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Research Papers

Calculation of the Time-Averaged Flow in Squirrel-Cage Blowers by Substituting Blades With Equivalent Forces

[+] Author and Article Information
Markus Tremmel

Neurosurgery Department, University at Buffalo, 437 Biomedical Research Building, Buffalo, NY 14214mtremmel@buffalo.edu

Dale B. Taulbee

MAE Department, University at Buffalo, 315 Jarvis Hall, Buffalo, NY 14260trldale@eng.buffalo.edu

Center for Computational Research, University at Buffalo, 701 Ellicott St., Buffalo, New York, 14203.

J. Turbomach 130(3), 031001 (Apr 01, 2008) (12 pages) doi:10.1115/1.2775483 History: Received May 16, 2006; Revised April 08, 2007; Published April 01, 2008

Radial fans of the squirrel-cage type are used in various industrial applications. The analysis of such fans via computational fluid mechanics can provide the overall fan performance coefficients, as well as give insights into the detailed flow field. However, a transient simulation of a 3D machine using a sliding grid for the rotating blades still requires prohibitively large computational resources, with CPU run times in the order of months. To avoid such long simulation times, a faster method is developed in this paper. Instead of solving the transient Navier–Stokes equations, they are first averaged over one impeller rotation, and then solved for the mean flow since only this flow is of practical interest. Due to the averaging process, the blades disappear as solid boundaries, but additional equation terms arise, which represent the blade forces on the fluid. An innovative closure model for these terms is developed by calculating forces in 2D blade rows with the same blade geometry as the 3D machine for a range of flow parameters. These forces are then applied in the 3D machine, and the resulting 3D time-averaged flow field and performance coefficients are calculated. The 3D flow field showed several characteristic features of squirrel-cage blowers, such as a cross-flow pattern through the fan at low flow coefficients, and a vortexlike flow pattern at the fan outlet. The 3D fan performance coefficients showed an excellent agreement with experimental data. Since the 3D simulation solves for the mean flow, it can be run as a steady-state problem with a comparatively coarse grid in the blade region, reducing CPU times by a factor of about 10 when compared to a transient simulation with a sliding grid. It is hoped that these savings in computational cost will encourage other researchers and industrial companies to adopt the new method presented here.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Horizontal cross section of g-car fan (schematic)

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Figure 2

Vertical cross section of g-car fan (schematic)

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Figure 3

Blade geometry of g-car fan, top view (schematic)

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Figure 4

Cut in z plane through time-averaged 3D blower, top view (schematic)

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Figure 5

Equivalent 2D periodic machine (rotating domain, schematic)

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Figure 6

2D channel flow field, qin′=4.2m2∕s, win=0%; (a) Relative velocity V⃗, (b) static pressure p

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Figure 7

2D channel flow field, qin′=4.2m2∕s, win=100%; (a) Relative velocity V⃗, (b) static pressure p

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Figure 8

2D channel flow field, qin′=4.2m2∕s, win=200%; (a) Relative velocity V⃗, (b) static pressure p

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Figure 9

Inviscid force distribution in 2D channel at qin′=4.2m2∕s; (a) Radial component Finv(r), (b) tangential component Finv(θ)

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Figure 10

Fluctuation force distribution in 2D channel at qin′=4.2m2∕s; (a) Radial component Fflu(r), (b) tangential component Fflu(θ)

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Figure 11

Total force distribution in 2D channel at qin′=4.2m2∕s; (a) Radial component Ftot(r), (b) tangential component Ftot(θ)

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Figure 12

Torque coefficient from 2D channel, effect of blade thickness

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Figure 13

Total pressure coefficient from 2D channel, effect of blade thickness

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Figure 14

Grid for g-car fan (inlet region not shown)

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Figure 15

Torque coefficient results

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Figure 16

Pressure coefficient results

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Figure 17

Vin=4.5m∕s, flow field in the midspan plane; (a) Velocity V⃗¯, (b) total pressure pt¯

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Figure 18

Vin=4.5m∕s, flow field in the yz plane; (a) Velocity V⃗¯, (b) static pressure p¯

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Figure 19

Vin=1.5m∕s, flow field in the midspan plane; (a) Velocity V⃗¯, (b) total pressure pt¯

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Figure 20

Vin=1.5m∕s, flow field in the yz plane; (a) Velocity V⃗¯, (b) static pressure p¯

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