A method for forming an additional component of an airfoil

Abstract

The present invention discloses a method for forming an additional component of an airfoil, which can adjust the structure of the airfoil to reduce the frequency f when air flows along the flow direction from the leading edge of the airfoil to the trailing edge of the airfoil. 峰值 The method is applicable to an additional component with a slot configuration and double root trailing edge serrations (abbreviated as "DRooTES").

Description

Background Technology

[0001] This application relates to a method for forming additional components of an airfoil, and to reducing the frequency f when air flows in a flow direction from the leading edge of the airfoil to the trailing edge. 峰值 A method for measuring the amplitude of sound produced at a location.

[0002] It is well known that harmful noise is essentially a form of pollution that affects health, especially near airports and wind farms. Studies have shown that noise pollution from aviation and wind farms can have adverse health effects, leading to irritability, sleep disorders, and cognitive impairment. To protect public health, the aviation and wind energy sectors have implemented strict noise regulations. The European Commission has set a target of reducing aviation noise emissions by 65% ​​by 2050 compared to 2000 levels. However, global civil aviation traffic is projected to grow by 4% to 5% annually, with even greater growth in the Middle East and Asia. Furthermore, the European Wind Energy Association published a report in 2014 on a projected energy capacity scenario for 2030, indicating that wind power will generate 320 gigawatts of electricity, 78% of which will be produced by onshore wind farms.

[0003] The rapid development of the aviation industry and the significant increase in the number of onshore wind farms in EU member states will inevitably lead to increased aerodynamic noise pollution. Aircraft noise is primarily generated by jet engines and lift devices during takeoff and landing. While jet engine technology has reduced jet noise, the noise generated by high-bypass fan blades has increased.

[0004] The mechanical noise of wind turbines is mainly caused by the moving parts inside the gearbox and generator.

[0005] However, recent advancements in high-precision gear tooth profile design and casing sound insulation have reduced the sources of mechanical noise. In contrast, the aerodynamic noise generated by wind turbine blades is much more difficult to reduce. To protect local residential areas, the maximum noise level at 350m from a wind turbine is currently limited to 35-45 dB(A). Therefore, wind turbine companies typically reduce turbine speeds in high-wind-speed scenarios to suppress aerodynamic noise levels and keep them below the limits. However, this inherently reduces the utilization rate of available wind energy resources. Therefore, reducing noise without decreasing rotor speed would make wind energy cheaper, thus becoming a more attractive alternative to fossil fuels. Quantitatively, a further 1 dB reduction in noise from current levels could significantly increase wind power output.

[0006] Aerodynamic noise can be generated at both the leading and trailing edges of an airfoil. Airfoil noise is generated at the leading edge through interaction with atmospheric turbulence, or at the trailing edge through turbulence in the boundary layer that forms and scatters sound across the blade surface. Leading-edge noise and trailing-edge noise are distinct, unrelated noise sources. Trailing-edge noise (often also called self-noise) remains one of the most relevant noise sources to the aviation and wind turbine industries.

[0007] As is known from existing technology, trailing edge noise reduction can be achieved by using a simple sawtooth trailing edge. First, the noise reduction achieved through a sawtooth trailing edge is related to the destructive interference caused by the phase lag mechanism of turbulent noise scattering on the inclined edge. Second, the root of the sawtooth trailing edge is effective against turbulent noise radiation. Third, two noise sources with a longitudinal displacement of 180° phase angle, such as the case of a leading edge slit, have been shown to minimize the destructive interference of aerodynamic noise.

[0008] CN 109292076 A1 (Harbin Institute of Technology) discloses a low self-noise airfoil structure with a multi-wavelength serrated trailing edge. The airfoil body is detachably connected to the noise-reducing trailing edge plate via a connector.

[0009] WO 2017 / 220594 A1 (LM Wind Power) discloses a wind turbine blade comprising two or more serrations disposed along a portion of its trailing edge.

[0010] US 2012 / 027590 A1 (Bone) discloses a rotor blade assembly and a method for reducing noise in wind turbine rotor blades.

[0011] WO 2019 / 158876 A1 (Safran Aircraft Engine) discloses an aerodynamic profile comprising a body and a porous sound-absorbing region.

[0012] US 2017 / 0174320 (Amazon Technologies) discloses a system, method, and apparatus for actively adjusting the position of one or more propeller blade treatment elements of an aircraft propeller blade during aircraft operation.

[0013] US Patent 2017 / 0022820 A1 (Rolls-Royce) discloses an airfoil for a gas turbine having a series of first and second grooves cut into the leading edge of the airfoil itself. The grooves are cut to reduce leading-edge noise of the airfoil as follows:

[0014] f0=U / 2h tt

[0015] Where f0 is the reduced noise frequency, U is the air velocity across the leading edge, and h is the noise frequency. ttIt is the height difference between the adjacent valleys of the first and second grooves.

[0016] Gruber, Azarpeyvand, and Joseph compared trailing edge noise reduction measurements obtained by using sawtooth and slit teeth on the NACA651210 airfoil in their paper “Reducing Airfoil Trailing Edge Noise by Introducing Sawtooth and Slit Trailing Edge Geometry” (Proceedings of the 20th International Congress of Acoustics, ICA 2010). Summary of the Invention

[0017] The inventive step of this application lies in providing a more accurate equation as defined in claim 1, addressing the incorrect equation disclosed in US 2017 / 0022820 A1. Furthermore, compared to the method disclosed in US 2017 / 0022820 A1 of cutting grooves into the airfoil itself, the method of constructing a separate component for the airfoil according to the equation of this invention and attaching it to the trailing edge of the airfoil yields improved results.

