CN112874756A - Airfoil configuration capable of improving separation characteristic of large attack angle - Google Patents

Airfoil configuration capable of improving separation characteristic of large attack angle Download PDF

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CN112874756A
CN112874756A CN202110309948.5A CN202110309948A CN112874756A CN 112874756 A CN112874756 A CN 112874756A CN 202110309948 A CN202110309948 A CN 202110309948A CN 112874756 A CN112874756 A CN 112874756A
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wing
elliptical
airfoil
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米百刚
詹浩
白璇
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Northwestern Polytechnical University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B64C—AEROPLANES; HELICOPTERS
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Abstract

The invention discloses an airfoil profile structure capable of improving the separation characteristic of a large attack angle and a design method thereof, wherein the airfoil profile structure comprises a main wing and an elliptical wing, the elliptical wing is arranged on a suction surface of a front edge point of the main wing through a pipe string structure, and under the action of incoming flow, alternate lower vortex shedding is generated on two sides of the elliptical wing; the pipe string structure comprises a first fixed ring lock, a second fixed ring lock and a rotary bolt, wherein the first fixed ring lock is arranged at 25% of the spanwise direction of the main wing, the second fixed ring lock is arranged at 75% of the spanwise direction of the main wing, and the rotary bolt is arranged at 100% of the spanwise direction of the main wing; the airfoil configuration can effectively inhibit the separation of the airfoil large-attack-angle air flow under the conditions of basically not consuming energy and generating smaller additional resistance, reduces the resistance coefficient while improving the lift coefficient of the airfoil, and has the characteristics of greatly improving the lift-drag ratio of the airfoil and improving the aerodynamic performance of the large attack angle.

Description

Airfoil configuration capable of improving separation characteristic of large attack angle
Technical Field
The invention relates to the technical field of aerodynamic profile design of wings, in particular to an airfoil configuration capable of improving the separation characteristic of a large attack angle and a design method thereof.
Background
Under the condition of large attack angle incoming flow, the aircraft has large-scale airfoil flow separation, so that the lift coefficient of the airfoil is greatly reduced, the resistance coefficient is improved, the aerodynamic performance is rapidly deteriorated, and when airflow is separated on an upper boundary layer of the airfoil, the severe consequence of stall is caused, and an aviation accident is easy to occur; therefore, the research on an effective scheme for improving the flow field and inhibiting the flow separation of the airfoil profile has important significance for improving the maneuverability and the safety of the aircraft in a large attack angle state;
the essence of flow control is that the local or global flow change of a flow field is triggered by applying physical quantities such as force, mass, energy and the like to local flow and utilizing the hydrodynamic interaction between fluids; flow control methods can be classified into an active control method and a passive control method according to the presence or absence of additional auxiliary energy consumption; the most typical engineering application of the passive flow control technology is a vortex generator, and the main control mechanism is that the vortex generator generates vortex to transmit energy to a boundary layer with low energy so as to overcome the adverse pressure gradient and delay the separation of airflow, further increase the stall attack angle and the maximum lift coefficient of the wing, and generate the lift increasing action at the cost of resistance increase and lift-drag ratio reduction; except for the vortex generator, the slotting airfoil, the bionic node and the groove technology belong to the category of passive flow control. The control mode of active flow control is that appropriate disturbance is directly applied in a flow field, the flow control is realized by mutual coupling with the self-circumambient flow of the wing profile, the main ways of inhibiting the gas flow separation comprise modes of jet flow, blowing and suction, plasma release and the like, and compared with the passive flow control technology, the active flow control technology can still effectively control the flow of the wing profile in a non-design state, but correspondingly increases the weight and energy consumption of an aircraft; the airfoil leading edge vibration elliptical wing configuration is used as a flow control method, the working principle of the flow control method is similar to that of a vortex generator, the conventional vortex generator is usually arranged on the surface of a machine body, and longitudinal vortexes are generated to increase the mixing of fluid inside and fluid outside a boundary layer, so that momentum is transferred to the boundary layer, a boundary layer flow field in an inverse pressure gradient can be continuously attached to the surface of the machine body after additional energy is obtained, and the purpose of delaying or eliminating flow separation is achieved;
the main technology for inhibiting the separation of the airfoil large-attack-angle air flow and improving the aerodynamic performance of the airfoil at the present stage is a flow control technology, and the flow control technology can be divided into an active flow control technology and a passive flow control technology according to whether additional energy is needed during control; the active flow control controls the surrounding flow of the wing profile in a synthetic jet flow mode, an air blowing and air suction mode, a plasma releasing mode and the like, so that the aerodynamic characteristics of the wing profile are improved, the main defects are that extra energy consumption is needed, and the takeoff weight of the aircraft is increased due to the arrangement of relevant equipment for the active flow control in the wing, so that the economic performance of the aircraft is influenced to a certain extent; the passive control technology comprises a passive vortex generator, a speed-loss belt, a flap, a miniature small insert sheet, a rib and the like, and has the main defects that additional resistance is generated while the flow around the wing profile is influenced, and because the control mode and the control effect of the passive flow control are designed in advance, the passive flow control cannot normally play a role under the condition that the aircraft deviates from the design state, and even the aerodynamic characteristics of the wing profile are adversely affected.
