Air-breathing high subsonic wind tunnel with adjustable acoustic section and design method

Abstract

The present application relates to the technical field of aerodynamic ground test, in particular to a kind of air-breathing high subsonic wind tunnel based on adjustable sound velocity section and design method, air-breathing high subsonic wind tunnel includes horn gas collection section, fairing section, first contraction section, test section, Laval nozzle, connecting pipe and vacuum drive system. Vacuum drive is used to provide the pressure ratio required for wind tunnel start, to meet the wind speed test in the range of Mach number 0.4~0.8, solve the problem of high power demand of high subsonic wind tunnel, through the Laval nozzle arranged between test section and vacuum drive system, eliminate the influence of downstream disturbance on upstream, reduce the turbulence of wind tunnel, ensure the reliable, stable performance of medium / high subsonic wind tunnel test, and significantly reduce the test cost.

Description

Technical Field

[0001] This invention relates to the field of aerodynamic ground testing technology, and in particular to an air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section and its design method. Background Technology

[0002] Subsonic wind tunnels typically refer to wind tunnels where the Mach number (Ma, airflow velocity / local sound speed) in the test section is less than 0.8. They are key testing facilities for studying the aerodynamic characteristics of buildings, transportation vehicles, and subsonic aircraft. The performance of the wind tunnel's drive system directly determines its overall testing capability. Currently, mainstream wind tunnel drive systems use high-power motors to drive axial flow fans, with test section speeds generally not exceeding Ma 0.3. Typical structures include recirculating and direct-flow types.

[0003] The test speed requirements for buildings and ground transportation vehicles are all in the low subsonic range of Ma no greater than 0.3. With the high-speed rail speed level gradually moving towards 450km / h, the rollout of the 600km / h maglev train prototype, and the market demand for low-altitude aircraft stimulated by the low-altitude economy, there is an urgent need for medium to high subsonic ground test systems with Ma>0.4.

[0004] However, using a fan-driven system to achieve medium to high subsonic speeds (Ma>0.4), especially when Ma approaches 0.8, faces a series of technical limitations, restricting not only experimental efficiency but also economic viability and applicability. For example, based on the wind speed in the test section, the power required by the fan-driven system is enormous, and its efficiency decreases as the Mach number increases. The nonlinear increase in power demand stems primarily from two aspects: first, to increase the Mach number, a massive volume of air needs to be driven; second, the components in the wind tunnel loop (such as diffusers and corner deflectors) cause significant total pressure losses, which must be compensated for by the energy provided by the fan-driven system. Furthermore, when the wind tunnel operates at Mach number close to 0.8, the fan blades exhibit significant compressibility effects and shock wave problems, leading to further performance degradation of the fan-driven system. For instance, in the subsonic high-speed region, the superposition of the fan blade rotational speed and the incoming flow velocity may cause the relative Mach number in local areas of the fan blades to exceed 1, generating local shock waves. The occurrence of shock waves can cause shock wave drag, flow separation, and a sharp drop in efficiency. While improving fan blade design can delay the critical Mach number, it cannot fundamentally eliminate this physical limitation. This becomes an insurmountable aerodynamic barrier for fan-driven systems approaching the speed of sound.

[0005] Therefore, in the medium to high subsonic speed range (Ma=0.4~0.8), traditional fan drive systems face severe challenges in terms of performance, cost and feasibility, and different technical approaches need to be considered.

[0006] In the field of hypersonic wind tunnels, high-pressure drive and vacuum drive are commonly used to achieve high-speed airflow in the test section. High-pressure drive uses high-pressure air in a storage tank as the energy and gas source. The high-pressure air is released upstream of the wind tunnel, and the subsonic airflow is accelerated to supersonic speeds using a Laval nozzle with a contraction-expansion profile. Vacuum drive, on the other hand, creates low pressure downstream of the wind tunnel, and similarly uses a Laval nozzle to accelerate the subsonic airflow to supersonic speeds. These two methods can also be combined, i.e., simultaneously performing high-pressure blowing upstream and vacuum suction downstream. Currently, high-pressure drive and vacuum drive are only used in the field of supersonic wind tunnels; no publicly disclosed technology using these principles for subsonic wind tunnels has been found. Therefore, wind tunnel technology in the Mach number range of 0.4 to 0.8 remains undeveloped. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of the aforementioned background technology by providing a vacuum-driven subsonic wind tunnel to meet the requirements of wind tunnel tests in the Mach number range of 0.4 to 0.8, solving the problem of high electrical power requirements for high subsonic wind tunnels, while also reducing wind tunnel turbulence and further improving test reliability.

