Optimization method and application of layout position of towed pod on aircraft platform for low-frequency signal reconnaissance

Abstract

The present invention relates to the field of aircraft technology, and specifically discloses an optimization method and application for the layout position of a towed pod for low-frequency signal reconnaissance on a carrier platform, so as to solve the problem of how to combine a towed antenna with a platform to form a high-precision direction-finding and positioning array while causing less interference to the performance of the carrier platform. The specific steps include: Step 1: Using a CFD method to simulate the flow field of a clean carrier configuration, and obtain the wake field vortex distribution of the clean carrier configuration; Step 2: Introducing a sliding grid into the CFD method to calculate the wake field vortex distribution of the propeller configuration, and preliminarily determining the position of the towed pod based on the wake field vortex distribution of the clean carrier configuration and the wake field vortex distribution of the propeller configuration; Step 3: Constructing an aircraft full-model flow field by installing an actual pod, using a bidirectional fluid-solid coupling method and introducing a sliding network into the fluid calculation domain to simulate the influence of propeller rotation on the towed pod, and correcting the position of the towed pod.

Description

Technical Field

[0001] The present invention belongs to the technical field of aircraft, and in particular relates to a method for optimizing the layout position of a towed pod for low-frequency signal reconnaissance on an aircraft carrier platform and its application. Background Art

[0002] In the context of the information age, tasks such as communication reconnaissance and electronic countermeasures in the military field and disaster surveys and public security control in the civilian field have put forward higher requirements for radio monitoring. Due to the characteristics of electromagnetic signals, the propagation attenuation of lower-frequency electromagnetic waves in the atmosphere is lower than that of high-frequency electromagnetic waves. Low-frequency electromagnetic waves are widely used in many scenarios such as battlefield communications and emergency rescue. However, the wavelength of low-frequency electromagnetic waves is longer than that of high-frequency electromagnetic waves, making it more difficult to find their direction. Taking 100MHz electromagnetic waves as an example, the wavelength is 3 meters. In order to meet the accuracy requirements of low-frequency electromagnetic wave direction finding and positioning, the measurement baseline (the distance between different electromagnetic wave receiving sites) required by each receiving station is much higher than the wavelength of high-frequency electromagnetic waves. Therefore, the requirements for the detection platform are extremely high. The current low-frequency signal detection mainly relies on large ground-based radars and air-based drones.

[0003] Due to the long wavelength of low-frequency electromagnetic waves, the size of air-based drones cannot be too small. For example, the typical Global Hawk drone has a wingspan of 35 meters, which meets the requirements of carrying low-frequency electromagnetic waves, but its unit price exceeds hundreds of millions of dollars, which cannot be applied on a large scale. Small and medium-sized platforms are also faced with the problem of small size and inability to sink to the low frequency band for single-machine reconnaissance.

[0004] Due to the size limitation of small UAVs, the detection of low-frequency signals (below 100MHz) has a natural defect of too small baseline, which limits the reconnaissance efficiency of this type of UAV. The use of towed antennas is one of the feasible ways to break through this barrier. However, the towed antenna affects the flight environment of the UAV during operation, and the change of the UAV's posture also interferes with the working state of the antenna. Summary of the invention

[0005] In order to solve the problem of how to combine a towed antenna with a platform to form a high-precision direction-finding and positioning array while causing less interference to the performance of the carrier platform, the present invention constructs a towed antenna layout, in which two antenna units (antennas integrated on the pod) are dragged out of the aircraft body to form a long baseline, thereby meeting the requirements of low-frequency direction-finding and positioning.

[0006] In order to achieve the above-mentioned design objectives, the technical solutions adopted by the present invention are as follows:

[0007] An object of the present invention is to provide a method for optimizing the layout position of a towed pod for low-frequency signal reconnaissance on a carrier platform, the optimization method comprising the following steps:

[0008] Step 1: Use CFD method to simulate the flow field of the clean carrier configuration to obtain the vortex distribution of the wake field of the clean carrier configuration;

[0009] Step 2: Introduce the sliding grid into the CFD method to calculate the wake vortex distribution of the propeller configuration, and preliminarily determine the position of the towed pod based on the wake vortex distribution of the clean carrier configuration and the wake vortex distribution of the propeller configuration;

[0010] Step 3: Construct the full-model flow field of the aircraft by installing the actual pod, apply the bidirectional fluid-solid coupling method and introduce a slip network in the fluid calculation domain to simulate the influence of propeller rotation on the towed pod, and correct the position of the towed pod.

[0011] Furthermore, the specific operations of step 1 include:

[0012] Step 101: Use k-ω The SST turbulence model is used to simulate the flow field of the clean carrier configuration;

[0013] Step 102: Based on the flow field simulation results of step 101, the design area of ​​the towed pod is preliminarily determined to be the area between the main wing and the V-shaped tail.

