Classifications

• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
  • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
  • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
  • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
  • G10K11/1785—Methods, e.g. algorithms; Devices
  • G10K11/17857—Geometric disposition, e.g. placement of microphones
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
  • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
  • G10K11/1787—General system configurations
  • G10K11/17875—General system configurations using an error signal without a reference signal, e.g. pure feedback
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
  • G10K2210/10—Applications
  • G10K2210/111—Directivity control or beam pattern
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
  • G10K2210/10—Applications
  • G10K2210/112—Ducts
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
  • G10K2210/10—Applications
  • G10K2210/119—Radiation control, e.g. control of sound radiated by vibrating structures
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
  • G10K2210/10—Applications
  • G10K2210/128—Vehicles
  • G10K2210/1281—Aircraft, e.g. spacecraft, airplane or helicopter
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
  • G10K2210/30—Means
  • G10K2210/301—Computational
  • G10K2210/3051—Sampling, e.g. variable rate, synchronous, decimated or interpolated
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
  • G10K2210/50—Miscellaneous
  • G10K2210/507—Flow or turbulence

Definitions

• the invention relates to the active control to limit harmonic sound radiated towards the sidelines from ducts containing a subsonic, uniform flow. It is in particular applicable to limitation of noise radiated from circular ducts such a gas turbine intake
• Patent applications WO 95/19075 and WO 94/08540 both describe active controllers for flow ducts having internally located sensors and sound sources. No details however are given of the control algorithm.
• Patent US 5355417 discloses a configuration for the active control of aircraft engine inlet noise by including an array of circumferential ly arranged sound sources mounted inside an inlet duct as well as an array of sensors arranged in a ring. Again the active control algorithm is not disclosed in any great detail. Moreover the results of this system show an increase in sound propagated towards the sidelines, which are the important regions for sound reduction.
• a duct for fluid flow having means for e control of sound radiated therefrom, said duct comprising sound sensors located on the inner surface of said duct and grouped together in one or more planes transverse with respect to the duct axis and at least one secondary source whose operation is a function of sound received at said sound sensors characterised in that the axial spacing of said transverse planes is not more than 0 5 ⁇ m ⁇ n ( l+M zmaN ) where ⁇ ⁇ , ⁇ n is the wavelength corresponding to the radiated tone frequency of interest and M zmax is the maximum Mach number of the free stream flow in the duct
• the inventors By using sensors external to the engines to observe directly the far field radiated sound the inventors have determined a method to controls loudspeakers, or so called secondary sources, so as to minimise engine noise in the far field
• the invention also provides a method for the active control of sound radiated from a fluid flow duct comprising
• figure 1 shows a schematic diagram of a circular duct containing uniform axial flow comprising an arrav of sensors and secondary sources
• Figure l b shows the relationship between resultant wavenumber km. normal to the local avefront, the propagation angle ⁇ mn and axial wavenumber k zm ⁇
• Figure 2 shows the a typical variation of axial wavenumber with propagation angle with the ideal receiver response
• Figure 3 shows the directivity function of a ten element line array at the design frequency steered at 45° for zero Mach number and Mach number equal to -0 5
• Figure 5 shows the change in modal amplitude verses propagation angle following the minimisation of the sum of squared signal at ten equally spaced line arrays comprising ten elements, each forming beams in the directions between 60° and 90° in 5° increments, in the example in figure 4
• Figure 7 shows the change in modal amplitude verses propagation angle following the minimisation of the sum of squared signal at ten equally spaced line arrays comprising ten elements, each forming beams in the directions between 30° and 60° in 5° increments, for the example of figure 5
• Figure 8 shows the relationship between phase veloc ⁇ t ⁇ . croup ⁇ eiocity and intake axial flow velocity in aduct
• Figure 9 shows an unflanged hard walled duct containing a subsonic intake flow Noise from aircraft cause annoyance in populated areas For an aircraft on approach and during takeoff these noise radiation angles are well away from the duct axis, towards the sidelines.
• control bandwidth means the band of angles (measured from 90° to the duct axis) over which the radiated sound is to be minimised
• control bandwidth means the band of angles (measured from 90° to the duct axis) over which the radiated sound is to be minimised
• the invention uses e.g. one or more circumferential arrays of appropriately phased sensors at the duct wall that can observe the acoustic pressure associated with those propagation angles that are responsible for the field radiated towards the sidelines.
• Figure la represents a circular, hard walled flanged duct (1) containing uniform, axial flow of Mach No. of M z (2).
• a ray-mode of acoustic pressure (sound) (2) transmitted along the duct and then radiated from the duct intake is shown and can be detected by a wall mounted line array, of appropriately phased (located) sensors (3)
• the figure shows the relationship between resultant wavenumber k mn normal to the local wavefront, the propagation angle ⁇ mn and axial wavenumber zmr ,.