Disclosure of Invention
Aiming at the existing problems, the invention aims to provide an airfoil configuration capable of improving the separation characteristic of a large attack angle and a design method thereof.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
an airfoil profile capable of improving the separation characteristic of a large attack angle comprises a main wing and an elliptical wing, wherein the elliptical wing is arranged on a suction surface of a front edge point of the main wing through a pipe string structure, and under the action of incoming flow, alternate lower vortex shedding is generated on two sides of the elliptical wing; the pipe string structure comprises a first fixed ring lock, a second fixed ring lock and a rotary bolt, wherein the first fixed ring lock is arranged at 25% of the spanwise direction of the main wing, the second fixed ring lock is arranged at 75% of the spanwise direction of the main wing, the rotary bolt is arranged at 100% of the spanwise direction of the main wing, and the other ends of the first fixed ring lock, the second fixed ring lock and the rotary bolt are connected with the elliptical wing.
Preferably, the elliptical wing is a front-back symmetrical wing, and the chord length of the elliptical wing is 1% of the chord length of the main wing.
Preferably, the elliptical wings are arranged in front of and above the suction surface of the wing profile leading edge point of the main wing, and the distances from the centers of the elliptical wings to the leading edge point are 4-6% chord length of the wing profile of the main wing when the elliptical wings are arranged.
Preferably, the vibration form of the elliptical wing can be pitching motion or sinking and floating motion, and the motion equation is as follows: y — Asin (2 pi ft).
Preferably, when the elliptical wing does pitching motion, the amplitude is 0.1 to 0.3rad, and the frequency is 16 to 64.
Preferably, when the elliptical wings do ups and downs movement, the frequency has little influence on the control effect of the elliptical wings, and the amplitude is 0.5% -1% of the chord length of the main wing.
A design method of an airfoil profile capable of improving separation characteristics at a large attack angle comprises the following steps
S1, firstly, optimally designing the configuration parameters of the static elliptical wing arranged on the front edge of the wing profile by using a numerical simulation method based on a two-dimensional Reynolds average Navier-Stokes equation:
s2, on the basis that a static elliptical wing structure is arranged at the front edge of the wing profile, the static elliptical wing structure with the optimal effect is used, the elliptical wing is endowed with a certain vibration form, the vibration elliptical wing structure arranged at the front edge of the wing profile is optimally designed, and the vibration frequency and amplitude are respectively used as design variables;
and S3, calculating the airfoil under the condition of a large attack angle, and selecting proper elliptical wing vibration parameters by taking the maximum lift-drag ratio and the effect of inhibiting flow separation on the airfoil as optimization targets to complete the design of the airfoil configuration.
Preferably, the process of optimally designing the profile parameters for setting the static elliptical wing configuration at the leading edge of the airfoil profile by using a numerical simulation method based on a two-dimensional reynolds average Navier-Stokes equation in step S1 includes:
s101, respectively taking chord lengths of the elliptical wings and the position relation between the elliptical wings and the wing profiles as design variables, and calculating lift-drag ratios of the wing profile configurations of the elliptical wings with different chord lengths at different positions of the wing profile front edge under the condition of a large attack angle;
and S102, comparing the calculation result with the original wing profile, and selecting a proper elliptical wing size and a proper setting position by taking the maximum lift-drag ratio as an optimization target.
