A method and structure for suppressing high speed boundary layer second mode waves to delay transition

Abstract

This invention discloses a method and structure for suppressing the second mode wave of a high-speed boundary layer to delay transition, relating to the field of boundary layer flow control technology. The method for suppressing the second mode wave of a high-speed boundary layer to delay transition includes: determining the synchronization point of a conical high-speed boundary layer according to the design incoming flow conditions; and setting an open cavity between the leading edge of the conical high-speed boundary layer and the synchronization point. The large-sized open cavity on the surface of the conical high-speed boundary layer can effectively suppress the growth of the second mode wave, thereby delaying the transition of the high-speed boundary layer. This is beneficial for achieving laminar flow design of the conical high-speed boundary layer and reducing aerodynamic losses and aerodynamic heat caused by transition in the high-speed boundary layer.

Description

Technical Field

[0001] This invention relates to the field of boundary layer flow control technology, and more specifically, to a method for suppressing high-speed boundary layer second-mode waves to delay transition. Furthermore, this invention also provides a structure for applying the above-described method for suppressing high-speed boundary layer second-mode waves to delay transition. Background Technology

[0002] The transition of high-speed boundary layers leads to a sharp increase in wall friction and heat flux, making it a cutting-edge and hotly debated topic in fluid mechanics research. For different high-speed boundary layers, various instabilities may exist during the transition process, including first-mode instability, second-mode instability, Görtler instability, crossflow instability, and adhesion line instability.

[0003] When the Mach number comes When the frequency is greater than 3.7, in addition to the unstable mode corresponding to the TS wave, a series of high-frequency unstable modes characterized by acoustic disturbances also exist in the boundary layer. In high-speed boundary layer studies, the mode corresponding to the TS wave is the first mode wave, and the aforementioned high-frequency unstable modes are referred to as the second mode wave, third mode wave, etc., according to their frequencies from low to high. Among them, the second mode wave is the most unstable disturbance.

[0004] In the Mach number of the flow At lower values, the first mode wave exhibits the greatest growth rate; when the incoming Mach number is lower... When the value is ≥4, the growth rate of the second mode wave increases rapidly, becoming the most unstable disturbance and playing a dominant role in the transition of the boundary layer.

[0005] In summary, how to suppress the growth of the second mode wave in the high-speed boundary layer to delay the transition is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a method for suppressing the second mode wave of a high-speed boundary layer to delay the transition, by using a large-sized open cavity to suppress the growth of the second mode wave, thereby suppressing the transition of the high-speed boundary layer.

[0007] Furthermore, the present invention also provides a structure for suppressing high-speed boundary layer second-mode waves and delaying transition by applying the above-described method for suppressing high-speed boundary layer second-mode waves.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for suppressing high-speed boundary layer second-mode waves to delay transition includes:

[0010] Determine the synchronization point of the conical high-speed boundary layer based on the design flow conditions. ;

[0011] The leading edge of the conical high-speed boundary layer and the synchronization point An open cavity is set between them.

[0012] Preferably, the leading edge and synchronization point of the conical high-speed boundary layer An open cavity is provided between the two, including:

[0013] Determine the boundary layer thickness at the starting position of the opening cavity. ;

[0014] Using the boundary layer thickness at the starting position of the opening cavity The cavity depth d of the opening cavity is subjected to unquantized processing, and the cavity depth d satisfies 2. ≤d<4 ;

[0015] The flow length l of the opening cavity is determined based on the cavity depth d, and the length-to-depth ratio l / d of the opening cavity is less than 10.

[0016] Preferably, the length-to-depth ratio l / d of the opening cavity satisfies 5 < l / d ≤ 8.

[0017] Preferably, the flow distance W from the starting position of the opening cavity to the leading edge of the conical high-speed boundary layer satisfies... / 2<W<2 / 3.

[0018] Preferred options also include:

[0019] Wind tunnel experiments were conducted on a concave cone-shaped high-speed boundary layer and a corresponding non-concave cone-shaped high-speed boundary layer to obtain power spectral density maps.

