CN111976959A - Shock absorption strut capable of being used for noise reduction of undercarriage and noise reduction method - Google Patents
Shock absorption strut capable of being used for noise reduction of undercarriage and noise reduction method Download PDFInfo
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- CN111976959A CN111976959A CN202010917357.1A CN202010917357A CN111976959A CN 111976959 A CN111976959 A CN 111976959A CN 202010917357 A CN202010917357 A CN 202010917357A CN 111976959 A CN111976959 A CN 111976959A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C25/00—Alighting gear
- B64C25/001—Devices not provided for in the groups B64C25/02 - B64C25/68
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C25/00—Alighting gear
- B64C25/32—Alighting gear characterised by elements which contact the ground or similar surface
- B64C25/58—Arrangements or adaptations of shock-absorbers or springs
- B64C25/60—Oleo legs
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C25/00—Alighting gear
- B64C25/001—Devices not provided for in the groups B64C25/02 - B64C25/68
- B64C2025/003—Means for reducing landing gear noise, or turbulent flow around it, e.g. landing gear doors used as deflectors
Abstract
The invention provides a shock absorption strut for noise reduction of an undercarriage and a noise reduction method, wherein the shock absorption strut is a cylindrical strut array and comprises a plurality of cylindrical struts which have the same diameter and parallel axes and have certain intervals; the arrangement mode of each cylindrical support is as follows: n rows of array struts are arranged in parallel from front to back along the incoming flow direction of the airflow, and the connecting line of each row of array struts is vertical to the incoming flow direction of the airflow; each row of array struts is arranged by a plurality of cylindrical struts at equal intervals; and the two adjacent rows of array pillars are arranged in a staggered manner. (1) By adopting the cylindrical support column array structure, the separation flow and the vortex with small and medium sizes can be locked inside the cylindrical support column array and do not develop outwards any more, so that the separation and pressure pulsation generated when the airflow flows through the support columns of the landing gear can be reduced, and the aerodynamic noise and vibration of the landing gear are reduced. (2) The landing gear support column system adopts a passive noise reduction method, does not need an additional control system and energy input, and has the advantages of simple structure, reliable performance and convenient use.
Description
Technical Field
The invention belongs to the technical field of flow control, and particularly relates to a shock absorption strut for noise reduction of an undercarriage and a noise reduction method.
Background
With the development of the civil aviation industry, the problem of aircraft noise has become one of the more and more concerned problems in the aviation industry, and the main sources of modern aircraft noise are engine noise and body noise. With the advent of higher bypass ratio engines and the application of "quiet" engine technology, engine noise levels will be reduced to levels on par with or even lower than body noise. The influence of the aerodynamic noise of the airframe is more and more obvious, and particularly, the noise of the airframe is obviously increased after the high lift device is unfolded and the undercarriage is put down when the aircraft is in an approach landing state. Therefore, the current research focus is: how to effectively reduce the noise generated by the landing gear.
Noise generation of landing gear is associated with its complex appearance because the landing gear disrupts the aerodynamic characteristics of the aircraft, creating rather complex airflow movements that make the landing gear a more significant source of noise than the wings and tail. There are studies that show that landing gear noise accounts for 25% of the total aircraft noise in the case of engine shut-down and without the high lift device on. In addition, since the landing gear is located at the bottom of the aircraft, the shielding effect of the fuselage wings and the like on landing gear noise is very limited, thereby having a serious influence on environmental noise around airports.
Since the beginning of the 70 s in the 20 th century, a great deal of experimental research work was carried out on the aerodynamic noise of the body. In 1971, the U.S. department of aerospace (NASA) study showed that: aircraft noise problems are the biggest hurdle to the development of the civil aviation industry. The body noise comprises high lift device noise, landing gear noise and the like, and early researches are focused on establishing an airplane high lift device model and carrying out noise analysis. Over time, although the complex geometric shape of the landing gear and the aerodynamic action form a complex flow field structure, which brings many difficulties for research, the research on the aerodynamic noise of the landing gear is still steadily advanced.
The research work on landing gear noise was originally traced back to the 70 s of the 20 th century, where Heller and Dobrzynski performed flight tests on moderately complex 2-and 4-wheeled landing gear models, and landing gear noise data were obtained and compared for the first time. And then, Fink establishes a noise prediction model based on the test data of the two. The Zawodny et al performs blowing test and flight test on the G550 nose landing gear; guo carries out noise test on a nose landing gear and a main landing gear of Boeing 737, and provides a noise prediction empirical model of the landing gear; NASA has carried out wind tunnel test and flight test on the aerodynamic noise of a main landing gear with wave sound 787 full size in the QTD II technical research of 2005; the european union has conducted experimental and simulation work on low noise landing gear design in the EU silent plan. The Chinese airplane strength research institute carries out a great deal of research work on the nose landing gear of a certain airplane; the Ningfang of the northwest industry university puts forward a corresponding noise prediction method for each type of components based on an FW-H equation; related work on noise tests and simulations of landing gear components has also been carried out by Longshui et al, university of Nanjing aerospace.
After a great deal of research on the aerodynamic noise of the aircraft landing gear, researchers have cleaned the acoustic characteristics of the aerodynamic noise of the aircraft landing gear and proposed a number of methods and measures for reducing the aerodynamic noise of the aircraft landing gear.