[0008] To achieve the above objectives, the present invention provides an air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section, comprising a horn-shaped air collection section, a rectification section, a first contraction section, a test section, a Laval nozzle, a connecting pipe, and a vacuum drive system. The horn-shaped air collection section is located at the first end of the air-inhaling high subsonic wind tunnel and is connected to the atmospheric environment. The horn-shaped air collection section serves as a stationary airflow inlet. The rectifying section is located between the horn-shaped air collection section and the first contraction section, and is used to reduce the turbulence of the wind tunnel and ensure uniform airflow. The first end of the first contraction section is connected to the horn-shaped air collection section, and the size of the first end of the first contraction section gradually decreases towards the second end, so that the air is gradually accelerated to the target speed. The first end of the test section is connected to the second end of the first contraction section. The test section is used to make the air reach a stable target speed. The test section is equipped with a test model to conduct medium subsonic environment tests or high subsonic environment tests. The first end of the Laval nozzle is connected to the second end of the test section, and the second end of the Laval nozzle is connected to the vacuum drive system through the connecting pipe. The Laval nozzle includes a gradually decreasing nozzle contraction section, a gradually increasing nozzle expansion section, and a throat between the nozzle contraction section and the nozzle expansion section. The nozzle contraction section is located near the first end of the Laval nozzle, and the nozzle expansion section is located near the second end of the Laval nozzle. The vacuum drive system includes a vacuum tank and a vacuum pump. The vacuum tank uses the vacuum pump to generate a vacuum to draw air from the wind tunnel.

[0009] Furthermore, the throat of the Laval nozzle is available in various sizes.

[0010] Furthermore, the Laval nozzle includes a first fixed portion, a replaceable portion, and a second fixed portion. The first fixed portion is a part of the nozzle converging section, the second fixed portion is a part of the nozzle expanding section, and the replaceable portion is composed of a part of the nozzle converging section, the throat, and a part of the nozzle expanding section. The first fixed portion and the second fixed portion are both fixedly installed, and the replaceable portion has various throat sizes and is replaceable.

[0011] Furthermore, the throat of the replaceable part is configured as a detachable structure, allowing throats of different sizes to be connected to the air-breathing high subsonic wind tunnel through disassembly and assembly.

[0012] Furthermore, the Laval nozzle can be configured with an adjustable throat profile to directly adjust the throat size.

[0013] Furthermore, the test section is also equipped with an observation window, which is used to observe the internal condition of the test section and for non-contact measurement.

[0014] This invention also provides a design method for an air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section, used to design the aforementioned air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section, comprising the following steps: S1. Determine the target Mach number and test section size to be achieved in the wind tunnel, and use the vacuum tank for vacuum drive. Adopt the air intake principle and establish the core airflow path as the first contraction section → test section → Laval nozzle → connecting pipe → vacuum tank. S2. Based on the target Mach number, the cross-sectional area of ​​the test section, and the airflow parameters, the throat area of ​​the Laval nozzle is deduced using the continuity equation and the isentropic relationship. The airflow through the wind tunnel is locked. The nozzle contraction section ensures that the airflow can be smoothly accelerated and reach the speed of sound at the throat, forming a congested aerodynamic barrier. The exit area of ​​the nozzle expansion section determines the degree of airflow expansion. The design goal is to ensure that the disturbance behind the nozzle will not propagate forward and interfere with the upstream subsonic section. S3, Based on the volume of the vacuum tank, the stable operating time of the wind tunnel depends on the process of the pressure inside the vacuum tank rising from the lowest stable back pressure to the critical choking back pressure; based on the required effective operating time and the locked mass flow rate, the minimum total volume of the vacuum tank can be deduced. S4 uses numerical simulation to simulate the wind tunnel and observe the flow field quality throughout the entire cycle of startup, choke establishment, and pressure recovery in the vacuum tank.

