Research Papers: Gas Turbines: Aircraft Engine

Effects of Scalloping on the Mixing Mechanisms of Forced Mixers With Highly Swirling Core Flow

[+] Author and Article Information
Ali Mahallati

e-mail: ali.mahallati@nrc-cnrc.gc.ca
Gas Turbines, Aerospace, National Research Council of Canada,
Ottawa, ON K1A 0R6, Canada

Mark Cunningham

Installation and Turbine Aerodynamics,
Pratt & Whitney Canada,
QCJ4G 1A1, Canada

Julio Militzer

Department of Mechanical Engineering,
Dalhousie University,
Halifax, NS B3H 4R2, Canada

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received October 8, 2012; final manuscript received November 26, 2012; published online June 10, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(7), 071202 (Jun 10, 2013) (10 pages) Paper No: GTP-12-1397; doi: 10.1115/1.4024043 History: Received October 08, 2012; Revised November 26, 2012

This paper presents a detailed experimental and computational investigation of the effects of scalloping on the mixing mechanisms of a scaled 12-lobe turbofan mixer. Scalloping was achieved by eliminating approximately 70% of the lobe sidewall area. Measurements were made downstream of the mixer in a co-annular wind tunnel, and the simulations were carried out using an unstructured Reynolds averaged Navier–Stokes (RANS) solver, Numeca FINE/Hexa, with k-ω SST model. In the core flow, the swirl angle was varied from 0deg to 30deg. At high swirl angles, a three-dimensional separation bubble was formed on the lobe's suction surface penetration region and resulted in the generation of a vortex at the lobe valley. The valley vortex quickly dissipated downstream. The mixer lobes removed most of the swirl, but scalloped lobes removed less swirl in the region of the scalloped notch. The residual swirl downstream of the scalloped mixer interacted with the vortices and improved mixing rates compared to the unscalloped mixer. Core flow swirl up to 10deg provided improved mixing rates and reduced pressure and thrust losses for both mixers. As core flow swirl increased beyond 10deg, the mixing rate continued to improve, but pressure and thrust losses declined compared to the zero swirl case. Lobe scalloping, in high swirl conditions, resulted in better mixing and improved pressure loss over the unscalloped mixer but at the expense of reduced thrust.

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Fig. 1

Cutaway of the test section

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Fig. 2

Lobed mixer geometry

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Fig. 3

Computational mesh

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Fig. 4

Experimentally measured flowfields downstream of the mixers at baseline

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Fig. 5

Axial decay of streamwise circulation at baseline

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Fig. 6

Radial distribution of swirl angle at the x/Dh = 0.07 plane for 10 deg and 30 deg swirl cases

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Fig. 7

CFD predicted static pressure distribution and surface oil-flow visualization on the core surface of lobe valley

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Fig. 8

Experimentally measured flowfields downstream of the mixers at 30 deg swirl

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Fig. 9

CFD predicted streamwise vorticity fields with 30 deg inlet swirl

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Fig. 10

CFD predicted streamwise vorticity field at the mixer valley trailing edge

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Fig. 11

Streamwise circulation at the x/Dh = 0.07 plane

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Fig. 12

CCW streamwise circulation downstream of the mixers

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Fig. 13

CFD predicted normalized turbulent kinetic energy at 30 deg swirl

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Fig. 14

Static pressure mixing index

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Fig. 15

Total pressure and thrust loss of the mixers



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