The aeroacoustic properties of landing gear noise are:
the shock strut and torsion arm structure are important components of the nose landing gear of an aircraft and are important sources of aerodynamic noise of the landing gear, and the main reason for the noise problem of modern landing gears is the increasing length of the landing gear. As the nacelle diameter of high bypass ratio engines continues to increase, it is necessary to increase the length of the landing gear in order to maintain the net distance of the wing-mounted engine nacelle to the ground. Landing gear noise is due to disturbances in the airflow pressure as it flows through the landing gear, and is aerodynamic in nature. Research shows that peak sound sources of aerodynamic noise of the undercarriage are mainly distributed at the lower part between a damping strut of the undercarriage and a torsion-proof arm, the peak sound sources are interference sound of the damping strut and the torsion-proof arm, airflow flows through the damping strut to generate airflow separation, unstable vortex shedding is formed, the vortex flows along with the airflow and collides with the downstream torsion-proof arm, and therefore strong noise is generated.
Currently, methods for noise reduction of landing gears mainly include the following three categories:
(1) changing the path and speed of flight of an aircraft
Generally, increasing the altitude and decreasing the flight speed of an aircraft during approach may reduce the aerodynamic noise of the landing gear. Therefore, the optimal combination of landing speed and altitude of the aircraft is sought, and the noise reduction effect can be achieved without changing the structure and the appearance of the landing gear. However, as the landing speed decreases, it is necessary to increase the angle of attack of the aircraft or to increase the camber of the flaps in order to meet the lift requirement, which not only increases the aerodynamic noise of the high lift device, but also leads to an increase in the drag of the aircraft, and ultimately to an increase in the power and noise of the engine.
(2) Active noise reduction method
Plasma noise reduction is one of the methods of active noise reduction. According to the method, air is ionized through a plasma exciter, a directional jet flow is generated under the action of an electric field force, the airflow flowing through the surface of the landing gear is controlled by the directional jet flow generated by the induction of the directional jet flow, and the flow separation and the pressure pulsation are reduced, so that the aerodynamic noise and the vibration of the surface of the landing gear are reduced.
Another active noise reduction method is the air film method. The principle is as follows: additional laminar flow is added to the cylindrical surface of the landing gear, and is referred to as the "air film". The air film generates laminar flow around and behind the landing gear, so that a turbulence separation point moves backwards, a turbulence area is obviously reduced, and noise generated by turbulence is greatly reduced, namely blunt body streaming noise of the landing gear is reduced.
Furthermore, there is a noise reduction method for interference noise and strut noise caused by the mutual position of the landing gear structural parts based on edge jets. The method applies vertical airflow on the edge of the leeward side of the torque arm, so that a closed space is formed among the torque arm, the jet flow plane and the strut, the flow separation condition at the rear side of the torque arm can be effectively improved, pressure pulsation generated by falling off of wake vortexes caused by the torque arm and impacting the strut is weakened, the purpose of reducing the strength of a sound source is achieved, and meanwhile, the edge jet flow also effectively reduces the strength of blunt body streaming noise, so that the noise of the strut is obviously reduced.
(3) Passive noise reduction method
Reducing the length of the landing gear is a straightforward passive noise reduction method. Because the noise of the landing gear mainly comes from the shock absorption strut, the range of noise generation can be effectively reduced by reducing the length of the landing gear, and therefore the purpose of noise reduction is achieved.
Another passive noise reduction method is to optimize the landing gear profile, i.e. to install fairings, fairing nets, fairing shells, etc. The complicated airflow flow field structure formed by the interaction of the complicated geometric shape of the undercarriage and the aerodynamic force optimizes the shape of the undercarriage to enable the undercarriage to be more streamlined, so that the complexity of the flow field can be reduced, the airflow separation is reduced, the surface pressure pulsation of the undercarriage is reduced, and the noise of the undercarriage can be reduced to a certain degree.
The method for reducing the noise of the landing gear mainly has the following defects:
(1) the active noise reduction method can realize effective control of flow and noise on the premise of not changing the overall aerodynamic shape, but the method not only needs additional energy input, but also needs corresponding sensors, controllers, actuators and the like to work cooperatively, thereby increasing the complexity of the system and reducing the reliability; (2) in the passive noise reduction method, because the diameter of a nacelle of an engine with a high bypass ratio is continuously increased, and the design requirement of an aircraft tail wiping angle on the height of an undercarriage is met, the reduction of the length of the undercarriage is not suitable in engineering practice. Optimizing the landing gear profile is a popular method, but this method typically requires the installation of fairings around the landing gear structure, which increases the structural weight, resulting in a reduction in payload that is unacceptable to aircraft designers and airlines; secondly, the presence of the shaping device also places higher demands on the space of the landing gear bay.
Therefore, how to effectively reduce the noise of the landing gear, meanwhile, the complexity of the system cannot be increased, the reliability of the system cannot be reduced, the structural weight cannot be increased, the effective load of the aircraft cannot be reduced, and the problem which needs to be solved at present is urgently solved.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a shock absorption strut for noise reduction of an undercarriage and a noise reduction method, which can effectively solve the problems.
