CN116225073B - CFD method-based method for rapidly determining attack angle of plane - Google Patents
CFD method-based method for rapidly determining attack angle of plane Download PDFInfo
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Abstract
The invention discloses a method for quickly determining the flying attack angle of a plane based on a CFD (computational fluid dynamics) method, which relates to the technical field of aviation aircrafts. The invention has the advantages of high speed and high accuracy; the invention can give out the information of the flight attack angle of the plane under the real formation flight environment, and can provide important flight attack angle basis for the actual aircraft formation flight test.
Description
Technical Field
The invention relates to the technical field of aviation aircrafts, in particular to a method for quickly determining a flying attack angle of a plane of a assistant aircraft based on a CFD method.
Background
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Aircraft formation flight receives wide attention from aviation countries in the world because of its drag reduction advantages. At present, the aircraft formation flight modes are numerous, including aerial oiling machines and aerial oil receiving machines for formation flight, unmanned aerial vehicles for formation flight, and unmanned aerial vehicles as 'loyalty bureau' with unmanned aerial vehicles for accompanying flight. Because of the small distance between the aircrafts, a relatively serious aerodynamic interference phenomenon is necessarily generated, and especially when the air-jet aircraft is influenced by washing flow caused by a long aircraft, the aerodynamic characteristics of the air-jet aircraft can be changed to a certain extent.
How to accurately determine the incidence angle of the plane under the pneumatic interference is an important precondition for developing the formation flight of the aircraft. The existing method for determining the aircraft flight attack angle mainly comprises the methods of mathematical modeling, wind tunnel test, flight test and the like. Among these research methods, engineering methods based on theoretical mathematical models (such as horseshoe vortex models) have the problems of insufficient calculation accuracy, low reliability and the like, and it is difficult to accurately evaluate the aerodynamic interference between aircrafts, so that the flight attack angle of the aircraft cannot be accurately determined. The wind tunnel test method has high cost and long test period. For the formation flight of a plurality of aircrafts, the wind tunnel test is difficult to implement or even can not be completed. In addition, the wind tunnel test has the problem of supporting interference, and can also have a certain influence on determining the aircraft incidence angle of the plane. Similar to wind tunnel test, the flight test has high cost and high cost. On the premise of not definitely interfering the influence and the flight attack angle, the formation flight test is directly carried out, so that the danger is high, and the accident of the robot destruction and the death is caused under serious conditions. The computational fluid dynamics method (CFD method for short) can accurately simulate the aerodynamic characteristics and aerodynamic interference characteristics of the aircraft, and on the premise that the computational hardware conditions are met and the computational resources are rich, the CFD method is easy to implement for determining the flight attack angle of the plane in formation, and has relatively low cost and good safety.
Whether the CFD method or the wind tunnel test method is adopted, the methods need to gradually approach the real flight attack angle of the plane through a bisection method when determining the flight attack angle of the plane. For a certain formation flight state, this will lead to the CFD method requiring calculation of more attack angle states for the plane, consuming more calculation resources and making the calculation period longer. Therefore, aiming at the problem of calculating the flight attack angle of the plane in formation flight, a rapid determination method capable of accurately evaluating the flight attack angle of the plane in formation flight needs to be developed.
Disclosure of Invention
The invention aims at: aiming at the problems existing in the background technology, the method for quickly determining the aircraft flying attack angle based on the CFD method is provided, the calculation grid of the formation aircraft is generated by fixing horizontal free incoming flow and adjusting the attack angle of the formation aircraft in flying, the lift coefficient of the formation aircraft under 2 attack angles is calculated by adopting the CFD method, and then the real flying attack angle of the formation aircraft under the gravity balance of the lift and the self is obtained by drawing the intersection point of the lift coefficient curve of the formation aircraft in flying and the lift coefficient curve of the formation aircraft in flying under the independent cruising flight or by adopting a calculation formula.