[0018] Furthermore, equivalent inventive equations can be used to adjust noise reduction achievable from airfoils with slit teeth (as disclosed in Gruber, Azarpeyvand, and Joseph above).

[0019] A first aspect of the invention provides a method for forming additional components for an airfoil having a leading edge and a trailing edge, the components being formed to reduce the impact force when air flows at a free-flow velocity U. ∞ When flowing along the flow direction from the leading edge of the airfoil to the trailing edge of the component at frequency f 峰值 The method for determining the amplitude of the sound produced at a given location includes the steps of:

[0020] (a) Select the frequency f of the sound to be lowered 峰值 ;

[0021] (b) Choose the free-flow velocity of the air U ∞ ;

[0022] (c) Provide a component having an engagement edge for engaging with the trailing edge of an airfoil, and a trailing edge opposite to the engagement edge;

[0023] (d) The trailing edge of the component is formed into multiple pairs of peaks, each pair having a first valley, a first peak, a second valley, a second peak that is farther from the joint edge than the first peak, and a third valley, wherein the first valley is located on one side of the first peak, the second valley is located between the first peak and the second peak, and the third valley is located on the other side of the second peak opposite to the second valley.

[0024] (e) wherein the first and third valleys of each pair of peaks are generally located on the first axis, the second valley of each pair of peaks is generally located on the second axis, and the second peak of each pair of peaks is located on the third axis; and,

[0025] (f) Wherein, the component is formed according to the following formula:

[0026] in In the range of 0.4 to 0.8, and

[0027] Where h′ is the shortest distance between the first and second axes, h″ is the shortest distance between the second and third axes, and f 峰值 It is the frequency of the sound to be reduced, and U ∞ It is the free-flow velocity of air in the direction of flow as it passes the trailing edge of the component.

[0028] In one embodiment, h′=h″.

[0029] For each of the multiple pairs of peaks, the shortest distance from the first peak to the first axis can be the same.

[0030] The third valley of the first pair of peaks can be the first valley of the second pair of peaks adjacent to the first pair of peaks.

[0031] A method for reducing the speed of air in free flow at velocity U ∞ When flowing along the flow direction from the leading edge of the airfoil to the trailing edge, at frequency f 峰值 A method for determining the amplitude of sound generated at a given location, the method comprising the steps of:

[0032] (a) Additional components for forming the airfoil according to the above method, and

[0033] (b) Attach the component to the airfoil.

[0034] This method may additionally include the steps of forming multiple components and attaching the multiple components to the airfoil. For example, three components may be formed and attached to the airfoil; wherein the first component is near the tip of the airfoil, the second component is near the middle of the airfoil, and the third component is near the opposite end of the airfoil to the tip.

[0035] In one embodiment, the components may be identical. However, in another alternative embodiment, the components may have different h' and / or h" values.

[0036] A second aspect of the invention provides a method for forming additional components for an airfoil having a leading edge and a trailing edge, forming components to reduce the impact force when air flows at a free-flow velocity U. ∞ When flowing along the flow direction from the leading edge of the airfoil to the trailing edge of the component at frequency f 峰值 The method for determining the amplitude of the sound produced at a given location includes the steps of:

[0037] (a) Select the frequency f of the sound to be lowered峰值 ;

[0038] (b) Choose the free-flow velocity of the air U ∞ ;

[0039] (c) Provide a component having an engagement edge for engaging with the trailing edge of an airfoil, and a trailing edge opposite to the engagement edge;

[0040] (d) The trailing edge of the component is formed into multiple peaks separated by multiple valleys, wherein each peak is connected to a valley on both sides of the peak by a wall substantially perpendicular to the trailing edge, each peak has a width (a) substantially parallel to the trailing edge, and each valley has a width (W) substantially parallel to the trailing edge, the width (W) also being the gap between adjacent peaks, the multiple peaks are substantially located on a first axis, and the multiple valleys are substantially located on a second axis, the shortest distance from the first axis to the second axis being defined as H; and

[0041] (e) Wherein, the component is formed according to the following formula:

[0042] in It is in the range of 0.4 to 0.8.

[0043] In one embodiment, the gap (W) between adjacent peaks is correlated with the spanwise length scale (L) of the turbulent vortex. y The ratio of W / L satisfies the expression 0.2 ≤ W / L y ≤0.5.

[0044] A method for reducing the speed of air in free flow at velocity U ∞ When flowing along the flow direction from the leading edge of the airfoil to the trailing edge, at frequency f 峰值 A method for determining the amplitude of sound generated at a given location, the method comprising the steps of:

[0045] (a) Additional components for forming the airfoil according to the above method, and

[0046] (b) Attach the component to the airfoil.

[0047] This method may additionally include the step of forming multiple components and attaching the multiple components to the airfoil. For example, three components may be formed and three components may be attached to the airfoil; wherein the first component is near the tip of the airfoil, the second component is near the middle of the airfoil, and the third component is near the opposite end of the airfoil to the tip.

[0048] In one embodiment, the components may be identical. However, in an alternative embodiment, the components may have different H values.

