A nozzle, method, and open wind tunnel for improving flow field quality

Abstract

This invention provides a nozzle, method, and open-face wind tunnel for improving flow field quality. The nozzle for improving flow field quality has a coaxial double-layer jet, comprising a main jet and an outer jet coaxial with and surrounding the main jet, wherein the outer jet has a lower velocity than the main jet. This invention directly alters the starting position of the shear layer of the open-face wind tunnel jet, i.e., the nozzle structure, minimizing the generation of large-scale vortex structures and effectively maintaining good flow field quality in the wind tunnel test section (downstream of the nozzle).

Description

Technical Field

[0001] This invention relates to the field of wind tunnel testing technology, and more specifically, to a nozzle, a method for improving the flow field quality of an open wind tunnel, and an open wind tunnel. Background Technology

[0002] A wind tunnel is a pipe with a specific profile that uses artificial methods to generate controlled airflow through a test section. Wind tunnel testing involves placing a flying object or its model in the artificial flow field of the wind tunnel test section to observe its flow state and measure relevant physical quantities. Test sections are classified into open and closed types based on their structure. An open wind tunnel generates a free jet in front of the test section and utilizes the relatively uniform airflow in the core region of the jet for aerodynamic testing, such as... Figure 1 As shown.

[0003] Due to the instability of the shear layer (Kelvin-Helmholtz, KH) at the jet boundary, the free jet will generate large-scale vortex structures at a certain distance downstream of the nozzle due to shear layer instability. These vortex structures interact with the collector downstream of the open wind tunnel test section and the pressure pulsations reflected by it, resulting in low-frequency pressure oscillations in the flow field of the test section. These low-frequency pressure oscillations degrade the flow field quality and severely affect the aerodynamic and aeroacoustic measurements of the test model. Therefore, it is particularly important to conduct high-quality aerodynamic and aerodynamic noise test studies in an open wind tunnel, improve the flow field quality of the wind tunnel, and obtain a relatively stable flow and acoustic field test environment.

[0004] like Figure 2 As shown, during the open-circuit wind tunnel test, the airflow exits from the nozzle, passes through the jet test section, and enters the collector. The KH instability of the jet shear layer leads to the generation of large-scale vortex structures at the jet boundary of the test section. These instability-generated vortex structures propagate downstream with the shear layer and impact the collector, generating a new pressure wave that propagates upstream at the speed of sound. This new pressure wave acts on the jet nozzle, disturbing the jet shear layer and further promoting its instability, thus forming a low-frequency oscillating loop in the test section. Therefore, the two key locations for improving flow field quality are the initiation point of the shear layer and the location of the new pressure wave—the nozzle and the impact point—the collector inlet.

[0005] Currently, both domestic and international methods for improving flow field quality at nozzles involve installing vortex generators with different shapes and structures. Installing vortex generators at the nozzle typically reduces the effective core test area of ​​the test section and introduces high-frequency background noise, which has a significant impact on acoustic measurements. Methods for improving flow field quality at collectors, both domestically and internationally, generally involve collector structure optimization. Collector structure optimization usually requires time-consuming wind tunnel experiments and iterative design, and modifications to the collector often affect the pressure distribution in the test area. Furthermore, since the collector is downstream of the jet, large-scale vortex structures have already formed; collector structure optimization can only reduce the intensity of reflected pressure waves, but cannot fundamentally suppress the generation of large-scale vortex structures. Summary of the Invention

[0006] The present invention aims to provide a nozzle, method and open wind tunnel for improving the flow field quality of open wind tunnels, so as to avoid the generation of large-scale vortex structures to the greatest extent from the starting position of the shear layer at the nozzle, thereby maintaining good flow field quality in the wind tunnel.

[0007] The present invention provides a nozzle with coaxial double-layer jet for improving the flow field quality of an open wind tunnel.

[0008] In one embodiment, the coaxial double-layer jet includes:

[0009] Main jet;

[0010] And an outer jet that is coaxial with and surrounds the main jet;

[0011] The velocity of the outer jet is lower than that of the main jet.

[0012] In one embodiment, the nozzle includes an outer ring, an inner ring disposed inside the outer ring, and an inflow ring disposed at the inlet of the inner ring; the inner ring and the outer ring are fixedly connected by a plurality of connecting plates (104).

[0013] In one embodiment, the cross-sectional shape of the connecting plate between the inner and outer rings is streamlined.

[0014] The present invention also provides a method for improving the flow field quality of an open wind tunnel, comprising:

[0015] The design features a nozzle with a coaxial double-layer jet;

[0016] The flow field quality of the open wind tunnel is improved by employing the nozzle with coaxial double-layer jets.

[0017] In one embodiment, the method of designing a nozzle having a coaxial double-layer jet includes:

[0018] A coaxial outer jet is wrapped around the main jet at the nozzle, thus forming a coaxial double-layer jet; the jet velocity of the outer jet is lower than that of the main jet.

