CN115659486A - Bionic near space aircraft wing modification design method - Google Patents
Bionic near space aircraft wing modification design method Download PDFInfo
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- CN115659486A CN115659486A CN202211155134.1A CN202211155134A CN115659486A CN 115659486 A CN115659486 A CN 115659486A CN 202211155134 A CN202211155134 A CN 202211155134A CN 115659486 A CN115659486 A CN 115659486A
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Abstract
The invention provides a bionic near space aircraft wing modification design method, which comprises the following steps: acquiring a wing chamber structure on the surface of a dragonfly wing and a corrugated structure on the cross section of the dragonfly wing; designing a bionic wing chamber structure according to the dragonfly wing surface wing chamber structure; smoothly connecting extreme points of a dragonfly cross section fold corrugated structure to obtain a bionic wing profile structure; manufacturing the wings according to the bionic wing section structure, and arranging the bionic wing chamber structure at a position before the starting point of transition of the wing surface boundary layer. According to the bionic near space aircraft wing modification design method, the bionic modified wing is designed according to the cross section structure of the dragonfly wing and the wing chamber structure of the dragonfly wing, the starting position of transition of the wing surface boundary layer is controlled by arranging the proper dragonfly wing chamber simulation structure on the wing, the transition of the boundary layer to a turbulent boundary layer is promoted, and the wing surface boundary layer is more stable.
Description
Technical Field
The invention belongs to the technical field of aviation, and particularly relates to a wing modification design method of a bionic near space aircraft.
Background
A close-proximity spacecraft is a type of aircraft that operates in an airspace ranging from 20km to 100km from sea level, i.e., at an altitude above the highest altitude at which existing aircraft can control flight, but below the lowest altitude at which satellites maintain low-earth orbit flight. Within the height range, compared with the ground communication relay station, the communication coverage area is wider; compared with satellite communication, the method has the advantages of short delay time, recyclability, timely update of an information system and the like; a more significant advantage is that within this altitude range, the aircraft has a higher solar energy utilization. Therefore, in recent years, the design of the near space aircraft is biased to the design of the high-altitude solar long-endurance unmanned aerial vehicle, so that the design of a novel wing with higher load and working efficiency is particularly important for the design of the near space aircraft.
The flow of the surface layer of the wing surface is a main reason influencing the working efficiency of the wing surface and is closely related to flow separation. Under the condition of low Reynolds number, because viscous acting force is enhanced, most of the wing surface boundary layer is in a laminar state, although the resistance generated by the laminar boundary layer is smaller than that of the turbulent boundary layer, under the condition of existence of a backpressure gradient, the anti-interference capability of the laminar boundary layer is weaker than that of the turbulent boundary layer, and the capability of the turbulent boundary layer for resisting the separation of the boundary layers is also stronger. If laminar flow separation occurs, the drag produced by the airfoil will be much greater than the increased drag of the turbulent boundary layer compared to the laminar boundary layer.
Currently, active and passive flow control techniques are often employed for flow within the boundary layer. The traditional control method for the boundary layer of the wing comprises the steps of adding a flap, a boundary layer blowing and sucking device and the like, but in practical application, the problems of complex structure, low reliability, heavy weight, difficulty in implementation and the like exist.
Disclosure of Invention
In view of the above, the invention aims to provide a method for designing a wing modification of a bionic near space aircraft, so as to solve the problem that active control of flow in an existing wing boundary layer is applied to a wing of the near space aircraft, so that the method is difficult to realize.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
the invention provides a bionic near space aircraft wing modification design method, which comprises the following steps:
acquiring a wing chamber structure on the surface of a dragonfly wing and a corrugated structure on the cross section of the dragonfly wing;
designing a bionic wing chamber structure according to the dragonfly wing surface wing chamber structure;
smoothly connecting extreme points of a dragonfly cross section fold corrugated structure to obtain a bionic wing section structure;
manufacturing the wings according to the bionic wing section structure, and arranging the bionic wing chamber structure at a position before the starting point of transition of the wing surface boundary layer.
Further, the bionic wing-chamber structure is designed according to the dragonfly wing surface wing-chamber structure, and comprises:
designing the shape of a bionic wing chamber structure according to the shape of the wing chamber structure on the surface of the dragonfly wing;
obtaining the size of the bionic wing-chamber structure according to the ratio of the characteristic length of the wing-chamber structure on the surface of the dragonfly wing to the wingspan of the dragonfly wing;
determining the depth of the bionic wing chamber structure according to the thickness of the boundary layer of the bionic wing chamber structure at the corresponding position on the surface of the wing;
the method is characterized in that the configuration mode of the bionic wing chamber structure is designed according to the configuration mode of the dragonfly wing surface wing chamber structure.