[0014] Furthermore, the specific operations of step 2 include:

[0015] Step 201: using a CFD method to analyze the influence of propeller slipstream, using a sliding grid to separate the propeller rotating area from the stationary area, and calculating the vortex distribution of the wake field of the propeller configuration;

[0016] Step 202: Based on the wake field vortex distribution of the propeller configuration calculated in step 201, the towed pod design area determined in step 102 is preliminarily corrected to obtain the towed pod position. The towed pod position is below the main wing and is located in the wake area between the V-shaped tail and the main wing tip.

[0017] Furthermore, the position of the towed pod determined in step 2 based on the wake field vortex distribution of the clean carrier configuration and the wake field vortex distribution of the propeller configuration is below the main wing and in the wake region between the V-shaped tail and the wing tip of the main wing.

[0018] Furthermore, according to the position of the towed pod determined in step 202, the preliminary layout of the towed pod is as follows: the antenna site on the carrier platform is a fixed site, and the two pod auxiliary antenna sites towed from the fuselage are retractable mobile sites. The baseline distance between the fixed site and the two retractable mobile sites is 5.8m, and the baseline distance between the two retractable mobile sites is 1.45m.

[0019] Furthermore, the specific operation of correcting the position of the towed pod according to the simulation results in step 3 is as follows:

[0020] The specific operation of correcting the position of the towed pod according to the simulation results in step 3 is as follows:

[0021] (1) Move the connection position between the towed pod and the main wing to a point where the wing tip is within 90% to 100% of the half-span of the aircraft's symmetry plane;

[0022] (2) A winglet is constructed at the wingtip. The winglet is bent upward along the wingtip and transfers the wingtip vortex in the vertical direction of the wingtip and is distributed opposite to the position of the towed pod.

[0023] Furthermore, the final layout of the towed pods after correction in step 3 is as follows: the baseline distances between the fixed site on the carrier platform and the two towed pods are both greater than λ / 2, and the baseline distance between the two towed pods is greater than λ / 2, and the value of λ is 10m.

[0024] Another object of the present invention is to provide a towed antenna carrier platform for low-frequency signal reconnaissance, wherein the towed antenna carrier platform comprises a towed pod and a carrier platform obtained by the above-mentioned optimization method.

[0025] Furthermore, the specific layout of the three stations on the towed antenna carrier platform is as follows: the baseline distance between the fixed station on the carrier platform and the two retractable mobile stations is 7.0m, and the baseline distance between the two retractable mobile stations is 5.8m.

[0026] Another object of the present invention is to provide a towed antenna carrier platform for low-frequency signal reconnaissance and its application in the lateral positioning of a single machine of low-frequency signal.

[0027] Another object of the present invention is to provide an application in the design of a towed antenna carrier platform, a carrier electronically small low-frequency broadband active antenna and a carrier data link antenna for low-frequency signal reconnaissance.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) The pod with a negative angle of attack designed in the present invention will not affect the aircraft during the process of being dropped from the main wing, and will not collide with the main wing and the inverted V-shaped vertical tail during the release process.

[0030] (2) The present invention constructs a winglet at the wingtip of the main wing, so that the wingtip vortex can be moved away from the pod towed at the wingtip in the vertical direction, thereby meeting the working condition of stable towing of the pod.

[0031] (3) By placing the towed pod at the wingtip, the requirement that the baseline between the carrier radiation source receiving point and the two towed pod radiation source receiving points is greater than λ / 2 (5m) can be met. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of basic dragging; (a) side view; (b) top view;

[0033] Figure 2 Simulate 3D radiation pattern for data link antenna; (a) Simulate configuration of data link antenna for upright V-tail carrier; (b) Simulate configuration of data link antenna for inverted V-tail carrier; (c) Radiation pattern of data link antenna for upright V-tail carrier; (d) Radiation pattern of data link antenna for inverted V-tail carrier;

[0034] Figure 3 The calculation domain of pod delivery and the mesh of pod surface; (a) pod delivery calculation domain; (b) pod surface mesh;

[0035] Figure 4 The diagram of the antenna pod delivery process; (a) side view of the pod delivery process; (b) front view of the pod delivery process;

[0036] Figure 5 The calculation domain for the clean carrier configuration;

[0037] Figure 6 The surface mesh and volume mesh of the computational domain for the clean carrier configuration; (a) the surface mesh of the computational domain; (b) the volume mesh of the computational domain;

[0038] Figure 7 The wake flow field distribution of the clean carrier configuration; (a) top view of the flow field; (b) side view of the flow field;

[0039] Figure 8 It is the pod towing area in the clean carrier configuration;

