Spectral Leading Edge Serrations for the Reduction of Aerofoil-Turbulence Interaction Noise

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment

Abstract

The Department for Transport forecasts that by 2020 the number of passengers using UK airports will be around 400 million, compared to 200 million today. Aviation noise represents a major obstacle to the future expansion of many existing airports and thus the growth in the capacity of the air transport system. In 2001 the Advisory Council for Aeronautics Research in Europe (ACARE) set out a target to reduce perceived aviation noise to one half of the current level by 2020. To achieve the ACARE target by the year 2020 a "technology breakthrough" is urgently needed. Wind turbine manufacturers also require new technology for the significant reduction of aerodynamic noise in order to make wind turbines more acceptable to communities, especially concerned with onshore wind farms. Such a technology breakthrough can only be achieved through a fundamental evaluation and re-design of aerofoils, particularly the "leading edges" (LE), since upstream turbulent flows impinging on the LE of an aerofoil is believed to be the dominant source mechanism of broadband noise in turbofan engines (rotor wakes scattered by the outlet guide vanes - OGV) and wind farms (upstream rotor wakes scattered by the downstream turbine blades). In turbofan engines, it is envisaged that new LE design would be applied to the OGV since noise reductions can only be achieved by modifying the OGV response or the rotor wake turbulence (much more difficult).

The proposed 30-month research project aims to develop and investigate new aerofoil LE designs for the reduction of the broadband noise generated by the interaction between the aerofoil's LE and impinging turbulent flows, whilst minimising its impact on aerodynamic performance. The new aerofoil LE designs will be constructed by combining "smooth" spectral (wavy) serrations with multiple wavelengths, which has never before been attempted. In this project, a coordinated aeroacoustic and aerodynamic study of this new LE topology is proposed, particularly focused on the effects of smaller wavelengths (comparable to the impinging turbulence length scale), which are expected to be effective in reducing noise without making a significant impact on aerodynamic performance. The proposed project will take full advantage of the experimental and computational expertise of the two investigators. The successful outcome of this project will lead to a new aerofoil LE design that offers maximum noise reduction and minimum aerodynamic penalty. The commercial and academic impact of this work is potentially substantial.

The proposed research programme will be largely split and managed in four stages: 1) testing baseline aerofoil models for calibration and validation purposes; 2) identifying the most effective Fourier modes of the proposed LE serrations with respect to noise reduction; 3) combining the identified individual Fourier modes into an integrated spectral LE design (8 models in total) and testing the aerodynamic performance as well as the overall noise reduction; and 4) further understanding and improving the most favourable design found in Stage 3 via detailed numerical simulations. The experimental measurements will be performed in our AWT (anechoic wind tunnel) facilities. The numerical simulations will be carried out by using CAA (computational aeroacoustics) techniques. The CAA and AWT activities are closely coordinated and mutually supportive to ensure maximum value to the project. The proposed study will be based on a NACA65(1)-210 aerofoil with the Reynolds number up to 1.1x10^6 and the Mach number of 0.3 to 0.6. The length scales of impinging free-stream turbulence will be determined and generated in accordance with the guidelines from the industrial partners representing the aero-engine and wind turbine industries.

Planned Impact

A reduction in aerofoil noise will have benefit in a variety of applications including aircraft engines, high-lift devices and wind turbines, which in turn will make a significant impact to environmental noise. The proposed research will benefit the general public, particularly those in areas surrounding airports or wind farms, suffering from physical/mental health implications due to long-term exposure to environmental noise. The proposed work is intended to deliver a practically viable aerofoil leading edge design concept that can be adopted in the near future by the industrial partners to achieve significant reductions in environmental noise levels.

Aviation noise represents a major obstacle to the future expansion of many existing airports and thus the growth in the capacity of the air transport system. Regulations in aviation noise are becoming increasingly stricter in response to which aircraft manufactures strive to develop quieter aircraft. Although steep approach operation is becoming widespread to reduce noise emissions in urban airports, a technology breakthrough is urgently required in order to achieve genuine noise reductions at source. Recent advances in novel low-noise engine technologies such as ultra-high bypass ratio and low-speed fans have led to significant reductions in jet noise and fan tone noise. However, fan broadband noise particularly due to outlet guide vanes (OGV) is not significantly affected by these technologies and is now one of the major noise sources in a modern aero-engine. Its attenuation is the primary objective of this proposal.