Further, the shape of the bionic wing-chamber structure is at least one of a quadrangle, a pentagon and a hexagon.
Furthermore, the bionic wing-chamber structure is arranged in at least one of staggered arrangement and aligned arrangement.
Further, the obtaining of the size of the bionic wing-chamber structure according to the ratio of the characteristic length of the dragonfly wing surface wing-chamber structure to the wingspan of the dragonfly wing comprises:
the value of the ratio of the characteristic length of the dragonfly wing surface wing chamber structure to the wingspan of the dragonfly wing is selected from any one of 0.008 to 0.04;
and acquiring the wingspan length of the wing, and acquiring the size of the bionic wing chamber structure according to the selected numerical value.
Further, the determining the depth of the bionic wing chamber structure according to the boundary layer thickness of the bionic wing chamber structure at the corresponding position on the surface of the wing includes:
obtaining the thickness value of the boundary layer of the wing surface corresponding to the bionic wing chamber structure;
and taking the thickness value as the depth value of the bionic wing-chamber structure.
Further, after the step of designing the bionic wing-chamber structure according to the dragonfly wing surface wing-chamber structure, the method further comprises the following steps:
and chamfering the bionic wing chamber structure.
Further, after the wing is manufactured according to the bionic wing section structure and the bionic wing chamber structure is arranged at a position before the starting point of transition of the wing surface boundary layer, the method further comprises the following steps:
according to different transition modes on the wing surface, the shape, the size, the depth and the arrangement mode of the bionic wing chamber structure are adjusted.
Compared with the prior art, the bionic near space aircraft wing modification design method has the following advantages:
according to the bionic close space aircraft wing modification design method, the bionic modified wing is designed according to the cross section structure of the dragonfly wing and the wing chamber structure of the dragonfly wing, the starting position of transition of the front surface layer of the wing is controlled by arranging the proper dragonfly wing chamber simulating structure on the wing, the transition of the front surface layer to a turbulent flow front surface layer is promoted, the front surface layer of the wing is more stable, the wing has higher anti-interference capability, the flow loss caused by flow separation is reduced, the purpose of improving a flow field is achieved, the wing load is favorably improved, and the pneumatic performance of the wing is enhanced. In addition, the invention only needs to carry out simple structural arrangement of the bionic wing chamber on the surface of the wing, has the advantages of simple structure and convenient design and adjustment, and simultaneously increases the practicability of the engineering by adopting chamfering treatment on the bionic wing chamber structure.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is a schematic flow chart of a method for designing a wing modification of a bionic near space vehicle according to an embodiment of the present invention;
fig. 2 is a cloud diagram of the speed of a pleated plate at the cross section of a dragonfly wing in a wing modification design method of a bionic near space vehicle according to an embodiment of the invention;
fig. 3 is a schematic diagram of a cross-sectional structure of a wing and a bionic wing section structure thereof in a method for designing a wing modification of a bionic near space vehicle according to an embodiment of the present invention;
FIG. 4 is a cloud chart of the distribution of the turbulence intensity and boundary layer thickness of the prototype wing in the method for designing the wing modification of the bionic near space vehicle according to the embodiment of the present invention;
FIG. 5 is a schematic flow chart of a method for designing a wing modification of a bionic close-space vehicle according to a second embodiment of the present invention;
fig. 6 is a schematic view of a typical structure of a dragonfly wing surface in a bionic near space vehicle wing modification design method according to a second embodiment of the present invention;
fig. 7 is a schematic diagram of a simulation result of an influence of different bionic wing chamber depths on a transition start position in a wing modification design method of a bionic near space vehicle according to a second embodiment of the present invention;
FIG. 8 is a schematic structural diagram of a modified wing in a method for designing a bionic close-proximity space vehicle wing modification provided by a second embodiment of the present invention;
fig. 9 is a friction coefficient diagram of 50% span-wise plane prototype wings, aligned modified wings and staggered modified wings in the method for designing a bionic near space vehicle wing modification according to the second embodiment of the present invention;
fig. 10 is a shape factor distribution diagram of a boundary layer of a prototype wing and a modified wing in a bionic near space vehicle wing modification design method according to the second embodiment of the present invention;
FIG. 11 is a cloud chart of surface shear stress of a modified wing model in a method for designing a bionic near space vehicle wing modification provided by a second embodiment of the present invention;
fig. 12 is a schematic flow chart of a method for designing a wing modification of a bionic close-proximity space vehicle according to a third embodiment;
fig. 13 is a schematic structural diagram of a bionic wing chamber structure after chamfering processing in the method for designing a wing modification of a bionic near space vehicle according to the third embodiment.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Example one
Fig. 1 is a schematic flow chart of a method for designing a wing modification of a bionic near space vehicle according to an embodiment of the present invention, where the method may be used for designing a wing modification of a near space vehicle, and specifically includes the following steps:
compared with an active control technology, the passive control technology has the characteristics of low cost and easiness in implementation, shows high-efficiency control capability in recent research, and has high application potential; the dragonfly has excellent flight capability in low Reynolds number flight, so that a new research idea is provided for the design of wings of an adjacent space aircraft by combining bionics.
