Study of the Aero-Acoustic and Aerodynamic Effects of Soft Coating upon Airfoil

Vad, János; Koscsó, Gábor; Gutermuth, Miklós; Kasza, Zsolt; Tábi, Tamás; Csörgő, Tibor

doi:10.1299/jsmec.49.648

Cited by 18 publications

(13 citation statements)

References 8 publications

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“…In general, solid structures covered with hairs or fibres, such as fluffy bodies, are known to affect the generation of flow induced noise [16,17]. The present investigation intends to describe the consequence of the presence of hairy flaps on the noise generated by cylinders in a flow, especially regarding the spectral modification and possible acoustic damping impact of such flaps.…”

Section: Introductionmentioning

confidence: 99%

Vortex shedding noise of a cylinder with hairy flaps

Kamps

Geyer

Sarradj

et al. 2017

Journal of Sound and Vibration

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This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link AbstractThis study describes the modification of acoustic noise emitted from cylinders in a stationary subsonic flow for a cylinder equipped with flexible hairy flaps at the aft part as a passive way to manipulate the flow and acoustics. The study was motivated by the results from previous water tunnel measurements, which demonstrated that hairy flaps can modify the shedding cycle behind the cylinder and can reduce the wake deficit. In the present study, wind tunnel experiments were conducted on such a modified cylinder and the results were compared to the reference case of a plain cylinder. The acoustic spectrum was measured using two microphones while simultaneously recording the flap motion. To further examine the flow structures in the downstream vicinity of the cylinder, constant temperature anemometry measurements as well as flow visualizations were also performed. The results show that, above a certain Reynolds number, the hairy flaps lead to a jump in the vortex shedding frequency. This phenomenon is similarly observed in the water flow experiments as a jump in the non-dimensional Strouhal number that is related to the change of the shedding cycle. This jump appears to be coupled to a resonant excitation of the flaps and a considerable increase of the flapping amplitude. The specific Reynolds number at which the jump Email addresses: Laura.Kamps@imfd.tu-freiberg.de (Laura Kamps), Thomas.Geyer@b-tu.de (Thomas F. Geyer) Preprint submitted to Journal of Sound and Vibration October 11, 2016 occurs is higher in the present case, which is attributed to the lower added mass in air as compared with the one in water. The flow visualizations confirmed that such action of the flaps lead to a more slender elongated shape of the time-averaged separation bubble. In addition, the hairy flaps induce a noticeable reduction of the tonal noise as well as broadband noise as long as the flaps do not touch each other.

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Section: Introductionmentioning

confidence: 99%

Vortex shedding noise of a cylinder with hairy flaps

Kamps

Geyer

Sarradj

et al. 2017

Journal of Sound and Vibration

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“…Lilley (1998), for example, proposed that the downy surface helps in dampening the aerodynamic effects that create flight noise. Vad et al (2006) demonstrated noise reduction in the human hearing range in an RAF-6E profile with an artificial downy surface that was inspired by the surface of owl feathers. Chen et al (2012) conducted noise measurements on feathers of B. bubo, and the common buzzard (Buteo buteo), a member of the family of diurnal raptors.…”

Section: Functional Aspects Of the Velvet-like Surfacementioning

confidence: 99%

“…The silent flight of owls (Strigiformes) is a model system for biomimetic research (Vad et al 2006;Bachmann et al 2011;Kl€ an et al 2012;Winzen et al 2012Winzen et al , 2014aWinzen et al ,b,c, 2015Clark et al 2014;Winzen & Roidl, 2016). Morphological specializations such as the leading-edge serrations, the trailingedge fringes, a soft dorsal surface and a wing shape optimized for slow flight are well known, but their exact function is still a matter of debate and often not well understood (Fatio, 1866;Mascha, 1904;Graham, 1934;Sick, 1937;Hertel, 1963).…”

Section: Introductionmentioning

confidence: 99%

Distribution of the characteristics of barbs and barbules on barn owl wing feathers