The invention has the beneficial effects that: the invention discloses an airfoil profile configuration capable of improving separation characteristic of a large attack angle and a design method thereof, compared with the prior art, the improvement of the invention is as follows:
(1) aiming at the problems in the prior art, the invention designs an airfoil profile configuration capable of improving the separation characteristic of a large attack angle, the configuration can effectively inhibit the separation of the airflow of the airfoil profile at the large attack angle under the conditions of basically not consuming energy and generating small additional resistance, the lift coefficient of the airfoil profile is improved, the resistance coefficient is reduced at the same time, the lift-drag ratio of the airfoil profile is greatly improved, and the aerodynamic performance of the large attack angle is improved;
(2) meanwhile, the main mechanisms of the configuration for inhibiting airflow separation and improving the aerodynamic performance of the large attack angle of the wing are that shedding vortexes generated by the elliptic wings arranged at the front edges of the main wings and wake vortexes generated by vibration interact with the boundary layer of the wing profile, so that momentum is introduced into the boundary layer, and the functions of delaying airflow separation and increasing lift and reducing drag are achieved; meanwhile, as the rear stagnation point of the lifting surface moves backwards, the pressure intensity of the lower surface of the front edge with the elliptical wing configuration is higher than that of the original wing profile, so that the wing profile has better aerodynamic characteristics with a large attack angle; and through in the experiment, compare this wing section leading edge vibration elliptical wing configuration with the wing section that does not set up the elliptical wing, the suppression effect of elliptical wing to flow separation is showing, original big separation bubble has disappeared totally or has become the very little separation bubble of being close to wing section trailing edge on the wing section, and the lift coefficient improves simultaneously, and the drag coefficient descends, and the lift-drag ratio improves to about 3 times of original wing section by a wide margin, therefore this wing section configuration has the lift-drag ratio that can promote the wing section by a wide margin, improves big attack angle aerodynamic performance's advantage.
Drawings
FIG. 1 is a global view of the configuration of the elliptical wing of the present invention disposed forward of the airfoil leading edge point.
FIG. 2 is a partial view of an elliptical wing of the present invention disposed at the leading edge of an airfoil in a point forward configuration.
FIG. 3 is a global view of the configuration of the elliptical wing of the present invention disposed over the leading edge point of the airfoil.
FIG. 4 is a partial view of an airfoil leading edge with an elliptical wing disposed above the airfoil leading edge point in accordance with the present invention.
Fig. 5 is a global view of the installation form of the elliptical wing and the main wing of the present invention.
FIG. 6 is a partial view of a stationary looped cable positioned 25% of the main span of the present invention.
FIG. 7 is a flow chart of the original airfoil and the forward vibrating elliptical airfoil configuration flow field of example 2 of the present invention.
Fig. 8 is a mach number cloud chart (Ma ═ 0.15) of the original airfoil profile and the configuration of the leading vibration elliptical airfoil in embodiment 2 of the invention.
FIG. 9 is a comparison of aerodynamic performance parameters of the original airfoil of example 2 of the present invention and a configuration of the present invention design.
FIG. 10 is a flow chart of the original airfoil and leading vibration elliptical airfoil configuration flow field of example 3 of the present invention.
Fig. 11 is a mach number cloud (Ma ═ 0.15) of the original airfoil and the configuration of the leading vibration elliptical airfoil in example 3 of the present invention.
FIG. 12 is a comparison of aerodynamic performance parameters of the original airfoil of example 3 of the present invention and a configuration of the present invention design.
FIG. 13 is a flow chart of the original airfoil and leading vibration elliptical airfoil configuration flow field of example 4 of the present invention.
Fig. 14 is a mach number cloud (Ma ═ 0.15) of the original airfoil profile and the configuration of the leading vibration elliptical airfoil in example 4 of the present invention.
FIG. 15 is a comparison of aerodynamic performance parameters of the original airfoil of example 4 of the present invention and a configuration of the present invention design.
Wherein: fig. 7-1 is a flow chart of a flow field of an original airfoil configuration of NACA0012 in example 2 of the present invention, and fig. 7-2 is a flow chart of a flow field of a leading vibration elliptical wing configuration in example 2 of the present invention; fig. 8-1 is a mach number cloud chart of an original airfoil configuration of NACA0012 in example 2 of the present invention, and fig. 8-2 is a mach number cloud chart of a leading vibration elliptical wing configuration in example 2 of the present invention; FIG. 9-1 is a comparison graph of the lift coefficient of the original airfoil profile of the embodiment 2 of the present invention and the configuration of the present invention, FIG. 9-2 is a comparison graph of the drag coefficient of the original airfoil profile of the embodiment 2 of the present invention and the configuration of the present invention, and FIG. 9-3 is a comparison graph of the lift coefficient of the original airfoil profile of the embodiment 2 of the present invention and the configuration of the present invention;
FIG. 10-1 is a flow chart of a flow field of an original airfoil configuration NACA0012 of embodiment 3 of the present invention, and FIG. 10-2 is a flow chart of a flow field of a leading vibration elliptical wing configuration of embodiment 3 of the present invention; fig. 11-1 is a mach number cloud chart of an original airfoil configuration of NACA0012 in example 3 of the present invention, and fig. 11-2 is a mach number cloud chart of a leading vibration elliptical wing configuration in example 3 of the present invention; FIG. 12-1 is a comparison graph of the lift coefficient of the original airfoil profile of the embodiment 3 of the present invention and the configuration of the present invention, FIG. 12-2 is a comparison graph of the drag coefficient of the original airfoil profile of the embodiment 3 of the present invention and the configuration of the present invention, and FIG. 12-3 is a comparison graph of the lift coefficient of the original airfoil profile of the embodiment 3 of the present invention and the configuration of the present invention;
fig. 13-1 is a flow chart of a flow field of an original airfoil configuration of NACA0012 in example 4 of the present invention, and fig. 13-2 is a flow chart of a flow field of a leading vibration elliptical airfoil configuration in example 4 of the present invention; fig. 14-1 is a mach number cloud chart of an original airfoil configuration of NACA0012 in example 4 of the present invention, and fig. 14-2 is a mach number cloud chart of a leading vibration elliptical wing configuration in example 4 of the present invention; FIG. 15-1 is a comparison graph of the lift coefficient of the original airfoil profile of the embodiment 4 of the present invention and the configuration of the present invention, FIG. 15-2 is a comparison graph of the drag coefficient of the original airfoil profile of the embodiment 4 of the present invention and the configuration of the present invention, and FIG. 15-3 is a comparison graph of the lift coefficient of the original airfoil profile of the embodiment 4 of the present invention and the configuration of the present invention;
1. the main wing, 2, the elliptical wing, 3, the leading edge point, 4, the center of the elliptical wing, 5, the first fixed ring lock, 6, the second fixed ring lock, and 7, the rotating bolt.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the following further describes the technical solution of the present invention with reference to the drawings and the embodiments.