The invention provides a bionic near space vehicle wing modification design method, which aims at passively controlling and adjusting the boundary layer flow condition of the wing surface of a near space vehicle when the near space vehicle runs under the working condition of low Reynolds number. The dragonfly has super flight capability, and researches show that the wing structure of the dragonfly can well regulate and control the surface airflow of the dragonfly, so that the modified wing is designed according to the structural characteristics of the dragonfly wing, and the wing can well regulate and control the surface airflow of the dragonfly wing.
102, designing a bionic wing-chamber structure according to the dragonfly wing surface wing-chamber structure;
through analyzing the dragonfly wing, the typical structure on the wing is divided into two aspects, one is a cross section fold-shaped structure of the wing; and the second is a wing chamber structure with different shapes and arrangement modes on the surface of the wing. Therefore, the wing chamber structure extracted from the dragonfly wing is subjected to modification scheme setting corresponding to the wing of the adjacent space aircraft, so that subsequent wing modification and optimization are facilitated.
103, smoothly connecting extreme points of a dragonfly cross section fold corrugated structure to obtain a bionic wing profile structure;
fig. 2 is a cloud graph of speed of a cross-sectional corrugated plate of a dragonfly wing in a wing modification design method of a bionic close space vehicle according to an embodiment of the present invention, as shown in fig. 2; the method is characterized in that a typical wrinkle corrugated structure on the cross section of a dragonfly wing is extracted, a modeling is carried out to obtain a wrinkle plate with the same wrinkle shape, and basic information of a flow field of the wrinkle plate can be known by using simulation software when the wrinkle plate runs at an attack angle of 0 degrees. In the velocity cloud chart, it can be seen that the corrugated grooves of the corrugated plate are filled in the distribution range of the low velocity region in the flow field of the surface of the corrugated plate. Based on the thought, the extreme points of the dragonfly cross section fold-shaped structure are smoothly connected to obtain a novel bionic wing section structure, and the requirement of the wing for modification can be met.
In addition, in the embodiment, only the airfoil section after the extreme points of the corrugated structure are connected is taken, and no design requirement is made on the internal skeleton support of the airfoil. As the bionic wing section structure mainly plays a role, a person skilled in the art can select a proper wing section internal framework support according to actual needs in actual application, and the details are not repeated here.
Fig. 3 is a schematic diagram of a cross-sectional structure of a wing and a bionic wing section structure thereof in a bionic near space vehicle wing modification design method provided by an embodiment of the invention. In the practical application process, the cross section structure in the middle of the dragonfly wing can be extracted to obtain the section structure of the bionic wing, and the technical personnel in the field can also extract the cross section structures of other positions of the dragonfly wing according to the actual requirements and carry out corresponding comparison tests to obtain the optimal section structure of the bionic wing, so that the subsequent modification effect of the wing is better. In addition, during actual design, the bionic wing profile structure at different positions of the wing can be determined in a targeted manner according to the cross section structures at different positions of the dragonfly wing, so that a wing modification structure closer to the dragonfly wing is obtained, and a person skilled in the art can select the bionic wing profile structure according to actual needs, so that the wing has better flight performance, and the details are not repeated herein.
And 104, manufacturing the wing according to the bionic wing section structure, and arranging the bionic wing chamber structure at a position before the starting point of transition of the boundary layer on the surface of the wing.
In the practical application process, in order to manufacture the wing, firstly, extreme points of the corrugated structure are connected smoothly according to the corrugated structure of the cross section of the dragonfly wing, and a novel wing profile is obtained. And secondly, a wing chamber structure consisting of a wing vein and a wing membrane on the surface of the dragonfly wing needs to be referred, and the wing surface is reasonably arranged, so that a bionic non-smooth surface passive control method is obtained, and the passive control of the flow in the boundary layer is realized.
The aircraft wing surface transition structure has the advantages that the appropriate dragonfly-imitated wing chamber structure is arranged at the position, before the starting point occurs, of the aircraft wing corresponding to the transition of the surface layer, so that the starting position of the transition of the surface layer of the wing surface is controlled, the transition of the surface layer to the turbulent surface layer can be promoted, the surface layer of the wing surface is further promoted to be more stable, the anti-interference capability is higher, and the flow loss caused by flow separation is reduced.