The technical scheme adopted by the invention is as follows:
the invention provides a shock absorption strut for noise reduction of an undercarriage, wherein the shock absorption strut is a shock absorption strut of the undercarriage, the upper end of the shock absorption strut is connected with an aircraft body, and the lower end of the shock absorption strut is connected with an aircraft wheel;
the shock absorption support columns are cylindrical support column arrays and comprise a plurality of cylindrical support columns with the same diameter, parallel axes and a certain distance; the arrangement mode of each cylindrical support is as follows: n rows of array struts are arranged in parallel from front to back along the airflow incoming flow direction, n is a natural number, and the connecting line of each row of array struts is vertical to the airflow incoming flow direction; each row of array struts is arranged by a plurality of cylindrical struts at equal intervals; and the two adjacent rows of array pillars are arranged in a staggered manner.
Preferably, n rows of array struts, in a front-to-back direction, are sequentially denoted as: a row 1 array strut, a row 2 array strut, an nth row array strut;
recording the direction of the connecting line of each row of array struts as the X direction; recording the incoming flow direction of the airflow as the Y direction;
determining an X-direction central line L1 and a Y-direction central line L2 in n rows of array struts; the arrangement mode of each cylindrical support is as follows: symmetrically arranged by taking the central line L1 in the X direction as a symmetrical line; the Y-direction center line L2 is a line of symmetry and is arranged symmetrically.
Preferably, n rows of array struts, in a front-to-back direction, are sequentially denoted as: a row 1 array strut, a row 2 array strut, an nth row array strut;
for the array struts in odd-numbered sequence rows, the number of the cylindrical struts included in each row of array struts is the same, and is p;
for even-numbered sequence rows of array pillars, each row of array pillars comprises the same number of cylindrical pillars, q.
Preferably, q-p is equal to 1, i.e.: the number of the array pillars in the even-numbered sequence rows is 1 more than that of the array pillars in the odd-numbered sequence rows;
all the array struts of each odd-numbered sequence row are arranged in a rectangular array form; all the array pillars of each even-numbered sequence row are arranged in a rectangular array form.
Preferably, the number of the cylindrical pillars included in each row of the array pillars is gradually increased at an increasing interval of 1 from the row 1 of the array pillars to the direction of the X-direction center line L1; from the X-direction center line L1 to the n-th row of array pillars, the number of cylindrical pillars included in each row of array pillars is gradually reduced at decreasing intervals of 1.
Preferably, when n is an odd number, the central row is the g-th row of array pillars, and the number of the cylindrical pillars included in each row of array pillars is gradually increased by taking 1 as an increasing interval from the 1 st row of array pillars to the g-1 st row of array pillars; the number of the cylindrical pillars included in the g-th row of array pillars is one less than that of the cylindrical pillars included in the g-1 st row of array pillars;
the number of the cylindrical pillars included in the g +1 th row of array pillars is one more than that of the cylindrical pillars included in the g th row of array pillars; from the g +1 th row array strut to the n-th row array strut, the number of the cylindrical struts included in each row of array struts is gradually reduced by 1 as a descending interval.
Preferably, when n is an odd number, the central row is the g-th row of array pillars, and the number of the cylindrical pillars included in each row of array pillars from the 1 st row of array pillars to the g-th row of array pillars is gradually increased by taking 1 as an increasing interval;
from the g row array strut to the n row array strut, each row of array struts comprises the number of cylindrical struts, and the number of the cylindrical struts is gradually reduced by taking 1 as a descending interval.
Preferably, the distance from the center of the cylindrical strut array to the outermost edge of the cylindrical strut is R, and is equal to the section radius of the solid strut of the landing gear;
the height of the cylindrical strut array is equal to that of the solid strut of the landing gear;
the section radius of each cylindrical strut of the cylindrical strut array is R, and the relation between R and R is that R/R is 5-15;
the center distance between two adjacent cylindrical struts in each row of array struts is v; the relation between v and 2r is that v/2r is 1.1-3.
Preferably, the row spacing between each row of array struts is u; the center distance between two adjacent cylindrical struts in each row of array struts is v;
then: and u/v is sin60 deg..
