Tonal noise generation mechanisms in low-speed mixed-flow fans

2014 ◽  
Author(s):  
Timothy J. Newman ◽  
Anurag Agarwal ◽  
Ann Dowling ◽  
Ryan Stimpson
Keyword(s):  
Noise Generation ◽  
Tonal Noise ◽  
Mixed Flow ◽  
Low Speed ◽  
Generation Mechanisms

scholarly journals Exterior Noise Due to Interaction of Tyre-Thermoplastic Transverse Rumble Strips

2017 ◽  
Vol 42 (3) ◽  
pp. 449-457 ◽  
Author(s):  
Zaiton Haron ◽  
Mohd Hanifi Othman ◽  
Lim Meng Hee ◽  
Khairulzan Yahya ◽  
Mohd Rosli Hainin ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Surface Texture ◽  
Sound Level ◽  
Vehicle Speed ◽  
Noise Generation ◽  
Octave Band ◽  
Trade Off ◽  
Low Speed ◽  
The Public ◽  
Generation Mechanisms

AbstractTransverse rumble strips (TRS) are a common choice to reduce vehicle speed and increase driver alertness on roadways. However, there is a potential trade-off using them on rural roadway due to the noise problem created when vehicles go over the strips. The present study investigated the noise level, spectral analysis, and the possible noise generation mechanism when the TRS is hit by a vehicle. Tenraised- rumbler (RR) and three-layer-overlapped (TLO) TRS were selected in this study as they have received complaints from the public. Results showed that RR generated a relatively higher noise and impulse at a low speed, and increased sound level in each octave band. Based on these results, RR may irritate human ears even when the vehicle travels at a low speed. It was found that RR increased all noise generation mechanisms of tyre-pavement interaction whilst TLO increased structural resonance, sidewall and surface texture vibration.

scholarly journals Aeroacoustic Analysis of the Tonal Noise of a Large-Scale Radial Blower

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Aurélien Marsan ◽  
Stéphane Moreau
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Navier Stokes ◽  
Noise Generation ◽  
Tonal Noise ◽  
Radiated Noise ◽  
Rotating Blades ◽  
Reynolds Averaged Navier Stokes ◽  
Generation Mechanisms ◽  
Made In

Large-scale radial blowers are widely used in factories and are one of the main sources of noise. The present study aims at identifying the noise generation mechanisms in such a radial blower in order to suggest simple modifications that could be made in order to reduce the noise. The flow in a representative large-scale radial blower is investigated thanks to unsteady Reynolds-averaged Navier–Stokes (URANS) numerical simulations. The radiated noise is calculated, thanks to an in-house propagation code based on the Ffowcs Williams Hawkings' (FWH) analogy, SherFWH. The results highlight the main noise generation mechanisms, in particular the interaction between the rotating blades and the tongue, and the interaction between the rotating blades and the trapdoors located on the volute sidewall. Some modifications of the geometry are suggested.

Tonal Noise Reduction in a Radial Fan With Forward-Curved Blades

2014 ◽  
Author(s):  
Manoochehr Darvish ◽  
Bastian Tietjen ◽  
Daniel Beck ◽  
Stefan Frank
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Aerodynamic Performance ◽  
Computational Aeroacoustics ◽  
Experimental Measurements ◽  
Noise Generation ◽  
Tonal Noise ◽  
Outlet Angle ◽  
And Performance ◽  
Impeller Geometry

The main focus of this work is on the geometrical modifications that can be applied to the fan wheel and the volute tongue of a radial fan to reduce the tonal noise. The experimental measurements are performed by using the in-duct method in accordance with ISO 5136. In addition to the experimental measurements, CFD (Computational Fluid Dynamics) and CAA (Computational Aeroacoustics) simulations are carried out to investigate the effects of different modifications on the noise and performance of the fan. It is shown that by modifying the blade outlet angle, the tonal noise of the fan can be reduced without affecting the performance of the fan. Moreover, it is indicated that increasing the number of blades leads to a significant reduction in the tonal noise and also an improvement in the performance. However, this trend is only valid up to a certain number of blades, and a further increment might reduce the aerodynamic performance of the fan. Besides modifying the impeller geometry, new volute tongues are designed and manufactured. It is demonstrated that the shape of the volute tongue plays an important role in the tonal noise generation of the fan. It is possible to reduce the tonal noise by using stepped tongues which produce phase-shift effects that lead to an effective local cancellation of the noise.