Fig. 4 is a cloud chart of prototype turbulence intensity and boundary layer thickness distribution in a method for designing a wing modification of a bionic close space vehicle according to an embodiment of the present invention, as shown in fig. 4, the present invention first determines a chordal reynolds number (Rex) at a transition start point based on the chordal reynolds number (Rex), and then arranges bionic wing chamber structures with specific parameters at different positions before the transition start point.
In order to clearly illustrate the arrangement position of the dragonfly-like wing-chamber structure, the embodiment is combined with the actual operation parameters of the adjacent space aircraft to carry out numerical simulation. Illustratively, from fig. 4, the reynolds number in the chord direction is 1.5 × 10 6 The turbulence intensity in the nearby boundary layer begins to change, and the thickness δ (x) of the boundary layer begins to increase, so that the transition process of the boundary layer nearby the position can be judged to start, and therefore, if the bionic wing chamber structure is arranged before the position, the transition of the boundary layer promotion to the turbulence boundary layer can be promoted, the wing surface boundary layer can be further promoted to be more stable, and the flow loss caused by flow separation is reduced.
In the flying process of the aircraft, the boundary layer existing on the surface of the wing can be twisted, and further, the boundary layer is developed into a turbulent flow boundary layer. The anti-interference capability of the laminar boundary layer before transition is weak, and the anti-interference capability of the boundary layer can be effectively improved though the resistance of the turbulent boundary layer can be increased. Illustratively, when the attack angle is zero, the transition starting position of the boundary layer can be clearly seen through the abrupt change position of the friction coefficient. The exchange between the fluid in the boundary layer and the main momentum is enhanced, and the shearing stress is increased. After the transition is completed, the friction coefficient value tends to be stable, and at the moment, the boundary layer develops into a fully developed turbulent boundary layer.
Compared with the prior art, the wing with the bionic wing chamber structure and the bionic wing profile structure is designed according to the wing chamber structure on the surface of the dragonfly wing and the corrugated structure on the cross section of the dragonfly wing, so that the flight performance of the wing in the flight near space can be improved; in addition, the starting position of transition of the wing surface boundary layer is controlled by arranging a proper dragonfly-like wing chamber structure on the wing, so that the transition of the boundary layer is promoted to be a turbulent boundary layer, the wing surface boundary layer is more stable, the wing has higher anti-interference capability, the flow loss caused by flow separation is reduced, and the flight performance of the wing is further improved.
Example two
FIG. 5 is a schematic flow chart of a method for designing a wing modification of a bionic near space vehicle according to a second embodiment of the present invention; in this embodiment, the bionic wing-chamber structure is designed according to the dragonfly wing surface wing-chamber structure, and specifically optimized as follows: designing the shape of a bionic wing chamber structure according to the shape of the wing chamber structure on the surface of the dragonfly wing; obtaining the size of the bionic wing-chamber structure according to the ratio of the characteristic length of the wing-chamber structure on the surface of the dragonfly wing to the wingspan of the dragonfly wing; determining the depth of the bionic wing chamber structure according to the thickness of the boundary layer of the bionic wing chamber structure at the corresponding position on the surface of the wing; the method is characterized in that the configuration mode of the bionic wing chamber structure is designed according to the configuration mode of the dragonfly wing surface wing chamber structure.
Correspondingly, the method for designing the wing modification of the bionic near space vehicle provided by the embodiment specifically comprises the following steps:
fig. 6 is a schematic view of a typical structure of a dragonfly wing surface in a bionic near space aircraft wing modification design method according to a second embodiment of the present invention, as shown in fig. 6, by analyzing distribution of a wing chamber structure on the dragonfly wing surface, the shape of the wing chamber structure is mainly quadrilateral, pentagonal, and hexagonal; the arrangement mode is staggered arrangement or equidistant alignment arrangement. The extraction and modeling treatment of the typical wing chamber structure of the dragonfly wing surface can obtain five typical structures, namely, aligned quadrangles, staggered quadrangles, aligned pentagons, staggered pentagons and staggered hexagons. Thus, the shape of the biomimetic wing-chamber structure may be at least one of quadrilateral, pentagonal, and hexagonal.
the ratio of the characteristic length of the bionic wing-chamber structure to the wing span length is designed by referring to the value of the ratio of the characteristic length of the wing-chamber on the dragonfly wing to the wing span length, so that the universality of the design method is ensured. Wherein, the characteristic length of the bionic wing chamber structure is the diameter length of the circumscribed circle of the designed bionic wing chamber shape (namely quadrangle, pentagon and hexagon). In the practical application process, the ratio of the characteristic length of the surface wing-chamber structure to the wing length of the dragonfly wing is within the range of 0.008 to 0.04 by actually measuring the dragonfly wing surface.