The invention also provides a noise reduction method of the shock absorption strut for noise reduction of the landing gear, which comprises the following steps:
during the takeoff and landing stages of the airplane, the undercarriage performs retraction and release actions, and when the undercarriage is in the retraction and release process and the landing state, and airflow passes through the shock-absorbing strut, as the shock-absorbing strut is a cylindrical strut array, a part of the airflow flows along the outer surface of the cylindrical strut at the outer boundary position in the cylindrical strut array and develops downstream to form external airflow; the other part of the airflow enters the internal gaps of the cylindrical strut array to form internal airflow;
for internal gas flow, on the one hand, due to the staggered arrangement of the individual cylindrical struts, the gas flow will necessarily pass over the outer surface of a certain cylindrical strut, thereby playing a role of reducing the speed of the flow of the internal airflow, finally, the speed of the airflow flowing out from the right back of the cylindrical strut array is reduced, the airflow flowing out from the internal clearance of the cylindrical strut array enters the right back area of the cylindrical strut array, the capability of resisting the adverse pressure gradient of the airflow at the right back of the cylindrical strut array is enhanced, therefore, no low pressure region is formed right behind the cylindrical strut array, and therefore, the pressure difference across the cylindrical array is reduced, the range and the degree of an airflow separation area right behind the cylindrical strut array are further reduced, the stability of airflow is improved, and the pressure pulsation of the airflow flowing through the cylindrical strut array is reduced, so that the pneumatic noise and the vibration are reduced;
on the other hand, in the process that the internal airflow flows through the cylindrical strut array, the cylindrical strut array is designed in an arrangement mode, so that only a plurality of small separation vortexes exist in the cylindrical strut array, and each small separation vortex is stabilized in a specific small area to the maximum extent, so that the internal flow field of the cylindrical strut array is more regular and stable, and the internal aerodynamic noise and vibration of the cylindrical strut array are obviously reduced; wherein, the mode of production of separating little swirl does: for all cylindrical pillars from the 1 st row array pillar to the n-1 st row array pillar, the two types are distinguished, and one type is a bistable cylindrical pillar; the other is a monostable cylindrical pillar; the number of the bistable cylindrical pillars is far larger than that of the monostable cylindrical pillars; for the bistable cylindrical post K1, a small separating vortex is formed behind the bistable cylindrical post K1 when the airflow passes through, and meanwhile, the bistable cylindrical post K1 has two symmetrical left and right cylindrical posts downstream, which are respectively: the cylindrical support K2 and the cylindrical support K3 stabilize the separated small vortex in a specific small area through the constraint action of the cylindrical support K2 and the cylindrical support K3 on the separated small vortex, and the separated small vortex cannot continuously diffuse and develop outwards;
for the monostable cylindrical strut K4, when the airflow flows through, a small separation vortex is formed behind the monostable cylindrical strut K4, meanwhile, the cylindrical strut K5 is arranged on only one side of the downstream of the monostable cylindrical strut K4, the diffusion speed and the diffusion area of the small separation vortex are reduced through the constraint effect of the cylindrical strut K5 on the small separation vortex, and the monostable cylindrical struts K4 of the cylindrical strut array are all arranged in a symmetrical mode in the whole view, so that the interaction compensation of the small separation vortices generated by the monostable cylindrical strut K4 does not damage the stability of the airflow flowing through the inside of the cylindrical strut array, and further inhibits noise and vibration.
The damping strut for noise reduction of the landing gear and the noise reduction method provided by the invention have the following advantages:
(1) by adopting the cylindrical support column array structure, the separation flow and the vortex with small and medium sizes can be locked inside the cylindrical support column array and do not develop outwards any more, so that the separation and pressure pulsation generated when the airflow flows through the support columns of the landing gear can be reduced, and the aerodynamic noise and vibration of the landing gear are reduced.
(2) The landing gear support column system adopts a passive noise reduction method, does not need an additional control system and energy input, and has the advantages of simple structure, reliable performance and convenient use.
Drawings
FIG. 1 is a schematic structural view of a shock strut that may be used to reduce noise in landing gears according to the present invention;
FIG. 2 is a schematic view of an array of cylindrical posts provided by the present invention;
FIG. 3 is a schematic view of the arrangement of the center lines of a cylindrical strut array according to the present invention;
FIG. 4 is a schematic view of an array of cylindrical posts provided by the present invention;
FIG. 5 is a schematic view of an array of cylindrical posts provided by the present invention;
FIG. 6 is a schematic view of an array of cylindrical posts provided by the present invention;
FIG. 7 is a schematic view of a cylindrical strut array landing gear strut streaming flow field of the present invention;
FIG. 8 is a schematic view of a conventional landing gear strut bypass flow field.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Compared with the traditional solid support column system of the landing gear, the shock absorption support column provided by the invention can obviously reduce aerodynamic noise and vibration generated by the landing gear when the aircraft takes off and lands, so that the environmental protection performance and the riding comfort of the aircraft are improved.
The damping strut for noise reduction of the undercarriage provided by the invention is the undercarriage damping strut, the upper end of the damping strut is connected with an aircraft body, and the lower end of the damping strut is connected with aircraft wheels. As shown in fig. 1, the whole structure of the landing gear is a schematic diagram, wherein, 1 is a wheel; 2-wheel shaft; 3-array type piston rod; 4-array hydraulic rods; 5, a joint; 6-a torsion arm; the array type piston rod and the array type hydraulic rod are combined to form the shock absorption strut, and the shock absorption strut is of a telescopic structure through the combination of the array type piston rod and the array type hydraulic rod.
The invention improves the shock-absorbing strut between the airplane wheel and the airplane body from a single solid strut of the traditional undercarriage into a cylindrical strut array, wherein the cylindrical strut array comprises a plurality of cylindrical struts which have the same diameter, parallel axes and certain intervals; the arrangement mode of each cylindrical support is as follows: n rows of array struts are arranged in parallel from front to back along the airflow incoming flow direction, n is a natural number, and the connecting line of each row of array struts is vertical to the airflow incoming flow direction; each row of array struts is arranged by a plurality of cylindrical struts at equal intervals; and the two adjacent rows of array pillars are arranged in a staggered manner.
