Unsteady flow and mechanism motion coupling simulation method

Abstract

The invention provides an unsteady flow and mechanism motion coupling simulation method, which comprises the following steps of: carrying out unsteady flow calculation by adopting a CFD (Computational Fluid Dynamics) method fused with a nested grid, and obtaining aerodynamic force of each separation part of an aircraft by integrating solid wall surface pressure and friction force; aerodynamic force, gravity and other main power are used as driving for system separation; carrying out multi-body system motion calculation, solving a multi-body dynamic differential-algebraic equation of the system, and obtaining rotation time characteristics of each separation part; based on CFD flow field information, extracting a spatial scale and a local information propagation speed of the key flow structure, and obtaining an unsteady flow time feature of the dominant aerodynamic performance key flow structure; and determining a time step length according to the rotation time characteristic and the unsteady flow time characteristic, and entering the next flow field propulsion and mechanism movement propulsion. By applying the technical scheme, the technical problem that high-precision simulation of a complex mechanism separation scheme cannot be met in the prior art can be solved.

Description

Technical Field

[0001] The invention belongs to the technical field of unsteady flow and mechanism motion coupling simulation, and in particular relates to an unsteady flow and mechanism motion coupling simulation method. Background Art

[0002] Separation is a necessary part of the mission profile of various aircraft, and the safety analysis of the separation process is one of the core tasks of system design. In the low-speed domain, such as the delivery of various aircraft payloads, whether external or internal, the constraint involvement process between the separation components and the carrier aircraft has little effect, and due to the small dynamic pressure, the main force of separation is mainly dominated by gravity. The insecurity mainly comes from the torque interference of the carrier aircraft on the load. Generally, the unsteady and nested (deformed) grids of mature commercial software or self-developed CFD programs are competent.

[0003] In the high-speed domain, the dynamic pressure is generally high, the aerodynamic force is relatively large, and the gravity is relatively small. The separation form generally relies on aerodynamic surfaces or jets, forming two major technical approaches: hot separation and cold separation. In various interstage separations, the unsteadiness of the flow begins to become the main risk point. Due to the characteristics of slow response of the grid force measurement and CTS method mechanism, some unsteady effects are ignored or simplified, and the high dynamic process cannot be captured. The calculation method based on unsteady flow becomes a more important analysis tool. Especially for the high-speed related separation of complex-shaped aircraft, the movement of the mechanism in the early stage of separation often plays a decisive role in the safety of the separated components. Due to the extremely high cost and time cost, the wind tunnel test gradually separated from the scheme design and became the final verification link. The scheme design mainly relies on simulation. In the earliest practice, the main method of obtaining data was the independent analysis of mechanism motion and aerodynamic force. CFD was responsible for the aerodynamic data of different positions. As the known right-hand side of the mechanism motion equation, the multi-body kinematic equation mostly uses commercial software. Ignoring the unsteady coupling effect will lead to excessive calculation deviation. Subsequently, the solution method of unsteady flow and mechanism motion was developed, which proved its necessity and effectiveness in practice.

[0004] As parallel separation forms began to emerge, the complexity of the separation mechanism also increased. The multi-body dynamics equations based on independent variables and the special constraint equations could not even be expressed explicitly. The number of components, constraint forms, and number of constraints varied greatly among different separation methods, and the approach to customization based on separation characteristics was challenged.

[0005] Table 1 gives the classification of CFD and mechanism motion coupling simulation methods, as well as the characteristics, applicability and representatives of each method.

[0006] Table 1 Classification of CFD and mechanism motion coupling simulation methods

[0007]

[0008] Summary of the invention

[0009] The present invention aims to solve at least one of the technical problems existing in the prior art.

