The Silent flight of owls
Name:
Date:
Introduction
Owls are a group on nocturnal birds. They belong to the order Strigiformes which has two families; the Tytonidae also called the barn owls and related species, and the Strigidae known as the typical Owls. The owls are raptures; they feed on other animals given their unique features and particular adaptations. Some of these features are the art of silent flight, exceptional vision, acute hearing, and powerful beaks and talons.
The relevance of this study draws interest from the aviation industry. Even though the aircraft and birds flight base several notable differences. The bird’s flight could still be used to solve specific problems in airplanes. One of such issues is the mechanism that could be used to reduce noise production during flight could be reduced. In as much as noise is a by-product of flight, it has been responsible for health issues like an increase in blood pressure in addition to causing discomfort. Therefore, noise reduction in flight should be eliminated.
The study will establish whether owls have a silent flight compared to other birds, the reasons for such flights and how these could be used to reduce noise in the aircraft. It is the belief of the study that the Unique Owls characteristics could be a role model for technical applications that will help reduce noise in aircraft.
Literature
To determine the truth of the say that owls produce less noise during flight compared to other birds, Sarradj, Fritzsche and Geyer (2011) in their study or the flight of the barn owl reported that, the noise produced by an owl was about 4dB below the noise produced by other species of birds for frequencies above the 1.6 kHz third octave band. In another study by Geyer, Sarradj and Fritzsche (2014) investigating the aerodynamics performance of prepared wings at 0.5 spanwise position of the ban owl, the researcher established that at higher Strouhal numbers (1000 in this case) the wings of owl species tested produces less noise of between 5-10dB compared to wings of other species. These results were also shared by the experiment by Chen et al. for frequencies above 400 Hz (2014).
As argued by Geyer, Claus, and Sarradj (2016), the owl’s feathers (see figure 1 in the appendix) possess three linked to the quiet flight; the porous and soft wing upper surface, fringes at the trailing edge and the comb-like structures (serrations) at the leading edge of the wing. The serration is responsible for noise reduction during the time of glide as a result of a small increase in lift preventing laminar separation (Lilley, 1998). The shape of the serrations may change depending on the owl species and therefore the three-dimensions that were of considerations were length, width, thickness as well as the three-dimensional position angles. Narayanan et al. (2015) in their experimental investigation to reduce broadband noise using the leading-edge serrations due to turbulence established that, there was an insignificant noise reduction at low frequencies which graduated to significance in the mid frequency ranges. The experiment also established that there was a link between the amplitude of the serrations and noise reduction; however, the spacing had no link to noise reduction.
The Shinkansen train in Japan design was inspired by the motivation to reduce noise using the special owl features. The design involved the presence of comb-like pantograph for the train. The result of the modification was fewer vibrations experienced and therefore less noise produced (ISSUU, 2012).
Discussion
In summary, Serrations influence aerodynamic performance and noise production. The study has shown that the presence of the serrations in the owl wing is the cause of silence of its flight. This can be applied in the airplane designs as was done in the Shinkansen train design reported at (ISSUU, 2012). The study has also established the effect of serration on flight noise reduction is a factor of shape and amplitude (Narayanan et al., 2015)) However, the influence of size is still a matter or discussions. There is also conjecture in the relation of the lifestyle of the whole and the nature of the serration as the different owl a species register difference in serrations types. Despite all these, the aspect of serration has been proven to be critical in the reduction of noise as a result of turbulence.
Future studies should endeavor to establish the relationship between the size of serrations to flight noise reduction. The effect of twisting and tilting serrations should also be investigated as these may prove critical to aerodynamic performance and noise-reduction in flights.
References
Sarradj, E., Fritzsche, C., & Geyer, T. (2011). Silent owl flight: bird flyover noise measurements. AIAA Journal, 49(4), 769-779.
Geyer T, Sarradj E, Fritzsche C. 2014. Measuring owl flight noise. In INTER-NOISE and NOISE-CON Congress and Conf. Proc., pp. 183–198. Institute of Noise Control Engineering.
Geyer, T. F., Claus, V. T., & Sarradj, E. (2016). Silent owl flight: The effect of the leading-edge comb on the gliding flight noise. In 22nd AIAA/CEAS Aeroacoustics Conference (p. 3017)
Geyer TF, Wasala SH, Carter JE, Norris SE, Sarradj E. 2016Experimental investigation of leading edge hook structures for wind turbine noise reduction. AIAA Paper 2016-2954.
Chen K, Liu Q, Liao G, Yang Y, Ren L, Yang H, Chen X. 2012The sound suppression characteristics of wing feather of the owl (Bubo bubo). J. Bionic Eng.9, 192–199.
Lilley, G. M., A Study of the Silent Flight of the Owl. 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, AIAA paper 1998-2340 (1998)
Narayanan S, Chaitanya P, Haeri S, Joseph PF, Kim JW, Polacsek C. 2015Airfoil noise reductions through leading-edge serrations. Phys. Fluids 27, 025109.
ISSUU (2012). zq2. [online]. Retrieved from: https://issuu.com/eggermont/docs/zq_issue_02final/15?e=15278665/11095381;
Lilley, G. M., A Study of the Silent Flight of the Owl. 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France,
Appendix
Figure 1. Owl Wing
Source: (Sarradj, Fritzsche & Geyer, 2011).