A hypersonic static wind tunnel nozzle outlet acoustic wave control method and wind tunnel

Abstract

The present invention discloses a method for controlling the sound wave at the nozzle outlet of a hypersonic static wind tunnel and a wind tunnel. The method comprises the following steps: obtaining a given outlet sound wave; propagating the outlet sound wave in reverse to the throat of the nozzle to obtain a first sound field at the nozzle throat; arranging a speaker array upstream of the nozzle, starting the speaker array and forming a second sound field at the nozzle throat; controlling the amplitude, frequency and phase of the sound wave emitted by each speaker in the speaker array, and when the first sound field is consistent with the second sound field, completing the matching of the sound wave parameters of the speaker array with the outlet sound wave. The present invention is applied to the technical field of hypersonic wind tunnels, and by matching the sound wave at the nozzle throat, the nozzle outlet sound wave can be controlled, and then the influence of the sound wave on the boundary layer transition can be evaluated based on the controllable nozzle outlet sound wave in the study of hypersonic boundary layer transition.

Description

Technical Field

[0001] The invention relates to the technical field of hypersonic wind tunnels, and in particular to a method for controlling acoustic waves at a hypersonic static wind tunnel nozzle outlet and a wind tunnel. Background Art

[0002] In the field of hypersonics, boundary layer transition has always been a key factor affecting the design of air-breathing hypersonic aircraft. After the boundary layer transitions from laminar flow to turbulent flow, the flow parameters change significantly, such as the friction resistance and heat flow in the turbulent state become 3 to 5 times that of the laminar state, which directly affects the aerodynamic design and aerodynamic thermal protection of the aircraft. However, researchers' understanding of hypersonic boundary layer transition is extremely limited, because there is a lot of noise in conventional wind tunnels for hypersonic aircraft experiments, which will cause the boundary layer to transition prematurely.

[0003] Wind tunnel noise can be divided into three parts: sound waves, vortex waves and entropy waves. Among them, sound waves dominate at high Mach numbers, so it is of great significance to study the effect of sound waves on boundary layer transition. Some scholars have placed a sound source in the supersonic region upstream of the test section to experimentally study the effect of sound waves on boundary layer transition. However, the sound source in the supersonic flow will generate leading edge shock waves, which will affect the flow field. In addition, the sound source needs to be placed below the flat plate of the test section, which is easy to block the flow channel. Specifically:

[0004] In the prior art, there is a solution to install a sound source on the leading edge of a test plate. This solution directly installs the sound source above the test plate at the transition of the boundary layer. The advantage is that it is easy to implement, and only a hole needs to be opened on the plate to place the speaker. However, the disadvantage is that the sound waves emitted by the speaker are directly injected into the bottom layer of the boundary layer, which can only affect the boundary layer in the Mach wave radiation area and cannot be injected upstream. In addition, the number of speakers in supersonic flow is limited, and it is easy to generate installation shock waves, which interfere with the flow field;

[0005] There is also a solution in the prior art to set an additional flat plate mounted sound source upstream of the test plate. In this solution, an additional flat plate mounted sound source is set upstream of the test plate, and the additional plate is located below the test plate. The advantage of this solution is that the sound waves emitted by properly arranged speakers can affect the downstream boundary layer, but the plate on which the speakers are installed will have an installation shock wave, and an overly large speaker will block the flow field. Summary of the invention

[0006] In view of the problem that the acoustic wave disturbance is difficult to control in the study of hypersonic boundary layer transition in the above-mentioned prior art, the present invention provides a method for controlling acoustic waves at the nozzle outlet of a hypersonic static wind tunnel and a wind tunnel, which achieves controllable acoustic waves at the nozzle outlet by matching acoustic waves at the nozzle throat, and then the influence of acoustic waves on boundary layer transition can be evaluated based on controllable nozzle outlet acoustic waves in the study of hypersonic boundary layer transition.

[0007] To achieve the above object, the present invention provides a method for controlling acoustic waves at a hypersonic static wind tunnel nozzle outlet, comprising the following steps:

[0008] Get the given exit sound wave;

[0009] The exit sound wave is propagated in the reverse direction to the throat of the nozzle to obtain the first sound field at the throat of the nozzle;

[0010] Arranging a speaker array upstream of the nozzle, starting the speaker array and forming a second sound field at the nozzle throat;

[0011] The amplitude, frequency and phase of the sound waves emitted by each speaker in the speaker array are controlled. When the first sound field is consistent with the second sound field, the sound wave parameters of the speaker array are matched with the outlet sound waves.