The main technology for inhibiting the separation of the airfoil large-attack-angle air flow and improving the aerodynamic performance of the airfoil at the present stage is a flow control technology, and the flow control technology can be divided into an active flow control technology and a passive flow control technology according to whether additional energy is needed during control. The active flow control controls the surrounding flow of the wing profile in the modes of synthetic jet flow, air blowing and air suction, plasma release and the like, so that the aerodynamic characteristics of the wing profile are improved. The passive control technology comprises a passive vortex generator, a speed-loss belt, a flap, a miniature small insert sheet, a rib and the like, and has the main defects that additional resistance is generated while the flow around the wing profile is influenced, and the problem that the passive flow control cannot normally play a role under the condition that the aircraft deviates from a design state and even has adverse influence on the aerodynamic characteristics of the wing profile is solved because the control mode and the control effect of the passive flow control are designed in advance.
Referring to fig. 1-9, an airfoil configuration for improving separation characteristics at a large angle of attack and a design method thereof are disclosed, the airfoil configuration for improving separation characteristics at a large angle of attack comprises a main wing 1 and an elliptical wing 2, the elliptical wing 2 is arranged on a suction surface of a leading edge point 3 of the main wing 1 through a pipe string structure, the elliptical wing 2 is extremely tiny relative to the main wing 1, and under the action of incoming flow, alternate downward-blowing vortexes are generated on two sides of the elliptical wing 2, so that the elliptical wing 2 is subjected to transverse and flow-direction pulsating pressure, and vibration is induced; the string structure is similar to a stringed instrument, fixing keys are arranged at intervals in the installation process of the elliptical wings 2 to control the positions of the elliptical wings 2, first fixing ring locks 5, second fixing ring locks 6 and rotating bolts 7 are arranged at the positions of 25% of the spanwise direction of the main wings, 75% of the spanwise direction of the main wings and 100% of the spanwise direction of the main wings respectively, the other ends of the first fixing ring locks 5, the second fixing ring locks 6 and the rotating bolts 7 are connected with the elliptical wings 2, namely the elliptical wings are divided into three sections according to 0% -25%, 25% -75% and 75% -100% of the spanwise length of the main wings through the first fixing ring locks 5, the second fixing ring locks 6 and the rotating bolts 7, and meanwhile the tightness of the elliptical wings 2 is adjusted through the rotating bolts 7 at the tail ends of the main wings.
Preferably, the elliptical wing 2 is a front-back symmetrical wing, and the chord length of the elliptical wing 2 is 1% of the chord length of the main wing 1, and the specific dimension is determined according to the chord length of the main wing 1.
Preferably, the arrangement form of the elliptical wing 2 on the main wing 1 is two arrangement forms, namely the elliptical wing 2 is arranged in front of and above the suction surface of the front edge point of the wing profile of the main wing 1, and the distance from the center 4 of the elliptical wing 2 to the front edge point 3 is 4-6% of chord length of the wing profile of the main wing 1.
Preferably, the vibration form of the elliptical wing 2 can be pitch motion or heave motion, and the motion equation is as follows: y is Asin (2 pi ft), and both vibration forms can achieve good control effect;
(1) when the elliptical wing 2 does pitching motion, the amplitude is 0.1 to 0.3rad, and the frequency is 16 to 64;
(2) when the elliptical wings do ups and downs movement, the frequency has little influence on the control effect, and the amplitude is 0.5 to 1 percent of the chord length of the main wing 1.