[0020] Based on the power spectral density maps of the concave cone-shaped high-speed boundary layer and the non-concave cone-shaped high-speed boundary layer, the peak power spectral density corresponding to the second mode is determined respectively.

[0021] Preferably, the synchronization point of the conical high-speed boundary layer is determined according to the designed flow conditions. ,include:

[0022] Determine the basic flow field of the boundary layer based on the design flow conditions;

[0023] Based on linear stability theory and The method calculates the synchronization point of the conical high-speed boundary layer. .

[0024] Preferred options also include:

[0025] Numerical simulations or wind tunnel experiments were conducted on the concave conical high-speed boundary layer to determine the synchronization point of the concave conical high-speed boundary layer. ;

[0026] By adjusting the size and initial position parameters of the opening cavity, numerical simulation or wind tunnel experiments are conducted on the new concave conical high-speed boundary layer to determine the corresponding synchronization point. until No further increase, at the aforementioned synchronization point As a new synchronization point .

[0027] Preferably, the adjustment of the size and starting position parameters of the opening cavity includes:

[0028] Keeping the starting position and length-to-depth ratio l / d of the opening cavity constant, the cavity depth d of the opening cavity is adjusted.

[0029] Alternatively, the cavity depth d and length-to-depth ratio l / d of the opening cavity can be kept constant, while adjusting the starting position of the opening cavity.

[0030] A structure for suppressing high-speed boundary layer second-mode waves to delay transition, manufactured using the method for suppressing high-speed boundary layer second-mode waves to delay transition as described in any of the preceding claims, includes an open cavity disposed on the outer periphery of an inner cone in a combustion chamber, the open cavity being located at the leading edge and synchronizing point of the inner cone. between.

[0031] Preferably, the opening cavity is located at the radial joint of the inner cone.

[0032] The method for suppressing the second mode wave of a high-speed boundary layer and delaying transition provided by this invention is applicable at the leading edge and synchronization point of a conical high-speed boundary layer. An open cavity is provided between the two sides. The large-sized open cavity suppresses the growth of the second mode wave, thereby suppressing the transition of the high-speed boundary layer, which is conducive to realizing the laminarization design of the conical high-speed boundary layer.

[0033] Furthermore, the present invention also provides a structure for suppressing high-speed boundary layer second-mode waves and delaying transition by applying the above-described method for suppressing high-speed boundary layer second-mode waves, which effectively reduces the surface aerodynamic heat generated by the incoming flow. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0035] Figure 1 A schematic diagram of the structure of the concave cone-shaped high-speed boundary layer model constructed by the method of delaying transition to suppress the second mode wave of the high-speed boundary layer provided by the present invention;

[0036] Figure 2 for Figure 1 A schematic diagram of the concave cone-shaped high-speed boundary layer model;

[0037] Figure 3 The power spectral density diagram of a cone-shaped high-speed boundary layer model without cavities;

[0038] Figure 4 The power spectral density diagram of the concave cone-shaped high-speed boundary layer model;

[0039] Figure 5 The surface temperature rise distribution of a cone-shaped high-speed boundary layer model without cavities is shown in the diagram.

[0040] Figure 6 This is a surface temperature rise distribution diagram for a concave cone-shaped high-speed boundary layer model.

[0041] Figures 1-6 middle:

[0042] 1-Leading edge; 2-Opening cavity; 3-Left edge. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] The core of this invention is to provide a method for suppressing the second mode wave of a high-speed boundary layer to delay transition. This method utilizes a large-sized open cavity to suppress the growth of the second mode wave, thereby suppressing the transition of the high-speed boundary layer.

[0045] Furthermore, the present invention also provides a structure for suppressing high-speed boundary layer second-mode waves and delaying transition by applying the above-described method for suppressing high-speed boundary layer second-mode waves.

[0046] The method for suppressing high-speed boundary layer second-mode waves to delay transition provided by the present invention includes:

[0047] Step S1: Determine the synchronization point of the conical high-speed boundary layer based on the design inflow conditions. ;

[0048] Step S2, at the leading edge 1 and synchronization point of the conical high-speed boundary layer An open cavity 2 is provided between them.