[0019] The present invention also provides an open wind tunnel, comprising a stabilizing section, a contraction section, a sump chamber, and a first diffusion section connected in sequence. The contraction section and the sump chamber are connected by a nozzle, and the sump chamber and the first diffusion section are connected by a collector. The section between the nozzle and the collector is a test section, and the nozzle has a coaxial double-layer jet.

[0020] In one embodiment, the coaxial double-layer jet includes:

[0021] Main jet;

[0022] And an outer jet that is coaxial with and surrounds the main jet;

[0023] The velocity of the outer jet is lower than that of the main jet.

[0024] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0025] 1. This invention directly changes the starting position of the jet shear layer in the open wind tunnel, i.e., the structure of the nozzle, which avoids the generation of large-scale vortex structures to the greatest extent and effectively maintains good flow field quality in the wind tunnel test section (downstream of the nozzle).

[0026] 2. The present invention has a simple structure and is easy to optimize and improve existing open wind tunnel nozzles.

[0027] 3. The nozzle structure of the present invention is located upstream of the wind tunnel flow field and does not affect the structure of other sections downstream of the wind tunnel.

[0028] 4. The present invention has diverse implementation forms in terms of specific building materials and construction methods, and has few limitations. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of an open-face wind tunnel structure.

[0031] Figure 2 This is a schematic diagram illustrating the generation and propagation of large-scale vortex structures.

[0032] Figure 3This is a schematic diagram of the nozzle structure of the coaxial double-layer jet in an embodiment of the present invention.

[0033] Figure 4 This is a schematic diagram of the jet flow from the nozzle of the coaxial double-layer jet in an embodiment of the present invention, wherein the arrow indicates the jet flow direction.

[0034] Figure 5a This is a schematic diagram of the evolution of the jet shear layer when the jet velocity of the external jet is zero.

[0035] Figure 5b A schematic diagram of the evolution of the jet shear layer when there is an outer jet coaxial with and surrounding the main jet, and the jet velocity of the outer jet is 0.6 times that of the main jet.

[0036] Figure 5a and Figure 5b In this context, x represents the length of the jet shear layer.

[0037] Figure 6a This is a front view of one implementation structure of the nozzle in an embodiment of the present invention.

[0038] Figure 6b for Figure 6a BB section view.

[0039] Figure 6c for Figure 6a CC section view.

[0040] Figure 7a When the connecting plate is an arc Figure 6a Sectional view of AA.

[0041] Figure 7b When the connecting plate is airfoil-shaped Figure 6a Sectional view of AA.

[0042] Reference numerals: 1-Main jet, 2-Outer jet, 10-Contraction section, 20-Containment chamber, 21-Nozzle, 22-Collector, 23-Test section, 30-First diffusion section, 40-Stabilization section, 101-Outer ring, 102-Inner ring, 103-Inlet ring, 104-Connecting plate. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0045] Example 1

[0046] Due to shear layer instability, the free jet will generate large-scale vortex structures a certain distance downstream of nozzle 21. Further instability of these large-scale vortex structures will cause the flow to enter a turbulent state further downstream. The design of nozzle 21 in the open wind tunnel needs to maximize the size of the jet core region in the test section 23, which is unaffected by large-scale vortices and turbulence in the shear layer, to facilitate the measurement of physical parameters of the test model. Therefore, delaying or suppressing the generation of large-scale vortex structures is of great significance for improving the flow field quality of the open wind tunnel. To this end, this embodiment proposes a nozzle 21 for improving the flow field quality of the open wind tunnel, such as... Figure 3 As shown, the nozzle 21 has a coaxial double-layer jet. In this embodiment, the coaxial double-layer jet includes:

[0047] Main jet 1;

[0048] And an outer jet 2 that is coaxial with and surrounds the main jet 1. Preferably, the jet velocity of the outer jet 2 is lower than that of the main jet 1.

[0049] Therefore, the nozzle 21 of the present invention wraps an outer jet 2 around the main jet 1, such as Figure 4 As shown, reducing the intensity of the jet boundary shear layer can suppress shear layer instability, delay the generation of large-scale vortex structures, extend the length of the jet center potential cone, and suppress high-frequency noise. Figure 5a and Figure 5b A diagram illustrating the jet shear vortex structure obtained using the large eddy simulation method for the nozzle 21 used to improve the flow field quality of the open wind tunnel in this embodiment is provided. Figure 5a The jet velocity U of external jet 2 CF The case where it is zero (i.e., there is no external jet 2), Figure 5b It is a main jet 1 surrounded by an outer jet 2 that is coaxial with and encloses the main jet 1, and the jet velocity of the outer jet 2 is U. CF It is 0.6 times the jet velocity U of the main jet 1 J The situation is as follows. It can be seen that when the external jet 2 is present, the instability of the shear layer is greatly delayed, and the potential flow cone in the jet core region is also greatly elongated. It is evident that the coaxial double-layer jet of nozzle 21 has a significant effect on maintaining the instability of the shear layer and improving the flow field quality.