Preferably, the airfoil profile of the main wing 1 is a NACA0012 airfoil profile, which is a subsonic high-lift common airfoil profile, and other airfoil profiles can be selected according to the actual needs of the aircraft.
Example 1: a design method of an airfoil configuration capable of improving the separation characteristic at a large attack angle comprises the following steps
S1, firstly, optimally designing the configuration parameters of a static elliptical wing configuration arranged on the front edge of the wing profile by using a numerical simulation method based on a two-dimensional Reynolds average Navier-Stokes equation;
s2, on the basis that a static elliptical wing structure is arranged at the front edge of the wing profile, the static elliptical wing structure with the optimal effect is used, the elliptical wing is endowed with a certain vibration form, the vibration elliptical wing structure arranged at the front edge of the wing profile is optimally designed, and the vibration frequency and amplitude are respectively used as design variables;
and S3, calculating the airfoil under the condition of a large attack angle, and selecting proper elliptical wing vibration parameters by taking the maximum lift-drag ratio and the effect of inhibiting flow separation on the airfoil as optimization targets to complete the design of the airfoil configuration.
Preferably, the process of optimally designing the profile parameters for setting the static elliptical wing configuration at the leading edge of the airfoil profile by using a numerical simulation method based on a two-dimensional reynolds average Navier-Stokes equation in step S1 includes:
s101, respectively taking chord lengths of the elliptical wings and the position relation between the elliptical wings and the wing profiles as design variables, and calculating lift-drag ratios of the wing profile configurations of the elliptical wings with different chord lengths at different positions of the wing profile front edge under the condition of a large attack angle;
and S102, comparing the calculation result with the original wing profile, and selecting a proper elliptical wing size and a proper setting position by taking the maximum lift-drag ratio as an optimization target.
Example 2: in the embodiment, a numerical simulation method based on a Reynolds average Navier-Stokes equation is adopted to carry out numerical simulation on the aerodynamic characteristics of the large attack angle of the elliptical wing configuration with the vibrating wing profile leading edge, and the verification proves that the elliptical wing configuration with the vibrating wing profile leading edge can effectively inhibit airflow separation and remarkably improve the aerodynamic characteristics of the large attack angle of the wing under the state of the large attack angle, wherein the simulation process comprises the following steps:
s1, arranging a vibration elliptical wing structure in front of a front edge of an airfoil profile as a simulation object, wherein a main wing profile is an NACA0012 airfoil profile, the length of an elliptical wing chord is 1% of the chord length of the main wing, the main wing profile is arranged right in front of a front edge point of the airfoil profile, and the distance between the center of the elliptical wing and the front edge point is 4% of the chord length of the main wing; taking the elliptical wing as an example of sinking and floating motion, the motion equation is as follows: y is Asin (2 pi ft), the amplitude is 1% of the chord length of the main wing, and the frequency is 16;
s2, obtaining a flow field flow diagram of a single NACA0012 airfoil profile and an improved configuration designed by the invention under the conditions that the incoming flow Mach number is 0.15 and the attack angle is 18 degrees in a figure 7; it can be seen that in a large attack angle state, serious airflow separation occurs on the upper surface of a single NACA0012 airfoil, and most of the area of the upper surface of the airfoil is covered by large separation bubbles, so that the pressure of the upper surface of the airfoil is obviously increased, and the loss of the lift characteristic of the large attack angle of the airfoil is serious; compared with the original wing profile, the front-mounted vibrating elliptical wing structure designed by the invention can play a good role in inhibiting flow separation at a large attack angle, and the original larger separation bubbles on the wing profile are changed into smaller separation bubbles at the tail edge of the wing profile, so that the front-mounted vibrating elliptical wing structure has important significance in improving the stall attack angle and the aerodynamic performance of the wing profile at the large attack angle;
s3, FIG. 8 is a Mach number cloud chart of the original airfoil profile of NACA0012 and the configuration of the vibrating elliptical wing at the leading edge of the airfoil profile under the condition that the attack angle is 18 degrees; as can be seen from fig. 8, compared with the original airfoil shape, the flow velocity of the lower surface of the front edge vibration elliptical wing structure designed by the invention is relatively low, and the flow velocity of the upper surface of the front edge vibration elliptical wing structure is relatively high, which is significant for improving the pressure difference between the upper surface and the lower surface of the lifting surface;
s3, in the case that the incoming flow Mach number is 0.15, comparing aerodynamic performance parameters of the original airfoil profile and the airfoil profile leading edge vibrating elliptical wing configuration designed by the invention when the incoming flow attack angle is calculated to be 0-20 degrees; it can be seen from fig. 9 that at low angles of attack, the airfoil leading edge oscillating elliptical wing configuration does not adversely affect the aerodynamic performance of the airfoil, and the lift-to-drag ratio is slightly higher than the original airfoil. When the incoming flow attack angle is larger than 12 degrees, the resistance coefficient of the designed configuration of the invention is slightly increased, and the lift-drag ratio is reduced. The original airfoil enters a stall area when the attack angle is 16 degrees, the lift-drag ratio is sharply reduced, the lift-increasing effect of the configuration designed by the invention is obvious under the condition of large attack angle, and the stall attack angle is delayed to 18 degrees;
the results verified by the numerical simulation method show that the airfoil leading edge vibrating elliptical wing configuration designed in the example can effectively inhibit airflow separation in a subsonic high-attack-angle state, greatly improve the lift characteristic and lift-drag ratio of the airfoil under the condition of basically not generating additional resistance, delay the stall attack angle, effectively improve the aerodynamic performance, and remarkably improve the maneuverability and the economy of the aircraft.