[0049] It should be noted that step S1 involves designing the incoming flow conditions, including the incoming flow Mach number. , incoming Reynolds number half-angle of a cone Wall temperature ratio Surface roughness And the free-flow perturbation degree Tu, and the synchronization point This refers to the flow direction where the phase velocities of fast and slow sound waves are the same in high-speed boundary layer flow.

[0050] Among them, the incoming Mach number Flow Reynolds number The cone half-angle is determined based on the design flight conditions of the hypersonic vehicle. The core geometric parameters of a hypersonic vehicle are determined based on its aerodynamic performance requirements; wall temperature ratio. The surface roughness is determined based on the design flight conditions and thermal protection system requirements of the hypersonic vehicle; The free-flow disturbance degree Tu is determined based on the aerodynamic performance requirements and actual manufacturing capabilities of the hypersonic vehicle; the free-flow disturbance degree Tu is determined by the incoming flow environment. During wind tunnel experiments, the free-flow disturbance degree Tu is determined based on the design and operating conditions of the wind tunnel itself. During numerical simulation, the free-flow disturbance degree Tu is determined based on the numerical simulation method used, which will not be elaborated here.

[0051] Preferably, in order to save research costs, step S1 can be set to include,

[0052] Step S11: Determine the basic flow field of the boundary layer based on the designed inflow conditions;

[0053] Step S12, based on linear stability theory and Method for calculating the synchronization point of a conical high-speed boundary layer .

[0054] It should be noted that in order to suppress the growth of the second mode wave and suppress the transition from laminar to turbulent flow, at the leading edge 1 and synchronization point of the conical high-speed boundary layer... An open cavity 2 is provided between them, such as Figure 1 and Figure 2 As shown, the open cavity 2 is used to suppress the growth of the second mode wave and suppress the laminar transition process.

[0055] The flow length l of the open cavity 2 is much greater than its cavity depth d, and the sidewall effect can be ignored. The cavity depth d and flow length l of the open cavity 2 can determine the cavity flow mode through the length-to-depth ratio l / d, and then affect the laminar-turbulent transition of the high-speed boundary layer through shear layer evolution, shock wave-expansion wave system and acoustic feedback resonance.

[0056] The dimensional parameters such as the cavity depth d and the flow direction length l, as well as the initial position parameters of the open cavity 2, can be obtained through wind tunnel experiments and / or numerical simulation experiments in order to determine the optimal dimensions and initial position parameters of the open cavity 2 under the designed inflow conditions.

[0057] Preferably, considering the actual development process of disturbances in the conical high-speed boundary layer flow, the flow direction distance W from the starting position of the opening cavity 2 to the leading edge 1 of the conical boundary layer can be set to satisfy... / 2<W<2 / 3, so that the open cavity 2 can effectively suppress the development of the second mode wave and suppress the laminar transition process.

[0058] In this embodiment, at the leading edge 1 and synchronization point of the conical high-speed boundary layer An open cavity 2 is provided between them. The large-sized open cavity 2 is used to suppress the growth of the second mode wave, thereby suppressing the transition of the high-speed boundary layer.

[0059] Considering that the characteristic length L of the boundary layer varies for different hypersonic vehicles, in order to eliminate the influence of absolute size, the full-size vehicle is mapped by a scaled-down model using flow similarity. The size and initial position parameters of the opening cavity 2 need to be dimensionless.

[0060] Preferably, step S2 can be configured to include:

[0061] Step S21: Determine the boundary layer thickness at the starting position of the opening cavity 2. ;

[0062] Step S22, utilizing the boundary layer thickness at the initial position of the opening cavity 2 The cavity depth d of the open cavity 2 is dimensionless, and the cavity depth d satisfies 2 ≤d<4 ;

[0063] Step S23: Determine the flow length l of the open cavity 2 based on the cavity depth d of the open cavity 2. The length-to-depth ratio l / d of the open cavity 2 is less than 10.