Advanced Numerical Methods for the Prediction of Tonal Noise in Turbomachinery—Part I: Implicit Runge–Kutta Schemes

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Graham Ashcroft ◽  
Christian Frey ◽  
Kathrin Heitkamp ◽  
Christian Weckmüller
Keyword(s):  
Stokes Equations ◽  
Temporal Integration ◽  
Aerodynamic Noise ◽  
Navier Stokes ◽  
Noise Generation ◽  
Academic Problems ◽  
Tonal Noise ◽  
Navier Stokes Equations ◽  
Runge Kutta ◽  
The Stability

This is the first part of a series of two papers on unsteady computational fluid dynamics (CFD) methods for the numerical simulation of aerodynamic noise generation and propagation. In this part, the stability, accuracy, and efficiency of implicit Runge–Kutta schemes for the temporal integration of the compressible Navier–Stokes equations are investigated in the context of a CFD code for turbomachinery applications. Using two model academic problems, the properties of two explicit first stage, singly diagonally implicit Runge–Kutta (ESDIRK) schemes of second- and third-order accuracy are quantified and compared with more conventional second-order multistep methods. Finally, to assess the ESDIRK schemes in the context of an industrially relevant configuration, the schemes are applied to predict the tonal noise generation and transmission in a modern high bypass ratio fan stage and comparisons with the corresponding experimental data are provided.

Steady State Engine Test Demonstration of Performance Improvement With an Advanced Turbocharger

2013 ◽  
Author(s):  
Harold Sun ◽  
Dave Hanna ◽  
Liangjun Hu ◽  
Eric Curtis ◽  
James Yi ◽  
...  
Keyword(s):  
Steady State ◽  
Performance Improvement ◽  
High Efficiency ◽  
Combustion Engine ◽  
Load Condition ◽  
Department Of Energy ◽  
Speed Ratio ◽  
Mixed Flow ◽  
Turbine Wheel ◽  
Low Speed

Heavy EGR required on diesel engines for future emission regulation compliance has posed a big challenge to conventional turbocharger technology for high efficiency and wide operation range. This study, as part of the U.S. Department of Energy sponsored research program, is focused on advanced turbocharger technologies that can improve turbocharger efficiency on customer driving cycles while extending the operation range significantly, compared to a production turbocharger. The production turbocharger for a medium-duty truck application was selected as a donor turbo. Design optimizations were focused on the compressor impeller and turbine wheel. On the compressor side, advanced impeller design with arbitrary surface can improve the efficiency and surge margin at low end while extending the flow capacity, while a so-called active casing treatment can provide additional operation range extension without compromising compressor efficiency. On the turbine side, mixed flow turbine technology was revisited with renewed interest due to its performance characteristics, i.e. high efficiency at low-speed ratio, relative to the base conventional radial flow turbine, which is relevant to heavy EGR operation for future diesel applications. The engine dynamometer test shows that the advanced turbocharger technology enables over 3% BSFC improvement at part-load as well as full-load condition, in addition to an increase in rated power. The performance improvement demonstrated on engine dynamometer seems to be more than what would typically be translated from the turbocharger flow bench data, indicating that mixed flow turbine may provide additional performance benefits under pulsed exhaust flow on an internal combustion engine and in the low-speed ratio areas that are typically not covered by steady state flow bench tests.

Boundary-layer instability noise on aerofoils

1999 ◽  
Vol 382 ◽  
pp. 27-61 ◽  
Author(s):  
EMMA C. NASH ◽  
MARTIN V. LOWSON ◽  
ALAN McALPINE
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Noise Generation ◽  
Tonal Noise ◽  
Instability Waves ◽  
S Waves ◽  
Pressure Surface ◽  
Boundary Layer Instability ◽  
Moderate Reynolds Number ◽  
Tollmien Schlichting

An experimental and theoretical investigation has been carried out to understand the tonal noise generation mechanism on aerofoils at moderate Reynolds number. Experiments were conducted on a NACA0012 aerofoil section in a low-turbulence closed working section wind tunnel. Narrow band acoustic tones were observed up to 40 dB above background noise. The ladder structure of these tones was eliminated by modifying the tunnel to approximate to anechoic conditions. High-resolution flow velocity measurements have been made with a three-component laser-Doppler anemometer (LDA) which have revealed the presence of strongly amplified boundary-layer instabilities in a region of separated shear flow just upstream of the pressure surface trailing edge, which match the frequency of the acoustic tones. Flow visualization experiments have shown these instabilities to roll up to form a regular Kármán-type vortex street.A new mechanism for tonal noise generation has been proposed, based on the growth of Tollmien–Schlichting (T–S) instability waves strongly amplified by inflectional profiles in the separating laminar shear layer on the pressure surface of the aerofoil. The growth of fixed frequency, spatially growing boundary-layer instability waves propagating over the aerofoil pressure surface has been calculated using experimentally obtained boundary-layer characteristics. The effect of boundary-layer separation has been incorporated into the model. Frequency selection and prediction of T–S waves are in remarkably good agreement with experimental data.

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