Therefore, in the practical application process, the value of the ratio of the characteristic length of the dragonfly wing surface wing chamber structure to the wingspan of the dragonfly wing is selected from any one of 0.008 to 0.04; and then acquiring the wingspan length of the wing, and calculating to obtain the size of the bionic wing chamber structure according to the selected numerical value. The value of the ratio of the characteristic length of the dragonfly wing surface wing chamber structure to the wingspan of the dragonfly wing should be the same as the value of the ratio of the characteristic length of the bionic wing chamber structure to the wingspan length of the wing, the characteristic length of the bionic wing chamber structure can be calculated under the condition that the wingspan length of the wing is known, and then the actual size of the bionic wing chamber structure is obtained according to the selected bionic wing chamber structure shape.
Illustratively, the shape of the bionic wing chamber structure is selected to be a quadrangle, and the diameter of a circumscribed circle of the quadrangle is equal to the characteristic length of the bionic wing chamber structure. Accordingly, the pentagon and hexagon are the same and will not be described herein. Therefore, the size parameters of the bionic fin structure can be obtained by calculating the characteristic length of the bionic fin chamber structure.
204, determining the depth of the bionic wing chamber structure according to the thickness of the boundary layer of the bionic wing chamber structure at the corresponding position on the surface of the wing;
specifically, obtaining the thickness value of the boundary layer of the position of the wing surface corresponding to the bionic wing chamber structure; and determining the depth of the bionic wing-chamber structure by taking the thickness value as the depth value of the bionic wing-chamber structure. The thickness value of the boundary layer at the corresponding position of the bionic wing chamber structure is used as the depth of the bionic wing chamber structure, so that the bionic wing chamber structure has a good regulation and control effect on a flow field.
Fig. 7 is a schematic diagram of a simulation result of the influence of different bionic wing chamber depths on the transition starting position in the bionic near space vehicle wing modification design method according to the second embodiment of the present invention, and as shown in fig. 7, two bionic wing chamber structures with different depths, namely 1 mm and 3 mm equivalent to the boundary layer thickness value at the transition position, are arranged at a position where the wing chord reynolds number is 0. Therefore, the regulation and control effect of the structural depth on the flow field can be clearly seen to have larger influence, and the bionic structure can have better regulation and control effect on the flow field by adopting the depth value equal to the thickness value of the boundary layer.
optionally, the bionic wing-chamber structure is arranged in at least one of a staggered arrangement and an aligned arrangement. For example, a quadrilateral bionic wing-chamber structure is taken as an example, at least one row of the quadrilateral bionic wing-chamber structure can be arranged on the wing, and the quadrilateral bionic wing-chamber structure can realize the modification of the wing in an equidistant alignment arrangement and/or staggered arrangement mode. When the bionic wing chamber structures are arranged in a staggered mode, the three adjacent bionic wing chamber structures are arranged in a triangular mode. Correspondingly, the pentagonal bionic wing chamber structure and the hexagonal bionic wing chamber structure are the same, the pentagonal bionic wing chamber structure can realize the modification of the wing by adopting staggered arrangement and/or equidistant alignment arrangement, and the hexagonal bionic wing chamber structure can realize the modification of the wing by adopting a staggered arrangement mode.
Fig. 8 is a schematic structural diagram of a modified wing in a method for designing a wing modification of a bionic close-proximity space vehicle according to a second embodiment of the present invention, where as shown in fig. 8, two rows of bionic wing-chamber structures are disposed on the wing, and quadrilateral bionic wing-chamber structures are disposed on the wing in a staggered manner. The purpose of transition control can be achieved by adopting a row of quadrangular bionic wing chamber structures, and the resistance of the wing surface can be reduced to a certain extent by adopting a plurality of rows of quadrangular bionic wing chamber structures, so that the technical personnel in the field can also set the row number of the quadrangular bionic wing chamber structures according to actual needs.
Fig. 9 is a diagram of the friction coefficient of a prototype wing with a 50% spanwise plane, modified wings with aligned arrangement and staggered arrangement in the method for designing a wing modification of a bionic close-space aircraft according to the second embodiment of the present invention, as shown in fig. 9, it can be known that compared with the case where a transition of the prototype starts at about 60% of the chord length, both wing modifications allow the transition of the modified boundary layer to occur in advance due to the existence of the bionic structure by comparing and analyzing three examples of the prototype wing, the modified wings with aligned arrangement and staggered arrangement quadrilateral bionic wing chamber structures starting to be arranged in the forward direction at the position where the chordwise reynolds number is 0.