The technical scheme of the invention is as follows:
a method for quickly determining the attack angle of a plane based on a CFD method comprises the following steps:
step S1: generating a separate computer calculation grid for aerodynamic force calculation for the individual wing aircraft;
step S2: for the calculation grid of the independent plane, calculating the aerodynamic characteristics of the plane during the independent cruising flight by a CFD method to obtain the cruising Mach number Ma and cruising attack angle of the independent plane
Lift coefficient>
；
Step S3: generating a formation calculation grid for aerodynamic force numerical calculation based on a preset formation flight attitude for formation flight;
step S4: aiming at the formation calculation grid, calculating the aerodynamic characteristics of formation flight under a preset formation flight attitude by a CFD method to obtain the situation that the incidence angle of the plane in the formation flight is
Lift coefficient>
；
Step S5: adjusting the attack angle of the plane to
Generating a formation calculation grid again based on the formation flight attitude after the adjustment of the incidence angle of the wing plane;
step S6: aiming at the regenerated formation calculation grid, calculating the aerodynamic characteristics of the formation flight under the formation flight attitude after the adjustment of the attack angle of the plane by a CFD method to obtain the plane in the formation flight with the attack angle of the plane as the attack angle
Lift coefficient>
；
Step S7: based on lift coefficient
Lift coefficient->
And lift coefficient->
The real flight attack angle of the formation in-flight plane lift and the plane under the self gravity balance is obtained through calculation or drawing.
Further, the step S1 includes:
determining an aircraft model as a plane in convoy flight and determining the cruise Mach number Ma of the aircraft model during its cruise flight alone and the cruise attack angle during its cruise flight alone
；
Wherein the plane aircraft is placed horizontally in the calculated coordinate system.
Further, the step S3 includes:
step S31: determining a formation flight scheme;
step S32: presetting formation flight attitude;
step S33: based on the formation flight attitude preset in step S32, a formation calculation grid for aerodynamic force numerical calculation is generated.
Further, the step S31 includes:
aiming at double-plane formation, acquiring a determined aircraft model serving as a long plane in formation flight, a distance between the long plane and a wing plane, and attack angles of the long plane and the wing plane; wherein the incidence angle of the flying medium-length aircraft is formed
Indicating (I)>
The value is the cruising attack angle corresponding to Mach number Ma when the long aircraft flies alone; the attack angle of the bureau is +.>
Indicating, the attack angle of the wing>
The preliminary setting is cruise attack angle corresponding to cruise Mach number Ma when the wing aircraft is flown alone>
I.e. +.>
=/>
；
For a double-aircraft formation aircraft model consisting of a long aircraft and a wing aircraft, setting an origin of a model coordinate system, namely a calculation coordinate system, on the center of gravity of the long aircraft, and prescribing that an X axis points to the left from the front to the back along a horizontal plane, a Z axis points to the left in the horizontal plane perpendicular to the X axis, and a Y axis is vertically upwards positive according to a right-hand rule, so that the flow direction distance between the center of gravity of the long aircraft and the center of gravity of the wing aircraft is
The vertical distance is->
The lateral distance is>
。
Further, the step S32 includes:
rotating a horizontally placed long machine around a transverse axis passing through the center of gravity
Angle, rotate the horizontally placed plane about a transverse axis passing through the centre of gravity +.>
An angle;
and prescribing the rotation angle
Or->
And when the value is positive, the aircraft is rotated in the head-up direction.
Further, step S5 includes:
continuously rotating the plane around a transverse axis passing through the center of gravity based on the formation flying posture preset in the step S32
An angle; wherein the rotation angle->
When the value is negative, the aircraft is rotated towards the direction of low head; after adjustment, the attack angle of the wing plane relative to the horizontal free incoming flow is +.>
The method comprises the steps of carrying out a first treatment on the surface of the The attack angle posture of the long machine in formation relative to the horizontal free incoming flow is kept unchanged and is still +.>
The method comprises the steps of carrying out a first treatment on the surface of the For the attack angle adjustment of the planeAnd regenerating the formed formation calculation grid according to the formed formation flight attitude.
Further, in the step S7, the real flight attack angle of the plane is obtained by the following method:
in a rectangular coordinate system diagram, according to the lift coefficient
And lift coefficient->
Is mapped (+)>
，/>
) And (/ ->
，/>
) Straight line of two points->
Wherein the abscissa +.>
The axis is the attack angle of the plane, the ordinate +.>
The shaft is the lift coefficient of the plane;
according to the lift coefficient
Draw->
Is a straight line of (2);
obtaining
Straight line and->
Intersection of straight lines, which intersection is associated with an abscissa value +.>
I.e. the real flight attack angle of the plane in the current formation flight.
Further, in the step S7, the real flight attack angle of the plane is calculated by the following formula:
wherein:
Compared with the prior art, the invention has the beneficial effects that:
1. a method for quickly determining the attack angle of the plane of a plane based on CFD (computational fluid dynamics) method considers the balance of the lift force and self gravity of the plane by cruising the attack angle when determining the attack angle of the plane, the method is more in line with the actual flight demand, has stronger authenticity and has important engineering application value.
2. Compared with wind tunnel test, the method for quickly determining the flying attack angle of the plane based on the CFD method is simple, convenient to implement, free of interference influence of the tunnel wall or the supporting rod, relatively high in accuracy and relatively low in cost.