[0040] Fig. 9 Schematic diagram of propeller configuration calculation domain and details; (a) overall calculation domain; (b) schematic diagram of aircraft and propeller; (c) schematic diagram of rotating domain; (d) schematic diagram of stationary area;

[0041] Fig.10 Schematic diagram of computational domain mesh; (a) computational domain surface mesh; (b) computational domain volume mesh;

[0042] Fig.11 The wake flow field distribution when the propeller speed is 60 rad / s; (a) top view of the flow field; (b) side view of the flow field;

[0043] Fig.12 The nacelle drag area to account for propeller slipstream;

[0044] Fig.13 This is the preliminary layout of the towed pod; (a) side view; (b) top view;

[0045] Fig.14 Geometric deformation diagram; (a) front view; (b) side view;

[0046] Fig.15 The basic drag fluid-solid coupling flow field diagram; (a) front view; (b) side view; (c) top view;

[0047] Fig.16 is the forward drag flow field diagram (t=0.1s);

[0048] Fig.17 This is a schematic diagram of the towing pod flipping;

[0049] Fig.18 It is a wingtip drag fluid-structure coupling configuration;

[0050] Fig.19 The wing tip drag fluid-solid coupling flow field diagram; (a) t=0.05s; (b) t=0.1s; (c) t=0.15s; (d) t=0.2s;

[0051] Fig. 20 It is a fluid-structure coupling configuration of a wingtip towing pod with winglets;

[0052] Fig.21 The fluid-solid coupling flow field diagram of the wing tip dragging of the winglet pod; (a) t=0.05s; (b) t=0.1s; (c) t=0.15s; (d) t=0.2s;

[0053] Fig. 22 The final configuration diagram of the pod towing; (a) side view; (b) top view;

[0054] Fig.23 The influence of the time measurement error of the spanwise motion of the radiation source on the fusion positioning and linear Kalman filter; (a) time measurement error 3ns; (b) time measurement error 0.2ns; (c) time measurement error 0.02ns; (d) time measurement error 0.002ns;

[0055] Fig.24 The influence of the time measurement error of the axial motion of the radiation source on the fusion positioning and linear Kalman filter; (a) time measurement error 3ns; (b) time measurement error 0.2ns; (c) time measurement error 0.02ns; (d) time measurement error 0.002ns;

[0056] Fig.25The influence of the time measurement error of oblique motion on the fusion positioning and linear Kalman filter; (a) time measurement error 3ns; (b) time measurement error 0.2ns; (c) time measurement error 0.02ns; (d) time measurement error 0.002ns;

[0057] Fig.26 It is a simulation model of the pod antenna;

[0058] Fig. 27 The simulation results of the pod antenna; (a) 3D radiation pattern; (b) 3D radiation pattern of the pod antenna;

[0059] Fig.28 It is a coupled simulation model for the small low-frequency broadband active antenna of the carrier electronics;

[0060] Fig.29 Coupling simulation of small low-frequency broadband active antenna for airborne electronics; (a) 3D radiation pattern of antenna; (b) 3D radiation pattern of airborne antenna; (c) E plane; (d) H plane;

[0061] Fig.30 Antenna radiation pattern after optimal installation position; (a) Antenna 3D radiation pattern; (b) Airborne antenna 3D radiation pattern. DETAILED DESCRIPTION

[0062] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art will make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0063] 1. The overall design idea of ​​the flight platform for single-machine direction finding and positioning of low-frequency signals:

[0064] The detection frequency band has strict requirements on antennas and layout. This paper selects the commonly used low-frequency band of 30MHz for communication reconnaissance for design. The wavelength of this frequency band is λ=10m. According to the conventional requirements of communication reconnaissance direction finding and positioning, the spacing between receiving antennas or units must be above λ / 2, and the longer the baseline, the higher the reconnaissance accuracy. Therefore, the minimum requirement for the receiving limit of the present invention is 5m, that is, the flying platform needs to form at least a triangular design space with a side length greater than 5m, which is difficult for most drones. Therefore, in order to realize low-frequency signal reconnaissance on small unmanned platforms, the present invention constructs a towed antenna layout form, and drags the two antenna units out of the body by towing to form a long baseline, thereby meeting the low-frequency direction finding and positioning requirements.

[0065] The carrier aircraft is a propeller-powered inverted V-tail high aspect ratio straight-wing aircraft with a length of 3m, a wingspan of 6m, and a height of 0.64m (excluding landing gear). Figure 1 Middle (a), Figure 1 As shown in (b).