Specifically, the 50% spanwise plane friction coefficient graph of the analytical model shows that the Reynolds number of the prototype graph in the chord direction is about 1.6x10 6 I.e., a sudden and sharp increase in the coefficient of friction at about 60% chord length, indicates a transition in the interface layer at this point. Comparing two same bionic wing chamber structure shapes of the quadrangles aligned and staggered, but different arrangement modes can show that transition of the modified wing surface at the boundary layer of the bionic wing chamber structure arrangement position rapidly occurs to change into a turbulent flow boundary layer. Meanwhile, the rapid change of the friction coefficient at the position where the bionic structure is arranged can be clearly seen.
In the verification case, six rows of identical quadrangular finned chamber structures can be arranged at the leading edge part of the model, and the six rows of quadrangular finned chamber structures are arranged at intervals along the airflow along the downstream direction at the position where the chordwise reynolds number is 0. It was found that the two kinds of the aligned quadrangle and the staggered quadrangle respectively show 6 fluctuation trends and 3 fluctuation trends on the 50% spanwise plane, and the starting positions of the fluctuations correspond to the arrangement positions of the 6 wing-chamber structures contained on the plane by the aligned quadrangle and the 3 wing-chamber structures contained on the plane by the staggered quadrangle. Therefore, the dragonfly-like wing chamber structure is arranged on the wing, and the control effect on transition of the interface layer is better.
Fig. 10 is a profile of shape factors of boundary layers of a prototype wing and a modified wing in a method for designing a wing modification of a bionic near space vehicle according to the second embodiment of the present invention, as shown in fig. 10, the characteristics of the working environment of the near space vehicle are integrated, boundary conditions and initial conditions are set, and a preliminary modification effect is explored by comparing the prototype, the square wing chamber structures arranged in alignment and quadrilateral, and the square wing chamber structures arranged in staggered manner. The modification effect is shown in fig. 10, compared with the prototype, the transition position of the modified wing is advanced to the bionic structure arrangement position, and the transition is completed near the bionic structure arrangement position, so that the modified wing is developed into a complete turbulent flow.
As shown in fig. 10, the shape factor H is a parameter for measuring the laminar flow state, and it is generally considered that the shape factor of the laminar flow state should be greater than 2; the shape factor of the turbulent state is about 1.5 generally, and the smaller H value indicates that the speed type section is fuller, which means that the momentum exchange between layers is stronger, so that the boundary layer is not easy to separate. It is apparent from fig. 10 that the shape factor of the modified wing is reduced compared to the prototype wing, and therefore the rate of change of the shape factor is quantitatively analyzed, and R represents the rate of change of the surface of the modified wing relative to the smooth surface: this value is calculated by the following formula:
where prototype H represents the value of shape factor H corresponding to the prototype curve in the diagram and retrofit H represents the value of shape factor H corresponding to the aligned and staggered curves in the diagram.
Referring to fig. 10, the H prototype value is 1.42045, the H-align modification value is 1.352849, and the H-stagger modification value is 1.359966, so that the wing configuration with the aligned wing chamber structure can reduce the form factor at the wing trailing edge by about 4.7591% based on the above formula; and the shape factor at the wing trailing edge can be reduced by about 4.2581% for the wing chamber structure with the staggered arrangement. Therefore, the bionic wing chamber structures which are arranged in an aligned mode and a staggered mode have good modification effects on wings, but the arrangement mode of the aligned mode can enable the shape factor value to be reduced more.
Fig. 11 is a cloud diagram of surface shear stresses of a model of a modified wing in a bionic close-space aircraft wing modification design method according to the second embodiment of the present invention, and as shown in fig. 11, simulation software is used to perform simulation, so that compared with wing surface shear stresses of two arrangement modes, fig. 11 (a) shows that the wall shear stress of the modified wing aligned in the alignment is about 2.5, and fig. 11 (b) shows that the wall shear stress of the modified wing staggered in the alignment is about 2.7. The method for obtaining the numerical value of the shear stress on the surface of the wing by using simulation software is the prior art, and a person skilled in the art can select appropriate simulation software for simulation according to actual needs, and details are not repeated here.
In summary, analysis shows that both of the two modification modes can promote the transition of the modified wing boundary layer, and the factor value of the boundary layer shape is obviously reduced, so that the boundary layer velocity profile is more full, and the boundary layer obtains higher anti-interference capability. Meanwhile, compared with the surface shear stress values of the modified wings in the two arrangement modes, namely the surface friction resistance values generated by the two arrangement modes, according to a simulation result, the arrangement mode of alignment arrangement can reduce the form factor value more, and the generated resistance value is lower, so that the bionic wing chamber structure is arranged in an equidistant alignment arrangement mode, and the modification effect on the wings is relatively better.
and step 207, manufacturing the wing according to the bionic wing section structure, and arranging the bionic wing chamber structure at a position before the starting point of transition of the boundary layer on the surface of the wing.