3. Compared with formation flight tests, the method for rapidly determining the attack angle of the plane flying based on the CFD method is easy to implement, low in cost and good in safety and economy.
4. Compared with engineering theory methods such as horseshoe vortex, the method for quickly determining the aircraft flying attack angle based on the CFD method can capture the wing tip vortex of the aircraft, and has relatively high accuracy.
5. Compared with engineering theory methods such as horseshoe vortex and the like, the method for quickly determining the flying attack angle of the plane based on the CFD method is characterized in that the method adopts a two-step method compared with a 'bisection method' for gradually approaching the real flying attack angle of the plane, and does not need to calculate more attack angle states of the plane, so that the method consumes less calculation resources and has shorter calculation period.
6. The invention provides a method for quickly determining the attack angle of a plane based on a CFD (computational fluid dynamics) method, which provides an important reference basis for a plane flight test of an actual aircraft formation under a real formation flight environment.
7. A method for quickly determining the flying attack angle of a plane based on a CFD method provides a method for quickly and accurately determining the flying attack angle of the plane, the method provides an important method means for developing the research on the aerodynamic interference characteristics of the aircraft in the formation flight, and lays an important foundation for further developing the research on the control gesture balancing method of the formation aircraft.
Drawings
FIG. 1 is a flow chart of a method for quickly determining the angle of attack of a plane based on the CFD method;
FIG. 2 is a top view of an aircraft with a second embodiment of a wing layout;
FIG. 3 shows an aircraft with a certain flying wing layout and a free incoming flow angle of the second embodiment
Schematic of (2);
FIG. 4 is a top view of a two-aircraft fleet comprising two aircraft configurations according to an exemplary embodiment;
FIG. 5 shows that the free incoming flow angles between the plane and the horizontal direction are all
Is a schematic of an initial formation flight attitude;
FIG. 6 is a schematic diagram of a flight attitude of a dual-aircraft formation after adjustment of the angle of attack of a wing aircraft;
FIG. 7 shows a second embodiment
Straight line and->
Straight lines and schematic diagrams of intersection points thereof;
FIG. 8 shows a third embodiment
Straight line and->
Straight lines and their intersection point are schematic diagrams.
Reference numerals: 1-flying wing layout aircraft, 2-free incoming flow I, 3-plane gravity center, 4-transverse axis I, 5-long machine, 6-long machine gravity center, 7-transverse axis II and 8-free incoming flow II.
Detailed Description
It is noted that relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The features and capabilities of the present invention are described in further detail below in connection with examples.
Example 1
Referring to fig. 1, a method for quickly determining a plane flight attack angle based on a CFD method specifically includes the following steps:
step S1: generating a separate computer calculation grid for aerodynamic force calculation for the individual wing aircraft;
step S2: computing the wing position of a wing by a CFD method for a single wing computing gridAerodynamic characteristics of individual cruise flight to obtain cruise Mach number Ma and cruise attack angle of individual plane
Lift coefficient>
The method comprises the steps of carrying out a first treatment on the surface of the It should be noted that: wherein the attack angle between the plane and the free incoming flow is +.>
The Mach number of the free incoming stream is Ma;
step S3: generating a formation calculation grid for aerodynamic force numerical calculation based on a preset formation flight attitude for formation flight;
step S4: aiming at the formation calculation grid, calculating the aerodynamic characteristics of formation flight under a preset formation flight attitude by a CFD method to obtain the situation that the incidence angle of the plane in the formation flight is
Lift coefficient>
The method comprises the steps of carrying out a first treatment on the surface of the It should be noted that: wherein the free incoming flow is always in the horizontal direction, and Mach number of the free incoming flow is Ma; during the formation flight, the long aircraft has a pneumatic interference effect on the plane, so +.>
；
Step S5: adjusting the attack angle of the plane to
Generating a formation calculation grid again based on the formation flight attitude after the adjustment of the incidence angle of the wing plane; i.e. angle of attack for the plane of the formation in flight with respect to the horizontal free inflow +.>
Adjusting the variation amplitude of the attack angle to be +.>
，/>
And is typically negative;
step S6: aiming at the regenerated formation calculation grid, calculating the aerodynamic characteristics of the formation flight under the formation flight attitude after the adjustment of the attack angle of the plane by a CFD method to obtain the plane in the formation flight with the attack angle of the plane as the attack angle
Lift coefficient>
The method comprises the steps of carrying out a first treatment on the surface of the It should be noted that: wherein the free incoming flow is always in the horizontal direction, and the Mach number of the free incoming flow is still Ma;
step S7: based on lift coefficient
Lift coefficient->
And lift coefficient->
The real flight attack angle of the formation in-flight plane lift and the plane under the self gravity balance is obtained through calculation or drawing.
