Longitudinal coefficient estimation method and aerodynamic characteristic analysis system of wing-in-ground-effect ship

Abstract

The invention relates to a wing-in-ground-effect ship longitudinal coefficient estimation method and an aerodynamic characteristic analysis system thereof, and belongs to the technical field of wing-in-ground-effect ships. The method comprises the steps of preliminarily designing a ground-effect wing ship scheme, designing and manufacturing a wind tunnel model, obtaining data through three times of variable flight height tests, deriving a mathematical expression of a longitudinal aerodynamic coefficient of the ground-effect wing ship by using the data, and estimating longitudinal aerodynamic characteristics in any flight height state through the mathematical expression of the longitudinal aerodynamic coefficient of the ground-effect wing ship. Therefore, the test process is simplified and test times are reduced. According to the method, theoretical analysis is combined with a small amount of test data, so that the workload of the model blowing test is remarkably reduced, the research and development period is shortened, and the expenditure consumption is reduced. Meanwhile, according to the method, the key partial derivative and the relative ground-effect height in the stability calculation of the wing-in-ground-effect ship can be accurately obtained, the design efficiency and accuracy are improved, and the method plays an important role in promoting the development and application of the wing-in-ground-effect ship technology.

Description

Technical Field

[0001] The invention relates to the technical field of wing-in-ground-effect craft, in particular to a method for estimating a longitudinal coefficient of a wing-in-ground-effect craft and an aerodynamic characteristic analysis system thereof. Background Art

[0002] With the development of technology in the field of ground-effect wing-craft, the key technology of stable flight close to the water surface has emerged. This technology has the characteristics of providing efficient lift and good stability when flying close to the water surface at low altitude, which in turn led to the method of obtaining aerodynamic data through wind tunnel tests to analyze flight quality and the corresponding test equipment.

[0003] In related technologies, designers will first design a preliminary plan based on the design task book or technical specification, then design and process the model, and conduct wind tunnel tests on the model. Based on the aerodynamic characteristic data obtained by blowing, various calculations are performed to verify whether the design meets the requirements. However, if several or most items do not meet the requirements, the design scheme can only be modified, and the model will be processed for a second round of wind tests. Generally, it takes many cycles to get a plan that meets the design requirements for the next stage of detailed design.

[0004] Therefore, the above-mentioned wind tunnel test method and related design processes often require multiple cycles of design, model processing and wind blowing tests to obtain a solution that meets the design requirements, which is time-consuming and costly. Summary of the invention

[0005] In view of the shortcomings in the above-mentioned existing production technology, the applicant provides a method for estimating the longitudinal coefficient of a wing-in-ground-effect vehicle and an aerodynamic characteristics analysis system thereof, thereby obtaining the necessary aerodynamic characteristics data through theoretical estimation methods based on a small amount of wind tunnel model blowing data, shortening the design cycle, reducing test costs, lowering development costs, and improving design efficiency.

[0006] The technical solution adopted by the present invention is as follows: A method for estimating the longitudinal coefficient of a wing-in-ground-effect craft comprises the following steps:

[0007] Step 1: Preliminary design: According to the design task book or technical specification of the WIG craft, determine the wind tunnel model scale ratio of the preliminary scheme and design the wind tunnel model;

[0008] Step 2, wind tunnel model manufacturing and installation: processing the wind tunnel model based on the scale ratio, installing a simulated ground effect surface floor with adjustable height, wherein the relative height of the floor to the model is adjusted by a screw mechanism and a pull rod to simulate the change of flying height;

[0009] Step 3: Conduct 3 variable flight height tests, including 1 test in the no-ground effect state and 2 tests in the ground effect state. Measure the lift coefficient data in the no-ground effect state and the lift coefficient and pitching moment coefficient data at different flight heights in the ground effect state.

