Research Papers: Gas Turbines: Turbomachinery

The Influence of Reynolds Number and Roughness on the Efficiency of Axial and Centrifugal Fans—A Physically Based Scaling Method

[+] Author and Article Information
Peter F. Pelz

Professor, Head of Chair
Chair of Fluid Systems and Technology,
Technische Universität Darmstadt,
Magdalenenstr. 4,
Darmstadt 64287, Germany
e-mail: peter.pelz@fst.tu-darmstadt.de

Stefan S. Stonjek

Research Assistant
Chair of Fluid Systems and Technology,
Technische Universität Darmstadt,
Petersenstr. 30,
Darmstadt 64287, Germany
e-mail: stefan.stonjek@fst.tu-darmstadt.de

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 9, 2012; final manuscript received October 11, 2012; published online April 23, 2013. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(5), 052601 (Apr 23, 2013) (8 pages) Paper No: GTP-12-1323; doi: 10.1115/1.4022991 History: Received August 09, 2012; Revised October 11, 2012

There is a technical and economical need for a correction method to scale model test data, which fulfills five tasks: It should be (i) physically based, (ii) understandable and easy to apply, and (iii) universal, i.e., applicable to centrifugal as well as to axial machines of different specific speed. Moreover, the method should (iv) account for the aerodynamic quality of the machine and should (v) be reliable not only at peak efficiency, but also at off-design condition. Up to now, no method meets all five tasks. To fill that gap, a method developed at Technical University Darmstadt together with Forschungsvereinigung für Luft- und Trocknungstechnik e. V. (FLT) is introduced in this work. The method consists of three steps: Assuming the so-called master curve, scaling the efficiency itself and shifting the best efficiency point to a higher flow coefficient. For each step, a simple physical explanation is given. The validation of the method is done with test data of two axial fans with four different stagger angles and two centrifugal fans. In spite of its simplicity, the method shows a good agreement to test data compared with traditional and most recent scaling methods. A short overview about the advantages and disadvantages of compared methods and a conclusion is given at the end of this work.

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Fig. 1

Efficiency versus specific speed σ = ns/(157.8 min-1) [1]

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Fig. 2

Performance characteristics of axial fans of specific speed σ = 1.46 tested at the Chair of Fluid Systems Technology, TU Darmstadt, with the stagger angle Δβ0 = -6 deg. The Reynolds number differs from 6.1E5 to 8.6E6. The markers in (a) designate the peak efficiency points. For the fan description, see Hess [7].

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Fig. 3

Colebrook's interpolation (Eq. (15)) and scaling from small-model (sm) to full-scale machine (fs)

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Fig. 4

Uneven boundary layers on pressure and suction side. The difference between the left and right cascade is the Reynolds number and, hence, the boundary layer thickness. To achieve the optimal flow angle in the right cascade, the flow coefficient ϕ has to be changed to ϕ+Δϕ.

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Fig. 11

Ideal pressure coefficient and pressure loss coefficient [7]

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Fig. 5

Fan test stands at the Chair of Fluid Systems Technology. (1) Axial fan (sm), (2) axial fan (lm), (3) axial fan (aero acoustics), (4) centrifugal fan (lm).

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Fig. 6

Characteristic of the centrifugal fan with σ = 0.29 scaled up with different methods. The method of Hess is based on the Ackeret method.

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Fig. 7

Axial fan with stagger angle Δβ0 = +6 deg(σ = 1.64)

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Fig. 8

Axial fan with stagger angle Δβ0 = 0 deg(σ = 1.49)

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Fig. 9

Axial fan with stagger angle Δβ0 = -6 deg(σ = 1.46)

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Fig. 10

Axial fan with stagger angle Δβ0 = -12 deg(σ = 1.53)

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Fig. 12

Change in efficiency with increase of Mach number for a compressor of a turbocharger. Measurements done by Nakhjiri et al. [15].



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