Specifically, referring to fig. 2, n rows of array pillars are sequentially marked as: a row 1 array strut, a row 2 array strut, an nth row array strut;
recording the direction of the connecting line of each row of array struts as the X direction; recording the incoming flow direction of the airflow as the Y direction;
determining an X-direction central line L1 and a Y-direction central line L2 in n rows of array struts; the arrangement mode of each cylindrical support is as follows: symmetrically arranged by taking the central line L1 in the X direction as a symmetrical line; the Y-direction center line L2 is a line of symmetry and is arranged symmetrically.
As an example, FIG. 2, the cylindrical strut array has a total of 7 rows of array struts, FIG. 3, which is a schematic illustration of the X-direction centerline L1 and the Y-direction centerline L2 of the cylindrical strut array; as can be seen from fig. 3, the cylindrical strut arrays are arranged symmetrically with the X-direction center line L1 as a symmetry line; the Y-direction center line L2 is a line of symmetry and is arranged symmetrically.
It is emphasized that any shock strut formed by an array of cylindrical struts conforming to the above characteristics is within the scope of the present invention. For the convenience of understanding the present invention, several specific shock strut embodiments will be described below, but the following embodiments 1 to 1 and 2 are not intended to limit the present invention.
Example 1:
n rows of array struts, according to the direction from front to back, record as in proper order: a row 1 array strut, a row 2 array strut, an nth row array strut;
for the array struts in odd-numbered sequence rows, the number of the cylindrical struts included in each row of array struts is the same, and is p;
for even-numbered sequence rows of array pillars, each row of array pillars comprises the same number of cylindrical pillars, q.
Wherein q-p is equal to 1, i.e.: the number of the array pillars in the even-numbered sequence rows is 1 more than that of the array pillars in the odd-numbered sequence rows;
all the array struts of each odd-numbered sequence row are arranged in a rectangular array form; all the array pillars of each even-numbered sequence row are arranged in a rectangular array form.
For example, referring to fig. 2, for an odd-numbered sequence of rows of array struts, namely: row 1 array struts, row 3 array struts, row 5 array struts and row 7 array struts, each comprising 3 array struts; for an even number of rows of array struts, namely: row 2 array posts, row 4 array posts, row 6 array posts, each including 4 array posts.
Example 2:
from the 1 st row of array pillars to the direction of the X-direction central line L1, the number of the cylindrical pillars included in each row of array pillars is gradually increased by taking 1 as an increasing interval; from the X-direction center line L1 to the n-th row of array pillars, the number of cylindrical pillars included in each row of array pillars is gradually reduced at decreasing intervals of 1.
This case can be further subdivided into two cases:
(1) first case
When n is an odd number, the central row is the g-th row of array struts, and the number of the cylindrical struts included in each row of array struts from the 1 st row of array struts to the g-1 st row of array struts is gradually increased by taking 1 as an increasing interval; the number of the cylindrical pillars included in the g-th row of array pillars is one less than that of the cylindrical pillars included in the g-1 st row of array pillars;
the number of the cylindrical pillars included in the g +1 th row of array pillars is one more than that of the cylindrical pillars included in the g th row of array pillars; from the g +1 th row array strut to the n-th row array strut, the number of the cylindrical struts included in each row of array struts is gradually reduced by 1 as a descending interval.
For example, referring to fig. 4, the cylindrical strut array has a total of 5 rows of array struts, wherein the row 1 array strut includes 4 cylindrical struts; the 2 nd row array of pillars comprises 5 cylindrical pillars; the 3 rd row of array pillars comprises 4 cylindrical pillars; the 4 th row of array pillars comprises 5 cylindrical pillars; the 5 th row of array pillars comprises 4 cylindrical pillars.
For another example, referring to fig. 5, the array of cylindrical pillars has 7 rows of array pillars, wherein the 1 st row of array pillars includes 2 cylindrical pillars; the 2 nd row array of pillars comprises 3 cylindrical pillars; the 3 rd row of array pillars comprises 4 cylindrical pillars; the 4 th row of array pillars comprises 3 cylindrical pillars; the 5 th row of array pillars comprises 4 cylindrical pillars; the 6 th row of array pillars comprises 3 cylindrical pillars; the 7 th row of array posts comprises 2 cylindrical posts. .
(2) Second case
When n is an odd number, the central row is the g-th row of array struts, and the number of the cylindrical struts included in each row of array struts from the 1 st row of array struts to the g-th row of array struts is gradually increased by taking 1 as an increasing interval;
from the g row array strut to the n row array strut, each row of array struts comprises the number of cylindrical struts, and the number of the cylindrical struts is gradually reduced by taking 1 as a descending interval.
For example, referring to fig. 6, the cylindrical strut array has a total of 5 rows of array struts, wherein the 1 st row of array struts comprises 3 cylindrical struts; the 2 nd row array of pillars comprises 4 cylindrical pillars; the 3 rd row of array pillars comprises 5 cylindrical pillars; the 4 th row of array pillars comprises 4 cylindrical pillars; the 5 th row of array pillars comprises 3 cylindrical pillars.
The cylindrical pillar array provided by the present invention, as a preferred mode, with reference to fig. 7, has the following parameters:
(1) the distance from the center of the cylindrical support column array to the outermost edge of the cylindrical support column is R, and is equal to the section radius of the solid support column of the traditional undercarriage;
the height of the cylindrical strut array is equal to that of a solid strut of a traditional landing gear;
the section radius of each cylindrical strut of the cylindrical strut array is R, and the relation between R and R is that R/R is 5-15;
the center distance between two adjacent cylindrical struts in each row of array struts is v; the relation between v and 2r is that v/2r is 1.1-3.