[0010] Step 4: Establish a mathematical expression for the aerodynamic coefficients. Based on the test data in Step 3, derive the mathematical expressions for the lift coefficient and the pitching moment coefficient. Among them, the lift coefficient and the pitching moment coefficient have a linear relationship with the logarithm of the relative flight height.

[0011] Step 5: Use the derived mathematical expressions to calculate the estimated values of the longitudinal aerodynamic characteristics of the wing-in-ground effect vehicle at any flight height state.

[0012] As a further improvement of the above technical solution:

[0013] Preferably, the variable flight height test in Step 3 includes:

[0014] In the no-ground effect state, adjust the floor to a position far from the model to ensure that the wind tunnel test data is not affected by the ground effect of the floor, and measure the lift coefficient data at this time.

[0015] Preferably, the variable flight height test in Step 3 further includes:

[0016] Measure the lift coefficient and pitching moment coefficient data at different flight heights under two different ground effect states respectively.

[0017] Preferably, the wind tunnel model includes a floor, and the floor is connected to the upper wall of the wind tunnel through at least one pull rod, and a screw mechanism is provided at the connection. A wing-in-ground effect vehicle wind tunnel model is arranged below the floor, and the lower part of the wing-in-ground effect vehicle wind tunnel model is connected to a fairing arranged on the lower wall of the wind tunnel model.

[0018] More preferably, the front part of the wing-in-ground effect vehicle wind tunnel model is connected to a front fairing arranged on the lower wall of the wind tunnel model through a joint. The tail of the wing-in-ground effect vehicle wind tunnel model extends out a tail connecting rod, and the end of the tail connecting rod is connected to a rear fairing arranged on the lower wall.

[0019] Preferably, the screw mechanism and the pull rod are used to realize the up and down movement of the floor to simulate the change of the flight height of the wing-in-ground effect vehicle; the front fairing and the rear fairing are used to realize the rotation of the wing-in-ground effect vehicle wind tunnel model around the joint to simulate the change of the pitching angle of the wing-in-ground effect vehicle.

[0020] Preferably, the wind tunnel model adjusts the pitching angle to simulate different flight postures.

[0021] An aerodynamic characteristic analysis system for a wing-in-ground effect craft estimates the longitudinal aerodynamic coefficients of the wing-in-ground effect craft by using the above-mentioned longitudinal coefficient estimation method for the wing-in-ground effect craft, and outputs the stability calculation results.

[0022] The beneficial effects of the present invention are as follows:

[0023] The present invention overcomes the defects of the traditional method that it takes a long time and consumes a large amount of funds to obtain a solution that meets the design requirements through multiple cycles of design, model processing, and wind tunnel tests; only 3 variable flight height tests (including 1 test in the non-ground effect state and 2 tests in the ground effect state) are required to obtain the estimated values of the longitudinal aerodynamic characteristics of the wing-in-ground effect craft at any flight height state, thereby greatly reducing the workload of the model wind tunnel test, shortening the scheme design cycle, and reducing the development cost; the technical solution of the present invention can be widely applied to the longitudinal coefficient estimation of wing-in-ground effect craft with different aerodynamic layouts, and by adjusting the test parameters and the coefficients in the mathematical expressions, the present technical solution can adapt to the design requirements of different wing-in-ground effect craft, and has wide applicability. Description of the Drawings

[0024] Figure 1 It is a schematic structural diagram of the wind tunnel test device of the present invention.

[0025] Figure 2 For the present invention Schematic diagram of the curve.

[0026] Figure 3 For the present invention Schematic diagram of the curve.

[0027] Figure 4 For the C y ~ Schematic diagram of the curve.

[0028] Figure 5 For the m z ~θ curve schematic diagram.

[0029] Figure 6 It is a determination diagram of the ground effect height and the C value of the present invention.

[0030] Figure 7 It is a determination diagram of the M value of the present invention.

[0031] Figure 8 It is a schematic diagram of the longitudinal coefficient estimation method for the wing-in-ground effect craft of the present invention.

