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TECHNICAL PAPERS

Development of a Tip-Leakage Flow Part 2: Comparison Between the Ducted and Un-ducted Rotor

[+] Author and Article Information
Ghanem F. Oweis1

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2121

David Fry, Chris J. Chesnakas, Stuart D. Jessup

 Naval Surface Warfare Center, Carderock Division, Code 5400, 9500 MacArthur Blvd., West Bethesda, MD 20817-5700

Steven L. Ceccio

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109-2121ceccio@engin.umich.edu

1

Current address: Mechanical Engineering Department, American University of Beirut, 3 Dag Hammarskjold Plz., New York, NY 10017.

J. Fluids Eng 128(4), 765-773 (Mar 02, 2006) (9 pages) doi:10.1115/1.2201619 History: Received January 15, 2004; Revised March 02, 2006

The vortical flow in the tip region of a three-bladed rotor was examined using particle imaging velocimetry (PIV). The vortex forming at the tip of the un-ducted propeller was compared to the tip-leakage vortex of the ducted rotor. The planar flow fields were used to identify regions of concentrated vorticity and determine instantaneous vortex properties, revealing the presence of a primary tip-leakage vortex surrounded by a number of secondary vortices. Comparison between the ducted and un-ducted rotor indicated that the presence of the duct reduced the relative strength of the primary tip vortex, making its strength a smaller fraction of the overall shed circulation near the tip. The weaker tip-leakage vortex then became closer in strength to the other secondary vortices in the tip-flow region. However, for the rotor tip geometry considered here, the radius of the primary vortex core did not vary substantially between the ducted and un-ducted cases. The variability of the flow was larger for the ducted case, in terms of the primary vortex position, its identified circulation, core size, and inferred core pressure. This variability was also observed in the scaled velocity fluctuations near the core of the vortex.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of the propeller setup in the open jet test section, showing the drive shaft and its supporting struts; (a) the ducted configuration, and (b) the un-ducted configuration

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Figure 2

Iso-vorticity contours of the mean flow field of the tip vortex on the un-ducted rotor as a function of the distance downstream from the blade trailing edge (TE), s∕c. Shown are the fields for three propeller speeds (a) 300; (b) 600; and (c) 1200rpm. The coordinates are normalized by the propeller radius, RP, while vorticity is normalized by (U∞∕RP).

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Figure 3

Iso-vorticity contours of the mean flow field of the tip vortex on the ducted rotor as a function of the distance downstream from the blade TE, s∕c. Shown are the fields for three propeller speeds (a) 300; (b) 600; and (c) 1200rpm. The axes coordinates are normalized by RP, while vorticity is normalized by (U∞∕RP).

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Figure 4

Average number of identified vortices in the instantaneous flow field, N, for three different propeller speeds (300, 600, and 1200rpm) for the un-ducted configuration (a); and for the ducted configuration (b). The vertical bars indicate ± one standard deviation about the mean.

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Figure 5

Average circulation of the primary vortex, ΓO,1∕(U∞R), (thick lines) and the summed circulation of all the vortices identified in the instantaneous flow field, ∑iΓO,i∕(U∞R), (thin lines) for the same conditions of Fig. 4; (a) un-ducted configuration; (b) ducted configuration. The vertical bars indicate ± one standard deviation about the mean.

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Figure 6

Average radius of the primary vortex, a1∕RP, for the conditions of Fig. 4

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Figure 7

Average pressure coefficient of the primary vortex, CP,1, for the conditions of Fig. 4

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Figure 8

Histograms of (a) the number of vortices identified in the instantaneous flow field, (b) the circulation of the primary vortex, (c) the core radius of primary vortex, and (d) the pressure coefficient of primary vortex for the open rotor operating at 1200rpm

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Figure 9

Histograms of (a) the number of vortices identified in the instantaneous flow field, (b) the circulation of the primary vortex, (c) the core radius of primary vortex, and (d) the pressure coefficient of primary vortex for the ducted rotor operating at 1200rpm

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Figure 10

Scatter plots of the instantaneous position of the primary vortex (a), (c) and the instantaneous positions of the secondary vortices (b), (d) relative to the instantaneous primary vortex with downstream location s∕c. (a), (b) the open propeller; and (c), (d) the ducted propeller. The operating condition was 1200rpm.

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Figure 11

Vorticity contours of the averaged tip vortex field for different downstream locations s∕c: (a), (c) computed directly ω¯∕(2UC¯∕a1¯) and plotted in [x∕a¯,y∕a¯] coordinates; in (b), (d), the instantaneous fields were scaled and shifted prior to computing the average ω∕(2UC∕a1)¯, and plotted in [x∕a1,y∕a1]. Contours in (a), (b) are from the open rotor, and (c), (d) are from the ducted rotor operating at 1200rpm. The value of the contour at the vortex center (×) is noted below each frame.

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Figure 12

Velocity fluctuations (u′¯2+v′¯2)∕UC¯2. Otherwise the same as Fig. 1.

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