[0049] Another aspect of the invention provides a method for forming an additional component for an airfoil having a leading edge and a trailing edge, forming a component to reduce the impact of airflow at a flow velocity U along a flow direction from the leading edge of the airfoil through the trailing edge of the component at a frequency f. 峰值 The method for determining the amplitude of the sound produced at a given location includes the steps of:

[0050] (a) Select the frequency f of the sound to be lowered 峰值 ;

[0051] (b) Choose the airflow velocity U;

[0052] (c) Provide a component having an engagement edge for engaging with the trailing edge of an airfoil, and a trailing edge opposite to the engagement edge;

[0053] (d) The trailing edge of the component is formed into multiple pairs of peaks, each pair of peaks having a first valley, a first peak, a second valley, a second peak that is farther from the joint edge than the first peak, and a third valley, wherein the first valley is located on one side of the first peak, the second valley is located between the first peak and the second peak, and the third valley is located on the other side of the second peak opposite to the second valley.

[0054] (e) wherein the first and third valleys of each pair of peaks are generally located on the first axis, the second valley of each pair of peaks is generally located on the second axis, and the second peak of each pair of peaks is located on the third axis; and,

[0055] (f) Wherein, the component is formed according to the following formula:

[0056] h′=Uκ / 4f 峰值 ,in

[0057] Where h′ is the shortest distance between the first and second axes, h″ is the shortest distance between the second and third axes, and f 峰值 U is the frequency of the sound to be reduced, and U is the air velocity in the direction of airflow over the trailing edge of the component.

[0058] Another aspect of the invention proposes a method to reduce the frequency f when air flows at a flow velocity U along the flow direction from the leading edge of the airfoil to the trailing edge. 峰值 A method for measuring the amplitude of sound generated at a location, the method comprising the steps of: providing at least one component formed according to the above method, and attaching the at least one component to an airfoil.

[0059] Another aspect of the invention proposes an additional component for an airfoil having a leading edge and a trailing edge, forming the component to reduce the impact of airflow at a flow velocity U along the flow direction from the leading edge of the airfoil to the trailing edge of the component at a frequency f. 峰值 The amplitude of the sound generated at that location, the component includes:

[0060] The joining edge is used to join to the trailing edge of the airfoil;

[0061] The trailing edge opposite the joining edge; and

[0062] The surface between the mating edge and the trailing edge;

[0063] The trailing edge of the component is formed into multiple pairs of peaks. Each pair of peaks has a first valley, a first peak, a second valley, a second peak that is farther from the joint edge than the first peak, and a third valley. The first valley is located on one side of the first peak, the second valley is located between the first peak and the second peak, and the third valley is located on the other side of the second peak opposite to the second valley.

[0064] Among them, the first and third valleys of each pair of peaks are roughly located on the first axis, the second valley of each pair of peaks is roughly located on the second axis, and the second peak of each pair of peaks is located on the third axis;

[0065] Where h′ is the shortest distance between the first and second axes, and h″ is the shortest distance between the second and third axes; and

[0066] The maximum thickness of the component in the direction perpendicular to the surface is 0.5 mm to 10 mm.

[0067] Several preferred embodiments of the present invention will now be described with reference to the accompanying drawings, wherein:

[0068] Figure 1A This is a schematic diagram of the geometric parameters of SRooTES, DRooTES, and the trailing edge attachment of the slit;

[0069] Figure 1B This is a schematic diagram of DRooTES and slit trailing edge attachments for implementing the method according to the present invention;

[0070] Figure 1C This is a schematic diagram of the experimental setup for far-field noise measurement described in this invention;

[0071] Figure 2 Depicting the situation where 20m / s≤U ∞ Comparison of ΔPWL dB performance of slit trailing edge with different slit amplitudes H within the range of ≤60m / s, where λ=3mm;

[0072] Figure 3 Depicting the situation where 20m / s≤U ∞ Comparison of dimensionless frequencies with different slit amplitudes H within the range ≤60 m / s, where λ remains at 3 mm and W remains at 0.3 mm.

[0073] Figure 4 Depicting in U ∞ =30m / s and U ∞Comparison of ΔPWL and dB performance at the trailing edge of slits with different slit wavelengths λ (mm) at a speed of 60 m / s, with the slit root width W kept at 0.3 mm.

[0074] Figure 5 Depicting the situation where 20m / s≤U ∞ Comparison of ΔPWL dB performance of the trailing edge of the baseline and slit (different W / λ, but the same λ) within the range of ≤60m / s, where H=15mm and λ=3mm;

[0075] Figure 6 Depicting the situation where 20m / s≤U ∞ Comparison of ΔPWL dB performance of the baseline and DRooTES (with different h′) trailing edges in the range of ≤60m / s, where λ=3mm;

[0076] Figure 7 The paper compares the dimensionless frequencies of DRooTES with different amplitudes H within the range of 20 m / s ≤ U∞ ≤ 60 m / s, when h' ≠ h”, i.e., κ ≠ 1, where λ = 6 mm.

[0077] Figure 8 The dimensionless frequencies of DRooTES with different root-to-root amplitudes h' are compared within the range of 20 m / s ≤ U∞ ≤ 60 m / s, when h' = h”, i.e., κ = 1, where λ = 6 mm.