[0032] Figure 9 It is a calculation schematic diagram of the non-ground effect state wind tunnel test and the ground effect flight height H1, H2 wind tunnel tests of the present invention.

[0033] Wherein: 1. lead screw mechanism; 2. pull rod; 3. ground effect wing ship wind tunnel model; 4. front fairing; 5. joint; 6. tail connecting rod; 7. rear fairing; 8. floor. Specific embodiments

[0034] To make the above objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0035] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0036] In the present invention, unless otherwise clearly specified and limited, the terms "mounted", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In the present invention, unless otherwise clearly specified and limited, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over", and "on" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath", and "under" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0038] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are only for the purpose of illustration and do not represent the only implementation.

[0039] As Figures 1-9 shown, the present invention provides a method for estimating the longitudinal coefficient of a wing-in-ground effect vehicle, specifically including the following steps:

[0040] In this embodiment, preliminary design: According to the design task book or technical specification, first formulate a very rough design framework and analyze the possibility of realizing the framework, including analyzing the possibility of realizing the available power system, structural materials, construction technology, detection means, etc.; then complete a preliminary scheme design, and determine the scale ratio of the preliminary scheme wind tunnel model according to the test facilities, test instruments, and connection form of the wind tunnel model in the wind tunnel laboratory, and design the wind tunnel model. The purpose of the wind tunnel model test is to measure the aerodynamic characteristics of the design scheme model in different flight states, and to determine the aerodynamic efficiency of the component by changing the installation angle of the corresponding aerodynamic component. The test results can provide the relevant parameters required for stability calculation and provide a basis for further modification of the scheme. At the same time, it provides technical data for verifying whether the design method is effective and making necessary corrections.

[0041] In this embodiment, wind tunnel model design, manufacturing and installation: Complete the model processing and the processing of the connecting strut matching the wind tunnel balance according to the design drawings of the scaled wind tunnel model, and compile a wind tunnel test outline. Install the wind tunnel model in the wind tunnel laboratory, and at the same time install an adjustable-height floor simulating the ground effect surface, which can adjust the distance between the two relative to the wind tunnel model to simulate the change of the ground effect height. The parameters determining the steady longitudinal aerodynamic characteristics (aerodynamic force or aerodynamic moment) of the wing-in-ground effect vehicle are V, and (where V is the speed, is the relative flight height of the center of gravity of the wing-in-ground effect vehicle from the surface, is the average aerodynamic chord length of the wing-in-ground effect, H = the height of the center of gravity from the floor - the distance from the center of gravity to the reference line of the model, H is the flight height, is the pitch angle). The wind tunnel test is carried out according to the wind tunnel test outline. Since the change rate of the aerodynamic force (or aerodynamic moment) relative to the flight height h increases as h decreases, this is the influence of the ground effect. Therefore, when is relatively small, the test points of the test scheme should be denser, generally is: 0.075, 0.10, 0.15, 0.20, 0.30, 0.50, 0.80, ∞, ( indicating no floor), pitch angle is: The test outline will be implemented according to the test points of the above test plan.

[0042] Specifically, the wind tunnel test device includes a floor 8, and the floor 8 is connected to the upper wall of the wind tunnel model through a tie rod 2, and a lead screw mechanism 1 is arranged at the connection; a wing-in-ground-effect vehicle wind tunnel model 3 is arranged below the floor 8, and the lower part of the wing-in-ground-effect vehicle wind tunnel model 3 is connected to a fairing arranged on the lower wall of the wind tunnel model; the front part of the wing-in-ground-effect vehicle wind tunnel model 3 is connected to a front fairing 4 arranged on the lower wall of the wind tunnel model through a joint 5, the tail of the wing-in-ground-effect vehicle wind tunnel model 3 extends out a tail connecting rod 6, and the end of the tail connecting rod 6 is connected to a rear fairing 7 arranged on the lower wall; the front fairing 4 and the rear fairing 7 are used to realize the rotation of the wing-in-ground-effect vehicle wind tunnel model around the joint, simulating the change of the pitch angle of the wing-in-ground-effect vehicle; the wind tunnel model adjusts the pitch angle to simulate the change of the pitch angle of the wing-in-ground-effect vehicle The tail connecting rod 6 is used for the guiding function of the rear strut and the fairing 7.