Another principal application of the proposed technology is wind turbines. The implication of wind turbine noise is highlighted in a recent white paper, "Wind Turbine Acoustic Noise" by Rogers, Manwell & Wright. They measured a striking increase in noise levels by as much as 13dB(A) under certain conditions when measured at 180 meters from the base of a 10kW wind turbine at Rockport, MA, US. They argued that a buffer zone of almost half a kilometre would be required to meet Massachusetts noise regulations. Clearly, any reduction in broadband noise levels, which this proposal aims to achieve, would alleviate such local planning problems, leading to increased viability of power stations sited near populated areas.

Rolls-Royce and Vestas Technology UK have highlighted the importance of this proposal in their letters of support and have suggested interactive partnership throughout the lifetime of the project. Collaboration with Rolls-Royce will be developed through the two University Rolls-Royce Technology Centres (UTCs) at Southampton. The impact of the proposed research on the industrial partners will be maximised by delivering bi-annual progress reports and organising annual full-day mini-conferences in which they will provide confidential aerodynamic/aeroacoustic data and feedback for us to act upon. Vestas offers an opportunity for field testing of the proposed technology worth £30,000.

The impact of this work will be brought to the attention of the general public through the media towards the end of the second year when the field testing with Vestas is undertaken to verify the new design concept of the aerofoil leading edges developed for the reduction of environmental noise. The applicants of this project will arrange meetings with science journalists to publicise the field testing results via BBC News and local newspapers as well as the official website of the University of Southampton. In view of the sensitivity of wind turbine noise at the present time, dissemination of the results from this test will be of significant interest to the media. Successful dissemination of the outcome will certainly improve the general public's perception and acceptance of future wind farm planning and operation. We also plan to utilise the University's Open Days to showcase our interesting aerofoil designs to inspire and recruit the best young minds in this country.

Publications

10 25 50
 
Description In recent years at the University of Southampton, progress has been made to investigate and understand the effects of wavy leading edge (WLE) serrations on the reduction of aerofoil-turbulence interaction noise. Experimental measurements were performed to find the relationships between the geometric changes (serration amplitude and wavelength) and the level of noise reduction relative to the baseline case with a straight leading edge (SLE) [1]. It was found that the serration amplitude is the major parameter that controls the level of noise reduction, which confirmed the findings of an earlier study by Lau et al. [2]. The sound power spectra showed that the noise reduction begins to take place at a frequency where the corresponding hydrodynamic wavelength is around twice the serration length. In the meantime, high-resolution computational simulations were also performed to understand the noise reduction mechanisms associated with the source characteristics at the aerofoil surface [3]. The numerical results revealed two major mechanisms of noise reduction [4]. The first mechanism discovered is "source cut-off" effect. The oblique part of the WLE generates substantially weakened source power, which effectively leaves the peak and root areas as isolated discrete source spots. The second mechanism is "source phase-interference" effect. It was found that the WLE geometry produces an increased level of phase interference (more out-of-phase frequency components) in the source signals between the peak and the rest of the WLE.

[1] S Narayanan, P Chaitanya, S Haeri, PF Joseph, JW Kim, C Polacsek, Airfoil noise reductions through leading edge serrations, Physics of Fluids 27 (2) (2015) 025109.

[2] ASH Lau, S Haeri, JW Kim, The effect of wavy leading edges on aerofoil-gust interaction noise, Journal of Sound and Vibration 332 (24) (2013) 6234-6253.

[3] JW Kim, S Haeri, An advanced synthetic eddy method for the computation of aerofoil-turbulence interaction noise, Journal of Computational Physics 287 (2015) 1-17.