[0078] Figure 9 Depicting the situation where 20m / s≤U ∞ Comparison of ΔPWL, dB of SRooTES, DRooTES, and the trailing edge of the slit within the range of ≤60 m / s, where amplitude H and wavelength λ are maintained at 15 mm and 3 mm, respectively; and

[0079] Figure 10 Depicting the situation where 20m / s≤U ∞ Within the range of ≤60m / s, the ΔPWL, dB of SRooTES, DRooTES and the trailing edge of the slit are compared, with the amplitude H and wavelength λ maintained at 30mm and 3mm, respectively.

[0080] In this invention, the airfoil attachment used to implement the method according to the invention is referred to as a double-root trailing edge sawtooth (abbreviated as "DRooTES"), which not only improves the level of trailing edge noise reduction but also allows for fine-tuning of the frequency of interest to reduce noise itself. DRooTES adopts a naming convention analogous to standard sawtooths, which are referred to herein as "SRooTES" (single-root trailing edge sawtooth).

[0081] Naming conventions

[0082] f = frequency, Hertz (Hz)

[0083] H = Amplitude, meters (m)

[0084] λ = wavelength, m

[0085] h′ = Longitudinal displacement from root to root, millimeters (mm)

[0086] h″ = longitudinal displacement from root to tip, mm

[0087] φ = the angle of the tip of the secondary sawtooth, in degrees.

[0088] λ0 = Lateral displacement from the root to the middle root, mm

[0089] h = half amplitude, m

[0090] c0 = chord length, m

[0091] W = the width of the slit at the root, mm

[0092] a = slit width at the tip, mm

[0093] AoA,θ = Angle of attack

[0094] Θ = polar angle, degrees

[0095] U ∞ = Free-flow velocity, meters per second (m / s)

[0096] x = position on the airfoil

[0097] n = Convection velocity factor

[0098] = Factor for pressure-driven turbulent vortex propagation

[0099] PWL = Sound Power Level, decibels (dB)

[0100] ΔPWL = the difference in sound power levels, dB

[0101] OAPWL = Total Sound Power Level, dB

[0102] L y = Span-related length scale of turbulent eddies

[0103] scientific theory

[0104] This invention focuses on the characteristics and mechanisms of acoustic interference generated by DRooTES and the trailing edge of a slit on the trailing edge noise of a turbulent boundary layer. The basic theory of this work is interference based on wave theory. Interference takes two forms: constructive and destructive. Theoretically, when interference originates from two sound sources (such as...) Figure 1B When the acoustic radiations of S1 and S2 shown in the diagram are 180° (π) out of phase, perfect destructive interference occurs. The associated phase difference (or phase angle) can be expressed as nπ, where n = 1, 3, 5, etc. Destructive interference causes the acoustic radiations to cancel each other out. Conversely, when the acoustic radiations between the two sources are in phase (i.e., when n = 2, 4, 6, etc.), perfect constructive interference occurs, resulting in the acoustic radiation being amplified to the far field. As a general term, the following equation is defined to determine the phase angle.

[0105]

[0106] Where ω is the oscillation frequency, f is the frequency, l is the longitudinal displacement between the two sources, and U ∞ It is the free-flow velocity. Therefore, based on the distance between S1 and S2 (scattering sources), such as Figure 1A The h′ defined in the DRooTES case and the H defined in the trailing edge case shown, when the “out-of-phase” angle (destructive interference) is applied to Equation 1, lead to the following equation:

[0107]

[0108]

[0109] Where St is the Strouhal number, representing the dimensionless frequency corresponding to destructive interference at odd positions and constructive interference at even positions.

[0110] Detailed information on trailing edge parameters

[0111] The abbreviations used in this article are as follows: Slits and DRooTES.

[0112] Figure 1AThe geometric parameters for the trailing edge plate case are shown. For DRooTES, the geometric parameters are defined as sawtooth amplitude (H), sawtooth wavelength (λ), longitudinal displacement from root 1 to root 2 (h'), longitudinal displacement from root 2 to tip 2 (h”), angle of the sawtooth tip (φ), and lateral displacement of the sawtooth root (λ0). Unless otherwise stated, the longitudinal displacement from root 1 to root 2 (h') and the lateral displacement from root 1 to root 2 (λ0) are typically half of the amplitude (H) and wavelength (λ), respectively. For the slit, the geometric parameters are the slit amplitude (also defined as H), the slit wavelength (also defined as λ), the width of the sliding tip (a), and the width of the slit gap (W).

[0113] Experimental setup

[0114] For the toothed trailing edge, the chord length of the NACA65-(12)10 arc-shaped airfoil is c0 = 0.145 m to c0 = 0.170 m, while for the baseline (B) case, the (non-toothed) chord length is c0 = 0.1425 m to c0 = 0.155 m, and the spanwise length is 0.45 m. To ensure similar wetting surface area, different chord lengths are used for the baseline and toothed cases. The chord length for the non-toothed trailing edge (baseline) case is half the chord length for the toothed trailing edge in the Slits and DRooTES cases. It should be noted that SRooTES basically refers to a simple serrated trailing edge. The airfoil consists of two main parts: the main airfoil body and the detachable flat trailing edge. The main airfoil is made of aluminum alloy with surface pressure holes on both the upper and lower surfaces, and a 0.8 mm groove along the trailing edge. The 0.8 mm thick detachable flat plate is cut by laser to form different trailing edge shapes.

