Fan Noise Source Diagnostic Test - Rotor Alone Aerodynamic Performance Results

A set of aeroacoustic optimization strategies for axial fans is presented. Their efficiency is demonstrated for small axial fans. Thereby, the generated noise could be reduced significantly while retaining or even improving the aerodynamic performance. In particular, we discuss the following two optimization strategies in detail: Firstly, we consider the design of winglets using a parametric model for genetic optimization. The resulting winglet geometry helps to control the tip vortex over a large range of operating points, thereby reducing the generated noise. In addition, the power consumption of the fan could be reduced. Various choices of geometrical parameter sets for optimization are evaluated. Secondly, we discuss the reduction of fan noise via contour optimized turbulators. For axial fans it is desirable to reduce sound emission across a broad operating range, not just for the design point. However, operation in off-design points may be accompanied by flow separation phenomena, which contribute predominantly to noise generation and reduce the aerodynamic performance of the fan. Turbulators can help to minimize these adverse effects. The advantages of various contoured turbulator geometries are discussed for off-design operating points. The optimization of the above mentioned strategies was driven by aeroacoustic measurements via physical tests as well as numerical analysis based on the Lattice-Boltzmann method. The merits of either method are discussed with respect to the two optimization strategies.

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Evaluating the Aerodynamic Impact of Circumferentially Grooved Fan Casing Treatments With Integrated Acoustic Liners on a Turbofan Rotor

Volume 2A: Turbomachinery ◽

10.1115/gt2019-91369 ◽

2019 ◽

Cited By ~ 1

Author(s):

Richard F. Bozak ◽

Gary G. Podboy

Keyword(s):

Pressure Ratio ◽

Aerodynamic Performance ◽

Tip Clearance ◽

Tip Vortex ◽

Fan Noise ◽

Tip Leakage ◽

Fan Performance ◽

Acoustic Liners ◽

Rotor Stator Interaction ◽

Real Gas Effects

Abstract NASA is investigating the potential of integrating acoustic liners into fan cases to reduce fan noise, while maintaining the fans aerodynamic performance. An experiment was conducted to quantify the aerodynamic impact of circumferentially grooved fan cases with integrated acoustic liners on a 1.5 pressure ratio turbofan rotor. In order to improve the ability to measure small performance changes, fan performance calculations were updated to include real gas effects including the effect of humidity. For all fan cases tested, the measured difference in fan isentropic efficiency was found to be less than the measurement repeatability for a torque-based efficiency calculation (≈ 0.2%), however, an unintended tip clearance difference between configurations makes it difficult to determine if circumferentially grooved fan cases degraded fan performance. Fan exit turbulence measurements showed a 1.5% reduction in total turbulence intensity between hardwall and circumferentially grooved fan cases in the tip vortex region, which is attributed to a disruption in the formation of the tip leakage vortex. This decrease in fan exit turbulence could potentially lead to a 1–2dB reduction in broadband rotor-stator interaction noise. Reduced aerodynamic performance losses associated with over-the-rotor liners could enable further fan noise reduction.

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Numerical and Experimental Investigation of Flow Behaviour and Aerodynamic Noise in Axial Flow Fan of Air-Conditioner

Volume 7: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2011-45280 ◽

2011 ◽

Cited By ~ 1

Author(s):

Xifeng Zhao ◽

Jinju Sun ◽

Zhi Zhang

Keyword(s):

Hybrid Method ◽

Performance Test ◽

Noise Analysis ◽

Aerodynamic Performance ◽

Aerodynamic Noise ◽

Air Conditioner ◽

Acoustic Analogy ◽

Fan Noise ◽

Trailing Edge ◽

Impeller Blade

To improve aerodynamic performance and reduce noise for a split air conditioner outdoor unit fan, a hybrid method is developed, which combines the Computational Fluid Dynamics (CFD) flow simulation with Computational Aero Acoustics (CAA) noise analysis, where Large Eddy Simulation (LES) model and Ffowcs Williams-Hawkings (FW-H) acoustic analogy model are solved respectively for the unsteady flow characteristics and far field noise solutions. Experimental tests are conducted respectively for fan aerodynamic performance and acoustic behavior, with the aerodynamic performance test rig and semi-anechoic room. Numerical results demonstrates that the main dipole sound sources are located mainly on the blade trailing edge and tip surface, and shroud and casing inner surface, such a distribution is caused by fluctuations in instantaneous pressure associated with rotor-stator interaction. The casing dipole sources contribute largely to the total noise of the fan, and are the main causes for fan noise. It is demonstrated both numerically and experimentally that modifications of impeller blade geometry are effective to reduce the fan noise. Two redesign schemes, the concaved-trailing edge and flanging outer-edge blades, are used, but the latter is more effective in reducing the fan noise as well as shaft power simultaneously. The predicted SPL agrees well with the measured results at the fundamental frequency of the highest intensity, and the hybrid method used in the present study is justified.

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Effect of Rotor Tip Speed and Stator Sweep on Rotor-Stator Interaction

Volume 5: Turbo Expo 2004, Parts A and B ◽

10.1115/gt2004-54293 ◽

2004 ◽

Author(s):

Oliver V. Atassi ◽

Christopher M. Hall

Keyword(s):

Diagnostic Test ◽

Correlation Length ◽

Radial Distribution ◽

Noise Source ◽

Guide Vane ◽

Phase Variation ◽

Periodic Component ◽

Source Regions ◽

Rotor Stator Interaction ◽

Radial Phase

Data taken in the Source Diagnostic Test of the unsteady pressure on a fan-exit guide vane is analyzed to identify the dominant noise producing regions on the vane. The dominant noise source regions of the vane are identified as the outer fifty percent span of the vane. The sensitivity of this result to fan tip speed and exit guide vane sweep is studied. Sweep is seen to decrease the radial correlation length of the unsteady vane response and hence decrease the noise produced by wake-vane interaction. Results for the periodic component of the fan wakes show that the magnitude of the wake harmonics is largest in the outer fifty percent span of the duct and the radial phase variation is largest in the hub region. These results demonstrate a strong cause and effect relationship between the radial distribution of the wake harmonics and the dominant noise producing regions on the fan-exit guide vane.

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