[0066] Under its basic body size, the distance between the towed antenna and the carrier platform can barely meet the 5m baseline requirement, but it will have a greater impact on the platform. Therefore, this paper chooses this platform to carry out the collaborative design of the towed antenna and the platform. The design principles are:

[0067] (1) Taking the antenna as a constraint, consider the occlusion and impact of the platform on the antenna;

[0068] (2) Consider the impact of the pod release process on the carrier platform;

[0069] (3) Taking into account the platform characteristics and the disturbance of the platform to the towed antenna;

[0070] The impact of the platform on the antenna is mainly the shielding of the receiving antenna signal by the fuselage components. Since the data link antenna is installed on the vertical tail. Figure 2 Middle (a) ~ Figure 2 As shown in (d), if a vertical tail is placed upright, the fuselage and wings of the aircraft will block the data link antenna. In order to meet the working environment of the data link antenna, the present invention adopts an inverted V-tail layout.

[0071] Since it is too difficult to simulate the release of a towed pod under cable constraints, some simplifications are made to remove the cable constraints and abstract the release of the antenna pod into traditional load separation. The purpose is to study the separation and collision between the antenna and the pod and the changes in the dynamic aerodynamic characteristics of the antenna during the release process.

[0072] The antenna pod is simulated using nested grids (overset), and the calculation state is set the same as before. The specific parameters of the antenna pod are shown in Table 1.

[0073] ;

[0074] When the towed antenna pod is released, the relative speed of the antenna pod to the carrier aircraft is 0. It moves dynamically under the action of its own gravity and aerodynamic force. The computational domain and the pod surface mesh are as follows: Figure 3 Middle (a), Figure 3 As shown in (b), the simulation time is 0.5s. Figure 4 Middle (a), Figure 4(b) shows the simulation results of the carrier aircraft and antenna cabin. It can be seen that without considering the cable constraint, the initial placement position of the pod has a certain negative angle of attack, which can effectively prevent the load from colliding with the main wing of the carrier aircraft during the separation process. At the same time, the aerodynamic drag encountered by the load during the separation process will not cause the pod to decelerate rapidly, and will not affect the inverted V-tail at the rear.

[0075] The selection of a towed antenna mainly considers the impact of the aircraft wake on its attitude, and it needs to be able to operate in a stable towing area. The impact of the antenna on the platform is mainly aerodynamic drag. For this reason, the antenna design of the present invention adopts a conformal and rectified shape. The following is mainly to determine the layout design of the towed antenna and the carrier aircraft.

[0076] 2. Overall layout design of small flight platform:

[0077] 2.1 Simulation analysis of aircraft wake flow field:

[0078] According to the principle of collaborative design, the towed antenna must meet the requirements of sufficient baseline length layout on the one hand, and maintain attitude stability as much as possible on the other hand, that is, the towed part needs to be located in an area with less airflow disturbance of the carrier aircraft. Therefore, the present invention combines the CFD method to simulate and analyze the wake of the carrier aircraft, and determines the optimal towed antenna layout scheme by combining the baseline length requirements and disturbance.

[0079] First, a clean carrier configuration is selected to carry out the preliminary design of the towed antenna layout, the purpose of which is to quickly locate the initial towing position. The calculation domain of the clean carrier configuration is as follows: Figure 5 In order to more accurately describe the influence of the wake area, a local densification area is set, and its basic size is In principle, in order to capture the wake effect of the aircraft, it is necessary to use models such as DES / LES to carry out very accurate simulation calculations. However, the main purpose of this paper is to obtain the location of the area where the wake has less impact on the aircraft, and the requirement for accurate characterization of the local disturbance intensity is relatively low. Therefore, considering the calculation efficiency and accuracy, the DES / LES model is used. k-ω The SST turbulence model is used for flow field simulation.

[0080] The computational grid uses a Cartesian grid with good adaptability to the shape. The full-mode flow field grid size is 60 million. The grid is generated by first dividing the surface grid according to the size set by the object surface, and then using the three-dimensional octree method to generate the volume grid, such as Figure 6 Middle (a), Figure 6 As shown in (b). There are two layers of tetrahedral meshes between the surface mesh and the volume mesh. Since the calculation focuses on the aircraft wake field, the boundary layer mesh is not introduced when the mesh is generated. The calculation state is set as: flight altitude H = 1000m, flight speed V = 50m / s.

[0081] The simulation results are as follows: Figure 7 Middle (a), Figure 7 As shown in (b), the Q criterion is used to describe the vortex distribution generated by the entire machine body, and this value represents the separation strength of the spatial flow field. Figure 7 (a) shows that the places where the wake disturbance of the whole aircraft is more obvious mainly include three areas: 1) the wingtip vortex disturbance area, which is mainly due to the wake area formed by the wingtip vortex generated by the three-dimensional effect dragging to the spatial flow field. For large aircraft, the longitudinal size of this area can even reach tens of meters, and its internal rotation speed gradient is relatively large; 2) the horizontal tail wingtip vortex disturbance area, which is similar to the wingtip vortex of the wing, but because the size of the V-tail is small, its disturbance range and intensity are relatively small; 3) the fuselage rear body vortex system area, which is mainly due to the contraction of the fuselage rear body, causing the fuselage streamlines to converge and produce rotational disturbances, and its intensity rapidly decreases with the increase of longitudinal length. From the simulation results of the clean carrier configuration, the flow field disturbance in the area between the wing and the V-tail is relatively small. The reason is that the small part of the vortex dragged by the trailing edge of the wing is unstable and dissipates rapidly. Therefore, combined with the baseline scale requirements, it can be preliminarily determined that the towing cabin should be designed in this area. Its position is as shown in Figure 8 shown.