[0015] The above-described solution of the present invention has the following beneficial effects: The present invention provides an air-breathing high subsonic wind tunnel and its design method based on an adjustable sound velocity cross section. Unlike traditional continuous wind tunnels that use fans / compressors as power sources, this invention uses a vacuum drive system as a power source to construct an air-breathing working mode. Addressing the core pain point of vacuum-driven air-breathing wind tunnels—the continuous change in power source pressure during the test, which disrupts the flow field stability of the test section—this invention features an innovative design. Utilizing the physical nature of disturbance propagation direction in supersonic flow, namely that disturbance waves can never flow upstream and their impact is strictly limited to the downstream region, a supersonic isolation zone is actively created by using a Laval nozzle arranged between the test section and the vacuum drive system. This completely eliminates the impact of downstream disturbances on the upstream, thus all downstream disturbances are absolutely isolated downstream of the throat of the Laval nozzle, completely unable to reach the upstream test section. This ensures the reliable and stable conduct of medium / high subsonic wind tunnel tests and significantly reduces test costs. Other beneficial effects of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall setup of the present invention; Figure 2 This is a schematic diagram of the numerical simulation grid in an embodiment of the present invention; Figure 3 This is a schematic diagram of the Mach number distribution and measuring points in the flow field of the present invention, wherein the upper part is the Mach number and the lower part is the numerical schlieren. Figure 4 This is a graph showing the airflow velocity curve at the measuring point of the subsonic test section of the present invention. Detailed Implementation

[0017] The following specific examples illustrate the implementation of this disclosure. Those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0018] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0019] It should also be noted that the illustrations provided in the following embodiments are merely schematic representations of the basic concept of this disclosure. The illustrations only show components relevant to this disclosure and are not drawn according to the actual number, shape, and size of components in implementation. In actual implementation, the type, quantity, and proportion of each component can be arbitrarily changed, and the component layout may be more complex. Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0020] like Figure 1 As shown, embodiments of the present invention provide an air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section. It is driven by a vacuum drive system, using air intake to meet the testing requirements of medium / high subsonic environments in the test section. To address the impact of pressure changes in the vacuum drive system on the upstream subsonic airflow, a detachable Laval nozzle is installed between the upstream test section and the vacuum drive system. Different speed levels in the upstream test section can be achieved by replacing the Laval nozzle or adjusting the throat size.

[0021] Specifically, the air-breathing high subsonic wind tunnel provided in this embodiment mainly includes: a horn-shaped air intake section, which is located at the first end of the entire wind tunnel and is directly connected to the atmospheric environment, serving as a stationary airflow inlet; a rectifying section, located between the horn-shaped air intake section and the first contraction section, used to reduce the turbulence of the wind tunnel and ensure uniform airflow; a first contraction section, the first end of which is connected to the horn-shaped air intake section, and the size of the first end of the first contraction section gradually decreases towards the second end, so that the air gradually accelerates to the target speed through the contraction pipe; a test section, the first end of which is connected to the second end of the first contraction section, where air can reach a stable target speed after entering the test section from the first contraction section, and the test model is placed in the test section for medium subsonic environment tests or high subsonic environment tests; and a Laval nozzle, the first end of which is connected to the second end of the test section, and the second end of the Laval nozzle is connected to the vacuum drive system through a connecting pipe.

[0022] It's important to note that a Laval nozzle is a type of pipe capable of generating supersonic airflow, primarily consisting of a converging and then expanding section. When subsonic airflow enters the Laval nozzle, it is first accelerated in the gradually narrowing converging section. As the airflow reaches the throat, its velocity is precisely accelerated to the speed of sound. Once this speed is reached, the flow enters a "congested" state, and the airflow behaves in the opposite way to its subsonic state; the larger the cross-section, the faster the velocity. Therefore, after passing the throat, the airflow is further accelerated in the gradually expanding expanding section of the nozzle, ultimately becoming supersonic airflow.

[0023] In this embodiment, the nozzle contraction section is located near the first end of the Laval nozzle and connects to the second end of the test section; the nozzle expansion section is located near the second end of the Laval nozzle and connects to the first end of the connecting pipe, which in turn connects to the vacuum drive system. The vacuum drive system can employ a vacuum pump and / or a vacuum tank to provide sufficient suction energy to allow air to flow throughout the wind tunnel. For a high-subsonic wind tunnel with air intake, the vacuum pump and vacuum tank are installed simultaneously. The vacuum pump first evacuates the large-capacity vacuum tank to near-vacuum. During the test, the valve is opened, and the low pressure inside the vacuum tank instantly draws air from the wind tunnel. It should be noted that the biggest problem with conventional air intake vacuum drive systems is that the pressure inside the vacuum tank will rise, leading to unstable air pressure. However, in this embodiment, as long as the pressure in the test section reaches a critical value and establishes congestion, the pressure changes in the vacuum drive system will hardly affect the flow rate and velocity of the test section, ensuring stable test airflow. That is, the pressure rise in the vacuum tank is completely isolated by the "one-way aerodynamic barrier" of the Laval nozzle. Therefore, the entire air-breathing high subsonic wind tunnel does not require any other moving parts, greatly simplifying the overall structure.