[4] JW Kim, S Haeri, PF Joseph, On the reduction of aerofoil-turbulence interaction noise associated with wavy leading edges, Journal of Fluid Mechanics 792 (2016) 526-552.
Exploitation Route The findings will become useful information in the design of aerofoil-based blades and rotors for propellers, contra-rotating fans, turbofan outlet guide vanes, wind turbines, high-lift devices, etc.
Sectors Aerospace

Defence and Marine

Energy

URL https://scholar.google.co.uk/citations?hl=en&user=Z-vuWzkAAAAJ&view_op=list_works&sortby=pubdate
 
Description EPSRC IAA KTS with Vestas UK (EP/K503770/1)
Amount £52,236 (GBP)
Funding ID EP/K503770/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 04/2013 
End 05/2014
 
Description EPSRC Industrial CASE with DSTL
Amount £77,000 (GBP)
Funding ID 17000002 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start  
 
Description Innovate UK Knowledge Transfer Partnership with Vestas UK (KTP009787)
Amount £67,830 (GBP)
Funding ID KTP009787 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 11/2014 
End 11/2015
 
Title Dataset for "Aeroacoustic source mechanisms of a wavy leading edge undergoing vortical disturbances" 
Description Dataset for "Aeroacoustic source mechanisms of a wavy leading edge undergoing vortical disturbances" 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
Impact Benchmarking data for peers to use in their studies 
 
Title Dataset for "On the reduction of aerofoil-turbulence interaction noise associated with wavy leading edges" 
Description Dataset for "On the reduction of aerofoil-turbulence interaction noise associated with wavy leading edges" 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
Impact Benchmarking data for peers to use in their studies 
 
