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01.01 Fan and Turbomachinery Noise, Part 3

Experimental study of wavy trailing edge serrations on flat rotor blades
Time: 11:00 am

Author: sai Manikanta Kaja

Abstract ID: 1970

A detailed experimental study is conducted to observe the effect of various parameters like wavelength, depth of serrations, and pitch angle on serrated blades’ acoustic emissions at low speeds up to 2000 rpm. Experiments are conducted on flat blade rotors with sinusoidal serrations on the trailing edge of blades with different amplitudes and wavelengths. A total of 7 blades with different serration configurations, including a base configuration, are studied, five of them have serrations throughout the span of the blade, and one configuration has serration of varying amplitude on the farther half of the blade. It is observed that some blade configurations have resulted in tonal noise reduction noise as much as 8dB, whereas some of the serration configurations reduce very little to none, there is no significant effect of T.E serrations on the broadband noise emitted by the rotor. Directivity of noise generated from the rotor, the effect of serrations on the directivity of the noise is studied.

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Study on the effect of separation and reattachment flow between blades on fan noise
Time: 11:20 am

Author: Sho Kosaka

Abstract ID: 2142

With the growth of the EV/HV market, the main cause of cabin noise has changed from engine driving sound to air conditioner noise. The blower noise is the largest in the air conditioner noise, and the noise reduction is urgent. Separated and reattached flows between fan blades are considered to be the main sources of blower noise. In the past, we tried to reduce the noise by reducing the separation. This time, the blade shape to further reduce the separation was produced and evaluated. As a result, the noise was greatly reduced, but a new problem was found that there was a flow velocity condition in which the noise increased despite the small separation. Therefore, we visualized the flow between blades by PIV, investigated the state of separated and reattached flow in detail, and investigated the factors related to noise increase and decrease by measuring noise and pressure fluctuation of blade surface simultaneously. As a result, it was found that the noise generation condition in the separation reattachment flow between blades is not only the size of separation but also the distance of separation shear layer from blade surface and the strength of vortex generated in shear layer.

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Directivity of sound propagation from an commercial supersonic engine inlet
Time: 11:40 am

Author: Mitchell Sugar

Abstract ID: 2633

The effects of mean flow variations on sound propagation from an axisymmetric commercial supersonic engine inlet were studied using numerical methods. A finite element model of the inlet was constructed in Ansys Fluent and used to solve for flow fields given by different initial conditions. Results from this model were fed into the aeroacoustic solver, Actran, and used to calculate far field radiated noise as well as the directivity of that noise. The acoustic source of this noise was a plane wave of a known strength placed at the fan face. In addition to assessing the effects of mean flow on the radiated noise transfer functions, the duct modes of the model were compared across different flow regimes. Relationships between mean flow parameters and the directivity of duct modes are developed.  The results of this study will be used in further studies to gain a deeper understanding of how the underlying physics which govern the system create favorable or unfavorable directivity patterns.

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Industrial fan vibration signature characterization
Time: 12:00 pm

Author: Timothy Copeland

Abstract ID: 3181

Technique for measuring and reducing industrial fan vibration and noise is detailed.  A method used to characterize the vibration signature for 100% industrial fan systems shipped is described.  A fan system consists of motor, propeller and cage.  We measure triax accelerometer vibration, microphone (both sound pressure level in dBA and raw signal in Pa) along with the current of three phase power for each fan shipped.  Comparisons are done immediately with the ISO 14694:2003 standard and troubleshooting and design changes are implemented if vibration limits are exceeded.  The method and results are provided for several cases.  Troubleshooting and best practices are described for various designs.  A portable system takes measurements in the field which are compared to the factory baseline characterization in real time to solve installation problems.

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