[0010] The present invention provides a method for coupling simulation of unsteady flow and mechanism motion, the method comprising: using a CFD method with fused nested grids to perform unsteady flow calculations, obtaining the aerodynamic forces of each separated component of an aircraft by integrating solid wall pressure and friction, and using aerodynamic forces, gravity and other main forces as the driving force for system separation; performing multi-body system motion calculations, solving the system multi-body dynamics differential-algebraic equations, and obtaining the rotation time characteristics of each separated component; based on CFD flow field information, extracting the spatial scale of key flow structures and the local information propagation speed, and obtaining the unsteady flow time characteristics of key flow structures that dominate aerodynamic performance; determining the time step according to the rotation time characteristics and the unsteady flow time characteristics, and entering the next step of flow field advancement and mechanism motion advancement.

[0011] By applying the technical solution of the present invention, a method for coupling simulation of unsteady flow and mechanism motion is provided. The method is based on an autonomous and controllable CFD framework, introduces nested grid technology to describe the relative motion of components, and adopts non-independent generalized coordinates to realize automatic modeling of system differential-algebraic equations in view of the complex and changeable constraints of the separation mechanism. By extracting the time scale of the flow structure and the time scale of the rotation of the mechanism components during the separation process, a large time step can be used in the stable section to save computing resources, and high dynamic capture can be automatically achieved in the unsteady section. Compared with the prior art, the technical solution of the present invention can solve the technical problem that the prior art cannot meet the high-precision simulation of complex mechanism separation schemes. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0013] Figure 1 A schematic flow chart of a method for simulating the coupling of unsteady flow and mechanism motion provided according to a specific embodiment of the present invention is shown;

[0014] Figure 2 A schematic diagram of a flow time characteristic acquisition process according to a specific embodiment of the present invention is shown;

[0015] Figure 3 A schematic diagram of a process for obtaining rotation time characteristics provided according to a specific embodiment of the present invention is shown. DETAILED DESCRIPTION

[0016] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0018] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present invention. The technology, method and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments can have different values.

[0019] like Figure 1 As shown, according to a specific embodiment of the present invention, a method for coupling simulation of unsteady flow and mechanism motion is provided, the method comprising:

[0020] The unsteady flow calculation is performed using the CFD method with fused nested grids.

[0021] The aerodynamic forces of each separated component of the aircraft are obtained by integrating the solid wall pressure and friction force, and the aerodynamic force, gravity and other main forces are used as the driving force for system separation;

[0022] Perform multi-body system motion calculations, solve the system's multi-body dynamics differential-algebraic equations, and obtain the rotation time characteristics of each separate component;

[0023] Based on CFD flow field information, the spatial scale of key flow structures and the local information propagation speed are extracted to obtain the unsteady flow time characteristics of key flow structures that dominate aerodynamic performance;

[0024] The time step is determined based on the rotation time characteristics and the unsteady flow time characteristics, and the next step of flow field advancement and mechanism motion advancement is entered.

[0025] By applying this configuration, a simulation method for coupling unsteady flow and mechanism motion is provided. This method is based on an autonomous and controllable CFD framework, introduces nested grid technology to describe the relative motion of components, and uses non-independent generalized coordinates to achieve automatic modeling of system differential-algebraic equations for complex and changeable constraints of the separation mechanism. By extracting the flow structure time scale and the rotation time scale of the mechanism components during the separation process, a large time step can be used in the stable section to save computing resources, and high dynamic capture can be automatically achieved in the unsteady section.

[0026] Further, in the present invention, if Figure 2 As shown in the figure, for the flow time characteristics, the advantage of rich CFD flow field information is taken. The current entire spatial flow field information, including density, three-directional velocity and temperature (or pressure), is known. A typical cross section is cut to carry out flow structure identification, mainly the flow separation area close to the wall and the vortex structure of the flow separation area evolving in space. The maximum speed of information propagation in the local vicinity is detected, which can generally be taken as a combination of flow velocity and sound speed. The ratio of spatial scale and velocity is confirmed as the flow characteristic time scale. The specific calculation method is shown in formula (1).

[0027]

[0028] Among them, h F is the characteristic time scale of the flow, Q is the local flow field scalar, V is the local flow velocity, a is the local sound speed, is the gradient.

[0029] Further, in the present invention, if Figure 3 As shown in FIG, for the rotation time characteristics of each separate component of the system, the state of the historical system is known, such as the system's position (displacement and rotation angle), generalized velocity (velocity and angular velocity), and generalized acceleration (acceleration and angular acceleration). The time step at the next moment is estimated based on the time step at the previous moment or several time points. The specific calculation method is shown in formula (2).