[0043] In this embodiment, the aerodynamic characteristics of the wing-in-ground-effect vehicle include: C x = X / qS is the drag coefficient, C y = Y / qS is the lift coefficient, C z = Z / qS is the side force coefficient, m x = M x / qSb is the rolling moment coefficient, m y = M y / qSb is the yaw moment coefficient, m z = M z / qSb is the pitch moment coefficient, where S is the wing area, b is the span, q = ρV 2 / 2 is the velocity head, and ρ is the air density. For a wing-in-ground-effect vehicle flying far from the surface, its aerodynamic characteristics are essentially the same as those of an airplane. However, when the wing-in-ground-effect vehicle flies in the ground effect region, its aerodynamic characteristics show strong non-linear characteristics with the flight height, such as Figure 2 shown by the change of the aerodynamic lift coefficient C y with the relative flight height , clearly showing this non-linear characteristic. Here Figure 2 is just (at a certain fixed pitch angle ) of a test curve. When the pitch angle changes, Not only does the shape change, but it also moves up and down because for different C y∞ is different ( Figure 2 in is defined as the relative ground effect height, and C y∞ is the corresponding lift coefficient). When the relative flight height of a wing-in-ground effect craft is less than , the presence of the ground surface affects the aerodynamic characteristics of the wing-in-ground effect craft; while when the relative flight height is greater than , the presence of the ground surface no longer affects the aerodynamic characteristics of the wing-in-ground effect craft. Therefore, when , it can be considered that the wing-in-ground effect craft is flying within the ground effect region, and when , it can be considered that the wing-in-ground effect craft is flying outside the ground effect region, just like an airplane without the influence of ground effect. It can also be seen from Figure 2 that the closer the wing-in-ground effect craft is to the ground surface, the more intense the change in the lift coefficient. And the closer it is to , the smaller the change. If it is expressed by the rate of change of the lift coefficient with respect to the relative flight height, there is where is the partial derivative of the corresponding lift coefficient with respect to the relative flight height when is kept constant, that is, the slope of the curve at the point, and this value is negative. Similarly is the partial derivative of the corresponding lift coefficient with respect to the relative flight height when is kept constant, that is, the slope of the curve at the Figure 2 point, and this value is also negative. Since the larger the negative value, the steeper the slope and the more intense the change, and the smaller the value it represents, so, there is In short, indicates that although the partial derivative of the lift coefficient with respect to the flight height within the ground effect region is not a constant, the change is monotonic. And these basic characteristics of the lift coefficient of the wing-in-ground effect craft also represent the basic characteristics of other aerodynamic coefficients of the wing-in-ground effect craft, that is, they all change non-linearly with the relative flight height y defined by C is different from z defined by m In addition to changing non-linearly with the relative flight height , the aerodynamic coefficients of the wing-in-ground effect craft also change linearly with the pitch angle within a certain range, as shown in Figure 3 . To sum up, keeping the pitch angle remains unchanged, and the aerodynamic coefficient varies non-linearly with the relative flight height unchanged, the aerodynamic coefficient varies linearly with the pitch angle within a certain range when remains unchanged, which is the basic characteristic of the aerodynamic characteristics of a wing-in-ground-effect vehicle.