In this embodiment, specifically, the step S1 includes:
determining an aircraft model as a plane in convoy flight and determining the cruise Mach number Ma of the aircraft model when it is in cruise flight alone, i.e. its value is denoted Ma, and the cruise attack angle when it is in cruise flight alone
I.e. its value is +.>
And (3) representing.
Wherein, the plane aircraft is horizontally placed in a calculated coordinate system; i.e. the plane aircraft is horizontally arranged in the calculated coordinate system.
In this embodiment, specifically, the step S3 includes:
step S31: determining a formation flight scheme;
step S32: presetting formation flight attitude;
step S33: based on the formation flight attitude preset in step S32, a formation calculation grid for aerodynamic force numerical calculation is generated.
In this embodiment, specifically, the step S31 includes:
aiming at double-aircraft formation, acquiring a determined aircraft model serving as a long aircraft in formation flight and a distance between the long aircraft and a wing aircraft
,/>
,/>
) Attack angles of long plane and bureau plane, etc.; wherein the angle of attack of the flying team is +.>
The representation is made of a combination of a first and a second color,
the value is the cruising attack angle corresponding to Mach number Ma of the long aircraft during single flight, and the Mach number Ma is the cruising Mach number of the single plane; the attack angle of the bureau is +.>
Indicating, the attack angle of the wing>
The preliminary setting is cruise attack angle corresponding to cruise Mach number Ma when the wing aircraft is flown alone>
I.e. +.>
=/>
The method comprises the steps of carrying out a first treatment on the surface of the It should be noted that: />
Other angles of attack are also possible, typically not exceeding 10 °;
for a double-aircraft formation aircraft model consisting of a long aircraft and a wing aircraft, setting an origin of a model coordinate system, namely a calculation coordinate system, on the center of gravity of the long aircraft, and prescribing that an X axis points to the left from the front to the back along a horizontal plane, a Z axis points to the left in the horizontal plane perpendicular to the X axis, and a Y axis is vertically upwards positive according to a right-hand rule, so that the flow direction distance between the center of gravity of the long aircraft and the center of gravity of the wing aircraft is
The vertical distance is->
The lateral distance is>
。
In this embodiment, specifically, the step S32 includes:
known angle of attack for formation flying medium and long aircraft
And the attack angle of the bureau->
=/>
On the premise of keeping the free incoming flow unchanged along the horizontal direction, the angle of attack of the aircraft relative to the free incoming flow is changed by adjusting the included angle between the longitudinal axes of the extender and the wing machine relative to the horizontal free incoming flow;
rotating a horizontally placed long machine around a transverse axis passing through the center of gravity
Angle, rotate the horizontally placed plane about a transverse axis passing through the centre of gravity +.>
(i.e.)>
) An angle;
and prescribing the rotation angle
Or->
And when the value is positive, the aircraft is rotated in the head-up direction.
In this embodiment, specifically, step S5 includes:
the adjusting method comprises the following steps: continuously rotating the plane around a transverse axis passing through the center of gravity based on the formation flying posture preset in the step S32
An angle; wherein the rotation angle->
When the value is negative, the aircraft is rotated towards the direction of low head; after adjustment, the attack angle of the wing plane relative to the horizontal free incoming flow is +.>
The method comprises the steps of carrying out a first treatment on the surface of the The attack angle posture of the long machine in formation relative to the horizontal free incoming flow is kept unchanged and is still +.>
The method comprises the steps of carrying out a first treatment on the surface of the And regenerating a formation calculation grid aiming at the formation flight attitude of the wing aircraft with the adjusted incidence angle.
In this embodiment, specifically, in step S7, the real flight attack angle of the plane is obtained by the following manner:
in a rectangular coordinate system diagram, according to the lift coefficient
And lift coefficient/>
Is mapped (+)>
，/>
) And (/ ->
，/>
) Straight line of two points->
Wherein the abscissa +.>
The axis is the attack angle of the plane, the ordinate +.>
The shaft is the lift coefficient of the plane;
according to the lift coefficient
Draw->
Is a straight line of (2);
obtaining
Straight line and->
Intersection of straight lines, which intersection is associated with an abscissa value +.>
I.e. the real flight attack angle of the plane in the current formation flight.
