Tag Archives: noise

Sound from high-Reynolds number flow over bluff bodies

Posted on by

Purpose
– This paper aims to investigate the aerodynamic sound generated from flow over bluff bodies at a high Reynolds number. By taking circular and square cylinders as two representative geometries for the cross-section of bluff bodies, this study aims to clarify the difference in flow formation and sound generation between the two types of bluff bodies. Furthermore, the possibility for a downstream flat plate to be used as sound cancellation passive mechanism is also discussed in this study.

Design/methodology/approach
– Sound source from the near field is numerically solved by using the Unsteady Reynolds-Averaged Navier Stokes equations. While for the sound at far-field, the compact sound theory of Curle’s analogy is used.

Findings
– Magnitude of the generated sound is dominant by the aerodynamic forcer fluctuations, i.e. lift and drag, where the lift fluctuation gives the strongest influence on the sound generation. The square cylinder emits 4.7 dB higher than the sound emitted from flow over the circular cylinder. This relates to the longer vortex formation length for the case of square cylinder that provides space for more vortex to dissipate. It is suggested that downstream flat plate is possible to be applied for a sound cancellation mechanism for the case of circular cylinder, but it would be more challenging for the case of square cylinder.

Practical implications
– This study include implications for the development of noise reduction study especially in high-speed vehicles such as the aircrafts and high-speed trains.

Originality/value
– This study identified that there is possible method for sound cancellation in flow over bluff body cases by using passive control method, even in flow at high Reynolds number.

http://www.emeraldinsight.com/doi/full/10.1108/AEAT-06-2014-0086

email me (researchsukri[at]gmail.com) if you want the copy of the paper.

Flow modelling and noise generation of interacting prisms.

Posted on by

Noise generation is a significant issue for High-Speed Trains (HSTs), and as speeds increase aerodynamically generated noise becomes the dominant noise source. In this article, the effect of nose shape, carriage separation and yaw angle on the aerodynamics and noise generation are analysed using two prisms, representing a HST model. The aerodynamics are modelled using Computation Fluid Dynamics (CFD), and the flow velocity and turbulence intensity in various positions in the wake are compared with experimental hotwire data measured in the Anechoic Wind Tunnel (AWT) at The University of Adelaide, with good agreement. Finally, acoustic beamforming images of the noise generated by the interacting prisms measured in the AWT are presented. The acoustic results show that a blunt nose tends to increase noise at lower frequencies significantly, while increasing prism separation tends to increase noise over most frequencies, but most significantly at midfrequencies, and increasing yaw angle increases noise across all frequencies. Beamforming results show that at lower frequencies, this noise tends to be generated at the leading and trailing edges, while at higher frequencies the noise tends to be generated in the carriage gap.

AIAA Aviation,16-20 June 2014, Atlanta, GA, 20th AIAA/CEAS Aeroacoustics Conference.

Paper: AIAA 2014-3287

Two papers about passive flow and noise control have been accepted for publications

Posted on by

A simple but effective passive wake and noise control for bluff body applications, e.g., high rise buildings, side view mirror of passenger cars, landing gear system of aircrafts and etc., can be made practically possible by introducing a small flat plate downstream of the bluff bodies. [International Journal of Heat and Fluid Flow, and AIAA Journal]

TsAGI Starts Design Work On New Supersonic Business Jet. AIAA news

Posted on by

Flight International (3/15, Trimble) reports, “A major Russian aeronautical research agency has launched preliminary design work for a quiet supersonic business jet that could fly over populated areas.” The Central Aerohydrodynamic Institute (TsAGI) is working with Sukhoi and others on the plane that features “four engines mounted on top of the aft fuselage” and “twin vertical tails and long, thin wings” in concept art. With the work, the agency wants Russia to become a “technology leader” in the field.

Aircraft noise and vibration in helicopter operations create a safety issue. From AIAA news

Posted on by

Rosekind Says Pilot Fatigue Remains Top Issue. Aviation International News (2/13, Mark) reports the NTSB’s Mark Rosekind told the Heli-Expo audience this weekend, “Fatigue in the aviation industry has been on the NTSB’s Top 10 Most-Wanted list for two decades. … It still makes up six of our top 10 fears today.” Rosekind “dove right into the fatigue issue at the lead-off educational session at Heli-Expo 2012 in Dallas.” He said “aircraft noise and vibration in helicopter operations create special fatigue issues, as does the predominance of single-pilot, on-demand operations, often conducted at night.“