[0044] In this embodiment, the variation law of the lift coefficient C y and the pitching moment coefficient m z with respect to the relative flight height is as follows: A large number of wind tunnel test results show that the variation law of the lift coefficient C y with the relative flight height is non-linear and shows a relatively consistent monotonic trend. By sorting and analyzing a large amount of wind tunnel model blowing data, it is found that if the Figure 2 of the abscissa of the curve is changed to then is basically linear. Since within a certain range, the pitching moment coefficient m z has a linear relationship with the lift coefficient C y . Therefore, is a straight line, then should also be a straight line, and a large amount of wind tunnel test data also confirms this variation law. At the same time, it is also found that if the natural logarithm of the relative flight height is used as the abscissa, it also conforms to this "linear" law. As shown in Figure 3 , the data is based on the test data of a wing-in-ground-effect vehicle wind tunnel model, which was measured at relative flight heights 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.97, and pitch angles , and is plotted with as the abscissa. Figure 3 It shows that: If the errors existing in the test data itself are considered, it can be fully considered that when remains unchanged, the variation of C y with is indeed a straight line because almost all the test points are on the straight line.

[0045] In this embodiment, the mathematical expressions of the aerodynamic coefficients C y and m z are derived as follows:

[0046] Expression: Since within a certain value range, fixing is a straight line (as Figure 4 ); fixing Then is also a straight line (such as Figure 3 ), then there is: (indicating that when remains unchanged, the partial derivative of the aerodynamic lift coefficient with respect to the pitch angle is a function of and is independent of (indicating that when remains unchanged, the partial derivative of the aerodynamic lift coefficient with respect to is a function of and is independent of

[0047]

[0048] In the formula, is the relative ground effect height, and its limiting condition is (when the ground effect no longer exists), and is also limited, must make C y be within the linear segment. Among them, a ∞ is the slope of the lift line in the state without ground effect , and a ∞ is related to the aerodynamic layout. It can be seen from Equation 1 that when i.e., , This is the lift coefficient formula of the aircraft, that is, the state without ground effect. And from Figure 4 in the line, it can be seen that the slope of the straight line segment of the line should be the slope of the lift line in the state without ground effect ∞ , which can be obtained from Figure 4 . At the same time the intersection point of the line and the axis corresponds to the pitch angle called the pitch angle at zero lift This pitch angle at zero lift will be used to obtain the subsequent zero-lift moment coefficient In the lift coefficient formula of the ground effect wing ship, the C in Equation 1 is the cross-term coefficient, which is closely related to the aerodynamic layout. At the same time, a ∞ and C in Equation 1 are constants independent of and ;

[0049] Expression: Follow Very similar, such as Figure 5 Are different The m of the wind tunnel test data z ~θ curve. Through mathematical derivation, a simplified mathematical expression for the moment coefficient is obtained:

[0050]

[0051] In the formula, Is the zero-lift moment coefficient in the no-ground-effect state, which is closely related to the aerodynamic layout. Is the zero-lift moment coefficient in the no-ground-effect state Is the no-ground-effect state Moment coefficient curve Slope of, that is, the static stability in the no-ground-effect state. It can be seen from Equation 2 that when When,[[]]END]] This is the longitudinal moment formula for ordinary aircraft. Here Can be obtained through Figure 5 Of m z ~θ curve. As we already know, from Figure 4 In The line can obtain The intersection of the line and The pitch angle corresponding to the intersection of the axis and the pitch angle at zero lift is called the pitch angle at zero lift Using this pitch angle The corresponding position can be in m z ~θ curve in The corresponding Value, that is

[0052] Since With Very similar, that is, within a certain Value range, fixed Is a straight line. So from Figure 5 In A right triangle can be drawn on the line, and the slope of this right triangle is the static stability in the no-ground-effect state Similar to Equation 1 of the lift coefficient formula of the wing-in-ground-effect craft, M in Equation 2 of the moment coefficient formula of the wing-in-ground-effect craft is the cross-term coefficient, Is also closely related to the aerodynamic layout.