In this embodiment, specifically, the actual flight attack angle of the plane at step S7 may also be obtained by calculating the following formula:
wherein:
It should be noted that:
in the method, the plane and the plane can be aircraft models with the same aerodynamic shape or aircraft models with different aerodynamic shapes.
In the method, the lift coefficient curves of the independent plane on the change of the attack angle obey a certain distribution, and satisfy the functions
Requirements, in particular->
Wherein a and b are constants, +.>
Is the attack angle of the plane.
In the above method, it is assumed that the aerodynamic disturbance influence of the long machine on the plane is linear, i.e. the lift coefficient curve of the plane varies linearly over a small angle of attack.
In the above method, the free incoming flow is subsonic, i.e. the cruising mach number Ma is smaller than 1, and the Ma value is generally within 0.8.
In the method, the cruising Mach number of the plane when the plane solely flies is consistent with the Mach number of the plane in the formation flying.
In the above method, the calculation grid may be a structural grid, including a plurality of butt joint structural grids, an overlapping structural grid, or an unstructured grid.
In the method, generating the calculation grid refers to generating a structural grid or an unstructured grid for a mathematical model of the formation aircraft by adopting grid generation software such as PointWise, gridStar and the like; the digital-to-analog model can be an iges format file or other digital-to-analog formats.
In the above method, in step S31, the calculation coordinate system of the two-aircraft formation aircraft model composed of the extender and the auxiliary aircraft may also define that the Y axis is directed to the right side in the horizontal plane perpendicular to the X axis, and the Z axis is vertically upward as the right hand rule, at which time the vertical distance between the center of gravity of the extender and the center of gravity of the auxiliary aircraft becomes
The lateral distance becomes->
The flow direction distance is still->
。
In the above method, the determination of the angles of attack of the aircraft and the wing in the formation is carried out in a mathematical model of the formation aircraft, i.e. the aircraft and the wing are rotated by corresponding angles about transverse axes passing through the respective centers of gravity in the mathematical model of the formation aircraft.
Among the above methods, the CFD method is a computational fluid dynamics method, which means that the aerodynamic characteristics of the aircraft, including lift coefficient, etc., are obtained by performing the flow around the aircraft with commercial fluid dynamics calculation software such as FLUENT, CFL3D, etc., or with independently developed fluid dynamics calculation software or flow calculation programs such as FlowStar, PMB3D, etc.
In the above method, when the calculation grid adopts the overlapped structure grid or the non-structure grid, the step S5 and the step S6 may be combined, that is, when the overlapped structure grid is adopted as the calculation grid, the sub-grid of the plane is rotated by a corresponding angle around the transverse axis passing through the center of gravity, and when the non-structure grid is adopted as the calculation grid, the plane grid of the plane is rotated by a corresponding angle around the transverse axis passing through the center of gravity, and then the body grid is regenerated.
Among the above methods, a method of calculating the angle of attack of the plane 2 times is called a "two-step method" for the real flight angle of attack of the plane.
Example two
The second embodiment is a specific application of the method for quickly determining the attack angle of the plane of the helicopter based on the CFD method.
1) Aircraft model for a plane in convoy flight is determined to be an aircraft with an aircraft wing layout 1, as shown in fig. 2, with cruise mach number Ma and cruise attack angle Ma for cruise flight alone
。
2) A computational grid of individual flying-wing layout aircraft 1 is generated. Wherein the flying-wing layout aircraft 1 is placed horizontally in a computational grid.
3) Calculated by CFD method to obtain Mach number Ma and cruise attack angle of single flying wing layout aircraft 1 (i.e. single wing aircraft) at cruise
Lift coefficient>
. Wherein the flying-wing layout aircraft 1 placed horizontally and the free incoming flow are 2 (namely the included angle between the flying-wing layout aircraft placed horizontally and the flying-wing layout aircraft is +.>
Is +.f)>
As shown in fig. 3, the free incoming stream mach number is Ma.
4) A formation flight plan for the aircraft is determined. The formation is a two-machine formation, as shown in fig. 4. An aircraft model in formation flight as a long aircraft 5 is determined, which model is the same aircraft model as the flying wing layout aircraft 1. The distance between the long aircraft 5 and the flying wing layout aircraft 1 is respectively in three directions
,/>
,/>
As shown in fig. 4 and 5. Angle of attack of formation in-flight longeron 5>
Is->
I.e. +.>
=/>
. Attack angle of bureau>
The preliminary setting is cruise attack angle corresponding to cruise Mach number Ma when the wing aircraft is flown alone>
I.e. +.>
=/>
. The origin of the calculated coordinate system of the double-aircraft formation aircraft model consisting of the long aircraft 5 and the flying wing layout aircraft 1 is arranged on the center of gravity 6 of the long aircraft, the X axis points backwards from front along the horizontal plane, the Z axis points to the left in the horizontal plane perpendicular to the X axis, and the Y axis is vertically upwards positive according to the right hand rule.