[0064] It should be noted that, since the boundary layer flow state is the same in the concave conical high-speed boundary layer model and the corresponding non-concave high-speed conical boundary layer model before the initial position of the open concave cavity 2, the boundary layer thickness at the initial position of the open concave cavity 2 is... This is equal to the boundary layer thickness at the corresponding flow direction position of the high-speed conical boundary layer with a cavity-free design. The thickness of the high-speed conical boundary layer without cavities The design flow conditions and flow direction can be determined through calculation, numerical simulation, or wind tunnel testing.

[0065] It is necessary to explain steps S22 and S23 that the cavity depth d and the flow direction length l belong to the characteristic length of the open cavity 2. Therefore, the complex flow of the conical high-speed boundary layer is simplified by dimensionless processing, so as to determine the characteristic length range that can obtain the best suppression effect on the development of the second mode wave by controlling the characteristic length of the open cavity 2. For example, 2 ≤d<4 , l / d < 10.

[0066] Preferably, since the second mode wave becomes the most unstable perturbation in the high-speed boundary layer, the incoming Mach number... The length-to-depth ratio l / d of the main opening cavity 2 can be set to satisfy 5 < l / d ≤ 8.

[0067] Based on the above embodiments, in order to facilitate determining whether the size and initial position parameters of the opening cavity 2 effectively suppress the development of the second mode wave, the high-speed boundary layer second mode wave transition suppression method further includes:

[0068] Step S3: Conduct wind tunnel experiments on the concave cone-shaped high-speed boundary layer and the corresponding non-concave cone-shaped high-speed boundary layer to obtain the power spectral density map;

[0069] Step S4: Based on the power spectral density maps of the concave cone high-speed boundary layer and the non-concave cone high-speed boundary layer, determine the peak power spectral density corresponding to the second mode.

[0070] It is important to explain step S3. In the wind tunnel experiment, pressure sensors are used to acquire pressure pulsation signals of the concave cone-shaped high-speed boundary layer and the corresponding non-concave cone-shaped high-speed boundary layer, and data processing and plotting are performed accordingly. Figure 3 The power spectral density diagram shown.

[0071] For example, in a specific embodiment, the incoming Mach number =6, incoming Reynolds number =1.05×10 7The total length L of the model is 500mm, the flow distance W from the starting position of the opening cavity 2 to the leading edge 1 is 200mm, and the cavity depth d is 2. =2.5mm, length-to-depth ratio l / d=8. Its corresponding power spectral density diagram is as follows: Figure 3 and Figure 4 As shown, where Figure 3 The power spectral density plot is for a cone-shaped high-speed boundary layer model without cavities. Figure 4 The figure shows the power spectral density of a concave conical high-speed boundary layer, with x representing the flow direction coordinate.

[0072] Figure 3 Within the conical high-speed boundary layer, there exists a high-frequency second-mode wave with a dominant frequency of 220-280 kHz, and the dominant frequency of the second-mode wave shifts along the flow direction and towards lower frequencies. At the x=380 mm position, the amplitude of the second-mode wave reaches its maximum value, and then gradually decreases until it disappears at the x=440 mm position, at which point the second-mode wave disappears, and the laminar flow of the boundary layer breaks up, generating turbulence.

[0073] Figure 4 In the concave conical high-speed boundary layer, the second mode wave is suppressed along the flow direction, while the dominant frequency of the second mode wave moves along the flow direction and towards the lower frequency direction until the high-speed boundary layer is still in a laminar state at the position of x=460mm.

[0074] contrast Figure 3 and Figure 4 It can be seen that, at the same flow direction, the amplitude of the second mode wave corresponding to the concave-conical high-speed boundary layer is always smaller than that of the conical high-speed boundary layer. This fully demonstrates that the large-sized open concave cavity 2 can suppress the growth of the second mode wave, thereby suppressing the transition of the high-speed boundary layer.