[0082] Since the aircraft is a propeller tail thruster, the influence of propeller slipstream needs to be further considered to further correct the initially determined position of the towing tank. The CFD method is also used to analyze the influence of slipstream. The propeller area is separated from the stationary rotation domain using a sliding grid, and the two areas are linked using an interface, such as Fig. 9 Middle (a) - Fig. 9 As shown in (d). The physical quantity of the rotating domain is converted to the absolute coordinate system at the boundary grid of the interface and interpolated with the external field flux. The total number of computational grids is about 70 million, of which about 2 million are in the rotating area and about 68 million are in the static area. The grid diagram is shown in Fig.10 Middle (a), Fig.10 As shown in (b).

[0083] The calculation state is set as: flight altitude H = 1000m, flight speed V = 50m / s, propeller speed 60rad / s. The calculated results are also described by the Q criterion to describe the wake distribution, such as Fig.11 Middle (a), Fig.11 As shown in (b). It can be seen that when the tail propeller is rotated, the vortex distribution of the V-tail and the rear body along the flow direction is significantly enhanced, indicating that the propeller slipstream has a large range and intensity, but the boundary is still within the propeller blade diameter. There is no obvious interference with the position of the towing cabin set in the previous article. Therefore, considering the slipstream effect comprehensively, the position of the towed antenna is determined to be below the main wing, in the wake area between the V-tail and the main wing tip, as shown in Fig.12 shown.

[0084] In summary, the preliminary layout of the towed antenna designed in this paper is as follows Fig.13 Middle (a), Fig.13 As shown in (b), the station on the airborne platform is a fixed station, and the two stations towed from the fuselage are retractable mobile stations. The baseline lengths between the three stations are 5.8m, 5.8m and 1.45m respectively. The towed pod antenna is 5m away from the main wing. When using the towed antenna, the carrier aircraft must be in a cruising flight state. After stable flight, the towed pod can be released. After the position is locked, it can start to jointly detect the ground signal source with the fixed station of the fuselage.

[0085] 2.2 Fluid-structure coupling simulation considering the influence of wake field on towing system:

[0086] The previous simulation only considered the influence of the main wing and propeller wake field on the towed pod, and preliminarily determined the position of the towed pod. In this section, the full-model flow field of the aircraft is constructed by installing the actual pod, and the two-way fluid-structure coupling method is used and the sliding grid technology is introduced in the fluid calculation domain to simulate the influence of propeller rotation on the towed pod, so as to further correct the pod position.

[0087] Fig.14 Middle (a), Fig.14 (b) and Fig.15 Middle (a) - Fig.15 (c) shows the geometric deformation diagram and flow field diagram of the calculation process. From the simulation results, it can be seen that Fig.14 Middle (a), Fig.14 In the basic towing condition shown in (b), the pod is affected by the tip vortex of the inverted V-tail at t=0.2s, and the upper surface of the inner wing between the two pods is affected by the wingtip vortex, the pressure on the upper surface of the wing decreases, and the two pods flip outward and cannot perform stable towing. Fig.15 Middle (a) - Fig.15 (c) clearly shows the entire process of the two vortices formed by the coupling of the wingtip vortex generated by the V-shaped tail and the slipstream generated by the propeller, from their development and propagation to their impact on the towing of the towed pod.

[0088] The wingtip vortex generated by the V-shaped tail and the slipstream generated by the propeller propagate to the location of the towed pod at the simulation time of 0.1s, as shown in Fig.16 As shown, when viewed from the front of the aircraft, the rotating flow on the left is clockwise, and the rotating flow on the right is counterclockwise.

[0089] Since the speed of the two swirling flows is greater than that of the incoming flow, the lift on the inner wing of the towing pod is greater than that on the outer wing, causing both towing pods to flip outwards. Fig.17As shown, the pod cannot be towed stably, so the initially determined pod towing position needs to be corrected, and the inner wing of the towed pod should be away from the wingtip vortex generated by the V-tail.