[0053] In this embodiment, The expression and The method for determining the cross-term in the expression is as follows:

[0054] Such as Figure 6 As shown, the method for determining the relative ground-effect height Is as follows:

[0055] The relative ground effect height can be determined from the wind tunnel test data at three flight heights. The tests include one test in the non-ground effect state and two tests in the ground effect state. The wind tunnel model is tested three times at a certain fixed pitch angle with flight heights being and Since it is unknown but from Figure 2 it can be known that when the wing-in-ground-effect craft flies outside the ground effect region, just like an airplane, without the influence of ground effect, and the lift coefficient C y∞c is a fixed value. Therefore, the non-ground effect state test is carried out first. During the test, the floor needs to be adjusted to a position far away from the model (i.e., should be much greater than ) to ensure that the wind tunnel test data is not affected by the ground effect of the floor. The C y∞c obtained in this way should be accurate. Then, the tests with flight heights and are carried out respectively to obtain the corresponding and Finally, based on the test data, with as the abscissa and C y as the ordinate, two intersecting straight lines are drawn. One of the straight lines is the extension line of the connection between the two points and , and the other straight line is a horizontal line parallel to the abscissa with a value of C y∞c . The abscissa value corresponding to the intersection point of the two straight lines is and thus can be obtained. Since there are different straight lines for different , the intersection point changes with , and thus a series of relative ground effect heights varying with are obtained.

[0056] Method for determining the cross-term C in the expression:

[0057] Taking as an example, the corresponding relative ground effect height is From the simplified mathematical expression of the lift coefficient (Equation 1), the expression for the cross-term C is obtained:

[0058]

[0059] In Equation 3, a ∞ is the slope of the lift line in the non-ground effect state , and from Figure 4 of The slope, i.e., the value of a, can be obtained from the straight-line segment of the line. ∞ Since a in (Equation 1) ∞ and C are constants independent of and here, choose In this way, a ∞ , and are all determined. Only remains in (Equation 3). It can be obtained through the conversion graph of Figure 6 . Find the point on the abscissa . Draw a vertical line parallel to the C y ordinate through this point. The intersection point of this vertical line with the line formed by and or its extension line is the corresponding C y value, i.e., the value. Finally, substitute the above-obtained values into (Equation 3) to obtain the C value.

[0060] Determination method of the cross-term M in the expression:

[0061] Still taking as an example, the corresponding relative ground-effect height is From the simplified mathematical expression of the moment coefficient (Equation 2), the expression of the cross-term M is obtained:

[0062]

[0063] In Equation 4, is the zero-lift moment coefficient in the no-ground-effect state , is the slope of the moment coefficient curve in the no-ground-effect state , i.e., the static stability in the no-ground-effect state. As described above, through the line of Figure 4 and the line of Figure 5 and the can be obtained. Then, through the slope corresponding to the right-angled triangle on the Figure 5 line in , the static stability

[0064] of the no-ground-effect state is obtained. Similarly, since and M in Equation 2 are both constants independent of and here, choose In this way, and All have been determined. Only remains to be determined.

[0065] Since is very similar to and within a certain range, is a straight line, then should also be a straight line. For example, Figure 7 from converted to Similarly, on the abscissa find the point Draw a vertical line parallel to the m z ordinate through this point, which intersects with the line formed by and at the intersection point on the line connecting the two points or its extension line, and the corresponding m z value is obtained, that is, value. Finally, substitute the above obtained values into Equation Four to obtain the M value.

[0066] In this embodiment, the method for estimating the longitudinal coefficient of a wing-in-ground effect vehicle is as follows:

[0067] First, according to the design task book or technical specification (provided by the customer), conduct a preliminary design of the wing-in-ground effect vehicle, complete a preliminary design plan, determine the scale ratio of the preliminary design wind tunnel model, and design the wind tunnel model;

[0068] Second, complete the manufacture and installation of the wind tunnel model, and at the same time complete the installation of the adjustable-height floor simulating the ground effect surface. Conduct 3 variable flight height tests, namely: 1 non-ground effect state and 2 ground effect states; among them, in the non-ground effect state at a certain fixed pitch angle measure the lift coefficient data, which is a fixed value. Then change the pitch angle and measure and data, and plot the curve and curve. For the 2 ground effect states and at a certain fixed pitch angle measure and data;

