The paper aims at discovering the relationship between the spanwise gradient of blade circulation and the total efficiency gain due to forward sweep, in the case of low-speed axial flow fans, at the design point. For this purpose, an extensive set of literature data have been processed and evaluated by statistical means. A trend function has been established for quantifying the aforementioned relationship. By such means, it has been pointed out that the efficiency gain due to forward sweep tends to increase with the spanwise gradient of blade circulation. This means that the purposeful incorporation of forward sweep in the design process offers an increased potential for efficiency improvement in the case of rotors of controlled vortex design. The maximum efficiency gain has been observed to be 2% to 3%, due to an in-house developed design method. It has been noted that the efficiency improvement due to forward sweep tends to be minor for free-vortex rotors. Furthermore, the efficiency tends to deteriorate if spanwise decreasing blade circulation occurs in forward-swept rotors. Remarks have been made on the means of simultaneous reduction of loss and noise related to low-speed axial fans, for a prescribed aerodynamic performance.
de Wilt G. EU policies on energy efficiency and the impact on fan manufacturers. In: Keynote lecture, Fan2012, international conference on fan noise, technology and numerical methods, Senlis, France, April 2012.
2.
Directive No. 2009/125/EC of the European Parliament and of the Council of the European Union, of 21 October 2009, establishing a framework for the setting of ecodesign requirements for energy-related products. Official Journal of the European Union, 31 October 2009, pp. 10–35.
3.
Regulation of the European Commission (EU) No. 327/2011, of 30 March 2011, implementing Directive 2009/125/EC of the European Parliament and of the Council of the European Union with regard to ecodesign requirements for fans driven by motors with an electric input power between 125 W and 500 kW. Official Journal of the European Union, 6 April 2011, pp. 8–21.
4.
Energy conservation standards rulemaking framework for commercial and industrial fans and blowers. United States Department of Energy, Office of Energy Efficiency and Renewable Energy, Building Technologies Program. 28 January 2013.
5.
CorsiniADelibraGSheardAG. The application of sinusoidal blade-leading edges in a fan-design methodology to improve stall resistance. Proc IMechE, Part A: J Power and Energy. Epub ahead of print 12 December 2013. DOI: 10.1177/0957650913514229.
6.
VadJ. Forward blade sweep applied to low-speed axial fan rotors of controlled vortex design: an overview. ASME J Eng Gas Turb Power2013; 135. 012601–1:012601:9.
7.
Benedek T and Vad J. Concerted aerodynamic and acoustic diagnostics of an axial flow industrial fan, involving the phased array microphone technique. ASME paper GT2014-25916, 2014.
8.
VadJ. Incorporation of forward blade sweep in preliminary controlled vortex design of axial flow rotors. Proc IMechE, Part A: J Power and Energy2012; 226: 462–478.
9.
VadJ. Energiahatékony axiális átömlésű ventilátor-járókerekek tervezése [Design of energy-efficient axial flow fan rotors]. Energiagazdálkodás2012; 53: 8–10 [in Hungarian].
10.
CorsiniARispoliF. Using sweep to extend the stall-free operational range in axial fan rotors. Proc IMechE, Part A: J Power and Energy2004; 218: 129–139.
11.
MohammedKPPrithvi RajD. Investigation on axial flow fan impellers with forward swept blades. ASME J Fluids Eng1977; 99: 543–547.
12.
RamakrishnaPVGovardhanM. Study of sweep and induced dihedral effects in subsonic axial flow compressor passages – part 1: design considerations – changes in incidence, deflection, and streamline curvature. Int J Rotating Mach2009; 2009: Article ID 787145, 11 pages–Article ID 787145, 11 pages.
13.
McNulty GS, Decker JJ, Beacher BF, et al. The impact of forward swept rotors on tip-limited low-speed axial compressors. ASME paper GT2003-38837, 2003.
14.
LiYQuangHDuZ-H. Optimization design and experimental study of low-pressure axial fan with forward-skewed blades. Int J Rotating Mach2007; 2007: Article ID 85275, 10 pages–Article ID 85275, 10 pages.
15.
Rohkamm H, Kosyna G, Saathoff H, et al. Enhancement of highly-loaded axial compressor stage performance using rotor blade tip tailoring, part II – experimental results. In: 6th European conference on turbomachinery fluid dynamics and thermodynamics, Lille, 7--11 March 2005, pp.100–110. Paris, France: ENSAM, SERAM.
16.
Beiler MG. Untersuchung der dreidimensionalen Strömung durch Axialventilatoren mit gekrümmten Schaufeln. Doctoral Dissertation, Universität-GH-Siegen, VDI Verlag, Reihe 7: Strömungstechnik, No. 298, Düsseldorf, 1996.
17.
Yamaguchi N, Tominaga T, Hattori S, et al. Secondary-loss reduction by forward-skewing of axial compressor rotor blading. In: Yokohama international gas turbine congress, Yokohama: Gas Turbine Society of Japan, 27 October–1 November 1991, pp.II.61–II.68.
18.
Meixner HU. Vergleichende LDA-Messungen an ungesichelten und gesichelten Axialventilatoren. Doctoral Dissertation, Universität Karlsruhe, VDI-Verlag, Reihe 7: Strömungstechnik, No. 266, Düsseldorf, 1995.
19.
HelmingK. Numerical analysis of sweep effects in shrouded propfan rotors. J Propul Power1996; 12: 139–145.
20.
Clemen C, Gümmer V, Goller M, et al. Tip-aerodynamics of forward-swept rotor blades in a highly-loaded single-stage axial-flow low-speed compressor. In: Proceedings of the 10th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery (ISROMAC10), Honolulu, 2004, paper no. 027.
21.
Vad J, Kwedikha ARA and Jaberg H. Influence of blade sweep on the energetic behavior of axial flow turbomachinery rotors at design flow rate. ASME paper GT2004-53544, 2004.
22.
VadJKwedikhaARAHorváthCS. Aerodynamic effects of forward blade skew in axial flow rotors of controlled vortex design. Proc IMechE, Part A: J Power and Energy2007; 221: 1011–1023.
23.
VadJ. Aerodynamic effects of blade sweep and skew in low-speed axial flow rotors at the design flow rate: an overview. Proc IMechE, Part A: J Power and Energy2008; 222: 69–85.
24.
Masi M, Piva M and Lazzaretto A. Design guidelines to increase the performance of a rotor-only axial fan with constant-swirl blading. ASME paper GT2014-27176, 2014.
25.
BenedekTTóthP. Beamforming measurements of an axial fan in an industrial environment. Period Polytech Mech Eng2013; 57: 37–46.
26.
LinnikYV. Méthode des moindres carrés. Éléments de la théorie du traitement statistique des observations, Paris: Dunod, 1963.
27.
DevoreJFarnumN. Applied statistics for engineers and scientists, 2nd ed. Belmont, CA: Thomson Brooks/Cole, 2005.