[0090] Move the connection position between the towed pod and the wing to the vicinity of the wing tip, that is, within the range of 90%-100% of the half-span of the wing tip from the aircraft symmetry plane. Fig.18 In the fluid-structure interaction model shown, only one side of the pod is simulated in order to reduce the fluid-structure interaction simulation time.

[0091] Fig.19 Middle (a) - Fig.19 (d) is the wake field diagram of wingtip drag, which shows the development and propagation of the main wing wingtip vortex and how the wingtip vortex affects the drag state of the pod. It can be seen from the observation that the pod towing near the wingtip is greatly affected by the wingtip vortex. The vertical displacement of the pod during the dragging process causes the distance between the wingtip vortex and the inner wing of the pod to decrease, thus interfering with the drag of the pod.

[0092] In order to reduce the influence of the wing tip vortex on the pod, a winglet is constructed at the wing tip to move the wing tip vortex away from the pod in the vertical direction, such as Fig. 20 shown.

[0093] Fig.21 Middle (a) - Fig.21 (d) is the wingtip drag fluid-solid coupling flow field diagram of the constructed winglet. It can be seen from the figure that by constructing the wingtip winglet, the wingtip vortex is vertically away from the towing pod and will not affect the stable towing of the pod.

[0094] In summary, the initially determined position of the towed antenna pod is corrected, and the towed pod is built at the wing tip. By building winglets, the wing tip vortices are guided out of the area that can affect the pod towing, thereby ensuring that the pod is in a stable towing state. The final pod towing configuration diagram is shown in the figure below. Fig. 22 Middle (a), Fig. 22 As shown in (b). The baseline distance between the main receiving station on the carrier aircraft and the two towed pod auxiliary receiving stations is greater than λ / 2 (5m), and the baseline distance between the two towed pod auxiliary receiving stations is also greater than λ / 2 (5m). It should be noted that the carrier aircraft platform has a large aspect ratio configuration. The closer to the wing tip, the greater the wing deformation. Although the towed pod can be connected to the wing tip to unload the wing, the structural strength of this part still needs to be strengthened.

[0095] 2.3 Conclusion:

[0096] The present invention uses an inverted V-tail pushback propeller-powered UAV as the carrier platform, and carries out the layout design of a towed low-frequency antenna pod considering the interference of the carrier aircraft. Based on the requirements of low-frequency band reconnaissance, the design principles of the towed antenna layout in this band are set; based on the CFD dynamic mesh technology, the dynamic release of the pod is studied; based on the CFD method, the influence area of ​​the carrier aircraft wake is analyzed, and the influence of the pushback propeller slipstream is further evaluated based on the sliding mesh, and the layout position of the pod is preliminarily determined based on the comprehensive baseline requirements and disturbance constraints; the fluid-solid coupling technology is used to study the influence of the aircraft wake field on the towed pod under different towing positions, and finally the pod towing position that meets the measurement baseline requirements is determined.

[0097] The main conclusions are as follows:

[0098] 1) The pod with a negative angle of attack will not affect the aircraft when it is dropped from the main wing, and will not collide with the main wing and the inverted V-shaped vertical tail during the release process.

[0099] 2) In the simulation of the bidirectionally coupled towed pod considering cable constraints, the towing position of the pod must fully consider the influence of the wingtip vortices generated by the inverted V-tail and the wingtip of the main wing. It is necessary to ensure that the small wing of the towed pod will not be affected by the wingtip vortices generated by the inverted V-tail and the wingtip of the main wing.

[0100] 3) By constructing winglets at the wingtips of the main wings, the wingtip vortices can be moved vertically away from the pod towed at the wingtips, meeting the working conditions of stable towing of the pod.

[0101] 4) By placing the towing pod at the wingtip, the requirement that the baseline between the carrier radiation source receiving point and the two towing pod radiation source receiving points is greater than λ / 2 (5m) can be met.

[0102] Embodiment 1:

[0103] This embodiment, based on the layout of the towed antenna carrier platform, conducts research on a single-machine detection method for low-frequency band signals to form a single-machine direction finding and positioning method for low-frequency band signals that is suitable for the towed layout.

[0104] The positioning result of the towed antenna in space will generate three spatial coordinates, namely the carrier space coordinates ( x a , y a ) and the spatial coordinates of the two towed pods ( x b , y b ), ( x c , y c). The towed pod will have a relative movement deviation due to the influence of airflow.

[0105] (1) Construct a three-station TDOA positioning simulation model for the spanwise motion of the radiation source. The distance between the receiving sites is 6 m, the radiation source is 55 km away from the receiving center, and the radiation source moves along the y The axis moves at a constant speed of 55km. The three-station TDOA positioning algorithm is used to locate the moving target, and the target position is estimated by the linear Kalman filter method. The measurement time error is introduced, and the simulation results show the influence of the time measurement error on the fusion positioning accuracy and the linear Kalman filter.

