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Research Papers: Fundamental Issues and Canonical Flows

The Effect of Streamtube Contraction on the Characteristics of a Streamwise Vortex

[+] Author and Article Information
Grant McLelland

Centre for Propulsion,
School of Aerospace, Transport and Manufacturing,
Cranfield University,
Bedford MK43 0AL, UK
e-mail: grantmclelland@yahoo.co.uk

David MacManus

Centre for Propulsion,
School of Aerospace, Transport and Manufacturing,
Cranfield University,
Bedford MK43 0AL, UK
e-mail: d.g.macmanus@cranfield.ac.uk

Chris Sheaf

Performance and Aero Thermal Systems,
Rolls Royce plc,
Derby DE22 8BJ, UK
e-mail: chris.sheaf@rolls-royce.com

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 1, 2014; final manuscript received January 21, 2015; published online March 9, 2015. Assoc. Editor: Alfredo Soldati.

J. Fluids Eng 137(6), 061204 (Jun 01, 2015) (13 pages) Paper No: FE-14-1486; doi: 10.1115/1.4029661 History: Received September 01, 2014; Revised January 21, 2015; Online March 09, 2015

The ingestion of a vortex by an aero-engine is potentially an area of concern for current and future aircraft-engine configurations. However, there are very little experimental data on the characteristics of a streamwise vortex undergoing ingestion through a contracting streamtube. To address this dearth of knowledge, the ingestion of a streamwise vortex has been studied experimentally using stereoscopic particle image velocimetry (stereo PIV). A subscale model of an aircraft intake has been used to generate a contracting capture streamtube, and an isolated streamwise vortex has been generated upstream of the intake using semispan NACA 0012 and delta wing vortex generators (VGs). A range of contraction ratios, vortex Reynolds numbers, and vortex initial conditions have been examined. Measurements on planes perpendicular to the freestream flow show that the vortex undergoes notable levels of intensification through the contraction streamtube. The characteristics of the vortex are dependent on the streamtube contraction level, the initial aerodynamic characteristics of the vortex, and the trajectory that the vortex follows inside the capture streamtube. Results from inviscid, incompressible vortex filament theory have been compared with the experimental data. At relatively low streamtube contraction ratios this theory provides a good estimate of the vortex characteristics. However, at higher contraction levels, there are notable levels of diffusion, which render the vortex less intense than that anticipated from vortex filament theory.

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References

Figures

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Fig. 1

Side-view schematic of wind-tunnel arrangement

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Fig. 2

Delta wing geometry

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Fig. 3

Circumferentially averaged profiles of vortex perturbation field as a function of nondimensional radius from the vortex center (r/rc) (a) tangential velocity normalized by freestream velocity (Vθ/W∞), (b) streamwise velocity normalized by freestream velocity (Vz/W∞), (c) streamwise vorticity normalized by wing chord length and freestream velocity (ωzDi/W∞), and (d) flow angularity [α = tan-1(Vθ,max/Vz)]. N12 and N6 refer to the NACA 0012 wing with αvg = 12 deg and 6 deg, respectively. D12 and D6 refer to the delta wing with αvg = 12 deg and 6 deg.

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Fig. 4

Vortex characteristics for centerline ingestion as a function of intake VR and normalized by unperturbed vortex measurements. NACA 0012 VG, αvg = 12 deg, Rec = 1.1 × 105. (a) Vortex centerline velocity magnitude (wc/wc,0), (b) vortex core radius (rc/rc,0), (c) peak tangential velocity (Vθ,max/Vθ,max,0), (d) peak streamwise vorticity (ωz,max/ωz,max,0), (e) average streamwise vorticity in vortex core (ωz,av/ωz,av,0), and (f) peak flow angle α* = (αmax/αmax,0).

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Fig. 5

Vortex characteristics during centerline ingestion as a function of chord Reynolds number, and normalized by unperturbed vortex measurements. NACA 0012 VG,αvg = 12 deg, VR = 4.9–5.2. (a) Vortex centerline velocity magnitude (wc/wc,0), (b) vortex core radius (rc/rc,0), (c) peak tangential velocity (Vθ,max/Vθ,max,0), (d) peak streamwise vorticity (ωz,max/ωz,max,0), (e) average streamwise vorticity in vortex core (ωz,av/ωz,av,0), and (f) peak flow angle α* = (αmax/αmax,0)[αmax = max(tan-1(Vθ/Vz))]. Note that Rev,0 = 2.4 × 104.

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Fig. 6

Vortex characteristics during centerline ingestion, NACA 0012 and delta wing VG, αvg = 12 deg and 6 deg, VR = 4.9, and normalized by unperturbed vortex measurements, where Rev,0 = 2.4 × 104, (a) vortex centerline velocity magnitude (wc/wc,0), (b) vortex core radius (rc/rc,0), (c) peak tangential velocity (Vθ,max/Vθ,max,0), (d) peak streamwise vorticity (ωz,max/ωz,max,0), (e) average streamwise vorticity in vortex core (ωz,av/ωz,av,0), and (f) peak flow angle α* = (αmax/αmax,0)[αmax = max(tan-1(Vθ/Vz))]. Note that Rev,0 = 2.4 × 104.

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Fig. 7

Vortex characteristics during centerline ingestion, as a function of intake VR for centerline (CL) and off-axis (OA) ingestion, and normalized by unperturbed vortex measurements. NACA 0012 VG, αvg = 12 deg, VR = 10.3 and 16.3. (a) Vortex centerline velocity magnitude (wc/wc,0), (b) vortex core radius (rc/rc,0), (c) peak tangential velocity (Vθ,max/Vθ,max,0), (d) peak streamwise vorticity (ωz,max/ωz,max,0), (e) average streamwise vorticity in vortex core (ωz,av/ωz,av,0), and (f) peak flow angle α* = (αmax/αmax,0)[αmax = max(tan-1(Vθ/Vz))].

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