• the in-duct 'error' sensing principle proposed here is based on the mode angle ⁇ mn which specifies the angle between the modal wavefront and the duct axis. More importantly the mode angle ⁇ mn in the duct, for both flanged and unflanged ducts, is also coincident with the angle of the principal lobe of far field radiation providing there is zero flow external to the duct. Even when the flow speeds inside and outside the duct are different, a unique and monotonic relationship exists between the transmission and radiation angle Much of the original mode-ray angle information pertaining to the transmitted sound field inside the duct is therefore preserved in the radiated sound field.
• the duct also contains one or more secondanv sources (4) preferably, as angular arrays, the control of which is dependent upon the received signals of the sensors
• the sensors are arranged in the figure as a series of annular rin ⁇ s
• the method is not limited to such an arrangement, and may include any suitable spacing e.g. the sensors may not form rings but may be clustered closer together over a small sector of the duct wall.
• the acoustic pressure in a circular duct satisfies the convected form of the wave equation written below in cylindrical co-ordinates.
• k is the free space wavenumber w/c.
• k rmn actually represents a combined radial-circumferential wavenumber.
• the resultant wavenumber in the duct k m consult is therefore equal to k - Mki mn
• Equation (4) can be re-arranged to express the axial wavenumber of the (m n) mode in terms of the propagation angle as
• the external far field acoustic pressure due to the (in /?/ ' mode from a flanged duct may be written in the form
• D m consult denotes the directivity function of the (m,n)' mode and R is the distance from the duct face to the observer.
• a wall mounted phased line array for the detection of modes by modal angle ⁇ m ⁇ has been shown to bear a definite and causal relationship to reductions in the in-duct sound field transmitted obliquely to the duct axis
• the objective is therefore to design a wall mounted sensor array comprising of a relatively small number of discrete sensors that has sufficiently good directivity to detect this change in the transmitted sound field
• the ideal receiver response is plotted in figure 4 and is a step function which detects only the signals arriving at large incidence angles to the array while rejecting signals transmitted at angles close to the duct axis
• Figure 4 also demonstrates that the ideal rece ⁇ er characteristics is a high pass filter of propagation angle which, by virtue of equation (5), is also a low pass filter of axial wavenumber It shows
• the highest frequency in the highest intake flow speed of interest Mz ma
• ⁇ m . cope f ⁇ which is the shortest wavelength in the radiation field
• the frequency, f max is known as the design frequency of the array
• z denotes the axial position of the first sensor in a wall mounted line array comprising L elements separated by a distance ⁇ z
• the t sensor is required to have the axial location z / given by
• ⁇ m ⁇ is the relative phase angle between adjacent sensors
• Equation ( 12) effectively specifies the complex weights w ⁇ (B(i) of a simple 'delay and add' line array beam former.
• the array elements are simply required to delay the signals at each sensor by an appropriate amount ⁇ f ⁇ ) which upon addition, causes the signals at each sensor to be summed perfectly in-phase.
• the beam steer angle are made such that they are made to scan the angles ⁇ from 90° to 90° to 90° - ⁇ in some appropriate incremental angle.
• ⁇ 0 is the beam steer angle
• the followmg describes relationships between the sensor (receiver) line array directivity characteristics and its relationship to mode detection.
• the directivity characteristics of the sensor (receiver) line array can be described by the normalised directivity function dfQ/Qn). This function specifies the array response at some angle ⁇ when the main beam is steered at an angle ⁇ o, and can be determined from
• Equation (21) is a geometric series that can be summed over L terms to give
• FIG. 3 shows the directivity function of a ten element line array at the design frequency, steered at 45° for zero Mach number (solid line) and with a Mach number equal to -0.5 (dashed line).
• solid line the design frequency
• -0.5 the Mach number equal to -0.5
• the lOdB beamwidth is about 20°.
• the presence of flow with speed equal to M. - -0.5 which is typical for an aircraft on approach, appears to cause no appreciable change in directivity characteristics apart from a slight narrowing of the main beam and a reduction in the number of side lobes.
• the effect of implementing this receiver array is to weight the modal contributions to the receiver by a factor equal to the array's directivity function dfld m ⁇ / ⁇ n) evaluated at the modal arrival angle ⁇ resort, n Steering of the array's mam beam in the direction of the mode angles closest to cut-off will therefore amplify the acoustic pressure propagating with those angles highlighted in figures 2 and 3 as being directly responsible for the reductions in the important band of radiation angles, i e those towards the sidelines The transmitted sound field whose propagation angles are diffracted outside the control region, i e .
• b(Q ⁇ embarka. ⁇ k ) denotes the complex signal produced after steering a beam at an angle Q n , by a receiver array located at the circumferential angle ⁇ around the duct wall and is computed from
• Figure 4 shows tests of the in-duct receiver array's ability to control the radiated sound towards the sidelines is from a duct without flow.
• a 10 x 10 sensor array is used comprising ten line array receivers equally spaced around the duct wall, each consisting of ten elements. The beams at each of the receivers are steered in the range of angles from 55° to 90° from the duct axis in increments of 5°. Eighteen secondary sources are driven to minimise the sum of squared signals produced by the ten independent receivers according to equation (24).
• a comparison between the radiated far field sound pressure level reductions, obtained by computer simulation versus polar angle produced by using the internal and external sensors is shown. These results represent the average reduction over twenty azimuthal angles.
