The Aerodynamic and Aeroacoustic Effect of Passive High Frequency Oscillating Trailing Edge Flaplets

2021 ◽  
pp. 413-425
Author(s):  
Edward Talboys ◽  
Thomas F. Geyer ◽  
Christoph Brücker
Keyword(s):  
High Frequency ◽  
Trailing Edge

Aerodynamic noise from an asymmetric airfoil with perforated extension plates at the trailing edge

2020 ◽  
pp. 1475472X2097838
Author(s):  
CK Sumesh ◽  
TJS Jothi
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Pore Diameter ◽  
Low Frequency ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Trailing Edge ◽  
High Frequency Noise ◽  
Displacement Thickness

This paper investigates the noise emissions from NACA 6412 asymmetric airfoil with different perforated extension plates at the trailing edge. The length of the extension plate is 10 mm, and the pore diameters ( D) considered for the study are in the range of 0.689 to 1.665 mm. The experiments are carried out in the flow velocity ( U∞) range of 20 to 45 m/s, and geometric angles of attack ( αg) values of −10° to +10°. Perforated extensions have an overwhelming response in reducing the low frequency noise (<1.5 kHz), and a reduction of up to 6 dB is observed with an increase in the pore diameter. Contrastingly, the higher frequency noise (>4 kHz) is observed to increase with an increase in the pore diameter. The dominant reduction in the low frequency noise for perforated model airfoils is within the Strouhal number (based on the displacement thickness) of 0.11. The overall sound pressure levels of perforated model airfoils are observed to reduce by a maximum of 2 dB compared to the base airfoil. Finally, by varying the geometric angle of attack from −10° to +10°, the lower frequency noise is seen to increase, while the high frequency noise is observed to decrease.

Implementation of the Ffowcs Williams-Hawkings Equation: Predicting the Far Field Noise From Airfoils While Using Boundary Layer Tripping Mechanisms

2018 ◽  
Author(s):  
Andrew L. Bodling ◽  
Anupam Sharma
Keyword(s):  
Boundary Layer ◽  
High Frequency ◽  
Permeable Surface ◽  
Far Field ◽  
Trailing Edge ◽  
Extraneous Noise ◽  
Field Noise ◽  
High Frequency Waves

A study was done to investigate how boundary layer tripping mechanisms can affect the ability of a permeable surface FW-H solver to predict the far field noise emanating from an airfoil trailing edge. The far field noise in a baseline airfoil as well as the baseline airfoil fitted with fin let fences was analyzed. Two numerical boundary layer tripping mechanisms were implemented. The results illustrated the importance of choosing a permeable integration surface that is outside any high frequency waves emanating from the trip region. The results also illustrated the importance of choosing a boundary layer tripping mechanism that minimizes any extraneous noise so that an integration surface can be taken close to the airfoil.

scholarly journals Blade-Vortex Interaction Noise Controller Based on Miniature Trailing Edge Effectors

2018 ◽  
Vol 23 (No 3, September 2018) ◽  
pp. 378-384 ◽  
Author(s):  
Sara Modini ◽  
Giorgio Graziani ◽  
Giovanni Bernardini ◽  
Massimo Gennaretti
Keyword(s):  
Potential Flow ◽  
High Frequency ◽  
Vortex Interaction ◽  
Trailing Edge ◽  
Computational Tools ◽  
Flow Simulations ◽  
Blade Vortex Interaction ◽  
Helicopter Main Rotor ◽  
Control Methodology ◽  
Blade Loads

The present work focuses on the alleviation of Blade Vortex Interaction (BVI) noise annoyance through a control methodology generating high-frequency aerodynamic BVI counter-actions. The low-power requirements make the Micro-Trailing Edge Effectors (MiTEs) particularly suited for this kind of application. The controller layout is set by observing the BVI scenario while the actuation law is efficiently synthesized through a process based on an analytical unsteady sectional aerodynamic formulation. The validation of the proposed control methodology is carried out through numerical investigations of a realistic helicopter main rotor in flight descent, obtained using computational tools for potential-flow aerodynamic and aeroacoustic analyses based on boundary element method solutions. In order to capture the aerodynamic influence of MiTEs through potential-flow simulations, the MiTEs are replaced by trailing edge plain flaps which provide equivalent aerodynamic responses. Results concerning the proposed controller capability to alleviate high-frequency blade loads and subsequent emitted noise from BVI events are presented and discussed.