In the second embodiment, the shape of the bionic wing-chamber structure is designed according to the shape of the wing-chamber structure on the surface of the dragonfly wing; then obtaining the size of the bionic wing-chamber structure according to the ratio of the characteristic length of the wing-chamber structure on the surface of the dragonfly wing to the wingspan of the dragonfly wing; then determining the depth of the bionic wing chamber structure according to the thickness of the boundary layer of the bionic wing chamber structure at the corresponding position on the surface of the wing; finally, designing a bionic wing chamber structure according to the arrangement mode of the dragonfly wing surface wing chamber structure, and obtaining the optimal wing modification design by adopting a quadrilateral equidistant alignment arrangement mode.
EXAMPLE III
Fig. 12 is a schematic flow chart of a method for designing a wing modification of a bionic near space vehicle according to a third embodiment of the present invention; in this embodiment, after designing the bionic wing-chamber structure according to the dragonfly wing surface wing-chamber structure, the following steps are added: and (5) chamfering the bionic wing chamber structure.
Correspondingly, the method for designing the wing modification of the bionic near space aircraft provided by the embodiment specifically comprises the following steps:
303, obtaining the size of the bionic wing-chamber structure according to the ratio of the characteristic length of the dragonfly wing surface wing-chamber structure to the wingspan of the dragonfly wing;
304, determining the depth of the bionic wing chamber structure according to the thickness of the boundary layer of the bionic wing chamber structure at the corresponding position on the surface of the wing;
305, designing an arrangement mode of a bionic wing-chamber structure according to the arrangement mode of the wing-chamber structure on the surface of the dragonfly wing;
fig. 13 is a schematic structural diagram of a bionic wing chamber structure after chamfering treatment in the method for designing a wing modification of a bionic near space vehicle according to the third embodiment. Because the connection part of the wing chamber structure consisting of the dragonfly surface structure wing veins and the wing membrane is smooth arc-shaped transition, the bionic wing chamber structure is chamfered when being designed, so that the surface of the bionic wing chamber structure forms smooth arc-shaped transition, the bionic wing chamber structure can be closer to the wing chamber structure of the dragonfly wing, the flying performance of the wing can be further improved, and the subsequent engineering practice application is facilitated.
In the practical application process, the fact that the edge of the dragonfly wing chamber is in a circular arc connection mode can be found through research on the practical dragonfly wing chamber, the control effect of the two schemes on the transition initial position in a flow field is not greatly different through comparison of two wing chamber structures without chamfers, and the bionic wing chamber subjected to chamfer processing is beneficial to improving the flight performance of wings; meanwhile, the practical applicability of engineering practice in practical application is considered, and the scheme of adding chamfers is adopted in the design.
and 308, manufacturing the wing according to the bionic wing section structure, and arranging the bionic wing chamber structure at a position before the starting point of transition of the surface boundary layer of the wing.
In the embodiment, after the bionic wing chamber structure is designed according to the dragonfly wing surface wing chamber structure, chamfering treatment is additionally carried out on the bionic wing chamber structure; through the steps, smooth arc-like transition can be formed on the surface of the bionic wing-chamber structure, so that the bionic wing-chamber structure is closer to the wing-chamber structure of the dragonfly wing, and subsequent engineering practice application is facilitated.
A transition, i.e. a transition from laminar flow to turbulent flow, characterizes a flow phenomenon. Transition can be classified into three types: a natural transition is twisted, a bypass transition is twisted, and a split transition is twisted. The natural transition occurs at low turbulence (Tu < 1%), and is considered to be one of the most popular transition forms. The bypass transition is caused by strong interference of external airflow (free flow turbulence), the interference in the boundary layer of the bypass transition is algebraically increased and does not follow an exponential law any more, namely the bypass transition is directly changed from laminar flow to turbulent flow without passing through a small interference increasing process of T-S waves. A typical example is a transition process in an impeller machine.
The Reynolds number is commonly used for judging the flowing state of viscous fluid, viscous force is dominant under the working condition of low Reynolds number, the viscous effect is important in the whole flow field, and most of the surfaces of wings are in a laminar flow state.
The chord Reynolds number is the local Reynolds number whose value changes with the change of the chord length. The friction resistance coefficient and the friction resistance coefficient are defined as the ratio of the flow direction wall shear stress to the inlet dynamic pressure, and the calculation formula is as follows:
wherein U is ∞ For local prevailing velocity, τ w Is the wall shear stress.