[0106] Fig.23 Middle (a) - Fig.23 (d) shows the influence of time measurement error on fusion positioning and linear Kalman filter. The most accurate common view timing center method has a timing accuracy of 3ns. Fig.23 As shown in (a), when a 3ns time measurement error is introduced into the simulation system, the error of the fusion positioning reaches 200m at a distance of 55km from the receiving center. As the radiation source moves away from the receiving center, the error of the fusion positioning gradually increases, and the error of the fusion positioning is as high as 1200m at a distance of 135km from the receiving center. Under the 3ns time measurement error, the error of the linear Kalman filter's estimation of the position is always below 200m. Fig.23 (b) shows the error values ​​of fusion positioning and linear Kalman filter under the time measurement error of 0.2ns. Under the time measurement error of 0.2ns, the prediction error of fusion positioning error Kalman filter is more than 10m. Fig.23 (c) shows the error value of fusion positioning and linear Kalman filter under the time measurement error of 0.02ns. Under the time measurement error of 0.02ns, the prediction error of fusion positioning error and Kalman filter is more than 1m. Fig.23 (d) is the error value of fusion positioning and linear Kalman filter under the time measurement error of 0.002ns. Under the time measurement error of 0.002ns, the prediction error of fusion positioning error Kalman filter is less than 1m. Therefore, when the time measurement error of the system is less than 0.02ns, the three-station TDOA positioning system can meet the requirements of medium and high precision positioning tasks.

[0107] Will Fig.23 Middle (a) - Fig.23 Table 2 can be obtained by converting the data in (d). It can be seen from the data in the table that the low time measurement accuracy has little impact on the direction finding task.

[0108] ;

[0109] (2) Construct another three-station TDOA positioning simulation model with the radiation source moving axially. The distance between the receiving sites is 6 m, the radiation source is 55 km away from the receiving center, and the radiation source moves along the x The axis moves at a constant speed of 55km. The three-station TDOA positioning algorithm is used to locate the moving target, and the target position is estimated by the linear Kalman filter method. The measurement time error is introduced, and the simulation results show the influence of the time measurement error on the fusion positioning accuracy and the linear Kalman filter, such as Fig.24 Middle (a) - Fig.24 As shown in (d), it can be seen that the positioning accuracy of the system for spanwise targets is one order of magnitude higher than that for axial targets.

[0110] Will Fig.24 Middle (a) - Fig.24 By converting the data in (d), we can get Table 3. From the data in the table, we can see that under the time measurement error of 3ns, the system can no longer accurately find the direction of the target 100km away.

[0111] ;

[0112] (3) Construct another three-station TDOA positioning simulation model with the radiation source moving obliquely. The distance between the receiving stations is 6m, the radiation source is 30km away from the receiving center, and the radiation source moves along the xy The moving target is located at a constant speed of 80 km between the axes. The three-station TDOA positioning algorithm is used to locate the moving target, and the target position is estimated by the linear Kalman filter method. The measurement time error is introduced, and the simulation results show the influence of the time measurement error on the fusion positioning accuracy and the linear Kalman filter, such as Fig.25 Middle (a) - Fig.25 As shown in (d), it can be seen that the system has good positioning performance for oblique moving targets.

[0113] Will Fig.25 Middle (a) - Fig.25 Table 4 can be obtained by converting the data in (d). From the data in the table, it can be seen that under a 3ns time measurement error, a 0.5° direction finding error will be introduced for a target 110km away, which does not meet the system's requirements for direction finding accuracy.

[0114] ;

[0115] Based on the above three types of three-station TDOA single-target direction-finding positioning error analysis, a three-station TDOA dual-target tracking simulation model is constructed. The three-station TDOA positioning model can achieve full-process accurate tracking and positioning of moving targets with multiple radiation sources.

[0116] The above simulation analysis shows that:

[0117] 1) For a time difference positioning system with three equidistant stations, the accuracy is lowest along the sighting line from receiving station to receiving station.

[0118] 2) Under the condition of equal time measurement error, the time difference positioning system with three equidistant stations has the highest positioning accuracy for oblique moving targets, the positioning accuracy for spanwise moving targets is lower than that for oblique moving targets, and the positioning accuracy for axial moving targets is the worst.

[0119] Embodiment 2:

[0120] This embodiment utilizes a towed payload integrated flight platform constructed for low-frequency signal reconnaissance to design a carrier-borne small low-frequency broadband active antenna.

[0121] Considering the electrical performance of the antenna when loaded into the pod, Fig.26 In the model shown, the monopole antenna is loaded into the towed pod, and the pod is set to be a wave-transmitting material. The simulation results are shown in Fig. 27 Middle (a), Fig. 27 As shown in (b), the 3D radiation pattern of the pod antenna shows that the lateral rolling of the pod does not affect the receiving performance of the antenna.

