Investigation on Unstable Pressure Distribution of an Axial Fan Blade with Difference of Setting Angle and Chord Length

The performance of an industrial fan was simulated using CFD and results were compared with the experimental data. The fan is used to cool a row of resistor networks which dissipate excess energy generated by regenerative power in an inverter application. It has a diameter of 24 inches (0.6096m) and rotates at different speeds ranging from 2500 to 3900 RPM depending on the requirements. CFD simulation results were also verified by simulating performance of the same fan at different speeds and comparing the results with what was expected from fan affinity laws. The CFD results matched almost exactly (with ∼0.2% difference for pressure at a given flow rate) with the performance being predicted by the affinity laws. The effect of variation of different parameters such as the blade length, number of blades, and blade chord length was studied. Increasing the blade length at the same RPM increased the mass flow rate (by ∼17%) for the same pressure. Increasing the chord length while keeping the same number of blades, at a given RPM, made the performance curve (pressure versus flow rate, i.e. PV curve) steeper and blades stalled at a higher mass flow rate (8.77 kg/sec compared to the previous 8.44 kg/sec). For the same total blade surface area, less number of blades with longer chords stalled at lower mass flow rates (9.22 kg/sec for a 33% shorter chord and 36 blades compared to 8.3 kg/sec for the original rotor which had 24 blades).

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A Ring Silencer Design for Reducing Noise of Axial Fan

Fluctuation and Noise Letters ◽

10.1142/s0219477503001348 ◽

2003 ◽

Vol 03 (03) ◽

pp. L259-L264

Author(s):

Jian-Da Wu ◽

Mingsian R. Bai

Keyword(s):

Helmholtz Resonator ◽

Boundary Region ◽

Acoustic Analogy ◽

Axial Fan ◽

Noise Sources ◽

Fan Noise ◽

Fluctuating Pressure ◽

Axial Fans ◽

Fan Blade ◽

Broadband Frequency

In this paper, a ring silencer design for reducing the noise of axial fans is presented. The noise sources on axial fans are usually caused by the fluctuating pressure distribution on the surface of fan blade. Most of the sources are near the trailing edge of blades or boundary region of blades. The ideation of proposed design is based on the principle of Helmholtz resonator for reducing the noise around the fan. The electro-acoustic analogy of this design is presented and simply discussed. Experimental measurement is carried out to evaluate the proposed design for reducing the axial fan noise. The result of experiment indicated that the ring silencer achieved 17 dB in blade passing frequency and 10 dB in other broadband frequency of power spectrum level.

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Fan Blade Design Methods: Cascade Versus Isolated Airfoil Approach — Experimental and Numerical Comparison

Volume 1: Aircraft Engine; Fans and Blowers; Marine ◽

10.1115/gt2016-56994 ◽

2016 ◽

Cited By ~ 1

Author(s):

Stefano Castegnaro

Keyword(s):

Reynolds Numbers ◽

Medium Size ◽

Numerical Comparison ◽

Blade Design ◽

Axial Fan ◽

Local Flow ◽

Flow Features ◽

Fan Blade ◽

Mixed Approach ◽

Cfd Analyses

Both cascade and isolated airfoil methods are considered valid in axial fan blade design, for high (σ≳1) and low (σ≲0.7) solidities respectively. For bladings that feature intermediate solidities the modified isolated approach is commonly employed. This method uses isolated airfoil data, with proper adjustments to take into account multiplane interference effects. Contrarily, the literature does not refer about modifications of the cascade approach to design medium solidity fans. Such method would use cascade data, properly adjusted for the blade sections at lower solidities. Thus, with the aim of comparing these two opposite design approaches (modified cascade versus modified isolated) for medium solidity blades, two free-vortex blading were designed for a 315 mm rotor-only axial fan and experimentally tested. CFD analyses were performed as well to obtain the local flow features. NACA-65 series airfoils were employed, as both cascade and isolated data are available for chord Reynolds numbers typical of axial fans applications. Results highlight the differences between the two approaches. Finally, a mixed approach that employs both isolated and cascade data is suggested as the most accurate one. Moreover, results also show the detrimental effects of the low chord Reynolds numbers on the performance of the blades. This effect should be taken into account in blade design for small-to-medium size machines.

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