[0069] Third, calculate the coefficients of the mathematical expression (Equation One) of the aerodynamic coefficient C y ;

[0070] ①, a ∞ : From the plotted Curve determination Slope a of the straight-line segment of the line ∞ , which is the no-ground-effect state Slope of the lift curve;

[0071] ②, C y∞c : At a certain fixed pitch angle , measure flight altitude test data;

[0072] ③, At a certain fixed pitch angle , measure the variable-flight-altitude test and data of three points, and plot the abscissa Convert to the abscissa of C y straight line, and the straight line is and the line connecting the two points, and its extension line will be parallel to another straight line abscissa, and the numerical value is C y∞c horizontal line intersects, and the abscissa value corresponding to the intersection point of the two straight lines is and thus can obtain ④, At the abscissa of the graph find the point Through this point, draw a vertical line parallel to the C y ordinate, and the intersection point with the line formed by and two points, or its extension line, is the corresponding C y value, that is value; ⑤, C: Substitute the obtained a ∞ , and into (Equation 3) to obtain the C value;

[0073] Fifth, calculate the coefficients of each term in the mathematical expression (Equation 2) of the aerodynamic coefficient m z ;

[0074] ①, By determining the intersection point of the curve and the axis, obtain the pitch angle at zero lift

[0075] ②, On the m z ~θ curve, determine the pitch angle corresponding value, that is

[0076] ③. On the line of m z ~θ, draw a right triangle. The slope of this right triangle is the static stability in the no-ground-effect state

[0077] ④. At a certain fixed pitch angle measure the data of the variable flight altitude test and two points, draw the abscissa Convert to abscissa of two points and and the line connecting the two points. On the abscissa find the point Through this point, draw a vertical line parallel to the m z ordinate, and the intersection point with the line formed by and two points, or its extension line, is the corresponding m z value, that is value;

[0078] ⑤. Substitute the above-obtained and into (Equation 4) to obtain the M value.

[0079] In this embodiment, using the mathematical expression (Equation 1) and mathematical expression (Equation 2), only 3 variable flight altitude tests are required to obtain the estimated value of the longitudinal aerodynamic characteristics of the wing-in-ground-effect vehicle at any flight altitude state, so as to determine the values of the aerodynamic lift and aerodynamic moment represented by these equations at each state at that time, thus greatly reducing the workload of the model wind tunnel test; it is also possible to simply and accurately obtain and these 2 partial derivatives, which are very important in the stability calculation of the wing-in-ground-effect vehicle. However, it is rather difficult to obtain them and large errors are likely to occur. The reason is that a large number of test points need to be added and the drawing needs to be precise in order to obtain the tangent line at each point on the curve. In this embodiment, using the or is a straight line feature, only draw a straight line passing through and lnH 2 these 2 corresponding points, and the slope of the straight line is or ​Using the test data at three flight heights, the relative ground effect height of different aerodynamic layouts can be obtained.

[0080] In other embodiments, the present invention further provides a ground effect vehicle aerodynamic characteristic analysis system, which adopts the above-mentioned longitudinal coefficient estimation method of the ground effect vehicle to estimate the longitudinal aerodynamic coefficient of the ground effect vehicle, so as to output the stability calculation result.

[0081] In summary, in this embodiment, through the analysis of a large number of wind tunnel test results, the present invention discovers that there is a linear relationship between the longitudinal aerodynamic coefficient of the ground effect vehicle and the logarithm of the relative flight height, and thus creatively derives the mathematical expression of and the mathematical expression of and ; second, only three variable flight height tests are required to obtain the estimated value of the longitudinal aerodynamic characteristics of the ground effect vehicle at any flight height state, thus greatly reducing the workload of the model blowing test; third, two partial derivatives

[0082] which are very important in the stability calculation of the ground effect vehicle and the relative ground effect height of different aerodynamic layouts can be obtained simply and accurately.