• the solid curve is the result of minimising the sound power radiated into a band of angles from 55° to 90° from the duct axis using a dense grid of external error sensors in the control region that afford perfect observability of the radiated field.
• loudspeaker or sources can be driven to minimise the noise in the far field.
• Figure 5 shows the change in modal amplitude verses propagation angle following the minimisation of the sum of squared signal at ten equally spaced line arrays comprising ten elements, each forming beams in the directions between 60° and 90° in 5° increments. The agreement between the two curves is extremely good.
• Figure 7 shows the change in modal amplitude verses propagation angle following the minimisation of the sum of squared signal at ten equally spaced line arrays comprising ten elements, each forming beams in the directions benveen 30° and 60° in 5° increments, for the case in figure 5.
• a large number of sensors is required to construct the array. About one hundred is anticipated to be necessary, although many more would of course be desirable. However the large number of sensors required does not translate to a correspondingly high processing bandwidth. The reason for this is the independence of the line arrays which is fundamental to ensuring robustness of the technique. One is not required to measure transfer functions between sensors on different line arrays Each receiver line array could therefore be allocated its own dedicated processor for forming the beams whose output could then be input to a mam processor for real time adaptation of the secondary sources
• the sensor array should be preferably located flush to the duct walls in order not to interfere with the passage of flow through the engine.
• the use of the sensor array is fundamentally dependent on the existence of a unique and simple relationship between the transmitted sound field and the radiated far field.
• the cost functions to be minimized depend on whether total sound power or sound pressure towards the sidelenes is to be reduced. In order to enable these cost functions, which are given hereinafter and hereinbefore, to be implemented, basic relationships and definitions are given.
• the sensor array described here is designed to detect the modes based on their different axial propagation angles ⁇ m ⁇ . By simple geometry this angle is also given by:
• c m ⁇ denotes the modal phase speed and may be regarded as a vector normal to the modal wavefront.
• a more fundamental variable is the angle with which acoustic energy is transmitted along the duct and this is related to the axial group velocity c gm ⁇ , where
• the angle with which acoustic energy is transmitted along the duct is identical to the angle of the mode peak pressure far field radiation lobe Q Pm ⁇ when the flow speed inside and outside the duct are equal.
• the in-duct axial propagation angle ⁇ m ⁇ which can be detected using the in-duct sensor array, and the radiated peak far field pressure angle ⁇ / > m ⁇ , are connected by the above two equations with cut-off ratio as the independent parameter.
• the angle of the modal peak far field pressure radiation lobe is closely related to the axial propagation angle.
• the deviation between the two angles increases with increasing Mach number.
• the range of axial propagation angles becomes smaller with increasing intake Mach number whereas the range of the principal radiation lobe angles remains distributed between 0° for the plane wave mode and 90° at cut ⁇ off, irrespective of flow speed.
• ⁇ m ⁇ is the real part of an effective modal admittance in the flow calculated from
• cost function of equation (36) is the summation over axial arrays at different azimuthal positions around the duct wall
• a cost function based on a single axial line array would, in the general case, be minimised by rotating various spinning modes to produce destructive interference at the azimuthal location coinciding with the location of the sensor array
• Minimising the sum of square outputs from several axiai arrays prevents this from occurring and ensures the correct control mechanism by reducing the appropriate modal amplitudes.
• the control mechanism underlying the reduction of sideline radiation is made clear by the relationship between the in-duct angles and those in the far field. Tie modes closest to cut-off must be attenuated in order to reduce the sideline radiation.
• a sketch of the duct, the control surface and axial sensor array configured to control sideline radiation is presented in figure 5 showing an unflanged circular hard walled duct containing a mean subsonic intake flovv. Enclosing the duct exit is a sector of a sphere of width ⁇ across which the sound power is to be minimised by a ring of secondary sources.
• a single axial sensor line array at the duct wail detects the transmitted sound field from which the field radiated towards the sidelines can be inferred.
• a suitable weighting function on which accounts for the importance to sideline radiation of near cut-off modes is the exponential function exp ⁇ - ⁇ ( ⁇ -m ⁇ - ⁇ ) ⁇ .
• ⁇ is an arbitrary constant which specifies the relative weighting assigned to the different modes according to propagation angle.
• a cost function for reducing sideline radiation incorporating this weighting function is expressed

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Multimedia (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)
• Pipe Accessories (AREA)

Priority Applications (3)

Applications Claiming Priority (4)

Publications (1)

Family

ID=26308956

Family Applications (1)

Country Status (4)

Families Citing this family (2)

Citations (4)

• 1997
  • 1997-03-10 DE DE69705211T patent/DE69705211T2/de not_active Expired - Fee Related
  • 1997-03-10 WO PCT/GB1997/000624 patent/WO1997035300A1/en active IP Right Grant
  • 1997-03-10 EP EP97906266A patent/EP0888607B1/de not_active Expired - Lifetime
  • 1997-03-10 ES ES97906266T patent/ES2157557T3/es not_active Expired - Lifetime

Patent Citations (4)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events