[0122] In order to ensure the consistency of the receiving units and eliminate the phase error between the receiving units, the impedance-matched electric small antenna is applied to the carrier platform, that is, the receiving unit of the carrier itself also uses this antenna form. In real working conditions, the structure and surface skin of the carrier are generally metal conductors. The size of the carrier is larger than that of the electric small antenna, which will block the directional pattern of the electric small antenna. At the same time, since the surface of the carrier is a good conductor, it will couple with the antenna. Therefore, the coupling simulation of the carrier and the electric small antenna is carried out to analyze the radiation pattern of the antenna and the carrier in the coupled state, and select the best installation position of the electric small antenna.

[0123] Build Fig.28 The simulation model of the carrier's electrically small low-frequency broadband active antenna coupling is shown. In order to simplify the calculation, the coupling between the electrically small antenna and the fuselage is mainly considered. At the same time, in order to expand the coverage of the electrically small antenna pattern, two electrically small monopole antennas are placed axially. The antenna pattern obtained after simulation is as follows Fig.29 Middle (a) - Fig.29 As shown in (d), it can be seen that the metal fuselage has an impact on the antenna's radiation pattern. The antenna facing the fuselage will be weakened, while the antenna facing away from the fuselage is not significantly affected.

[0124] The best distance between the antenna installation position and the fuselage is obtained by optimization, such as Fig.30 Middle (a), Fig.30 As shown in (d), the antenna's radiation pattern at this time can achieve the required coverage state.

[0125] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, so that those skilled in the art can understand and apply the present invention. It cannot be determined that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art of the present invention, some simple deductions or substitutions can be made without departing from the concept of the present invention, without creative labor. Therefore, simple improvements made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for optimizing the layout position of a towed pod for low-frequency signal reconnaissance on a carrier platform, characterized in that: The optimization method includes the following steps: Step 1: Use CFD method to simulate the flow field of the clean carrier configuration to obtain the vortex distribution of the wake field of the clean carrier configuration; Step 2: Introduce the sliding grid into the CFD method to calculate the wake vortex distribution of the propeller configuration, and preliminarily determine the position of the towed pod based on the wake vortex distribution of the clean carrier configuration and the wake vortex distribution of the propeller configuration; Step 3: The full-model flow field of the aircraft is constructed by installing the actual pod, and the bidirectional fluid-solid coupling method is used and a sliding network is introduced in the fluid calculation domain to simulate the influence of propeller rotation on the towed pod, and the position of the towed pod is corrected; The specific operations of step 1 include: Step 101: Use k-ω The SST turbulence model is used to simulate the flow field of the clean carrier configuration; Step 102: Based on the flow field simulation result of step 101, the design area of ​​the towed pod is preliminarily determined to be the area between the main wing and the V-shaped tail; The specific operations of step 2 include: Step 201: Analyze the influence of propeller slipstream using CFD method, separate the propeller rotating area from the stationary area using sliding grid, and calculate the vortex distribution of the wake field of the propeller configuration; Step 202: Based on the wake field vortex distribution of the propeller configuration calculated in step 201, the towed pod design area determined in step 102 is preliminarily corrected to obtain the towed pod position. The towed pod position is below the main wing and is located in the wake area between the V-shaped tail and the main wing tip.

2. The method for optimizing the layout position of a towed pod for low-frequency signal reconnaissance on a carrier platform according to claim 1, characterized in that: According to the position of the towed pod determined in step 202, the preliminary layout of the towed pod is as follows: the antenna site on the carrier platform is a fixed site, and the two pod auxiliary antenna sites towed from the fuselage are retractable mobile sites. The baseline distance between the fixed site and the two retractable mobile sites is 5.8m, and the baseline distance between the two retractable mobile sites is 1.45m.

3. The method for optimizing the layout position of a towed pod for low-frequency signal reconnaissance on a carrier platform according to claim 2, characterized in that: The specific operation of correcting the position of the towed pod according to the simulation results in step 3 is as follows: (1) Move the connection position between the towed pod and the main wing to a point where the wing tip is within 90% to 100% of the half-span of the aircraft's symmetry plane; (2) A winglet is constructed at the wingtip. The winglet is bent upward along the wingtip and transfers the wingtip vortex in the vertical direction of the wingtip and is distributed opposite to the position of the towed pod.

4. The method for optimizing the layout position of a towed pod for low-frequency signal reconnaissance on a carrier platform according to claim 3 is characterized in that: The final layout of the towed pods after the correction in step 3 is as follows: the baseline distances between the fixed site on the carrier platform and the two towed pods are both greater than λ / 2, and the baseline distance between the two towed pods is greater than λ / 2, where λ is 10m.

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