[0075] Besides the power spectral density plot, it can also be obtained through methods such as Figure 5 and Figure 6 The surface temperature rise distribution diagram shown determines whether the size and initial position parameter settings of the opening cavity 2 effectively suppress the development of the second mode wave. Figure 5 This is a surface temperature rise distribution diagram for a cone-shaped high-speed boundary layer model without cavities. Figure 6 This is a surface temperature rise distribution diagram for a concave cone-shaped high-speed boundary layer model.

[0076] Figure 6 The white, high-temperature zone only appears at the tail end of the model near the trailing edge 3, compared to... Figure 5 The white, high-temperature rising region appears at x=440mm. This region extends downstream along the flow direction, indicating that the transition of the high-velocity boundary layer is suppressed, and the synchronization point of the transition is... Move downstream in the model.

[0077] Based on the above embodiments, in order to obtain the optimal solution for the size and initial position parameters of the opening cavity 2, the following further steps are included:

[0078] Step S51: Perform numerical simulation or wind tunnel experiments on the concave conical high-speed boundary layer to determine the synchronization point of the concave conical high-speed boundary layer. ;

[0079] Step S52: Adjust the size and initial position parameters of the opening cavity 2, and conduct numerical simulation or wind tunnel experiments on the new concave cone-shaped high-speed boundary layer to determine the corresponding synchronization point. until No further increase, at the aforementioned synchronization point As a new synchronization point .

[0080] Steps S51 and S52 are used to synchronize the points mentioned in step S1. The flow direction coordinates are iterated to more accurately determine the starting position of the opening cavity 2; it should be noted that in steps S51 and S52, the synchronization point is determined. and synchronization point The flow direction and position must be the same to avoid errors introduced by differences in the method of determining the synchronization point, which would affect the determination of the optimal solution for the size and starting position of the opening cavity 2.

[0081] Considering the high cost of wind tunnel experiments, numerical simulation can be used to determine the synchronization point where the flow direction is no longer delayed. After determining the flow direction and location, further experimental verification will be conducted through wind tunnel experiments.

[0082] It should be noted that in step S52, the length-to-depth ratio of the opening cavity 2 to l / d is affected by the Mach number of the incoming flow. Impact, incoming Mach number Furthermore, the design flow conditions determine the range of values ​​for the length-to-depth ratio l / d of the opening cavity 2. Therefore, adjusting the size and initial position parameters of the opening cavity 2 mainly involves controlling the cavity depth d and the flow direction distance W from the initial position to the leading edge 1 of the conical boundary layer.

[0083] Preferably, step S52, adjusting the size and initial position parameters of the opening cavity 2, includes:

[0084] Keep the starting position and length-to-depth ratio l / d of the opening cavity 2 constant, and adjust the cavity depth d of the opening cavity 2.

[0085] Alternatively, the cavity depth d and length-to-depth ratio l / d of the opening cavity 2 can be kept constant, and the starting position of the opening cavity 2 can be adjusted.

[0086] In addition to the above-described method for suppressing the second mode wave of the high-speed boundary layer to delay transition, the present invention also provides a structure for suppressing the second mode wave of the high-speed boundary layer to delay transition using the method disclosed in the above embodiments. This structure includes an open cavity 2 located on the outer periphery of the inner cone of the combustion chamber, with the open cavity 2 located at the leading edge and synchronizing point of the inner cone. between.

[0087] An annular flow channel is provided between the inner cone of the combustion chamber and the outer shell of the combustion chamber. The flow within the annular flow channel can be regarded as a conical high-speed boundary layer. Therefore, by providing an open cavity 2 on the surface of the inner cone, the development of the second mode wave in the high-speed boundary layer can be suppressed, thereby suppressing and delaying the transition of the high-speed boundary layer, reducing flow losses, and reducing the aerodynamic heat on the surface of the inner cone, which is beneficial to improving the service life of the inner cone.

[0088] To ensure the strength of the inner cone and reduce the impact of the opening cavity 2 on its structural strength, preferably, the opening cavity 2 can be set at the radial joint of the inner cone. By utilizing the radial joint of the inner cone to arrange the opening cavity 2, the existing structure of the inner cone is utilized, which is beneficial to reduce processing costs and also reduces the impact on the strength of the inner cone itself.