Example 3: in the embodiment, a numerical simulation method based on a Reynolds average Navier-Stokes equation is adopted to carry out numerical simulation on the aerodynamic characteristics of the large attack angle of the elliptical wing configuration with the vibrating wing profile leading edge, and the verification proves that the elliptical wing configuration with the vibrating wing profile leading edge can effectively inhibit airflow separation and remarkably improve the aerodynamic characteristics of the large attack angle of the wing under the state of the large attack angle, wherein the simulation process comprises the following steps:
s1, arranging a vibration elliptical wing structure in front of a front edge of an airfoil profile as a simulation object, wherein a main wing profile is an NACA0012 airfoil profile, the length of an elliptical wing chord is 1% of the chord length of the main wing, the main wing profile is arranged right in front of a front edge point of the airfoil profile, and the distance between the center of the elliptical wing and the front edge point is 5% of the chord length of the main wing; taking the elliptical wing as an example of sinking and floating motion, the motion equation is as follows: y is Asin (2 pi ft), the amplitude is 1% of the chord length of the main wing, and the frequency is 16;
s2, obtaining a flow field flow diagram of a single NACA0012 airfoil profile and an improved configuration designed by the invention under the conditions that the incoming flow Mach number is 0.15 and the attack angle is 18 degrees in a diagram 10; it can be seen that in a large attack angle state, serious airflow separation occurs on the upper surface of a single NACA0012 airfoil, and most of the area of the upper surface of the airfoil is covered by large separation bubbles, so that the pressure of the upper surface of the airfoil is obviously increased, and the loss of the lift characteristic of the large attack angle of the airfoil is serious; compared with the original airfoil profile, the front-mounted vibrating elliptical wing structure designed by the invention can play a good role in inhibiting flow separation at a large attack angle, and the original larger separation bubbles on the airfoil profile become small separation bubbles at the tail edge of the airfoil profile, so that the front-mounted vibrating elliptical wing structure has important significance in improving the stall attack angle and the aerodynamic performance of the airfoil profile at the large attack angle;
s3, FIG. 11 is a Mach number cloud chart of the original airfoil profile of NACA0012 and the configuration of the vibrating elliptical wing at the leading edge of the airfoil profile under the condition that the attack angle is 18 degrees; as can be seen from fig. 11, compared with the original airfoil shape, the flow velocity of the lower surface of the leading edge vibration elliptical wing configuration designed by the invention is relatively low, and the flow velocity of the upper surface of the leading edge vibration elliptical wing configuration is relatively high, which is significant for improving the pressure difference between the upper surface and the lower surface of the lifting surface;
s3, in the case that the incoming flow Mach number is 0.15, comparing aerodynamic performance parameters of the original airfoil profile and the airfoil profile leading edge vibrating elliptical wing configuration designed by the invention when the incoming flow attack angle is calculated to be 0-20 degrees; it can be seen from fig. 12 that at low angles of attack, the airfoil leading edge oscillating elliptical wing configuration does not adversely affect the aerodynamic performance of the airfoil, and the lift-to-drag ratio is slightly higher than the original airfoil. The original airfoil enters a stall area when the attack angle is 16 degrees, the lift-drag ratio is sharply reduced, the lift-increasing effect of the configuration designed by the invention is obvious under the condition of large attack angle, and the stall attack angle is delayed to 19 degrees.