[0115] Figure 1A The geometric parameters for the trailing edge plate case are shown. These parameters are defined as the sawtooth amplitude (H), sawtooth wavelength (λ), longitudinal displacement from root 1 to root 2 (h'), longitudinal displacement from root 2 to tip 2 (h”), angle of the sawtooth tip (φ), and lateral displacement of the sawtooth root (λ0). Unless otherwise stated, the longitudinal displacement from root 1 to root 2 (h') and the lateral displacement from root 1 to root 2 (λ0) are half of the amplitude (H) and wavelength (λ), respectively. For the slit case, the geometric parameters are the slit amplitude (also defined as H), the slit wavelength (also defined as λ), the width of the sliding tip (a), and the width of the slit gap (W). This invention investigates four cases: baseline, SRooTES, DRooTES, and Slit. Figure 1B A more detailed comparison of the DRooTES and Slit geometries is provided below and will be referenced.

[0116] A 0.8 mm thick flat plate trailing edge can be inserted into a 0.8 mm groove along the rear end of the main airfoil. The serration amplitude (H) and wavelength (λ) of Slit, SRooTES, and DRooTES are taken at 5 mm intervals within the range of 5 mm ≤ H ≤ 30 mm, and at 3 mm ≤ λ ≤ 35 mm, respectively. The lateral displacement of the root 1 to the root 2 of DRooTES and the angle of the serration tip are taken at 1.5 mm intervals within the range of 1.5 mm ≤ λ0 ≤ 4.5 mm, and at 0° ≤ φ ≤ 84.3°, respectively. The baseline trailing edge is half the amplitude in the toothed case to ensure a similar wetting surface area as SRooTES and DRooTES. For ease of comparison between the trailing edge of SRooTES and DRooTES and the trailing edge of Slit, the baseline trailing edge is also assumed to be half the amplitude. Coarse sandpaper is used for an extended period on the upper and lower surfaces at a distance of 30 mm from the leading edge of the airfoil to ensure that the boundary layer fully enters a turbulent state. The sandpaper strips are 10 mm wide and 0.95 mm thick.

[0117] Wind tunnel equipment and instruments

[0118] The wind tunnel equipment and instruments used for far-field noise measurements are housed in the aeroacoustic facility at Brunel University, consisting of an open-jet wind tunnel housed within an anechoic chamber measuring 4m × 5m × 3.4m. The open nozzle measures 0.3m × 0.1m (width × height). An airfoil is attached to a sideplate flush with the nozzle lip. The open-jet wind tunnel operates at speeds up to U = 80m / s, with typical low-turbulence levels between 0.1% and 0.2%. Background noise (without the airfoil but with the sideplate) is primarily open-jet noise, which is significantly lower than the self-noise generated by the airfoil at the same flow velocity. All far-field noise measurements were performed at a geometric angle of attack (AoA) θ = 0°.

[0119] Far-field array noise measurement

[0120] Far-field array noise was measured using eight GRAS half-inch condenser microphones (46AE) mounted at polar angles of Θ = 10° intervals, ranging from Θ = 50° to Θ = 120°. The microphone at Θ = 90° was located 0.97 m above the midspan and trailing edge of the airfoil. Figure 1CThe experimental setup of the far-field array is shown. A gain of ±20 dB was applied to each microphone signal using a GRAS12AX4 channel constant current source (CCP) amplifier. Data was acquired using a 16-bit analog-to-digital card manufactured by National Instruments. The sampling frequency was 40 kHz, and the sampling time was 20 seconds. The data was windowed, and the power spectral density (PSD) of the 1 Hz bandwidth was calculated based on a 1024-point Fast Fourier Transform (FFT) and a 50% overlap time. Noise was calculated to obtain the sound power level (PWL) assuming spherical propagation from the trailing edge. Multiple values ​​of the free-flow velocity were taken at intervals of U = 10 m / s, ranging from U = 20 m / s to U = 60 m / s, to measure the noise levels.

[0121] Results and Discussion

[0122] The results will be presented in this section. This section covers the results when U ∞ Noise measurements were taken at 10 m / s intervals within the ranges of 20 m / s and 60 m / s, and at an angle of attack θ = 0°, using DRooTES and the trailing edge of the slit.

[0123] So far, the description of flow velocity has only referenced the free-flow value U in the general equations (Equations 1 and 2). ∞ However, when describing the acoustic destruction mechanism of DRooTES and the slit, the key parameter is not the free-flow velocity U. ∞ It is not the convective velocity U of the turbulent vortex, but the convective velocity U of the turbulent vortex. c It is important to note that the convective velocity of a turbulent vortex is also affected by the pressure-driven secondary flow structure along its edges. The net convective velocity u of the turbulent vortex has been determined. c Between 40% and 80% of the free-flow velocity value, that is, between and Therefore, for the trailing edge of DRooTES and Slit in this invention, the general expression in Equation 2 can be modified as follows:

[0124]

[0125] in, This is the convection velocity factor, with values ​​between 0.4 and 0.8. According to the definition in Equation 3, the destructive interference mechanism should occur at St = 0.5, 1.5, etc., between the roots of DRooTES and between the roots and tips of the trailing edge of Slit.