(2) The row spacing between each row of array struts is u; the center distance between two adjacent cylindrical struts in each row of array struts is v;
then: and u/v is sin60 deg..
The invention provides a noise reduction method of a shock strut for noise reduction of an undercarriage, which comprises the following steps:
during the takeoff and landing stages of the airplane, the undercarriage performs retraction and release actions, and when the undercarriage is in the retraction and release process and the landing state, and airflow passes through the shock-absorbing strut, as the shock-absorbing strut is a cylindrical strut array, a part of the airflow flows along the outer surface of the cylindrical strut at the outer boundary position in the cylindrical strut array and develops downstream to form external airflow; the other part of the airflow enters the internal gaps of the cylindrical strut array to form internal airflow;
for internal gas flow, on the one hand, due to the staggered arrangement of the individual cylindrical struts, the gas flow will necessarily pass over the outer surface of a certain cylindrical strut, thereby playing a role of reducing the speed of the flow of the internal airflow, finally, the speed of the airflow flowing out from the right back of the cylindrical strut array is reduced, the airflow flowing out from the internal clearance of the cylindrical strut array enters the right back area of the cylindrical strut array, the capability of resisting the adverse pressure gradient of the airflow at the right back of the cylindrical strut array is enhanced, therefore, no low pressure region is formed right behind the cylindrical strut array, and therefore, the pressure difference across the cylindrical array is reduced, the range and the degree of an airflow separation area right behind the cylindrical strut array are further reduced, the stability of airflow is improved, and the pressure pulsation of the airflow flowing through the cylindrical strut array is reduced, so that the pneumatic noise and the vibration are reduced;
on the other hand, in the process that the internal airflow flows through the cylindrical strut array, the cylindrical strut array is designed in an arrangement mode, so that only a plurality of small separation vortexes exist in the cylindrical strut array, and each small separation vortex is stabilized in a specific small area to the maximum extent, so that the internal flow field of the cylindrical strut array is more regular and stable, and the internal aerodynamic noise and vibration of the cylindrical strut array are obviously reduced; wherein, the mode of production of separating little swirl does:
for all cylindrical pillars from the 1 st row array pillar to the n-1 st row array pillar, the two types are distinguished, and one type is a bistable cylindrical pillar; the other is a monostable cylindrical pillar; the number of the bistable cylindrical pillars is far larger than that of the monostable cylindrical pillars; for the bistable cylindrical post K1, a small separating vortex is formed behind the bistable cylindrical post K1 when the airflow passes through, and meanwhile, the bistable cylindrical post K1 has two symmetrical left and right cylindrical posts downstream, which are respectively: the cylindrical support K2 and the cylindrical support K3 stabilize the separated small vortex in a specific small area through the constraint action of the cylindrical support K2 and the cylindrical support K3 on the separated small vortex, and the separated small vortex cannot continuously diffuse and develop outwards;
for the monostable cylindrical strut K4, when the airflow flows through, a small separation vortex is formed behind the monostable cylindrical strut K4, meanwhile, the cylindrical strut K5 is arranged on only one side of the downstream of the monostable cylindrical strut K4, the diffusion speed and the diffusion area of the small separation vortex are reduced through the constraint effect of the cylindrical strut K5 on the small separation vortex, and the monostable cylindrical struts K4 of the cylindrical strut array are all arranged in a symmetrical mode in the whole view, so that the interaction compensation of the small separation vortices generated by the monostable cylindrical strut K4 does not damage the stability of the airflow flowing through the inside of the cylindrical strut array, and further inhibits noise and vibration.
For example, referring to FIG. 7, there are 5 rows of cylindrical post arrays; in the row 1 to row 4 cylindrical strut arrays, there are a total of 4 monostable cylindrical struts, respectively F1, F2, F3 and F4; a total of 12 bistable cylindrical struts, H1, H2, H3, H4, H5, H6, H7, H8, H9, H10, H11 and H12; for bistable cylindrical struts, for example, for bistable cylindrical strut H5, a separate small vortex is formed behind bistable cylindrical strut H5 as the gas stream flows through, while downstream of bistable cylindrical strut H5 there are two symmetrical left and right cylindrical struts, respectively: the cylindrical support H8 and the cylindrical support H9 stabilize the separated small vortexes in a specific small area through the constraint action of the cylindrical support H8 and the cylindrical support H9 on the separated small vortexes, and the separated small vortexes cannot continue to diffuse outwards.
For the monostable cylindrical support F1, when the airflow flows through, a small separation vortex is formed behind the monostable cylindrical support F1, meanwhile, the monostable cylindrical support F1 is provided with the cylindrical support F3 on only one side downstream, and the diffusion speed and the diffusion area of the small separation vortex are reduced through the constraint effect of the cylindrical support F3 on the small separation vortex.