[0012] In one embodiment, the outlet sound wave is propagated in reverse to the throat of the nozzle to obtain the first sound field at the throat of the nozzle, specifically:

[0013] The linearized Euler equation is used as the control equation, and the time variable t in the control equation is changed to -t. At the same time, the outlet sound wave is used as the boundary condition to obtain the first sound field.

[0014] In one embodiment, the outlet sound wave exhibits one-dimensional, two-dimensional or three-dimensional characteristics in terms of amplitude, frequency and phase in space.

[0015] In one embodiment, the speaker array is arranged upstream of the nozzle, specifically:

[0016] A loudspeaker array is arranged on the stabilizing section upstream of the nozzle at a position corresponding to between the honeycomb network and an outlet of the stabilizing section.

[0017] To achieve the above object, the present invention further provides a wind tunnel, wherein the wind tunnel adopts the above method to achieve controllable outlet sound waves.

[0018] In one embodiment, it comprises a stabilizing section and a nozzle section connected in sequence, wherein the nozzle section comprises a contraction section, a throat and an expansion section connected in sequence, and a speaker array is arranged on the stabilizing section;

[0019] The outlet of the stabilizing section is connected to the inlet of the contracting section, and the cross section of the stabilizing section is consistent with the cross section of the inlet of the contracting section.

[0020] In one embodiment, the cross-section of the stabilizing section is a rectangular structure to facilitate installation of a speaker array.

[0021] The present invention provides the following beneficial technical effects:

[0022] 1. The present invention places the speaker array in the stable section of the wind tunnel. On the one hand, the flow velocity in the stable section of the wind tunnel is relatively low, and no installation shock wave will be generated, which has little impact on the downstream flow field, and more speakers can be installed; on the other hand, the airflow in the stable section of the wind tunnel is relatively uniform, and many methods in aeroacoustics can be used to control the distribution of sound waves reaching the nozzle inlet;

[0023] 2. The present invention takes into account that the wind tunnel nozzle is a closed channel on all sides, and uses the linearized Euler equation to propagate the sound wave distribution at the nozzle outlet in the opposite direction to the throat of the nozzle rather than the nozzle inlet, thereby avoiding the problem that a part of the sound wave at the nozzle inlet will be reflected by the contraction section; 3. The present invention can control the amplitude, frequency and phase of the sound wave, which is conducive to studying the influence of the sound wave on the boundary layer transition. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0025] Figure 1 is a flow chart of a control method in an embodiment of the present invention;

[0026] Figure 2 It is a schematic structural diagram of a wind tunnel component in an embodiment of the present invention;

[0027] Figure 3 Schematic diagram of one-dimensional sound waves at the nozzle outlet in an embodiment of the present invention;

[0028] Figure 4 Schematic diagram of two-dimensional sound waves at the nozzle outlet in an embodiment of the present invention;

[0029] Figure 5 Schematic diagram of reverse propagation of sound waves at the nozzle outlet in an embodiment of the present invention;

[0030] Figure 6 It is a schematic diagram of the forward propagation of the speaker array matching the nozzle throat sound wave in the embodiment of the present invention;

[0031] Figure 7 Schematic diagram of the controllable sound wave at the nozzle outlet of a static wind tunnel in an embodiment of the present invention;

[0032] Figure 8 Schematic diagram of early transition of the boundary layer caused by a sound wave with a large amplitude in an embodiment of the present invention;

[0033] Fig. 9 Schematic diagram of boundary layer delay transition caused by sound waves with smaller amplitude in an embodiment of the present invention.

[0034] Figure numbers: incoming flow 1, stable section 2, nozzle section 3, contraction section 4, throat 5, expansion section 6, speaker array 7, sound waves emitted by the speaker 8, second direction 9, nozzle throat sound waves 10, first direction 11, outlet sound waves 12.

[0035] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. Based on the embodiments of 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.