[0126] trailing edge of the slit

[0127] Slit width (H)

[0128] Figure 2 This shows that when the free flow velocity U∞ A comparison of the sensitivity of the trailing edge of the slit with different values ​​of H is presented. ΔPWL is defined as the difference in sound power level between the baseline trailing edge and the slit trailing edge, and is a function of frequency: ΔPWL = PWL B (f)-PWL Slit (f) It is important to note that a positive ΔPWL value indicates a decrease in noise level, while a negative ΔPWL value indicates an increase in noise level. The results clearly show that the trailing edge of the slit is most effective in the low-to-mid frequency range, achieving up to 7 dB of noise reduction. Compared to the baseline trailing edge, the trailing edge of the slit also causes a significant performance degradation, up to 5 dB. Furthermore, the unique peak values ​​of the noise reduction ΔPWL achieved by individual trailing edges do not appear to follow a specific U-wave pattern. ∞ The trend of the slit amplitude H is observed. The maximum ΔPWL, observed at the trailing edge of individual slits, exhibits a relationship between f and U. ∞ The relationship with H is as follows:

[0129] 1.f∝U ∞

[0130] 2.

[0131] Therefore, the sound frequency at which the maximum noise reduction occurs is related to the free flow velocity and the longitudinal displacement H between the two ends of the slit (root and tip).

[0132] Dimensionless frequency – slit amplitude, H

[0133] Figure 3 This demonstrates whether the application of the relationship between dimensionless frequency and broadband noise reduction at the trailing edge of the slit can be generalized under different slit amplitudes (H). Theoretically, when acoustic radiation is 180° out of phase between two sources, perfect destructive interference occurs, resulting in the cancellation of the acoustic radiation. See also Figure 1B This illustrates the initial assumption of destructive interference between two sources at the root and tip of the slit trailing edge. This implies that the dimensionless frequency (fH / uc, where l = H when it is the trailing edge of the slit) defined in Equation 3 should be equal to 0.5.

[0134] Figure 4 It is shown that for different slit amplitudes, the ΔPWL peak does indeed occur around St≈0.5 (except for U=60m / s, where slight fluctuations in the Strouhal number are noticeable). These experimental results confirm that the destructive interference mechanism associated with the 180° out-of-phase cancellation between the two sources (root and tip) minimizes noise.

[0135] also, Figure 3It is clearly shown that after all the ΔPWL peaks related to the slit configuration, there is an obvious decrease in ΔPWL (increase in noise) at St≈1, which is twice the Strouhal value of the maximum noise reduction discussed in the previous section. This provides another evidence for the existence of a sound interference mechanism between the sources at the trailing edge of the slit. In summary, the destructive interference mechanism (noise reduction) should occur at St = 0.5, 1.5, etc. between the root and the tip of the trailing edge of the slit. This is consistent with the experimentally observed destructive interference occurring at St≈0.5 and St≈1.5. On the other hand, constructive interference (increase in noise) occurs at St≈1.

[0136] Dimensionless frequency – wavelength (λ) when the width (W) at the slit root is constant.

[0137] Figure 4 The comparison of the sensitivities of dimensionless frequencies is shown when λ takes different values at the trailing edge of the slit, where the slit width W is constantly maintained at 0.3 mm. Figure 4 The results in [reference] were observed at all free-stream velocities. The results clearly show that, in sharp contrast to the reduction of the peak, λ has no effect on the dimensionless frequency. In addition, for all cases, the ΔPWL peak corresponds to destructive interference at St≈0.5 and St≈1.5, and constructive interference at St = 1. In the case where λ takes the maximum value at the trailing edge of the slit, the influence of the sound interference mechanism can still be observed, but compared with the case where λ takes the minimum value, the influence of this mechanism is greatly weakened.

[0138] Width (W) at the root of the slit when wavelength (λ) is constant.

[0139] Figure 5 The comparison of the broadband noise radiation at the trailing edge of the slit is shown when the aspect ratio W / λ takes different values, where λ is constantly maintained at 3 mm. The results clearly show that at all free-stream velocities, as W increases, the noise performance significantly decreases (ΔPWL is negative) in the mid-low frequency range. When W increases, the slit geometry becomes less and less compact, and even eventually exceeds the spanwise integral length scale of the turbulent vortices. At this time, the slit in the root region slowly changes to the straight trailing edge noise mechanism, which in turn weakens the noise reduction ability.

[0140] In these experiments, the best performance is achieved when W / λ = 0.15, with a maximum noise reduction of up to 6 dB; while the worst performance is achieved when W / λ takes the maximum value of 0.5. In the mid-high frequency range of 600 Hz < f < 20 kHz, it is observed that only when the setting of W / λ takes the maximum value (0.5), it will not cause an increase in noise, and even can slightly reduce the broadband noise at low speeds, up to 4 dB. On the other hand, all settings with smaller W / λ values will only cause an increase in noise. And the trailing edge of the slit with a smaller W / λ setting will cause a larger increase in noise. Based on the results presented so far, the following summary can be made:

[0141] 1) To facilitate broadband noise reduction at low and mid frequencies, a small W / λ needs to be set. This is to avoid the slit width being comparable to the spanwise integral length of the turbulent vortex, thus weakening the destructive interference mechanism.

[0142] 2) To avoid increased high-frequency noise, a large W / λ ratio needs to be set. This is to reduce the tendency for crossflow to pass through the slit and minimize flow leakage.

[0143] Noise reduction is affected by the slit gap (W) and the turbulent vortex near the trailing edge (L). y The influence of boundary conditions on the ratio of the input spanwise correlated length scales. Experiments show that, at f 峰值 The optimal condition for noise reduction is approximately 0.2 ≤ W / L. y ≤0.5 W / L y The lower and upper limits may fluctuate due to flow conditions (such as Reynolds number, Mach number, etc.).