Example 4: in the embodiment, a numerical simulation method based on a Reynolds average Navier-Stokes equation is adopted to carry out numerical simulation on the aerodynamic characteristics of the large attack angle of the elliptical wing configuration with the vibrating wing profile leading edge, and the verification proves that the elliptical wing configuration with the vibrating wing profile leading edge can effectively inhibit airflow separation and remarkably improve the aerodynamic characteristics of the large attack angle of the wing under the state of the large attack angle, wherein the simulation process comprises the following steps:
s1, arranging a vibration elliptical wing structure in front of a front edge of an airfoil profile as a simulation object, wherein a main wing profile is an NACA0012 airfoil profile, the length of an elliptical wing chord is 1% of the chord length of the main wing, the main wing profile is arranged right in front of a front edge point of the airfoil profile, and the distance between the center of the elliptical wing and the front edge point is 6% of the chord length of the main wing; taking the elliptical wing as an example of sinking and floating motion, the motion equation is as follows: y is Asin (2 pi ft), the amplitude is 1% of the chord length of the main wing, and the frequency is 16;
s2, obtaining a flow field flow diagram of a single NACA0012 airfoil profile and an improved configuration designed by the invention under the conditions that the incoming flow Mach number is 0.15 and the attack angle is 18 degrees in the figure 13; it can be seen that in a large attack angle state, serious airflow separation occurs on the upper surface of a single NACA0012 airfoil, and most of the area of the upper surface of the airfoil is covered by large separation bubbles, so that the pressure of the upper surface of the airfoil is obviously increased, and the loss of the lift characteristic of the large attack angle of the airfoil is serious; compared with the original wing profile, the front-mounted vibrating elliptical wing structure designed by the invention can play a better role in inhibiting flow separation at a large attack angle, the original larger separation bubbles on the wing profile become smaller separation bubbles, and the separation point moves backwards, so that the front-mounted vibrating elliptical wing structure has important significance in improving the stall attack angle of the wing profile and the aerodynamic performance at the large attack angle;
s3, FIG. 14 is a Mach number cloud chart of the original airfoil profile of NACA0012 and the configuration of the vibrating elliptical wing at the leading edge of the airfoil profile under the condition that the attack angle is 18 degrees; as can be seen from fig. 14, compared with the original airfoil shape, the flow velocity of the lower surface of the leading edge vibration elliptical wing configuration designed by the invention is relatively low, and the flow velocity of the upper surface of the leading edge vibration elliptical wing configuration is relatively high, which is significant for improving the pressure difference between the upper surface and the lower surface of the lifting surface;
s3, in the case that the incoming flow Mach number is 0.15, comparing aerodynamic performance parameters of the original airfoil profile and the airfoil profile leading edge vibrating elliptical wing configuration designed by the invention when the incoming flow attack angle is calculated to be 0-20 degrees; it can be seen from fig. 9 that at low angles of attack, the airfoil leading edge oscillating elliptical wing configuration does not adversely affect the aerodynamic performance of the airfoil, and the lift-to-drag ratio is slightly higher than the original airfoil. When the incoming flow attack angle is larger than 12 degrees, the resistance coefficient of the designed configuration of the invention is slightly increased, and the lift-drag ratio is reduced. The original airfoil enters a stall area when the attack angle is 16 degrees, the lift-drag ratio is sharply reduced, the lift-increasing effect of the configuration designed by the invention is obvious under the condition of large attack angle, and the stall attack angle is small and the stall attack angle is delayed by a small amplitude.
It can be seen from the above three embodiments that when the distance from the center of the elliptical wing to the leading edge point is increased to 6% of the chord length of the main wing, the control effect of the wing profile leading edge vibrating elliptical wing configuration on flow separation at a large attack angle is weakened, but the flow separation at the large attack angle of the wing profile can still be effectively inhibited under the condition of generating small additional resistance, so that the lift-drag ratio of the wing profile is improved; when the distance between the center of the elliptical wing and the front edge point exceeds the range of 6 percent of the chord length of the main wing, the control effect of the wing profile front edge vibration elliptical wing configuration is further weakened on the basis, and the ideal effect of improving the aerodynamic performance at the large attack angle is difficult to achieve at the moment.