[0037] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0038] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0039] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0041] In view of the fact that sound waves cannot be conveniently controlled in supersonic flow, the present embodiment discloses a method for controlling sound waves at the nozzle outlet of a hypersonic static wind tunnel. This method uses the outlet sound wave distribution as a boundary condition based on the inverse linearized Euler equation according to the required sound wave distribution at the nozzle outlet, and propagates the sound waves from the nozzle outlet back to the nozzle throat in reverse. Then, a speaker array is set in the nozzle stabilization section. By controlling the speaker array parameters, the corresponding sound wave distribution of the nozzle throat is matched, and finally the purpose of controlling the sound waves at the nozzle outlet is achieved.

[0042] refer to Figure 1 The hypersonic static wind tunnel nozzle outlet acoustic wave control method in this embodiment specifically includes the following steps:

[0043] Get the given exit sound wave;

[0044] The exit sound wave is propagated in the reverse direction to the throat of the nozzle to obtain the first sound field at the throat of the nozzle;

[0045] Arranging a speaker array upstream of the nozzle, starting the speaker array and forming a second sound field at the nozzle throat;

[0046] The amplitude, frequency and phase of the sound waves emitted by each speaker in the speaker array are controlled. When the first sound field is consistent with the second sound field, the sound wave parameters of the speaker array are matched with the outlet sound waves.

[0047] In this embodiment, an air-breathing supersonic static wind tunnel is used as the object. Figure 2 The wind tunnel includes a stable section 2, a nozzle section 3 and other components, wherein the nozzle section 3 includes a contraction section 4, a throat 5 and an expansion section 6, and the nozzle section 3 is in a binary form. The cross section of the stable section 2 of the wind tunnel is consistent with the inlet of the nozzle section 3, both of which are rectangular. A certain length is reserved between the honeycomb network and the outlet of the stable section 2 for the subsequent installation of the speaker array.

[0048] Based on the given outlet sound wave 12, the amplitude, frequency and phase of the outlet sound wave 12 in space can present one-dimensional characteristics, two-dimensional characteristics or three-dimensional characteristics. Figure 3 As shown, the parameters of the outlet sound wave 12 are consistent, and the sound wave is equivalent to a plane wave; the two-dimensional characteristics are as follows Figure 4 As shown, the parameters of the outlet sound wave 12 are different in one direction. The frequency and phase may be the same but the amplitude in a certain direction may change, or the amplitude and phase may be the same but the frequency in a certain direction may be different. In the three-dimensional case, the outlet sound wave 12 presents more complex characteristics, which is a routine operation in this field and will not be elaborated in detail.

[0049] The outlet sound wave 12 is propagated in the opposite direction to the throat 5 of the nozzle section 3 along the first direction 11 (i.e., the opposite direction of the incoming flow 1), and the nozzle throat sound wave 10, i.e., the first sound field, is obtained. The concept of sound wave reverse propagation is relatively common in aeroacoustics. For example, beamforming technology can infer the near-field sound source through the signal monitored by the far-field microphone. However, beamforming technology is only applicable to subsonic flow and cannot be used for supersonic flow in the nozzle expansion section 6. Figure 5 As shown, this embodiment adopts another reverse propagation method, namely, the linearized Euler equation, and uses the linearized Euler equation as the control equation. By changing the time variable t in the control equation to -t, and taking the nozzle outlet sound wave 12 as the boundary condition, the purpose of reverse propagation is finally achieved to obtain the first sound field. It should be noted that the premise of the reverse propagation of the linearized Euler equation is to meet the energy conservation condition, so this embodiment selects the end point of the reverse propagation as the throat 5 of the nozzle section 3, rather than the nozzle inlet. This is because a part of the sound wave at the nozzle inlet will be reflected by the contraction section, and only the unreflected part can pass through the throat 5 to reach the nozzle outlet, so the energy of the sound wave between the nozzle throat 5 and the expansion section 6 is conserved.

[0050] In the specific implementation process, the linearized Euler equation is used as the control equation, and the time variable t in the control equation is changed to -t, and the nozzle outlet sound wave 12 is used as the boundary condition, and the specific implementation method of the first sound field is obtained as follows:

[0051] The following three formulas are common control equations of the linearized Euler equations, which are the continuity equation, momentum equation, and energy equation from top to bottom. By giving the sound source distribution at the nozzle outlet as the boundary, the original change mode of the time term t in the control equation is changed from t=t+dt (dt>0) to t=t-dt, so that the defined sound source boundary can propagate in the reverse direction.