[0030]

[0031] in, is the estimated time step at the n+1th moment, h n+1-i is the time step at the n+1-ith moment, A iis the coefficient of the i-th template point, i=1,2,...k.

[0032] Furthermore, the estimated time step at the next moment is combined with the Taylor formula to obtain the system state estimate at the next moment. The specific calculation method is as shown in formula (3).

[0033]

[0034] in, Solve for the estimate of the variable at the n+1th moment, q n Solve for the variable for the nth time instant, Solve the first-order derivative of the variable for the nth moment, Solve the second-order derivative of the variable at the nth moment, where O is a high-order quantity.

[0035] At the same time, the system differential-algebraic equation is solved according to the estimated time step. The specific calculation method is as shown in Formula 4 to obtain the system state correction value at the next moment.

[0036]

[0037] in, is the system state correction at the n+1th moment, M n+1 is the mass matrix of the mechanism at time n+1, is the Jacobian matrix of the mechanism constraint at time n+1, F n+1 is the force applied to the mechanism at time n+1, λ n+1 is the Lagrange multiplier of the mechanism at time n+1, t n+1 Indicates the n+1 moment.

[0038] Define the norm of the system state prediction and system state correction vector angle at the next moment, and use the difference to obtain the rotation time characteristics. The specific calculation method is shown in Formula 5.

[0039]

[0040] Among them, h R is the mechanism motion time scale, that is, the rotation time characteristic scale; q n-1 Solve the variable for the n-1th moment, ‖ ‖1 means taking the maximum norm.

[0041] Furthermore, in the present invention, after obtaining the rotation time characteristics and the unsteady flow time characteristics, the time step is determined according to the rotation time characteristics and the unsteady flow time characteristics, and the next step of flow field advancement and mechanism motion advancement is entered according to the determined time step. The time step h at the n+1th moment n+1 The specific method of obtaining is as shown in formula (6).

[0042] h n+1=min(h F ,h R ) (6)

[0043] The unsteady flow of the present invention is based on the commonly used autonomous and controllable CFD framework in engineering. The nested grid technology is introduced to conveniently describe the relative motion of components. In view of the complex and changeable constraints of the separation mechanism, the non-independent generalized coordinates are used to realize the automatic modeling of the system differential-algebraic equations. By extracting the flow structure time scale and the rotation time scale of the mechanism components during the separation process, a large time step can be used in the stable section to save computing resources, and high dynamic capture can be automatically achieved in the unsteady section.

[0044] The present invention realizes CFD simulation of autonomous selection of constraint forms between separation components, and improves computational efficiency on the basis of capturing unsteady effects. Compared with the prior art, the present invention can capture unsteady effects in the separation process, and can autonomously adapt to different mechanism separation schemes, avoiding the inefficient customized development method in engineering, and can adaptively adjust the step size according to the significance of unsteady effects, achieving an organic unity of efficiency and precision.

[0045] The relevant technical terms used in the present invention are explained as follows:

[0046] CFD: Computational fluid dynamics, solving the Reynolds-averaged NS equations in a finite volume framework, modeling small turbulence scales into large-scale viscosity, flux calculation based on a simplified Riemann solver of characteristic line theory, including two major approaches: vector flux and differential flux, each with its own scope of application. Time is introduced to iterate within a pseudo-time step to simulate unsteady effects.

[0047] Nested grids: Different separated components generate fixed body grids respectively, including structured and unstructured organization forms. The flow field information around different components is exchanged between nested grids through hole interpolation, which facilitates the flow field calculation under relative motion between separated components.

[0048] Differential-algebraic equations: describe constrained multibody dynamics equations, where the differential equations express the system equilibrium under generalized forces, and the algebraic equations describe the constraint relationship between generalized coordinates. The difficulty of solving them is generally proportional to the index, which defines the maximum number of derivatives of ordinary differentials obtained by differentiating the constraint equations.