Title Improved aerofoil broadband noise reductions through the use of double-frequency leading edge serrations 
Description The present disclosure concerns an aerofoil, particularly but not exclusively, an aerofoil for a gas turbine engine having a reduced broadband noise profile in use. Noise from aircraft is an ongoing environmental concern. There are typically several sources of noise from an aircraft, including jet noise produced by shear interaction between the jet exhaust from gas turbine engines, and aerodynamic noise caused primarily by turbulent air created by the flow of air over aircraft surfaces. As aircraft engine bypass ratios are increased, aircraft aerodynamic noise is becoming a relatively large contributor to overall aircraft noise. In particular, turbulence created on the leading and trailing edges of aerofoil surfaces is thought to produce a significant proportion of noise produced by an aircraft. Noise created by these mechanisms often has a wide range of frequencies (known as "broadband noise"), and is particularly difficult to eliminate. Examples of aerofoils on aircraft include the wings and tail surfaces, as well as smaller components such as control surfaces and high lift devices such as flaps and slats. The gas turbine engines of the aircraft also typically include several aerofoils, including compressor and turbine rotors and stators, fan rotors and Outlet Guide Vanes (OGV). The gas turbine engine nacelle is also typically aerofoil shaped. It has been proposed to provide wave-like projections on the leading edge of an aerofoil, as proposed for example in US6431498. It is thought that such projections reduce drag as well as reduce noise to some extent, as evidenced for example in US2013164488. Such projections have been proposed for both fixed and rotating aerofoils, as proposed for example in US2011058955. However, such projections do not eliminate noise completely, and it is therefore desirable to provide an aerofoil having improved noise attenuation properties. The term "chord" will be understood to refer to the distance between the leading and trailing edge of an aerofoil, measured parallel to the normal airflow over the wing. The term "chordal" will be understood to refer to a direction parallel to the chord. The term "span" will be understood to refer to a direction generally normal to the chord, extending between a root and a tip of an aerofoil component. According to a first aspect of the disclosure there is provided an aerofoil component defining an in use leading edge and a trailing edge, at least one of the leading edge and the trailing edge defining a waveform profile, wherein the waveform profile extends in a spanwise direction and comprises a superposition of a first wave and a second wave, the first and second waves having different wavelengths such that the waveform profile defines a plurality of first and second generally chordwise extending recesses spaced in a spanwise direction and having a different extent in the chordwise direction. Advantageously, it has been found that the disclosed aerofoil provides reduce broadband noise when in use compared to prior arrangements. One or more first recess may be separated from a further first recess in a spanwise direction by one or more second recess. The first and second waves may have substantially the same amplitude. The waveform may comprise a sinusoidal wave. The waveform profile may be of the form c(r)=C_0+h_1 cos??(2pr/?_1 )?+ h_2 cos??(2pr/?_2 )? where c(r) is representative of the chordwise extent c of the leading or trailing edge from the mean chord line C_0 as a function of the span r, h_1 and h_2 are representative of the amplitude of the first and second waves respectively, and ?_1 and ?_2are representative of the wavelength of the first and second waves. ?_1may have a different value to ?_2. h_1 and h_2 may have the same value. In a first example, ?_1/c_0 has a value of 1/30, and ?_2/c_0 has a value of 2/30. In a second example, ?_1/c_0 has a value of 2/30, and ?_2/c_0 has a value of 1/10. In a third example, ?_1/c_0 has a value of 1/30, and ?_2/c_0 has a value of 1/10. ?_1/?_2 may be between ½ and 2. h/c_0 may have a value between 1/10 and 1/6. In a first example, h/c_0 has a value of 1/10. In a second example, h/c_0 has a value of 4/30. In a third example, h/c_0 has a value of 1/6. The aerofoil may have a cross sectional profile which may vary across the span of the aerofoil in accordance with the formula: y(x,r)={¦(f(x/c_0), 0 
IP Reference GB1512688.1 
Protection Patent application published
Year Protection Granted
Licensed Commercial In Confidence
Impact The present disclosure concerns an aerofoil, particularly but not exclusively, an aerofoil for a gas turbine engine having a reduced broadband noise profile in use. Noise from aircraft is an ongoing environmental concern. There are typically several sources of noise from an aircraft, including jet noise produced by shear interaction between the jet exhaust from gas turbine engines, and aerodynamic noise caused primarily by turbulent air created by the flow of air over aircraft surfaces. As aircraft engine bypass ratios are increased, aircraft aerodynamic noise is becoming a relatively large contributor to overall aircraft noise. In particular, turbulence created on the leading and trailing edges of aerofoil surfaces is thought to produce a significant proportion of noise produced by an aircraft. Noise created by these mechanisms often has a wide range of frequencies (known as "broadband noise"), and is particularly difficult to eliminate. Examples of aerofoils on aircraft include the wings and tail surfaces, as well as smaller components such as control surfaces and high lift devices such as flaps and slats. The gas turbine engines of the aircraft also typically include several aerofoils, including compressor and turbine rotors and stators, fan rotors and Outlet Guide Vanes (OGV). The gas turbine engine nacelle is also typically aerofoil shaped. It has been proposed to provide wave-like projections on the leading edge of an aerofoil, as proposed for example in US6431498. It is thought that such projections reduce drag as well as reduce noise to some extent, as evidenced for example in US2013164488. Such projections have been proposed for both fixed and rotating aerofoils, as proposed for example in US2011058955. However, such projections do not eliminate noise completely, and it is therefore desirable to provide an aerofoil having improved noise attenuation properties. The term "chord" will be understood to refer to the distance between the leading and trailing edge of an aerofoil, measured parallel to the normal airflow over the wing. The term "chordal" will be understood to refer to a direction parallel to the chord. The term "span" will be understood to refer to a direction generally normal to the chord, extending between a root and a tip of an aerofoil component. According to a first aspect of the disclosure there is provided an aerofoil component defining an in use leading edge and a trailing edge, at least one of the leading edge and the trailing edge defining a waveform profile, wherein the waveform profile extends in a spanwise direction and comprises a superposition of a first wave and a second wave, the first and second waves having different wavelengths such that the waveform profile defines a plurality of first and second generally chordwise extending recesses spaced in a spanwise direction and having a different extent in the chordwise direction. Advantageously, it has been found that the disclosed aerofoil provides reduce broadband noise when in use compared to prior arrangements. One or more first recess may be separated from a further first recess in a spanwise direction by one or more second recess. The first and second waves may have substantially the same amplitude. The waveform may comprise a sinusoidal wave. The waveform profile may be of the form c(r)=C_0+h_1 cos??(2pr/?_1 )?+ h_2 cos??(2pr/?_2 )? where c(r) is representative of the chordwise extent c of the leading or trailing edge from the mean chord line C_0 as a function of the span r, h_1 and h_2 are representative of the amplitude of the first and second waves respectively, and ?_1 and ?_2are representative of the wavelength of the first and second waves. ?_1may have a different value to ?_2. h_1 and h_2 may have the same value. In a first example, ?_1/c_0 has a value of 1/30, and ?_2/c_0 has a value of 2/30. In a second example, ?_1/c_0 has a value of 2/30, and ?_2/c_0 has a value of 1/10. In a third example, ?_1/c_0 has a value of 1/30, and ?_2/c_0 has a value of 1/10. ?_1/?_2 may be between ½ and 2. h/c_0 may have a value between 1/10 and 1/6. In a first example, h/c_0 has a value of 1/10. In a second example, h/c_0 has a value of 4/30. In a third example, h/c_0 has a value of 1/6. The aerofoil may have a cross sectional profile which may vary across the span of the aerofoil in accordance with the formula: y(x,r)={¦(f(x/c_0), 0
 