The working principle of the airfoil configuration capable of improving the separation characteristic of the large attack angle is as follows: when the vortex shedding mechanism works, fluid flows through the elliptical wing 2 arranged at the front edge of the wing profile to generate shedding vortices, and under the action of incoming flow, the elliptical wing can be subjected to pulsating pressure in the transverse direction and the flow direction to further trigger vibration, the shedding vortices and wake vortices generated by the vibration interact with a boundary layer of the main wing, so that momentum is introduced into the boundary layer, the capability of the boundary layer in resisting adverse pressure gradient is improved, and the functions of delaying air flow separation, increasing lift and reducing drag are achieved. Meanwhile, as the rear stagnation point of the lifting surface moves backwards, the pressure intensity of the lower surface of the front edge with the elliptical wing configuration is higher than that of the original wing profile, so that the wing profile has better aerodynamic characteristics with a large attack angle; compared with the airfoil without the elliptical wing, the elliptical wing has the advantages that the suppression effect of the elliptical wing on flow separation is obvious, original large separation bubbles on the airfoil completely disappear or become small separation bubbles close to the tail edge of the airfoil, the lift coefficient is improved, the drag coefficient is reduced, and the lift-drag ratio is greatly improved to about 3 times of that of the original airfoil.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (8)

1. An airfoil configuration for improving separation characteristics at high angles of attack, characterized by: the wing-shaped aircraft comprises a main wing (1) and an elliptical wing (2), wherein the elliptical wing (2) is arranged on a suction surface of a front edge point (3) of the main wing (1) through a pipe string structure; the pipe string structure comprises a first fixed ring lock (5), a second fixed ring lock (6) and a rotary bolt (7), wherein the first fixed ring lock (5) is arranged at 25% of the spanwise direction of the main wing (1), the second fixed ring lock (6) is arranged at 75% of the spanwise direction of the main wing (1), the rotary bolt (7) is arranged at 100% of the spanwise direction of the main wing (1), and the other ends of the first fixed ring lock (5), the second fixed ring lock (6) and the rotary bolt (7) are connected with the elliptical wing (2).
2. An airfoil configuration for improving separation characteristics at high angles of attack according to claim 1 wherein: the elliptical wing (2) is a front-back symmetrical wing type, and the chord length of the elliptical wing (2) is 1% of that of the main wing (1).
3. An airfoil configuration for improving separation characteristics at high angles of attack according to claim 1 wherein: the elliptical wing (2) is arranged in front of and above a suction surface of a wing section leading edge point of the main wing (1), and the distance between the center (4) of the elliptical wing (2) and the leading edge point (3) is 4% -6% chord length of the wing section of the main wing when the elliptical wing is arranged.
4. An airfoil configuration for improving separation characteristics at high angles of attack according to claim 1 wherein: the vibration form of the elliptical wing (2) can be pitching motion or sinking and floating motion, and the motion equation is as follows: y — Asin (2 pi ft).
5. An airfoil configuration for improving separation characteristics at high angles of attack according to claim 4 wherein: when the elliptical wing (2) does pitching motion, the amplitude is 0.1-0.3 rad, and the frequency is 16-64.
6. An airfoil configuration for improving separation characteristics at high angles of attack according to claim 4 wherein: when the elliptical wings (2) do ups and downs movement, the frequency has little influence on the control effect, and the amplitude is 0.5 to 1 percent of the chord length of the main wing (1).
7. A method of designing an airfoil configuration for improving separation characteristics at high angles of attack according to any one of claims 1 to 6, wherein: comprises the following steps
S1, firstly, optimally designing the configuration parameters of a static elliptical wing configuration arranged on the front edge of the wing profile by using a numerical simulation method based on a two-dimensional Reynolds average Navier-Stokes equation;
s2, on the basis that a static elliptical wing structure is arranged at the front edge of the wing profile, the static elliptical wing structure with the optimal effect is used, the elliptical wing is endowed with a certain vibration form, the vibration elliptical wing structure arranged at the front edge of the wing profile is optimally designed, and the vibration frequency and amplitude are respectively used as design variables;
and S3, calculating the airfoil under the condition of a large attack angle, and selecting proper elliptical wing vibration parameters by taking the maximum lift-drag ratio and the effect of inhibiting flow separation on the airfoil as optimization targets to complete the design of the airfoil configuration.
8. The method of claim 7, wherein the airfoil configuration is designed to improve separation characteristics at high angles of attack, and further comprises: the process of performing the optimal design on the profile parameters of the static elliptical wing configuration arranged at the leading edge of the airfoil profile by using the numerical simulation method based on the two-dimensional Reynolds average Navier-Stokes equation in the step S1 includes:
s101, respectively taking chord lengths of the elliptical wings and the position relation between the elliptical wings and the wing profiles as design variables, and calculating lift-drag ratios of the wing profile configurations of the elliptical wings with different chord lengths at different positions of the wing profile front edge under the condition of a large attack angle;
and S102, comparing the calculation result with the original wing profile, and selecting a proper elliptical wing size and a proper setting position by taking the maximum lift-drag ratio as an optimization target.
CN202110309948.5A 2021-03-23 2021-03-23 Airfoil configuration capable of improving separation characteristic of large attack angle Pending CN112874756A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114940257A (en) * 2022-06-06 2022-08-26 南京航空航天大学 Jet flow control-based flutter active suppression device for high aspect ratio flexible wing

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114940257A (en) * 2022-06-06 2022-08-26 南京航空航天大学 Jet flow control-based flutter active suppression device for high aspect ratio flexible wing

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