[0144] DRooTES

[0145] Comparison of noise results for DRooTES with different root-to-root amplitudes (h′)

[0146] Next, a new geometric feature was studied, which also utilized the additional root of acoustic interference. This new geometry is called DRooTES. Figure 6 This shows the amplitude h′ from root to root (see...) Figure 1B This section compares the broadband noise reduction (and noise increase) achieved by DRooTES at the baseline trailing edge for different amplitude values. Among all DRooTES cases, the case with the maximum amplitude h′ = 15 mm exhibits the best performance, particularly in U... ∞ The noise reduction reaches a maximum of 7dB at a speed of 60m / s. At the minimum amplitude h′ = 2.5mm, noise reduction is only observed at the trailing edge of the baseline in the high-frequency range. Generally, the noise reduction level decreases as the amplitude of the DRooTES decreases. In the high-frequency range, the noise increases with increasing amplitude, reaching a maximum of 2dB.

[0147] Dimensionless frequency – when the distance from root 1 to root 2 (h′) of DRooTES equals the distance from root 2 to tip (h″).

[0148] Suppose that in the case of DRooTES, there exists such... Figure 1B The destructive interference between the two sources shown is then expressed using the Strouhal number St. For a destructive interference of a DRooTES, the following condition must be satisfied:

[0149]

[0150] Where ω = 2πf. Same as the previous definition in the trailing edge of the slit, u cIt is the convective velocity resulting from the interaction between the turbulent vortex and the pressure-driven secondary flow. Empirical factor. Possible inequalities between h′ and h″ in frequency scaling are taken into account.

[0151] Figure 7 The dimensionless frequency fh′ / u is shown. c The spectral relationship between ΔPWL and the noise reduction is shown in the graph. It's important to note that since h′=h″i, κ=1, the maximum noise reduction (maximum ΔPWL) occurs at St≈0.5, very close to the value observed in the trailing edge case of the slit. This indicates that the same acoustic degradation mechanism also applies to DRooTES.

[0152] Dimensionless frequency—when the root 1 to root 2 (h′) of DRooTES ≠ the root 2 to tip (h″), and H is constant. When measuring 30mm

[0153] When h′≠h″, κ is no longer 1. (The factor is then considered.) Substitute into frequency scaling, Figure 8 The sensitivity of broadband noise radiation at various dimensionless frequencies is shown when h′ is different, and then h′ is adjusted accordingly to produce an overall constant H of 30 mm. The results show that all curves decrease significantly. Increasing the h′ value affects the maximum noise reduction peak. Optimal performance is achieved when h′ = 20 mm, with a maximum noise reduction of 8 dB, while at the same free-flow velocity, h′ = 5 mm only reduces noise by 5 dB. However, acoustic performance depends on geometric parameters and flow conditions.

[0154] Summarize

[0155] The following equations are used to determine the optimal geometry for the slit and DRooTES (H for the slit, h′ for the DRooTES):

[0156] For slits

[0157]

[0158] For DRooTES,

[0159]

[0160] Overall, the impact and f 峰值 The potential factors for the exact value of (the source of uncertainty) are:

[0161] 1) Turbulent eddies disperse into pressure waves near the root rather than right at the root, which affects the “real” longitudinal displacement between the slit root and tip.

[0162] 2) Variation in the range of convection velocity factors in turbulent vortices;

[0163] 3) Due to the presence of secondary flows (such as cross flows within the slit), there is another factor that affects the convective velocity of turbulent vortices, defined as

[0164] Comparison of SRooTES, DRooTES, and the trailing edge of the slit

[0165] Figure 9 Figure shows the comparison of trailing edges at different free-stream velocities when the amplitude is H = 15 mm. According to the maximum ΔPWL, the case with the best performance is the slit trailing edge, which can reduce up to 4.8 dB compared to the baseline trailing edge. Alternatively, compared to the slit trailing edge, DRooTES produces a significant broadband noise reduction over a larger frequency range of 100 Hz < f < 4 kHz at all free-stream velocities, up to 4.5 dB. In contrast, the slit based on the free-stream velocity achieves a reduction in the small frequency range of 100 kHz < f < 1.5 kHz. The case with the worst performance is SRooTES, which produces the least noise reduction in the mid-low frequency range. However, compared to DRooTES and the slit trailing edge, SRooTES produces the least noise increase in the high frequency range. In the high frequency range, the slit trailing edge produces the largest noise increase, followed by DRooTES.

[0166] Figure 10 Figure shows the comparison of trailing edges at different free-stream velocities when the amplitude is H = 30 mm. The one with the best performance is DRooTES, which can achieve a maximum noise reduction of 7.2 dB. Additionally, compared to the baseline, DRooTES produces the least noise increase and noise reduction in all frequency ranges. SRooTES produces a similar noise reduction in the low to mid-frequency range, but it produces the largest noise increase. The slit trailing edge produces a significant decrease at specific frequencies in the low to mid-frequency range and a similar decrease to DRooTES in the high frequency range.

[0167] In summary, Figure 9 and Figure 10 the results shown in

[0168] 1. Among all the trailing edge cases, DRooTES has a significant advantage in improving noise performance. When H = 15 mm and H = 30 mm, DRooTES achieves noise reductions of up to 4.5 dB and 7.2 dB respectively.