Title Improved aerofoil broadband noise reductions through the use of slitted root leading edge serrations 
Description The present disclosure concerns an aerofoil, particularly but not exclusively, an aerofoil for a gas turbine engine having a reduced broadband noise profile in use. Noise from aircraft is an ongoing environmental concern. There are typically several sources of noise from an aircraft, including jet noise produced by shear interaction between the jet exhaust from gas turbine engines, and aerodynamic noise caused primarily by turbulent air created by the flow of air over aircraft surfaces. As aircraft engine bypass ratios are increased, aircraft aerodynamic noise is becoming a relatively large contributor to overall aircraft noise. In particular, turbulence created on the leading and trailing edges of aerofoil surfaces is thought to produce a significant proportion of noise produced by an aircraft. Noise created by these mechanisms often has a wide range of frequencies (known as "broadband noise"), and is particularly difficult to eliminate. Examples of aerofoils on aircraft include the wings and tail surfaces, as well as smaller components such as control surfaces and high lift devices such as flaps and slats. The gas turbine engines of the aircraft also typically include several aerofoils, including compressor and turbine rotors and stators, fan rotors and Outlet Guide Vanes (OGV). The gas turbine engine nacelle is also typically aerofoil shaped. It has been proposed to provide wave-like projections on the leading edge of an aerofoil, as proposed for example in US6431498. It is thought that such projections reduce drag as well as reduce noise to some extent, as evidenced for example in US2013164488. Such projections have been proposed for both fixed and rotating aerofoils, as proposed for example in US2011058955. However, such projections do not eliminate noise completely, and it is therefore desirable to provide an aerofoil having improved noise attenuation properties. The term "chord" will be understood to refer to the distance between the leading and trailing edge of an aerofoil, measured parallel to the normal in use airflow over the wing. The term "chordal" will be understood to refer to a direction parallel to the chord. The term "span" will be understood to refer to a direction generally normal to the chord, extending between a root and a tip of an aerofoil component. According to a first aspect of the disclosure there is provided an aerofoil component defining an in use leading edge and a trailing edge, the leading edge comprising at least one serration defining an apex and a nadir, wherein the leading edge comprises a generally chordwise extending slot located at the nadir of each serration. Advantageously, it has been found that the disclosed aerofoil leading edge profile provides reduce broadband noise when in use compared to prior arrangements. Each serration may comprise, in sequence in a spanwise direction extending from the apex, a rearwardly inclined relative to an in use flow direction first portion, a rearwardly inclined second portion joined with the first portion at a first internal angle relative to the first portion of between 90° and 180°, a forwardly inclined relative to the in use flow direction third portion, and a forwardly inclined fourth portion joined with the third portion at a second internal angle relative to the third portion of between 90° and 180°. The first and / or fourth portion may comprise an angle relative to the in use flow direction between 45° and 90°, and may comprise an angle greater than 50°. The first portion of a first serration may be joined to a fourth portion of a second serration to form the apex. Alternatively, the first portion of a first serration may be joined to a fourth portion of a second serration via a sixth portion. The sixth portion may extend generally normally to the in use flow direction. The second portion may be joined to the third portion to form the slot. Alternatively, the second and third portions may be joined to one another by a fifth portion, the second, third and fifth portions defining the slot. The fifth portion may extend in a generally spanwise direction, generally normal to the in use flow direction. A spanwise length of the fifth portion may be at least 1mm. At least one of the second and third portions may extend generally parallel to the in use flow direction. At least one of the first, second, third and fourth portions may comprise a convex curve, and may comprise a section of a sinusoidal curvature. Alternatively, at least one of the first, second, third and fourth portions may comprise a straight edge. The waveform may comprise a sinusoidal wave. A chordwise distance between the apex and the nadir of each serration may be at least twice the spanwise distance between apexes of adjacent serrations. The aerofoil component may comprise an aerofoil of a gas turbine engine, such as an outlet guide vane (OGV). According to a second aspect of the present disclosure there is provided a gas turbine engine comprising an aerofoil component in accordance with the first aspect of the present disclosure. According to a third aspect of the present disclosure there is provided an aircraft comprising an aerofoil component in accordance with the first aspect of the present disclosure. The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects of the invention may be applied mutatis mutandis to any other aspect of the invention. 