scholarly journals Aerofoil self-noise radiations subjected to serration flap angles

2021 ◽  
Vol 62 (7) ◽  
Author(s):  
P. C. Woodhead ◽  
T. P. Chong ◽  
P. F. Joseph ◽  
A. Vathylakis
Keyword(s):  
Noise Reduction ◽  
Flat Plate ◽  
High Frequency ◽  
Cross Flow ◽  
Broadband Noise ◽  
The Self ◽  
Spanwise Direction ◽  
Trailing Edge ◽  
Blade Loading ◽  
Loading Effect

Abstract Besides the investigation of the aeroacoustics responses of an asymmetric aerofoil subjected to serrated trailing edge flap angles from negative (flap-down) to positive (flap-up), this paper also provides a new perspective on the physical mechanisms of broadband noise reduction by a serrated trailing edge. The blade-loading effect, which is a function of the length and flap angle for a straight/non-serrated trailing edge flat plate, plays a considerable role in the self-noise radiation that is hitherto less recognised. When the same trailing edge flat plate is cut into a sawtooth serration shape, the self-noise reduction will be underpinned simultaneously by both the serration effect (dominant) and the blade-loading effect. The results demonstrate that the far-field radiation of a serrated aerofoil can be manipulated significantly depending on the direction of the flap angle. In the flap-down configuration, the blade-loading will become a negative factor that causes a deterioration of the noise reduction performance across the entire frequency range. In the flap-up configuration, three spectral frequencies zones can be defined. At the low-frequency zone, the diminished cross-flow at the sawtooth gaps will impede the noise reduction capability. At the central-frequency zone, the re-distribution of the turbulence sources and reduction in the turbulence spanwise length scales will enhance the noise reduction performance. Improvement in the noise performance can also be achieved at the high-frequency zone owing to the lack of interaction between the cross-flow and sawtooth structure. A new concept is positively demonstrated by varying the serration flap angle as a periodic function across the spanwise direction (spanwise wavy serration). When compared to a non-flap serrated trailing edge, the spanwise wavy serration is found to further increase the noise reduction level between the central and high-frequency regions. Graphic abstract

scholarly journals Numerical analysis of a 3-D printed porous trailing edge for broadband noise reduction

2021 ◽  
Vol 926 ◽  
Author(s):  
C. Teruna ◽  
F. Avallone ◽  
D. Ragni ◽  
A. Rubio-Carpio ◽  
D. Casalino
Keyword(s):  
Noise Reduction ◽  
High Frequency ◽  
Dominant Role ◽  
Broadband Noise ◽  
Excess Noise ◽  
Entrance Length ◽  
Noise Mitigation ◽  
Trailing Edge ◽  
Turbulent Length Scale ◽  
Porous Insert

Lattice Boltzmann simulations were carried out to investigate the noise mitigation mechanisms of a 3-D printed porous trailing-edge insert, elucidating the link between noise reduction and material permeability. The porous insert is based on a unit cell resembling a lattice of diamond atoms. It replaces the last 20 % chord of a NACA 0018 at zero angle-of-attack. A partially blocked insert is considered by adding a solid partition between 84 % and 96 % of the aerofoil chord. The regular porous insert achieves a substantial noise reduction at low frequencies, although a slight noise increase is found at high frequencies. The partially blocked porous insert exhibits a lower noise reduction level, but the noise emission at mid-to-high frequency is slightly affected. The segment of the porous insert near the tip plays a dominant role in promoting noise mitigation, whereas the solid-porous junction contributes, in addition to the rough surface, towards the high-frequency excess noise. The current study demonstrates the existence of an entrance length associated with the porous material geometry, which is linked to the pressure release process that is responsible for promoting noise mitigation. This process is characterised by the aerodynamic interaction between pressure fluctuations across the porous medium, which is found at locations where the porous insert thickness is less than twice the entrance length. Present results also suggest that the noise attenuation level is related to both the chordwise extent of the porous insert and the streamwise turbulent length scale. The porous inserts also cause a slight drag increase compared to their solid counterpart.

scholarly journals Smart wing rotation and trailing-edge vortices enable high frequency mosquito flight