[0083] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0083] The above-described embodiments only express the implementation manners of the present invention, and the description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A method for estimating the longitudinal coefficient of a wing-in-ground-effect craft, characterized in that: The following steps are involved: Step 1: Preliminary design: According to the design task book or technical specification of the WIG craft, determine the wind tunnel model scale ratio of the preliminary scheme and design the wind tunnel model; Step 2, wind tunnel model manufacturing and installation: processing the wind tunnel model based on the scale ratio, installing a simulated ground effect surface floor with adjustable height, wherein the relative height of the floor to the model is adjusted by a screw mechanism and a pull rod to simulate the change of flying height; Step 3, conducting three variable flight altitude tests, including one out-of-ground effect state test and two ground effect state tests, measuring lift coefficient data in the out-of-ground effect state, and measuring lift coefficient and pitching moment coefficient data at different flight altitudes in the ground effect state; Step 4, establishing a mathematical expression of aerodynamic coefficients, and deriving mathematical expressions of lift coefficient and pitch moment coefficient based on the test data in step 3; wherein the lift coefficient and pitch moment coefficient are linearly related to the logarithm of the relative flight height; Step 5: Use the derived mathematical expressions to calculate the estimated values ​​of the longitudinal aerodynamic characteristics of the WIG craft at any flight altitude.

2. The method for estimating the longitudinal coefficient of a wing-in-ground-effect craft according to claim 1, wherein: The variable flight height test in step 3 includes: In the no-ground-effect state, the floor is adjusted to a position away from the model to ensure that the wind tunnel test data is not affected by the ground effect of the floor, and the lift coefficient data at this time is measured.

3. The method for estimating the longitudinal coefficient of a wing-in-ground-effect craft according to claim 1, wherein: The variable flight height test in step 3 also includes: Under two different ground effect conditions, the lift coefficient and pitch moment coefficient data at different flight altitudes were measured respectively.

4. The method for estimating the longitudinal coefficient of a wing-in-ground-effect craft according to any one of claims 1 to 3, characterized in that: The wind tunnel model comprises a floor, the floor is connected to the upper wall of the wind tunnel model through at least one tie rod, and a screw mechanism is arranged at the connection; A wing-in-ground-effect craft wind tunnel model is arranged below the floor, and the lower part of the wing-in-ground-effect craft wind tunnel model is connected to a guide cover arranged on a lower cave wall of the wind tunnel model.

5. The method for estimating the longitudinal coefficient of a wing-in-ground-effect craft according to claim 4, wherein: The front part of the WIG ship wind tunnel model is connected to a front fairing arranged on a lower cave wall of the wind tunnel model through a joint, a tail connecting rod extends from the tail part of the WIG ship wind tunnel model, and the end of the tail connecting rod is connected to a rear fairing arranged on the lower cave wall.

6. The method for estimating the longitudinal coefficient of a wing-in-ground-effect craft according to claim 4, wherein: The screw mechanism and the pull rod are used to realize the up and down movement of the floor, simulating the change of the flying height of the ground effect wing ship; the front fairing and the rear fairing are used to realize the rotation of the ground effect wing ship wind tunnel model around the joint, simulating the change of the ground effect wing ship pitch angle.

7. The method for estimating the longitudinal coefficient of a wing-in-ground-effect craft according to claim 4, wherein: The wind tunnel model simulates different flight postures by adjusting the pitch angle.

8. A wing-in-ground-effect vehicle aerodynamic characteristics analysis system, characterized in that: The longitudinal aerodynamic coefficient of the wing-in-ground-effect craft is estimated by using the longitudinal coefficient estimation method of the wing-in-ground-effect craft described in any one of claims 1 to 7, and the stability calculation result is output.

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