[0089] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0090] The method and structure for suppressing high-speed boundary layer second-mode waves and delaying transition provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for suppressing high-speed boundary layer second-mode waves to delay transition, characterized in that, include: Determine the synchronization point of the conical high-speed boundary layer based on the design flow conditions. ; At the leading edge (1) of the conical high-speed boundary layer and the synchronization point An open cavity is provided between them (2); The leading edge (1) and synchronization point of the conical high-speed boundary layer An opening cavity (2) is provided between them, including, Determine the boundary layer thickness at the starting position of the opening cavity (2). ; The boundary layer thickness at the starting position of the opening cavity (2) The cavity depth d of the opening cavity (2) is subjected to dimensionless processing in order to simplify the flow of the conical high-speed boundary layer and control the characteristic length of the opening cavity (2) through dimensionless processing. The cavity depth d satisfies 2 ≤d<4 ; Based on the cavity depth d of the opening cavity (2), the flow length l of the opening cavity (2) is determined, and the length-to-depth ratio l / d of the opening cavity (2) is less than 10.

2. The method for suppressing the second mode wave of a high-speed boundary layer to delay transition according to claim 1, characterized in that, The length-to-depth ratio l / d of the open cavity (2) satisfies 5 < l / d ≤ 8.

3. The method for suppressing high-speed boundary layer second-mode waves to delay transition according to claim 1, characterized in that, The flow distance W from the starting position of the open cavity (2) to the leading edge (1) of the conical high-speed boundary layer satisfies / 2<W<2 / 3.

4. The method for suppressing high-speed boundary layer second-mode waves to delay transition according to any one of claims 1-3, characterized in that, Also includes: Wind tunnel experiments were conducted on a concave cone-shaped high-speed boundary layer and a corresponding non-concave cone-shaped high-speed boundary layer to obtain power spectral density maps. Based on the power spectral density maps of the concave cone-shaped high-speed boundary layer and the non-concave cone-shaped high-speed boundary layer, the peak power spectral density corresponding to the second mode is determined respectively.

5. The method for suppressing high-speed boundary layer second-mode waves to delay transition according to any one of claims 1-3, characterized in that, The synchronization point of the conical high-speed boundary layer is determined based on the designed flow conditions. ,include: Determine the basic flow field of the boundary layer based on the design flow conditions; Based on linear stability theory and The method calculates the synchronization point of the conical high-speed boundary layer. .

6. The method for suppressing high-speed boundary layer second-mode waves to delay transition according to any one of claims 1-3, characterized in that, Also includes: Numerical simulations or wind tunnel experiments were conducted on the concave conical high-speed boundary layer to determine the synchronization point of the concave conical high-speed boundary layer. ; Adjust the size and initial position parameters of the opening cavity (2), and conduct numerical simulation or wind tunnel experiments on the new concave cone high-speed boundary layer to determine the corresponding synchronization point. until No further increase, at the aforementioned synchronization point As a new synchronization point .

7. The method for suppressing high-speed boundary layer second-mode waves to delay transition according to claim 6, characterized in that, The adjustment of the size and starting position parameters of the opening cavity (2) includes: The starting position and length-to-depth ratio l / d of the opening cavity (2) are kept constant, and the cavity depth d of the opening cavity (2) is adjusted. Alternatively, the cavity depth d and length-to-depth ratio l / d of the opening cavity (2) can be kept constant, and the starting position of the opening cavity (2) can be adjusted.

8. A structure for suppressing high-speed boundary layer second-mode waves to delay transition, manufactured using the method for suppressing high-speed boundary layer second-mode waves to delay transition as described in any one of claims 1-7, characterized in that, The inner cone of the combustion chamber includes an open cavity (2) located on its outer periphery, with the open cavity (2) situated at the leading edge and synchronizing point of the inner cone. between.

9. The structure for suppressing high-speed boundary layer second-mode waves and delaying transition according to claim 8, characterized in that, The opening cavity (2) is located at the radial joint of the inner cone.

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