Nature ◽  
2017 ◽  
Vol 544 (7648) ◽  
pp. 92-95 ◽  
Author(s):  
Richard J. Bomphrey ◽  
Toshiyuki Nakata ◽  
Nathan Phillips ◽  
Simon M. Walker
Keyword(s):  
High Frequency ◽  
Trailing Edge

scholarly journals Control of the Laminar-Turbulent Transition on the Wing Profile by Distributed Suction through a Finely Perforated Surface

2019 ◽  
Vol 14 (4) ◽  
pp. 28-54
Author(s):  
G. R. Grek ◽  
M. M. Katasonov ◽  
V. V. Kozlov ◽  
V. I. Kornilov ◽  
A. V. Kryukov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Frequency ◽  
Boundary Layer Separation ◽  
Experimental Investigations ◽  
Mean Flow ◽  
Trailing Edge ◽  
Turbulent Transition ◽  
External Acoustic Field ◽  
The Mean ◽  
Finely Perforated Surface

The results of experimental investigations of the influence of distributed suction through a finely perforated section of a symmetric airfoil on the spatial development of disturbances in the boundary layer are presented. It was found that distributed suction reduces by 10 times the intensity of natural disturbances of the boundary layer and by 20 times the intensity of artificial disturbances generated by an external acoustic field. A spectral analysis of disturbances showed that suction reduces the intensity of high-frequency fluctuations for both natural and forced disturbances. It was found that the distributed suction affects the average flow – when the suction is on, the separation of the boundary layer near the trailing edge of the wing is eliminated. It was found that distributed suction significantly affects the mean flow, up to eliminating the boundary-layer separation near the trailing edge of the wing.

On the viscous flow about the trailing edge of a rapidly oscillating plate

1975 ◽  
Vol 67 (4) ◽  
pp. 743-761 ◽  
Author(s):  
S. N. Brown ◽  
P. G. Daniels
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
High Frequency ◽  
Analytic Solutions ◽  
Trailing Edge ◽  
Kutta Condition ◽  
Sinusoidal Oscillations ◽  
Low Amplitude ◽  
Oscillating Plate ◽  
Uniform Stream

The incompressible laminar flow in the neighbourhood of the trailing edge of an aerofoil undergoing sinusoidal oscillations of high frequency and low amplitude in a uniform stream is described in the limit as the Reynolds number R tends to infinity. The aerofoil is replaced by a flat plate on the assumption that leadingedge stall does not take place. It is shown that, for oscillations of non-dimensional frequency $O(R^{\frac{1}{4}})$ and amplitude $O(R^{\frac{9}{16}})$, a rational description of the flow at the trailing edge is based on a subdivision of the boundary layer above the plate into five distinct regions. Asymptotic analytic solutions are found in four of these, whilst in the fifth a linearized solution yields an estimate for the viscous correction to the circulation determined by the Kutta condition.

The Microstructure of Steatite (Protoenstatite)

1985 ◽  
Vol 43 ◽  
pp. 236-237
Author(s):  
W. E. Lee ◽  
A. H. Heuer
Keyword(s):  
High Frequency ◽  
Glass Ceramics ◽  
Magnesium Silicate ◽  
Beam Current ◽  
Glassy Matrix ◽  
Angle Of Incidence ◽  
X Ray ◽  
Mechanical And Electrical Properties ◽  
Argon Ions ◽  
High Temperature Polymorph

IntroductionTraditional steatite ceramics, made by firing (vitrifying) hydrous magnesium silicate, have long been used as insulators for high frequency applications due to their excellent mechanical and electrical properties. Early x-ray and optical analysis of steatites showed that they were composed largely of protoenstatite (MgSiO3) in a glassy matrix. Recent studies of enstatite-containing glass ceramics have revived interest in the polymorphism of enstatite. Three polymorphs exist, two with orthorhombic and one with monoclinic symmetry (ortho, proto and clino enstatite, respectively). Steatite ceramics are of particular interest a they contain the normally unstable high-temperature polymorph, protoenstatite.Experimental3mm diameter discs cut from steatite rods (∼10” long and 0.5” dia.) were ground, polished, dimpled, and ion-thinned to electron transparency using 6KV Argon ions at a beam current of 1 x 10-3 A and a 12° angle of incidence. The discs were coated with carbon prior to TEM examination to minimize charging effects.

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