[0049] Generalized coordinates: used to describe the relative posture and position between multi-body components. They are also the variables to be solved. They are divided into non-independent generalized coordinates and independent generalized coordinates. When the system is simple, independent generalized coordinates can be found, and the established equations are ordinary differential equations, which are relatively simple to solve. However, when the system is complex, it is difficult to find non-independent generalized coordinates, and the established equations are differential-algebraic, which are relatively complex to solve.

[0050] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0051] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for coupling simulation of unsteady flow and mechanism motion, characterized in that: The unsteady flow and mechanism motion coupling simulation method comprises: The unsteady flow calculation is performed using the CFD method with fused nested grids. The aerodynamic forces of each separated component of the aircraft are obtained by integrating the solid wall pressure and friction force, and the aerodynamic force, gravity and other main forces are used as the driving force for system separation; Perform multi-body system motion calculations, solve the system's multi-body dynamics differential-algebraic equations, and obtain the rotation time characteristics of each separate component; Based on CFD flow field information, the spatial scale of key flow structures and the local information propagation speed are extracted to obtain the unsteady flow time characteristics of key flow structures that dominate aerodynamic performance; The time step is determined according to the rotation time characteristics and flow time characteristics, and the next step of flow field advancement and mechanism motion advancement is entered.

2. The unsteady flow and mechanism motion coupling simulation method according to claim 1 is characterized in that: The step of acquiring the flow time characteristics specifically includes: Based on CFD flow field information, extract flow field space solution variables; Cut typical cross sections to identify flow structures; Detect local flow velocity and sound speed; The flow time characteristics are obtained based on the local flow velocity and the speed of sound.

3. The unsteady flow and mechanism motion coupling simulation method according to claim 2 is characterized in that: according to The flow time characteristics are obtained, where h F is the characteristic time scale of the flow, Q is the local flow field scalar, V is the local flow velocity, a is the local sound speed, is the gradient.

4. The unsteady flow and mechanism motion coupling simulation method according to any one of claims 1 to 3, characterized in that: The step of acquiring the rotation time feature specifically includes: According to the known historical system status, the time step of the next moment is estimated by extrapolating the historical time step; The system state estimate at the next moment is obtained based on the estimated time step at the next moment combined with Taylor's formula; According to the estimated time step, the system differential-algebraic equation is advanced to obtain the system state correction value at the next moment; Define the norm of the system state prediction and system state correction vector angle at the next moment, and use the difference to obtain the rotation time characteristics.

5. The unsteady flow and mechanism motion coupling simulation method according to claim 4 is characterized in that: according to Estimate the time step of the next moment, where is the estimated time step at the n+1th moment, h n+1-i is the time step at the n+1-ith moment, A i is the coefficient of the i-th template point, i=1,2,...k.

6. The unsteady flow and mechanism motion coupling simulation method according to claim 5 is characterized in that: according to Get the system state estimate for the next moment, where: Solve for the estimate of the variable at the n+1th moment, q n Solve for the variable for the nth time instant, Solve the first-order derivative of the variable for the nth moment, Solve the second-order derivative of the variable at the nth moment, where O is a high-order quantity.

7. The unsteady flow and mechanism motion coupling simulation method according to claim 6, characterized in that: according to Get the system state correction value at the next moment, where: is the system state correction at the n+1th moment, M n+1 is the mass matrix of the mechanism at time n+1, is the Jacobian matrix of the mechanism constraint at time n+1, F n+1 is the force applied to the mechanism at time n+1, λ n+1 is the Lagrange multiplier of the mechanism at time n+1, t n+1 Indicates the n+1 moment.

8. The unsteady flow and mechanism motion coupling simulation method according to claim 7, characterized in that: according to Obtain the rotation time characteristics, where h R is the mechanism motion time scale, q n-1 Solve the variable for the n-1th moment, || ||1 means taking the maximum norm.

9. The unsteady flow and mechanism motion coupling simulation method according to claim 8, characterized in that: According to h n+1 =min(h F ,h R ) determines the time step, where h n+1 is the time step at the n+1th moment.

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