IP Reference GB1602895.3 
Protection Patent application published
Year Protection Granted
Licensed Commercial In Confidence
Impact The present disclosure concerns an aerofoil, particularly but not exclusively, an aerofoil for a gas turbine engine having a reduced broadband noise profile in use. Noise from aircraft is an ongoing environmental concern. There are typically several sources of noise from an aircraft, including jet noise produced by shear interaction between the jet exhaust from gas turbine engines, and aerodynamic noise caused primarily by turbulent air created by the flow of air over aircraft surfaces. As aircraft engine bypass ratios are increased, aircraft aerodynamic noise is becoming a relatively large contributor to overall aircraft noise. In particular, turbulence created on the leading and trailing edges of aerofoil surfaces is thought to produce a significant proportion of noise produced by an aircraft. Noise created by these mechanisms often has a wide range of frequencies (known as "broadband noise"), and is particularly difficult to eliminate. Examples of aerofoils on aircraft include the wings and tail surfaces, as well as smaller components such as control surfaces and high lift devices such as flaps and slats. The gas turbine engines of the aircraft also typically include several aerofoils, including compressor and turbine rotors and stators, fan rotors and Outlet Guide Vanes (OGV). The gas turbine engine nacelle is also typically aerofoil shaped. It has been proposed to provide wave-like projections on the leading edge of an aerofoil, as proposed for example in US6431498. It is thought that such projections reduce drag as well as reduce noise to some extent, as evidenced for example in US2013164488. Such projections have been proposed for both fixed and rotating aerofoils, as proposed for example in US2011058955. However, such projections do not eliminate noise completely, and it is therefore desirable to provide an aerofoil having improved noise attenuation properties. The term "chord" will be understood to refer to the distance between the leading and trailing edge of an aerofoil, measured parallel to the normal in use airflow over the wing. The term "chordal" will be understood to refer to a direction parallel to the chord. The term "span" will be understood to refer to a direction generally normal to the chord, extending between a root and a tip of an aerofoil component. According to a first aspect of the disclosure there is provided an aerofoil component defining an in use leading edge and a trailing edge, the leading edge comprising at least one serration defining an apex and a nadir, wherein the leading edge comprises a generally chordwise extending slot located at the nadir of each serration. Advantageously, it has been found that the disclosed aerofoil leading edge profile provides reduce broadband noise when in use compared to prior arrangements. Each serration may comprise, in sequence in a spanwise direction extending from the apex, a rearwardly inclined relative to an in use flow direction first portion, a rearwardly inclined second portion joined with the first portion at a first internal angle relative to the first portion of between 90° and 180°, a forwardly inclined relative to the in use flow direction third portion, and a forwardly inclined fourth portion joined with the third portion at a second internal angle relative to the third portion of between 90° and 180°. The first and / or fourth portion may comprise an angle relative to the in use flow direction between 45° and 90°, and may comprise an angle greater than 50°. The first portion of a first serration may be joined to a fourth portion of a second serration to form the apex. Alternatively, the first portion of a first serration may be joined to a fourth portion of a second serration via a sixth portion. The sixth portion may extend generally normally to the in use flow direction. The second portion may be joined to the third portion to form the slot. Alternatively, the second and third portions may be joined to one another by a fifth portion, the second, third and fifth portions defining the slot. The fifth portion may extend in a generally spanwise direction, generally normal to the in use flow direction. A spanwise length of the fifth portion may be at least 1mm. At least one of the second and third portions may extend generally parallel to the in use flow direction. At least one of the first, second, third and fourth portions may comprise a convex curve, and may comprise a section of a sinusoidal curvature. Alternatively, at least one of the first, second, third and fourth portions may comprise a straight edge. The waveform may comprise a sinusoidal wave. A chordwise distance between the apex and the nadir of each serration may be at least twice the spanwise distance between apexes of adjacent serrations. The aerofoil component may comprise an aerofoil of a gas turbine engine, such as an outlet guide vane (OGV). According to a second aspect of the present disclosure there is provided a gas turbine engine comprising an aerofoil component in accordance with the first aspect of the present disclosure. According to a third aspect of the present disclosure there is provided an aircraft comprising an aerofoil component in accordance with the first aspect of the present disclosure. The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects of the invention may be applied mutatis mutandis to any other aspect of the invention.
 
