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Research Papers

Tip Clearance Investigation of a Ducted Fan Used in VTOL Unmanned Aerial Vehicles—Part II: Novel Treatments Via Computational Design and Their Experimental Verification

[+] Author and Article Information
Ali Akturk

e-mail: akturkali@gmail.com

Cengiz Camci

Professor of Aerospace Engineering
e-mail: cxc11@psu.edu
Turbomachinery Aero-Heat Transfer Laboratory,
Department Aerospace Engineering,
Pennsylvania State University,
University Park, PA 16802

1Currently working in Siemens Energy Inc.

2Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received November 5, 2012; final manuscript received December 8, 2012; published online September 26, 2013. Editor: David Wisler.

J. Turbomach 136(2), 021005 (Sep 26, 2013) (9 pages) Paper No: TURBO-12-1213; doi: 10.1115/1.4023469 History: Received November 05, 2012; Revised December 08, 2012

Ducted fan based vertical lift systems are excellent candidates to be in the group of the next generation vertical lift vehicles, with many potential applications in general aviation and military missions. Although ducted fans provide high performance in many “vertical take-off and landing” (VTOL) applications, there are still unresolved problems associated with these systems. Fan rotor tip leakage flow adversely affects the general aerodynamic performance of ducted fan VTOL unmanned aerial vehicles (UAVs). The current study utilized a three-dimensional Reynolds-averaged Navier–Stokes (RANS) based computational fluid dynamics (CFD) model of ducted fan for the development and design analysis of novel tip treatments. Various tip leakage mitigation schemes were introduced by varying the chordwise location and the width of the extension in the circumferential direction. Reduced tip clearance related flow interactions were essential in improving the energy efficiency and range of ducted fan based vehicles. Full and inclined pressure side tip squealers were also designed. Squealer tips were effective in changing the overall trajectory of the tip vortex to a higher path in radial direction. The interaction of rotor blades and tip vortex was effectively reduced and the aerodynamic performance of the rotor blades was improved. The overall aerodynamic gain was a measurable reduction in leakage mass flow rate. This leakage reduction increased thrust significantly. Experimental measurements indicated that full and inclined pressure side tip squealers increased thrust obtained in hover condition by 9.1% and 9.6%, respectively. A reduction or elimination of the momentum deficit in tip vortices is essential to reduce the adverse performance effects originating from the unsteady and highly turbulent tip leakage flows rotating against a stationary casing. The novel tip treatments developed throughout this study are highly effective in reducing the adverse performance effects of ducted fan systems developed for VTOL UAVs.

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References

Figures

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Fig. 1

The near tip computational grid for squealer and inclined squealer rotor tips

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Fig. 2

Blade tip constant circumferential angle planes drawn for baseline rotor tip with 3.04% tip clearance

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Fig. 3

Tip treatments: (a) partial bump tip platform extension (t.p.e.), (b) full bump t.p.e., (c) full bump and partial squealer t.p.e., (d) full squealer t.p.e., (e) inclined full squealer t.p.e.

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Fig. 4

Blade tip constant circumferential angle planes drawn for “partial bump” tip extension with 3.04% tip clearance

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Fig. 5

Blade tip constant circumferential angle planes drawn for “full bump” tip extension with 3.04% tip clearance

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Fig. 6

Blade tip constant circumferential angle planes drawn for “full bump and partial squealer” tip extension with 3.04% tip clearance

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Fig. 7

(a) Full and (b) inclined squealer sketch

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Fig. 8

Blade tip constant circumferential angle planes drawn for “full squealer” tip extension with 3.04% tip clearance

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Fig. 9

Blade tip constant circumferential angle planes drawn for “inclined squealer” tip extension with 3.04% tip clearance

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Fig. 10

Comparison of computationally obtained total pressure distributions for all of the tip treatments and baseline rotor tip (3.04% tip clearance)

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Fig. 11

Streamlines around the inclined squealer rotor blade with 3.04% tip clearance and rotor hub at 2400 rpm

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Fig. 12

Squealer and inclined squealer tip extensions designed for SLA manufacturing (a) squealer t.p.e.(3.04% t.c.), (b) inclined squealer t.p.e. (3.04% t.c.), (c) inclined squealer t.p.e. (5.17% t.c.)

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Fig. 13

Inclined squealer t.p.e. applied to the rotor blade (5.17% tip clearance)

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Fig. 14

Measurements of thrust coefficient versus rotational speed for the rotor with squealer and inclined squealer tips at 3.04% tip clearance

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Fig. 15

Measurements of thrust coefficient versus rotational speed for rotor with squealer and inclined squealer tips at 5.17% tip clearance

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Fig. 16

Measured figure of merit versus rotational speed for rotor with squealer and inclined squealer tips at 3.04% tip clearance

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Fig. 17

Measured figure of merit versus rotational speed for rotor with squealer and inclined squealer tips at 5.17% tip clearance

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Fig. 18

Total pressure measured at downstream of the rotor at 2400 rpm for squealer tips with 3.04% tip clearance

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Fig. 19

Total pressure measured at downstream of the rotor at 2400 rpm for squealer tips with 5.17% tip clearance

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