5) And generating a formation calculation grid for the formation aircraft in the formation flight. The angle of attack of the aircraft relative to the free incoming flow is changed by adjusting the included angle between the longitudinal axis of the long aircraft 5 and the aircraft layout aircraft 1 relative to the free incoming flow II 8 (i.e. the free incoming flow in the horizontal direction) on the premise of keeping the free incoming flow unchanged in the horizontal direction, namely, the long aircraft 5 which is horizontally placed rotates around the transverse axis II 7 which passes through the center of gravity 6 of the long aircraftDynamic movement
=/>
Angle, the aircraft 1 with the flying wing layout placed horizontally is rotated about a transverse axis 4 passing through the center of gravity 3 of the aircraft>
=/>
Angle. Wherein the rotation angle->
Or->
And (3) turning the aircraft in the head-up direction with a positive value. From the above-described formation flying attitude, as shown in fig. 5, a formation calculation grid is generated.
6) For the formation calculation grid, calculating aerodynamic characteristics of the formation aircraft in the formation flight attitude by a CFD method to obtain the aircraft layout aircraft 1 in the formation flight with the attack angle being
Lift coefficient>
. Wherein the free incoming flow is always in the horizontal direction, and the Mach number of the free incoming flow is Ma.
7) Adjusting the incidence angle of the flying wing layout aircraft 1 in the formation flight
. On the basis of the above-mentioned formation flying gesture, the flying wing layout aircraft 1 is continuously rotated about the transverse axis 4 passing through the center of gravity 3 of the plane of the aikeng>
Angle. Wherein the rotation angle->
And negative, causing the vehicle to turn in the low heading direction. After adjustment, the aircraft 1 has an angle of attack relative to the free flow two 8
. The attack angle posture of the formation middle-length machine 5 relative to the free incoming flow II 8 is kept unchanged and is still +.>
=/>
. And regenerating a formation calculation grid according to the formation flight attitude of the bureau after the adjustment of the attack angle, as shown in fig. 6.
8) Calculating aerodynamic characteristics of the aircraft formed after the adjustment of the incidence angle of the plane by a CFD method to obtain the aircraft 1 with the flying wing layout in the formation flight with the incidence angle of
Lift coefficient>
. Wherein the free incoming flow is always in the horizontal direction, and the Mach number of the free incoming flow is still Ma.
9) Drawing 2 straight lines. In the rectangular coordinate system diagram, according to the calculated result of lift coefficient of incidence angle of the two plane in the formation flight, drawing the model
，/>
) And (/ ->
，/>
) Straight line of two points->
Wherein the abscissa +.>
The axis is the angle of attack of the aircraft 1 in the flying wing configuration, ordinate +.>
The axis is the lift coefficient of the flying-wing layout aircraft 1. The lift coefficient of the aircraft 1 when flying alone cruising according to the flying wing configuration +.>
Draw->
As shown in fig. 7.
10 Obtained)
Straight line and->
Intersection of straight lines. The intersection point corresponds to the abscissa value +.>
I.e. the real flight angle of attack of the flying wing layout aircraft 1 in the current formation flight, as shown in fig. 7.
11 In addition to passing through steps 9) to 10) above, it is possible to pass directly through the formula
And calculating to obtain the real flight attack angle of the flying wing layout aircraft 1 in formation flight.
Example III
The third embodiment is based on a one-time calculation process display of the method for quickly determining the attack angle of the aircraft based on the CFD method.
1) The aircraft model to be a plane in formation flight was determined to be an aircraft layout aircraft with cruise mach number ma=0.6 and cruise attack angle 5.15 ° at cruise flight alone.
2) A computational grid of individual flying wing layout aircraft is generated by GridStar grid generation software. The computing grid is a multi-block butt joint structure grid. Wherein a flying wing layout aircraft is placed horizontally in a computational grid.
3) The lift coefficient of an individual flying wing layout aircraft at Ma=0.6 and cruising attack angle of 5.15 degrees is calculated by FlowStar flow field calculation software
And approximately 0.315. Wherein the attack angle between a certain flying wing layout aircraft which is horizontally arranged and the free incoming flow is 5.15 degrees, and the Mach number of the free incoming flow is 0.6.