[0024] In this embodiment, based on the adjustable sound velocity cross-section, the Laval nozzle includes a first fixed part, a replaceable part, and a second fixed part. The first fixed part is a portion of the nozzle's contraction section, the second fixed part is a portion of the nozzle's expansion section, and the replaceable part consists of a portion of the nozzle's contraction section, a throat, and a portion of the nozzle's expansion section. Both the first and second fixed parts are fixedly installed, while the replaceable part can be fitted with various throat sizes to change the flow rate, thereby altering the airflow velocity in the test section and allowing for testing of the test model under different operating conditions.

[0025] In another embodiment, the throat size can be directly adjusted by designing the Laval nozzle as an adjustable profile, thereby achieving stepless adjustment of the Mach number.

[0026] As a preferred embodiment, the side of the test section in this embodiment is also provided with an observation window. Through the observation window, the internal condition of the test section can be observed, the state of the test model can be confirmed, and relevant parameters can be measured. That is, non-contact measurement can be performed to conveniently, quickly and without stopping the machine from measuring various parameters.

[0027] The following numerical simulation further verifies the air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section provided in this embodiment. A high-quality structured mesh is input into STAR CCM+ for calculation, such as... Figure 2 As shown in the figure, the left inlet is the atmospheric pressure boundary, and the right outlet is the low-pressure vacuum boundary. URANS was used to calculate the flow field development to steady-state process. The vacuum-driven system initiates subsonic velocity through suction until the Laval nozzle expansion section enters supersonic velocity, after which the subsonic velocity in the test section remains stable. The Mach number distribution of the flow field and the positions of the upstream and downstream measuring points in the test section are shown in the figure. Figure 3 As shown, the velocity data at the measuring point is as follows: Figure 4 As shown, after the Laval nozzle supersonic operation officially starts, the subsonic section exhibits good airflow stability under the supersonic pressure stabilization effect in the nozzle expansion section.

[0028] Based on the same inventive concept, this embodiment also provides a design method for an air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section, including the following steps: S1. Determine the target Mach number and test section size to be achieved in the wind tunnel, and use this to determine the selection of a vacuum tank for vacuum drive. Adopt the air intake principle and establish the core airflow path as the first contraction section → test section → Laval nozzle → connecting pipe → vacuum tank.

[0029] S2, based on the target Mach number, the cross-sectional area of ​​the test section, and the airflow parameters, uses the continuity equation and isentropic relationship to deduce the throat area of ​​the Laval nozzle in order to lock the airflow through the wind tunnel. The nozzle contraction section ensures that the airflow can be smoothly accelerated and reach the speed of sound at the throat, forming a congested aerodynamic barrier. The exit area of ​​the nozzle expansion section determines the degree of airflow expansion. The design goal is to ensure that the pressure fluctuations in and behind the nozzle expansion section will not propagate forward and interfere with the upstream subsonic section.

[0030] The continuity equation is as follows:

[0031] The isentropic relationship is as follows:

[0032] In the continuity equation, subscripts 1 and 2 represent variables at different cross-sectional locations. , , These represent the density, airflow velocity, and cross-sectional area of ​​the given cross-section, respectively; the subscripts in the isentropic formula... Represents the total parameters. Specific heat ratio of gases This represents the Mach number of the airflow.

[0033] S3, based on the volume of the vacuum tank, the stable operating time of the wind tunnel depends on the process of the pressure inside the vacuum tank rising from the lowest stable back pressure to the critical congestion back pressure; based on the required effective operating time and the locked mass flow rate, the minimum total volume of the vacuum tank can be deduced. The core formula originates from the law of mass conservation: downstream pressure rise rate ~ inflow gas mass / vacuum tank volume.