Displacement thickness delta * The distance, defined as the displacement of the free flow outward due to the presence of the boundary layer, is the ratio of the mass flow that takes effect due to the presence of the boundary layer to the mass flow in the ideal case. The calculation formula is as follows:
the momentum thickness θ is defined as the ratio of the momentum deficit due to the presence of the boundary layer to the fluid momentum in the ideal case. The calculation formula is as follows:
the shape factor is defined as the ratio of the displacement thickness to the momentum thickness, and is expressed as follows:
wherein h is the height of the boundary layer, rho and v are the actual density and the actual flow velocity in the boundary layer respectively, and rho e 、v e Respectively the density and velocity of the main flow region fluid.
The shape factor H is a parameter reflecting the velocity profile distribution shape in the boundary layer, and the smaller the H is, the fuller the velocity profile shape is, which means that the flow layers have stronger momentum exchange and the boundary layer is not easy to separate. It is generally believed that the shape factor of the laminar flow regime should be greater than 2; the turbulent regime shape factor is typically around 1.5.
The invention provides a novel bionic non-smooth surface mainly aiming at wings of a near space aircraft under a low Reynolds number operation condition, referring to a typical wing chamber structure on a dragonfly wing, and comprehensively considering a typical shape and an arrangement mode of the wing chamber structure, and provides a novel bionic wing section design method based on the dragonfly wing cross section structure. The principle and the method are different from the conventional non-smooth surface passive flow control method, mainly combined with bionics, and different typical structures of the cross section and the surface wing chamber of the dragonfly wing are reasonably analyzed and applied, so that the purpose of improving a flow field is achieved, the wing load is improved, and the aerodynamic performance of the wing is enhanced.
The invention mainly relates to a novel bionic non-smooth surface passive flow control method, and provides a bionic near space aircraft wing modification design method. The flow field is regulated and controlled by reasonably arranging the bionic wing chamber structure on the surface of the wing, and meanwhile, the chamfering treatment is carried out on the edge of the bionic wing chamber structure when the wing chamber is arranged, so that the engineering application is more convenient to realize.
In addition, the bionic wing chamber structure is arranged in front of the transition position of the surface layer, the shape factor value of the modified wing can be reduced while the transition starting point is controlled, and the anti-interference capability of the turbulent flow surface layer after the transition of the surface of the modified wing is further improved.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (7)
1. A bionic near space aircraft wing modification design method is characterized by comprising the following steps:
acquiring a wing chamber structure on the surface of a dragonfly wing and a corrugated structure on the cross section of the dragonfly wing;
designing a bionic wing chamber structure according to the dragonfly wing surface wing chamber structure;
smoothly connecting extreme points of a dragonfly cross section fold corrugated structure to obtain a bionic wing profile structure;
manufacturing the wings according to the bionic wing section structure, and arranging the bionic wing chamber structure at a position before the starting point of transition of the wing surface boundary layer.
2. The method of claim 1, wherein designing the bionic wing-chamber structure according to the dragonfly wing surface wing-chamber structure comprises:
designing the shape of a bionic wing chamber structure according to the shape of the wing chamber structure on the surface of the dragonfly wing;
obtaining the size of the bionic wing-chamber structure according to the ratio of the characteristic length of the wing-chamber structure on the surface of the dragonfly wing to the wingspan of the dragonfly wing;
determining the depth of the bionic wing chamber structure according to the thickness of the boundary layer of the bionic wing chamber structure at the corresponding position on the surface of the wing;
the method is characterized in that the configuration mode of the bionic wing chamber structure is designed according to the configuration mode of the dragonfly wing surface wing chamber structure.
3. The method of claim 2, wherein: the shape of the bionic wing-chamber structure is at least one of quadrangle, pentagon and hexagon.
4. The method of claim 2, wherein: the bionic wing-chamber structure is arranged in at least one of staggered arrangement and aligned arrangement.
5. The method of claim 2, wherein the obtaining dimensions of the biomimetic wing-chamber structure as a ratio of a characteristic length of a dragonfly wing surface wing-chamber structure to a wingspan of a dragonfly wing comprises:
the value of the ratio of the characteristic length of the dragonfly wing surface wing chamber structure to the wingspan of the dragonfly wing is selected from any one of 0.008 to 0.04;
and acquiring the wingspan length of the wing, and acquiring the size of the bionic wing chamber structure according to the selected numerical value.
6. The method of claim 2, wherein determining the depth of the biomimetic wing chamber structure based on the boundary layer thickness of the biomimetic wing chamber structure at the corresponding location on the surface of the wing comprises:
obtaining the thickness value of the boundary layer of the wing surface corresponding to the bionic wing chamber structure;
and taking the thickness value as the depth value of the bionic wing chamber structure.
7. The method of claim 1, wherein after designing the biomimetic wing-chamber structure according to the dragonfly wing surface wing-chamber structure, the method further comprises:
and chamfering the bionic wing chamber structure.
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