Title CANARD 
Description I am using an in-house code named CANARD (Compressible Aerodynamic \& Aeroacoustic Research coDe) that I have developed for my research projects over the last decade. The code has been extensively used in ARCHER and IRIDIS4 for the last several years in a previous EPSRC-funded project (EP/J007633/1) and also as part of UK Turbulence Consortium (EP/L000261/1) WP5 (Compressible Flows and Aeroacoustics). CANARD is a fully nonlinear compressible Navier-Stokes solver based on fourth-order wavenumber-optimised compact finite-difference schemes and multi-block structured grids. The solution is advanced in time by using the classical fourth-order Runge-Kutta scheme. Numerical resolution and stability are controlled by implementing sixth-order compact discrete filters for which the cut-off wavenumber can be precisely set to an optimal value to achieve the maximum spatial resolution attainable. Characteristics-based interface conditions are used to interconnect multiple block-structured mesh systems maintaining the high-order accuracy across the block boundaries. The far-field boundaries are carefully treated by using absorbing sponge-layer techniques and non-reflecting boundary conditions in order to prevent any outgoing waves/disturbances from returning to the computational domain. CANARD is also equipped with a synthetic divergence-free inflow-turbulence generator, an explicit shock-capturing scheme and a moving frame/grid technique as well. The code has been fully parallelised (including binary input-output routines) based on the MPI platform and its supralinear scalability (for at least up to 7,680 processor cores on 76.8M grid points) has been verified in ARCHER. 
Type Of Technology Software 
Year Produced 2015 
Impact I am using an in-house code named CANARD (Compressible Aerodynamic \& Aeroacoustic Research coDe) that I have developed for my research projects over the last decade. The code has been extensively used in ARCHER and IRIDIS4 for the last several years in a previous EPSRC-funded project (EP/J007633/1) and also as part of UK Turbulence Consortium (EP/L000261/1) WP5 (Compressible Flows and Aeroacoustics). CANARD is a fully nonlinear compressible Navier-Stokes solver based on fourth-order wavenumber-optimised compact finite-difference schemes and multi-block structured grids. The solution is advanced in time by using the classical fourth-order Runge-Kutta scheme. Numerical resolution and stability are controlled by implementing sixth-order compact discrete filters for which the cut-off wavenumber can be precisely set to an optimal value to achieve the maximum spatial resolution attainable. Characteristics-based interface conditions are used to interconnect multiple block-structured mesh systems maintaining the high-order accuracy across the block boundaries. The far-field boundaries are carefully treated by using absorbing sponge-layer techniques and non-reflecting boundary conditions in order to prevent any outgoing waves/disturbances from returning to the computational domain. CANARD is also equipped with a synthetic divergence-free inflow-turbulence generator, an explicit shock-capturing scheme and a moving frame/grid technique as well. The code has been fully parallelised (including binary input-output routines) based on the MPI platform and its supralinear scalability (for at least up to 7,680 processor cores on 76.8M grid points) has been verified in ARCHER. 
URL https://scholar.google.co.uk/citations?user=Z-vuWzkAAAAJ&hl=en