Fig. 8 is a schematic view of a streaming flow field of a conventional landing gear shock strut, and it can be seen from fig. 8 that the flow is separated at the downstream of two sides of a cylindrical strut, large periodic separation vortices appear in the wake flow, and the shedding of the vortices alternately generated can interact with the cylindrical wall surface, so that the structure generates severe vibration, and positive pressure and negative pressure alternately pressure pulsation is generated in the flow field, so that aerodynamic noise is generated. In addition, there is a significant "dead water zone" directly behind such solid cylindrical struts, which causes a large pressure differential resistance.
Fig. 7 is a schematic view of the array type shock strut circumfluence flow field provided by the invention, and as can be seen from fig. 7, for each cylindrical strut, the flow separation still exists, but the size thereof becomes smaller, and the generated separation vortex is limited within a fixed small range under the influence of the surrounding cylinders, and the separation vortex with stable small size appears behind each cylindrical strut, so that the array type shock strut overall flow field is more regular and stable. Directly behind the strut array the extent of the "dead water zone" is significantly reduced due to the supplementary energy of the flow within the array.
The shock-absorbing strut for reducing noise of the landing gear, provided by the invention, replaces a single solid strut independent and thick of the traditional landing gear by an array formed by a series of cylindrical struts, and the cross-sectional diameter of the cylindrical strut array is the same as that of the corresponding traditional landing gear strut. The front airflow incoming directions of all the cylindrical struts in the cylindrical strut array are staggered, so that when the landing gear is put down in the takeoff and landing stages of an airplane and airflow passes through the shock-absorbing struts, a part of the airflow flows along the periphery and develops downstream; the other part of the airflow enters the internal clearance of the shock absorption strut, and when the peripheral flow develops to the rear of the shock absorption strut, the capability of resisting the adverse pressure gradient is greatly improved due to the flow injection energy from the inside, so that the separation area is reduced; on the other hand, separation vortexes formed by the internal flow behind each small strut are acted by other struts and cannot be developed outwards, so that the flow field structure is more stable. This results in a more stable flow through the separation zone, a smaller separation zone and a smaller pressure pulsation, which ultimately results in a reduction of aerodynamic noise and a reduction of vibrations. The method has the following advantages:
(1) by adopting the cylindrical support column array structure, the separation flow and the vortex with small and medium sizes can be locked inside the cylindrical support column array and do not develop outwards any more, so that the separation and pressure pulsation generated when the airflow flows through the support columns of the landing gear can be reduced, and the aerodynamic noise and vibration of the landing gear are reduced.
(2) The landing gear support column system adopts a passive noise reduction method, does not need an additional control system and energy input, and has the advantages of simple structure, reliable performance and convenient use.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and improvements can be made without departing from the principle of the present invention, and such modifications and improvements should also be considered within the scope of the present invention.
Claims (10)
1. A shock strut for noise reduction of an undercarriage is characterized in that the shock strut is a shock strut for the undercarriage, the upper end of the shock strut is connected with an aircraft body, and the lower end of the shock strut is connected with an aircraft wheel;
the shock absorption support columns are cylindrical support column arrays and comprise a plurality of cylindrical support columns with the same diameter, parallel axes and a certain distance; the arrangement mode of each cylindrical support is as follows: n rows of array struts are arranged in parallel from front to back along the airflow incoming flow direction, n is a natural number, and the connecting line of each row of array struts is vertical to the airflow incoming flow direction; each row of array struts is arranged by a plurality of cylindrical struts at equal intervals; and the two adjacent rows of array pillars are arranged in a staggered manner.
2. A shock strut for reducing noise of a landing gear according to claim 1, wherein the n rows of array struts, in a forward to rearward direction, are sequentially: a row 1 array strut, a row 2 array strut, an nth row array strut;
recording the direction of the connecting line of each row of array struts as the X direction; recording the incoming flow direction of the airflow as the Y direction;
determining an X-direction central line L1 and a Y-direction central line L2 in n rows of array struts; the arrangement mode of each cylindrical support is as follows: symmetrically arranged by taking the central line L1 in the X direction as a symmetrical line; the Y-direction center line L2 is a line of symmetry and is arranged symmetrically.
3. A shock strut for reducing noise of a landing gear according to claim 2, wherein the n rows of array struts, in a forward to rearward direction, are sequentially: a row 1 array strut, a row 2 array strut, an nth row array strut;
for the array struts in odd-numbered sequence rows, the number of the cylindrical struts included in each row of array struts is the same, and is p;
for even-numbered sequence rows of array pillars, each row of array pillars comprises the same number of cylindrical pillars, q.
4. A shock strut for use in noise reduction of landing gears according to claim 3, characterised in that q-p is equal to 1, namely: the number of the array pillars in the even-numbered sequence rows is 1 more than that of the array pillars in the odd-numbered sequence rows;
all the array struts of each odd-numbered sequence row are arranged in a rectangular array form; all the array pillars of each even-numbered sequence row are arranged in a rectangular array form.
5. A shock strut for reducing noise of landing gear according to claim 2, wherein each row of array struts comprises a number of cylindrical struts which increases progressively at 1 increasing intervals in the direction from the row 1 array strut to the X-direction center line L1; from the X-direction center line L1 to the n-th row of array pillars, the number of cylindrical pillars included in each row of array pillars is gradually reduced at decreasing intervals of 1.
