques, 33271 Gijón (Asturias), Spain
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Eduardo Blanco Marigorta,
Eduardo Blanco Marigorta
Área de Mecánica de Fluidos,
Universidad de Oviedo
, Campus de Viesques, 33271 Gijón (Asturias), Spain
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Katia María Argüelles Díaz,
Katia María Argüelles Díaz
Área de Mecánica de Fluidos,
Universidad de Oviedo
, Campus de Viesques, 33271 Gijón (Asturias), Spain
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Carlos Santolaria Morros
Carlos Santolaria Morros
Área de Mecánica de Fluidos,
Universidad de Oviedo
, Campus de Viesques, 33271 Gijón (Asturias), Spain
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Jesús Manuel Fernández Oro
Área de Mecánica de Fluidos,
Universidad de Oviedo
, Campus de Viesques, 33271 Gijón (Asturias), Spaine-mail: jesusfo@uniovi.es
Rafael Ballesteros-Tajadura
Área de Mecánica de Fluidos,
Universidad de Oviedo
, Campus de Viesques, 33271 Gijón (Asturias), Spain
Eduardo Blanco Marigorta
Área de Mecánica de Fluidos,
Universidad de Oviedo
, Campus de Viesques, 33271 Gijón (Asturias), Spain
Katia María Argüelles Díaz
Área de Mecánica de Fluidos,
Universidad de Oviedo
, Campus de Viesques, 33271 Gijón (Asturias), Spain
Carlos Santolaria Morros
Área de Mecánica de Fluidos,
Universidad de Oviedo
, Campus de Viesques, 33271 Gijón (Asturias), SpainJ. Fluids Eng. Apr 2008, 130(4): 041101 (11 pages)
Published Online: April 1, 2008
Article history
Received:
July 24, 2007
Revised:
January 4, 2008
Published:
April 1, 2008
Citation
Fernández Oro, J. M., Ballesteros-Tajadura, R., Blanco Marigorta, E., Argüelles Díaz, K. M., and Santolaria Morros, C. (April 1, 2008). "Turbulence and Secondary Flows in an Axial Flow Fan With Variable Pitch Blades." ASME. J. Fluids Eng. April 2008; 130(4): 041101. https://doi.org/10.1115/1.2903523
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