[0034] S4 simulates the entire wind tunnel through numerical simulation, observing the flow field quality throughout the entire cycle of startup, clogging establishment, and pressure recovery in the vacuum tank.

[0035] The air-breathing high subsonic wind tunnel design method based on adjustable sound velocity cross section provided in this embodiment has the same inventive concept and beneficial effects as the aforementioned scheme, and will not be repeated here.

[0036] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0037] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A high subsonic wind tunnel with adjustable sound velocity cross section, characterized in that, It includes a horn-shaped gas collection section, a rectifier section, a first contraction section, a test section, a Laval nozzle, connecting pipes, and a vacuum drive system; The horn-shaped air collection section is located at the first end of the air-inhaling high subsonic wind tunnel and is connected to the atmospheric environment. The horn-shaped air collection section serves as a stationary airflow inlet. The rectifying section is located between the horn-shaped air collection section and the first contraction section, and is used to reduce the turbulence of the wind tunnel and ensure uniform airflow. The first end of the first contraction section is connected to the horn-shaped air collection section, and the size of the first end of the first contraction section gradually decreases towards the second end, so that the air is gradually accelerated to the target speed. The first end of the test section is connected to the second end of the first contraction section. The test section is used to make the air reach a stable target speed. The test section is equipped with a test model to conduct medium subsonic environment tests or high subsonic environment tests. The first end of the Laval nozzle is connected to the second end of the test section, and the second end of the Laval nozzle is connected to the vacuum drive system through the connecting pipe. The Laval nozzle includes a gradually decreasing nozzle contraction section, a gradually increasing nozzle expansion section, and a throat between the nozzle contraction section and the nozzle expansion section. The nozzle contraction section is located near the first end of the Laval nozzle, and the nozzle expansion section is located near the second end of the Laval nozzle. The vacuum drive system includes a vacuum tank and a vacuum pump. The vacuum tank uses the vacuum pump to generate a vacuum to draw air from the wind tunnel.

2. The air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section according to claim 1, characterized in that, The throat of the Laval nozzle is available in various sizes.

3. The air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section according to claim 2, characterized in that, The Laval nozzle includes a first fixed part, a replaceable part, and a second fixed part. The first fixed part is a portion of the nozzle's converging section, and the second fixed part is a portion of the nozzle's expanding section. The replaceable part consists of a portion of the nozzle's converging section, the throat, and a portion of the nozzle's expanding section. Both the first fixed part and the second fixed part are fixedly installed. The replaceable part has various throat sizes and is replaceable.

4. The air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section according to claim 3, characterized in that, The throat of the replaceable part is designed to be detachable, allowing throats of different sizes to be connected to the air-breathing high subsonic wind tunnel through disassembly and assembly.

5. The air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section according to claim 2, characterized in that, The Laval nozzle is equipped with an adjustable throat to directly adjust the throat size.

6. The air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section according to claim 1, characterized in that, The test section is also equipped with an observation window, which is used to observe the internal condition of the test section and for non-contact measurement.

7. A design method for an air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section, used for designing an air-breathing high subsonic wind tunnel based on an adjustable sound velocity cross section as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Determine the target Mach number and test section size to be achieved in the wind tunnel, and use the vacuum tank for vacuum drive. Adopt the air intake principle and establish the core airflow path as the first contraction section → test section → Laval nozzle → connecting pipe → vacuum tank. S2, based on the target Mach number, the cross-sectional area of ​​the test section, and the airflow parameters, utilizes the continuity equation. The throat area of ​​the Laval nozzle is derived from the isentropic relationship, which locks the airflow through the wind tunnel. The nozzle contraction section ensures that the airflow can be smoothly accelerated and reach the speed of sound at the throat, forming a congested aerodynamic barrier. The exit area of ​​the nozzle expansion section determines the degree of airflow expansion. The design goal is to ensure that pressure fluctuations in and behind the nozzle expansion section will not propagate forward and interfere with the upstream subsonic section. S3, Based on the volume of the vacuum tank, the stable operating time of the wind tunnel depends on the process of the pressure inside the vacuum tank rising from the lowest stable back pressure to the critical choking back pressure; based on the required effective operating time and the locked mass flow rate, the minimum total volume of the vacuum tank can be deduced. S4 uses numerical simulation to simulate the wind tunnel and observe the flow field quality throughout the entire cycle of startup, choke establishment, and pressure recovery in the vacuum tank.

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