6. A shock strut for noise reduction of landing gears according to claim 5, wherein when n is an odd number, the central row is the g-th row array strut, and the number of the cylindrical struts included in each row of array struts increases gradually at 1 increasing interval from the 1 st row array strut to the g-1 st row array strut; the number of the cylindrical pillars included in the g-th row of array pillars is one less than that of the cylindrical pillars included in the g-1 st row of array pillars;
the number of the cylindrical pillars included in the g +1 th row of array pillars is one more than that of the cylindrical pillars included in the g th row of array pillars; from the g +1 th row array strut to the n-th row array strut, the number of the cylindrical struts included in each row of array struts is gradually reduced by 1 as a descending interval.
7. A shock strut for noise reduction of landing gears according to claim 5, wherein when n is an odd number, the central row is the g-th row array strut, and each row of array struts comprises a gradually increasing number of cylindrical struts from the 1 st row array strut to the g-th row array strut at 1-step intervals;
from the g row array strut to the n row array strut, each row of array struts comprises the number of cylindrical struts, and the number of the cylindrical struts is gradually reduced by taking 1 as a descending interval.
8. A shock strut for use in noise reduction of landing gear according to claim 1, wherein the distance R from the centre of the array of cylindrical struts to the outermost edge of the cylindrical struts is equal to the cross-sectional radius of the solid struts of the landing gear;
the height of the cylindrical strut array is equal to that of the solid strut of the landing gear;
the section radius of each cylindrical strut of the cylindrical strut array is R, and the relation between R and R is that R/R is 5-15;
the center distance between two adjacent cylindrical struts in each row of array struts is v; the relation between v and 2r is that v/2r is 1.1-3.
9. A shock strut for use in noise reduction of landing gear according to claim 1, wherein the row spacing between rows of array struts is u; the center distance between two adjacent cylindrical struts in each row of array struts is v;
then: and u/v is sin60 deg..
10. A method of reducing the noise of a shock strut usable for reducing the noise of landing gears according to any one of claims 1 to 9, comprising the steps of:
during the takeoff and landing stages of the airplane, the undercarriage performs retraction and release actions, and when the undercarriage is in the retraction and release process and the landing state, and airflow passes through the shock-absorbing strut, as the shock-absorbing strut is a cylindrical strut array, a part of the airflow flows along the outer surface of the cylindrical strut at the outer boundary position in the cylindrical strut array and develops downstream to form external airflow; the other part of the airflow enters the internal gaps of the cylindrical strut array to form internal airflow;
for internal gas flow, on the one hand, due to the staggered arrangement of the individual cylindrical struts, the gas flow will necessarily pass over the outer surface of a certain cylindrical strut, thereby playing a role of reducing the speed of the flow of the internal airflow, finally, the speed of the airflow flowing out from the right back of the cylindrical strut array is reduced, the airflow flowing out from the internal clearance of the cylindrical strut array enters the right back area of the cylindrical strut array, the capability of resisting the adverse pressure gradient of the airflow at the right back of the cylindrical strut array is enhanced, therefore, no low pressure region is formed right behind the cylindrical strut array, and therefore, the pressure difference across the cylindrical array is reduced, the range and the degree of an airflow separation area right behind the cylindrical strut array are further reduced, the stability of airflow is improved, and the pressure pulsation of the airflow flowing through the cylindrical strut array is reduced, so that the pneumatic noise and the vibration are reduced;
on the other hand, in the process that the internal airflow flows through the cylindrical strut array, the cylindrical strut array is designed in an arrangement mode, so that only a plurality of small separation vortexes exist in the cylindrical strut array, and each small separation vortex is stabilized in a specific small area to the maximum extent, so that the internal flow field of the cylindrical strut array is more regular and stable, and the internal aerodynamic noise and vibration of the cylindrical strut array are obviously reduced; wherein, the mode of production of separating little swirl does: for all cylindrical pillars from the 1 st row array pillar to the n-1 st row array pillar, the two types are distinguished, and one type is a bistable cylindrical pillar; the other is a monostable cylindrical pillar; the number of the bistable cylindrical pillars is far larger than that of the monostable cylindrical pillars; for the bistable cylindrical post K1, a small separating vortex is formed behind the bistable cylindrical post K1 when the airflow passes through, and meanwhile, the bistable cylindrical post K1 has two symmetrical left and right cylindrical posts downstream, which are respectively: the cylindrical support K2 and the cylindrical support K3 stabilize the separated small vortex in a specific small area through the constraint action of the cylindrical support K2 and the cylindrical support K3 on the separated small vortex, and the separated small vortex cannot continuously diffuse and develop outwards;
for the monostable cylindrical strut K4, when the airflow flows through, a small separation vortex is formed behind the monostable cylindrical strut K4, meanwhile, the cylindrical strut K5 is arranged on only one side of the downstream of the monostable cylindrical strut K4, the diffusion speed and the diffusion area of the small separation vortex are reduced through the constraint effect of the cylindrical strut K5 on the small separation vortex, and the monostable cylindrical struts K4 of the cylindrical strut array are all arranged in a symmetrical mode in the whole view, so that the interaction compensation of the small separation vortices generated by the monostable cylindrical strut K4 does not damage the stability of the airflow flowing through the inside of the cylindrical strut array, and further inhibits noise and vibration.
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