[0052]

[0053]

[0054]

[0055] In the formula, ρ represents density, u represents velocity, p represents pressure, t represents time, is the specific heat ratio, and the superscript ' indicates the disturbance.

[0056] The sound wave parameters of the speaker array 7 upstream of the nozzle section 3 are controlled so that the speaker emits a sound wave 8 along a second direction 9 (i.e., the direction of the incoming flow 1) to match the nozzle throat sound wave 10. Figure 6As shown, the speaker array 7 is arranged in the stable section 2 upstream of the nozzle, and the rectangular stable section 2 is convenient for installing the array. In addition, the air flow velocity in the stable section 2 is only tens of meters per second, and the installation effect of the speaker array 7 has little effect on the flow field. Through the beamforming technology of aerodynamic acoustics, the characteristics of the sound waves emitted by different speakers in the speaker array 7 are obtained, thereby quickly evaluating the amplitude, frequency and phase of the sound waves 8 emitted by different speakers in the speaker array 7 in the nozzle throat 5. When the generated second sound field is consistent with the first sound field propagating in the reverse direction of the linearized Euler equation, the purpose of matching the sound waves of the present invention is achieved. Beamforming technology is a common technology in this field and will not be described in detail.

[0057] like Figure 7 As shown, by matching the sound wave at the throat 5 of the nozzle section 3, the nozzle outlet sound wave can be controlled. Based on the controllable nozzle outlet sound wave, as shown in FIG. Figure 8-9 As shown, the effect of sound waves on the boundary layer transition can be evaluated. When a sound wave with a larger amplitude is generated, the sound wave has a greater impact on the downstream flat-plate boundary layer, causing the boundary layer to transition earlier and the boundary layer thickness to increase significantly; when a sound wave with a smaller amplitude is generated, the sound wave has a greater impact on the downstream flat-plate boundary layer, causing the boundary layer to transition later and the boundary layer thickness to be relatively thin.

[0058] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for controlling acoustic waves at the nozzle outlet of a hypersonic static wind tunnel, characterized in that: The steps include: Get the given exit sound wave; The exit sound wave is propagated in the reverse direction to the throat of the nozzle to obtain the first sound field at the throat of the nozzle; Arranging a speaker array upstream of the nozzle, starting the speaker array and forming a second sound field at the nozzle throat; The amplitude, frequency and phase of the sound waves emitted by each speaker in the speaker array are controlled. When the first sound field is consistent with the second sound field, the sound wave parameters of the speaker array are matched with the outlet sound waves.

2. The method for controlling the acoustic wave at the nozzle outlet of a hypersonic static wind tunnel according to claim 1, characterized in that: The outlet sound wave is propagated in the reverse direction to the throat of the nozzle to obtain the first sound field at the throat of the nozzle, which is specifically: The linearized Euler equation is used as the control equation, and the time variable t in the control equation is changed to -t. At the same time, the outlet sound wave is used as the boundary condition to obtain the first sound field.

3. The method for controlling the acoustic wave at the exit of a hypersonic static wind tunnel nozzle according to claim 1 or 2, characterized in that: The outlet sound wave presents one-dimensional, two-dimensional or three-dimensional characteristics in terms of amplitude, frequency and phase in space.

4. The hypersonic static wind tunnel nozzle outlet acoustic wave control method according to claim 1 or 2, characterized in that: The speaker array is arranged upstream of the nozzle, specifically: A loudspeaker array is arranged on the stabilizing section upstream of the nozzle at a position corresponding to between the honeycomb network and an outlet of the stabilizing section.

5. A wind tunnel, characterized in that: The wind tunnel adopts the method described in any one of claims 1 to 4 to achieve controllable outlet sound waves.

6. The wind tunnel according to claim 5, characterized in that: It comprises a stabilizing section and a nozzle section connected in sequence, wherein the nozzle section comprises a contraction section, a throat and an expansion section connected in sequence, and a speaker array is arranged on the stabilizing section; The outlet of the stabilizing section is connected to the inlet of the contracting section, and the cross section of the stabilizing section is consistent with the cross section of the inlet of the contracting section.

7. The wind tunnel according to claim 6, characterized in that: The cross section of the stabilizing section is a rectangular structure, so as to facilitate the installation of a speaker array.

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