[0169] 2. For all the trailing edge cases, optimizing the geometric parameters according to different flow conditions can significantly improve the noise performance.

[0170] All optional features, preferred features, and modifications of the above embodiments and dependent claims can be used in all aspects of the invention taught herein. Furthermore, the various features of the dependent claims, as well as all optional features, preferred features, and modifications of the above embodiments, can be combined and interchanged with each other.

[0171] The disclosure of the UK patent application No. 1906920.2, which claims priority to this application, and the disclosure in the abstract accompanying this invention are incorporated herein by reference.

Claims

1. A method for forming an additional component for an airfoil having a leading edge and a trailing edge, the component being formed to reduce the ∞ In the flow direction from the leading edge of the airfoil to the trailing edge of the component at a frequency f 峰值 The amplitude of the sound generated at the location, the method comprising the following steps: (a) Select the frequency f of the sound to be reduced 峰值 ; (b) Choose the free flow velocity U of the air ∞ ; (c) providing a component having a joining edge for joining to a trailing edge of an airfoil and a trailing edge opposite the joining edge; (d) forming the trailing edge of the component into a plurality of pairs of peaks, each pair having a first valley, a first peak, a second valley, a second peak that is farther from the joining edge than the first peak, and a third valley, wherein the first valley is located on one side of the first peak, the second valley is located between the first peak and the second peak, and the third valley is located on the other side of the second peak opposite to the second valley; (e) wherein the first valley and the third valley of each pair of peaks are substantially located on a first axis, the second valley of each pair of peaks are substantially located on a second axis, and the second peak of each pair of peaks are located on a third axis; (f) And, wherein the component is formed according to the following formula: in In the range of 0.4 to 0.8, and Wherein, h′ is the shortest distance between the first axis and the second axis, h″ is the shortest distance between the second axis and the third axis, and f 峰值 is the frequency of the sound to be reduced, and U ∞ is the free stream velocity of air in the flow direction passing over the trailing edge of the component.

2. The method according to claim 1, wherein: h′=h″.

3. The method according to claim 1 or 2, wherein: For each pair of peaks in the plurality of pairs of peaks, the shortest distance from the first peak to the first axis is the same.

4. The method according to claim 1 or 2, wherein: The third valley of a first pair of peaks is the first valley of a second pair of peaks adjacent to the first pair of peaks.

5. A method for reducing the free flow velocity U ∞ When the flow direction flows from the leading edge of the airfoil to the trailing edge of the airfoil at a frequency f 峰值 The method of measuring the amplitude of the sound produced at The method comprises the following steps: (a) forming an additional component for an airfoil according to a method according to any one of claims 1 to 4, and (b) Attaching the component to the airfoil.

6. The method according to claim 5, wherein: The method comprises the steps of forming a plurality of components and attaching the plurality of components to the airfoil.

7. The method according to claim 6, wherein: Three components are formed and attached to the airfoil; wherein a first component is near the tip of the airfoil, a second component is near the middle of the airfoil, and a third component is near the other end of the airfoil opposite the tip.

8. The method according to claim 6 or 7, wherein: The components are identical.

9. The method according to claim 6 or 7, wherein: The components have different h' values ​​and / or h" values.

10. A method for forming an additional component for an airfoil having a leading edge and a trailing edge, the component being formed to reduce the ∞ In the flow direction from the leading edge of the airfoil to the trailing edge of the component at a frequency f 峰值 The amplitude of the sound generated at the location, the method comprising the following steps: (a) Select the frequency f of the sound to be reduced 峰值 ; (b) Choose the free flow velocity U of the air ∞ ; (c) providing a component having a joining edge for joining to a trailing edge of an airfoil and a trailing edge opposite the joining edge; (d) forming the trailing edge of the component into a plurality of peaks separated by a plurality of valleys, wherein each peak is connected to each valley on either side of the peak by a wall substantially perpendicular to the trailing edge, the plurality of peaks each having a width a substantially parallel to the trailing edge, the plurality of valleys each having a width W substantially parallel to the trailing edge, the width W also being the gap between adjacent peaks, wherein the plurality of peaks are substantially located on a first axis, the plurality of valleys are substantially located on a second axis, and wherein the shortest distance from the first axis to the second axis is defined as H; (e) and wherein the components are formed according to the following formula: in In the range of 0.4 to 0.

8.

11. The method according to claim 10, wherein: The gap W between adjacent peaks is related to the spanwise correlation length scale L of the turbulent eddy y The ratio satisfies the expression 0.2≤W / L y ≤0.

5.

12. A method for reducing the free flow velocity U ∞ When the flow direction flows from the leading edge of the airfoil to the trailing edge of the airfoil at a frequency f 峰值 A method for measuring the amplitude of a sound generated at a location, the method comprising the following steps: (a) forming an additional part of an airfoil according to the method of claim 10 or 11, and (b) Attaching the component to the airfoil.

13. The method according to claim 12, wherein: The method comprises the steps of forming a plurality of components and attaching the plurality of components to the airfoil.

14. The method according to claim 13, wherein: Three components are formed and attached to the airfoil, wherein a first component is near a tip of the airfoil, a second component is near a middle of the airfoil, and a third component is near another end of the airfoil opposite the tip.

15. The method according to claim 13 or 14, wherein: The components are identical.

16. The method according to claim 13 or 14, wherein: The components have different H values.

Images