Weger

Wagner

2017

Journal of Anatomy

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Owls are known for the development of a silent flight. One conspicuous specialization of owl wings that has been implied in noise reduction and that has been demonstrated to change the aerodynamic behavior of the wing is a soft dorsal wing surface. The soft surface is a result of changes in the shape of feather barbs and barbules in owls compared with other bird species. We hypothesized that as the aerodynamic characteristics of a wing change along its chordwise and spanwise direction, so may the shape of the barbs and barbules. Therefore, we examined in detail the shapes of the barbs and barbules in chordwise and spanwise directions. The results showed changes in the shapes of barbs and barbules at the anterior and distal parts of the wing, but not at more posterior parts. The increased density of hook radiates at the distalmost wing position could serve to stiffen that vane part that is subject to the highest forces. The change of pennulum length in the anterior part of the wing and the uniformity further back could mean that a soft surface may be especially important in regions where flow separation may occur.

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“…The aerodynamic and aeroacoustic features of a RAF6-E airfoil have been investigated e.g. by Vad et al (2006).…”

Section: CDmentioning

confidence: 99%

Beamforming studies on basic models of low-speed axial fan blade sections

Balla

Vad

2017

European Conference on Turbomachinery Fluid Dynamics and Hermodynamics

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The paper reports on establishing a beamforming dataset, relying on the phased array microphone (PAM) technique, on the broadband noise of rectilinear basic models of low-speed axial fan blade sections. A cambered plate profile is in the focus of the studies, in comparison with a flat plate and a traditional airfoil profile. At low Reynolds numbers, cambered plate blade sections have a potential to perform aerodynamically better than profiled airfoil sections. Thus, the established dataset aims at contributing to the design background of aerodynamically efficient, low-noise, low-Reynolds-number fans. The wind tunnel-PAM configuration enables the acoustic investigation over the plane being normal to the spanwise direction at midspan. An illustrative study on representative cases selected out of the dataset demonstrates the capabilities and limitations of the presently available experimental and evaluation method. Spatially simultaneously resolved information is presented on the signatures of systematically investigated classes of blade section noise. KEYWORDS beamforming, blade noise, cambered plate blade, low-speed axial fan, phased array microphone Abbreviations BG background LE leading edge PAM phased array microphone TE trailing edge 1. INTRODUCTION AND OBJECTIVES Axial flow fans characterized by blade sections of chord Reynolds numbers of Re £ 10 5 are termed herein as "low-Reynolds-number fans". Such fans are of relatively small size and/or rotor speed, e.g. cooling fans for computers (Huang, 2003) and for electric motors (Borges, 2012), or refrigerator fans (Gue et al., 2011). Axial fans are often required to provide a prescribed flow rate and/or total pressure rise even at moderate diameter and/or rotor speed. These requirements are in accordance with the constraints of limited available space and/or speed-the latter being constrained e.g. by a directly-driving electric motor-in industrial applications. For these fans, the flow coefficient and the total pressure coefficient may extend over F » 0.4 and Y » 0.6, incorporating operational ranges throttled significantly below the design flow rate (e.g. Corsini and Rispoli, 2004). Such fans are termed herein as "high-specific-performance fans". Their blade sections are often of high aerodynamic load-i.e. high lift coefficient-, high camber, and are often exposed to high a angles of attack. Cambered plate blades of circular arc camber line are often applied in axial fans, enabling a relatively simple and low-cost manufacturing technique. A further reason for choosing cambered plate blades appears in low-Reynolds-number fan applications. For Re £ 10 5 , a cambered plate section may perform aerodynamically better than a profiled airfoil section. The potential benefits are the following: higher maximum lift coefficient CL, and higher maximum lift-to-drag ratio CL/CD. Illustrative examples are given for such favourable trends by Carolus (2003), referring to Albring (1978). A comprehensive explanation is given herein on the basis of the experimental data and discussi...

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Study of the Aero-Acoustic and Aerodynamic Effects of Soft Coating upon Airfoil

Cited by 18 publications

References 8 publications

Vortex shedding noise of a cylinder with hairy flaps

Vortex shedding noise of a cylinder with hairy flaps

Distribution of the characteristics of barbs and barbules on barn owl wing feathers

Beamforming studies on basic models of low-speed axial fan blade sections

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