Research Papers: Gas Turbines: Turbomachinery

A Shape Memory Alloy-Based Morphing Axial Fan Blade—Part I: Blade Structure Design and Functional Characterization

[+] Author and Article Information
Annalisa Fortini, Mattia Merlin

Metallurgy Research Group,
Engineering Department in Ferrara (ENDIF),
Ferrara 44122, Italy

Alessio Suman, Nicola Aldi, Michele Pinelli

Fluid Machinery Research Group,
Engineering Department in Ferrara (ENDIF),
Ferrara 44122, Italy

1Corresponding author.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 15, 2015; final manuscript received July 22, 2015; published online September 1, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(2), 022601 (Sep 01, 2015) (8 pages) Paper No: GTP-15-1316; doi: 10.1115/1.4031272 History: Received July 15, 2015

The possibility to realize adaptive structures is of great interest in turbomachinery design, owing to the benefits related to enhanced performance and efficiency. To accomplish this, a challenging approach is the employment of shape memory alloys (SMAs), which can recover seemingly permanent strains by solid phase transformations whereby the so-called shape memory effect (SME) takes place. This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by SMA strips that works as actuator elements in the polymeric blade structure. Concerning the fan performance, this new concept differs from a conventional viscous fan clutch solution especially during the nonstationary operating conditions. The blade design was performed in order to achieve the thermal activation of the strips by means of air stream flow. Two polymeric matrices were chosen to be tested in conjunction with a commercially available NiTi binary alloy, whose phase transformation temperatures (TTRs) were experimentally evaluated by imposing the actual operating thermal gradient. The SMA strips were then thermomechanically treated to memorize a bent shape and embedded in the polymeric blade. In a specifically designed wind tunnel, the different polymeric matrices equipped with the SMA strips were tested to assess the fluid temperature and surface pattern behavior of the blade. Upon heating, they tend to recover the memorized shape and the blade is forced to bend, leading to a camber variation and a trailing edge displacement. The recovery behavior of each composite structure (polymeric matrix with the SMA strips) was evaluated through digital image analysis techniques. The differences between the blade shape at the initial condition and at the maximum bending deformation were considered. According to these results, the best coupling of SMA strips and polymeric structure is assessed and its timewise behavior is compared to the traditional timewise behavior of a viscous fan clutch.

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Fig. 1

Temperature trend during the engine warm-up [22]

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Fig. 2

DSC curves of the untreated NiTi material

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Fig. 3

Representative scheme of the SMA thermomechanical treatment

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Fig. 4

Fan setup and blade shape sketches

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Fig. 5

SBTF functional scheme

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Fig. 6

SBTF thermal performance

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Fig. 11

Blade shape evolution during the heating ramp at the tip view

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Fig. 10

Timewise evolution of air temperature, airfoil camber at the blade tip and rotational fan velocity

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Fig. 9

Blade tip superimpositions for activated and nonactivated conditions

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Fig. 8

Digital captures from recorded video at blade tip view

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Fig. 7

Temperature trends for Compound A: polymeric structure (H, M, and S) and SMA strips (SM and SS)




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