4) A formation flight plan for the aircraft is determined. The formation is a double-machine formation. The aircraft model of the long aircraft in the formation flight is the same as the aircraft model of the plane aircraft, and is also a certain flying wing layout aircraft. The distance between the bench and the bureau is respectively in three directions
=1.75b,/>
=0,/>
=0.89 b, where b is the span of a certain flying wing layout aircraft. Angle of attack of formation in flight of medium and long aircraft>
Is 5.15 deg.. Attack angle of bureau>
The preliminary setting was 5.15 °. For the double-machine formation, the origin of the calculated coordinate system is arranged on the gravity center of the long machine, the X axis points backwards from front to back along the horizontal plane, the Z axis points to the left side in the horizontal plane perpendicular to the X axis, and the Y axis is vertically upwards positive according to the right hand rule.
5) A computational grid is generated for the aforementioned formation aircraft. On the premise of keeping the free incoming flow unchanged along the horizontal direction, the angle of attack of the aircraft relative to the free incoming flow is changed by adjusting the included angle between the longitudinal axes of the long machine and the wing machine relative to the free incoming flow, namely, the long machine which is horizontally placed rotates 5.15 degrees around the transverse axis passing through the gravity center, and the horizontal plane is rotated 5.15 degrees around the transverse axis passing through the gravity center. Wherein the rotation angles are all larger than 0 degrees, so that the aircraft rotates in the head-up direction. And generating a calculation grid of the formation aircraft through GridStar grid generating software according to the formation flight attitude. The computational grid of the formation aircraft is an overlapping structural grid. The overlapping structural grid is made up of 1 background grid and 2 sub-grids. The 2 sub-grids are the sub-grids of the long machine and the sub-grids of the wing machine respectively.
6) Calculating aerodynamic characteristics of the formation aircraft under the flight attitude by FlowStar flow field calculation software to obtain lift coefficient of the plane in the formation flight when the attack angle is 5.15 DEG
And approximately 0.359. Wherein the free incoming flow is always in the horizontal direction, and the Mach number of the free incoming flow is 0.6.
7) Adjusting the incidence angle of the plane in the formation flight
. And continuously rotating the plane by-1.15 degrees around a transverse axis passing through the center of gravity on the basis of the formation flying gesture. The aircraft is turned in the low head direction because the turning angle is less than 0 deg.. After adjustment, the angle of attack of the wing plane with respect to the horizontal free inflow becomes 4 °. The angle of attack posture of the long machine in formation relative to the horizontal free incoming flow remains unchanged, and is still 5.15 degrees. And regenerating a calculation grid of the formation aircraft aiming at the formation flight attitude of the wing aircraft after the adjustment of the attack angle. The computational grid is still an overlapping structural grid.
8) The aerodynamic characteristics of the aircraft formed by the formation after the adjustment of the attack angle of the plane are calculated through FlowStar flow field calculation software, and the lift coefficient of the plane in the formation flight when the attack angle is 4 DEG is obtained
And approximately 0.285. Wherein the free incoming flow is always in the horizontal direction and comes freelyThe mach number of the stream is still 0.6.
9) According to the calculated lift coefficient results of the incidence angles (5.15 degrees and 4 degrees respectively) of the 2 plane in the formation flight, straight lines of the two points (4,2.85) and (5.15,0.359) are drawn in a rectangular coordinate system diagram
Wherein the abscissa +.>
The axis is the attack angle of the plane, the unit is the angle, the ordinate is +.>
The axis is the lift coefficient of the wing, as shown in figure 8. Plotting +.>
As shown in fig. 8.
10 Obtained)
Straight line and->
Intersection of straight lines. The corresponding abscissa value of the intersection point in the rectangular coordinate system diagram is about 4.47 degrees, namely the real flight attack angle of the plane in the current formation flight.
11 In addition to passing through steps 9) to 10) above, it is possible to pass directly through the formula
The actual flight attack angle of the plane in the formation flight is calculated to be about 4.47 degrees.
The foregoing examples merely represent specific embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the present application. It should be noted that, for those skilled in the art, several variations and modifications can be made without departing from the technical solution of the present application, which fall within the protection scope of the present application.
This background section is provided to generally present the context of the present invention and the work of the presently named inventors, to the extent it is described in this background section, as well as the description of the present section as not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.
Claims (8)
1. A method for quickly determining the attack angle of a plane based on a CFD method is characterized by comprising the following steps:
step S1: generating a separate computer calculation grid for aerodynamic force calculation for the individual wing aircraft;
step S2: for the calculation grid of the independent plane, calculating the aerodynamic characteristics of the plane during the independent cruising flight by a CFD method to obtain the cruising Mach number Ma and cruising attack angle of the independent plane
Lift coefficient>
；
Step S3: generating a formation calculation grid for aerodynamic force numerical calculation based on a preset formation flight attitude for formation flight;
step S4: aiming at the formation calculation grid, calculating the aerodynamic characteristics of formation flight under a preset formation flight attitude by a CFD method to obtain the situation that the incidence angle of the plane in the formation flight is
Lift coefficient>
；
Step S5: adjusting the attack angle of the plane to
And based on the adjustment of the angle of attack of the wing planeThe formed flying gesture regenerates formation calculation grid; wherein (1)>
Representing the magnitude of the change in the angle of attack;
step S6: aiming at the regenerated formation calculation grid, calculating the aerodynamic characteristics of the formation flight under the formation flight attitude after the adjustment of the attack angle of the plane by a CFD method to obtain the plane in the formation flight with the attack angle of the plane as the attack angle
Lift coefficient>
；
Step S7: based on lift coefficient
Lift coefficient->
And lift coefficient->
The real flight attack angle of the formation in-flight plane lift and the plane under the self gravity balance is obtained through calculation or drawing.
2. The method for quickly determining the attack angle of a plane based on the CFD method according to claim 1, wherein said step S1 comprises:
determining an aircraft model as a plane in convoy flight and determining the cruise Mach number Ma of the aircraft model during its cruise flight alone and the cruise attack angle during its cruise flight alone
；
Wherein the plane aircraft is placed horizontally in the calculated coordinate system.
3. The method for quickly determining the attack angle of a plane based on the CFD method according to claim 2, wherein said step S3 comprises:
step S31: determining a formation flight scheme;
step S32: presetting formation flight attitude;
step S33: based on the formation flight attitude preset in step S32, a formation calculation grid for aerodynamic force numerical calculation is generated.
4. A method for quickly determining the attack angle of a plane based on the CFD method according to claim 3, wherein said step S31 comprises:
aiming at double-plane formation, acquiring a determined aircraft model serving as a long plane in formation flight, a distance between the long plane and a wing plane, and attack angles of the long plane and the wing plane; wherein the incidence angle of the flying medium-length aircraft is formed
Indicating (I)>
The value is the cruising attack angle corresponding to Mach number Ma when the long aircraft flies alone; the attack angle of the bureau is +.>
Indicating, the attack angle of the wing>
The preliminary setting is cruise attack angle corresponding to cruise Mach number Ma when the wing aircraft is flown alone>
I.e. +.>
=/>
。
5. A method for quickly determining the aircraft flight attack angle based on the CFD method according to claim 3, wherein said step S32 comprises:
rotating a horizontally placed long machine around a transverse axis passing through the center of gravity
Angle, rotate the horizontally placed plane about a transverse axis passing through the centre of gravity +.>
An angle;
and prescribing the rotation angle
Or->
And when the value is positive, the aircraft is rotated in the head-up direction.
6. The method for quickly determining the aircraft flight attack angle based on the CFD method according to claim 4, wherein the step S5 comprises:
continuously rotating the plane around a transverse axis passing through the center of gravity based on the formation flying posture preset in the step S32
An angle; wherein the rotation angle->
When the value is negative, the aircraft is rotated towards the direction of low head; after adjustment, the attack angle of the wing plane relative to the horizontal free incoming flow is +.>
The method comprises the steps of carrying out a first treatment on the surface of the The attack angle posture of the long machine in formation relative to the horizontal free incoming flow is kept unchanged and is still
The method comprises the steps of carrying out a first treatment on the surface of the And regenerating a formation calculation grid aiming at the formation flight attitude of the wing aircraft with the adjusted incidence angle.
7. The method for quickly determining the attack angle of the plane of the wing aircraft based on the CFD method according to claim 6, wherein the actual attack angle of the plane of the wing aircraft in the step S7 is obtained by:
in a rectangular coordinate system diagram, according to the lift coefficient
And lift coefficient->
Is mapped (+)>
，/>
) And (/ ->
，/>
) Straight line of two points->
Wherein the abscissa +.>
The axis is the attack angle of the plane, the ordinate +.>
The shaft is the lift coefficient of the plane;
according to the lift coefficient
Draw->
Is a straight line of (2);
obtaining
Straight line and->
Intersection of straight lines, corresponding to abscissa values in rectangular coordinate system diagram
I.e. the real flight attack angle of the plane in the current formation flight.
8. The method for quickly determining the attack angle of the plane of the wing aircraft based on the CFD method according to claim 6, wherein the actual attack angle of the plane of the wing aircraft in the step S7 is calculated by the following formula:
wherein:
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