[0050] This invention introduces the fundamental fluid theory concept of coaxial double-layer jet into the design of open wind tunnels. By adjusting the thickness and flow rate of the outer jet 2, optimized jet parameters can be obtained without significantly altering the typical flow parameters of the open wind tunnel, thereby improving the flow field quality. The core of this invention is that the nozzle 21 can achieve coaxial double-layer jet. The specific building materials and construction methods of the nozzle 21 are not within the scope of this invention's claims; for example, conventional reinforced concrete materials and conventional civil engineering methods can be used.

[0051] A preferred implementation of the nozzle 21 is as follows: Figure 6a , 6b As shown in Figure 6c, the open wind tunnel is a single pipe, comprising a stabilizing section 40, a contraction section 10, a sump chamber 20, and a first diffuser section 30 connected in sequence. The nozzle 21 of this invention includes an outer ring 101, an inner ring 102 disposed inside the outer ring 101, and an inflow ring 103 disposed at the inlet of the inner ring 102; the inner ring 102 and the outer ring 101 are fixedly connected by several connecting plates 104. That is, in the conventional contraction section and the conventional nozzle ( Figure 6a An inner ring 102 is installed inside the outer ring 101. The inner ring 102 is connected to the outer ring 101 by several connecting plates 104 (such as the four connecting plates 104 in this embodiment, one above the other and one to the left and right). The outer ring 101 is fixed to the ground by a support. In order to guide the flow and reduce the disturbance to the external jet, the cross-sectional shape of the connecting plate 104 between the inner ring 102 and the outer ring 101 is streamlined, such as... Figure 7a The arc shape shown or as Figure 7b The airfoil shown is for reference only (all airfoils are within the scope of protection of this invention). An inlet ring 103 is installed at the inlet of the inner ring 102. Depending on the needs, by replacing the inlet ring 103 with one of different angles, the specific flow rates of the main jet 1 and the outer jet 2 can be changed, thereby altering the flow rate ratio between the main jet 1 and the outer jet 2. The connection between the inner ring 102 and the inlet ring 103 can be varied and selected as needed, such as by insertion / removal, bolting, or riveting.

[0052] Example 2

[0053] Using the same design concept as Example 1, this example provides a method for improving the flow field quality of an open wind tunnel, including:

[0054] The nozzle 21 is designed with a coaxial double-layer jet.

[0055] The flow field quality of the open wind tunnel is improved by employing the nozzle 21 with coaxial double-layer jets.

[0056] In this embodiment, the method for designing a nozzle 21 with a coaxial double-layer jet includes:

[0057] A coaxial outer jet 2 is wrapped around the main jet 1 at the nozzle 21, thus forming a coaxial double-layer jet. Preferably, the jet velocity of the outer jet 2 is lower than that of the main jet 1.

[0058] In this embodiment, the principle of the nozzle implementation structure and the method for improving the flow field quality of the open wind tunnel can be referred to in Embodiment 1, and will not be repeated here.

[0059] Example 3

[0060] like Figure 1 and Figure 3 As shown, this embodiment provides an open wind tunnel, which includes a stabilizing section 40, a contraction section 10, a sump chamber 20, and a first diffusion section 30 connected in sequence. The contraction section 10 and the sump chamber 20 are connected by a nozzle 21, and the sump chamber 20 and the first diffusion section 30 are connected by a collector 22. The section between the nozzle 21 and the collector 22 is a test section 23. The nozzle 21 has a coaxial double-layer jet.

[0061] In this embodiment, the coaxial double-layer jet includes:

[0062] Main jet 1;

[0063] And an outer jet 2 that is coaxial with and surrounds the main jet 1. Preferably, the jet velocity of the outer jet 2 is lower than that of the main jet 1.

[0064] The nozzle 21 used in this embodiment is the same as that in Embodiment 1, and its principle will not be repeated here.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A nozzle for improving the flow field quality of an open wind tunnel, characterized in that, In order to minimize the generation of large-scale vortex structures from the starting position of the shear layer at the nozzle, the nozzle (21) has a coaxial double-layer jet; The coaxial double-layer jet includes: a main jet (1); and an outer jet (2) that is coaxial with the main jet (1) and surrounds the main jet (1); the jet velocity of the outer jet (2) is lower than that of the main jet (1); The nozzle (21) includes an outer ring (101), an inner ring (102) disposed inside the outer ring (101), and an inlet ring (103) disposed at the inlet of the inner ring (102). The original contraction section and nozzle of the open wind tunnel are used as the outer ring (101), and an inner ring (102) is installed inside the outer ring (101). The inner ring (102) and the outer ring (101) are fixedly connected by several connecting plates (104). According to different needs, the specific flow rates of the main jet (1) and the outer jet (2) are changed by changing the inlet ring (103) at different angles, thereby changing the flow rate ratio of the main jet (1) and the outer jet (2).

2. The nozzle for improving the flow field quality of an open wind tunnel according to claim 1, characterized in that, The cross-sectional shape of the connecting plate (104) between the inner ring (102) and the outer ring (101) is streamlined.

3. A method for improving the flow field quality of an open wind tunnel, characterized in that, To minimize the generation of large-scale vortex structures starting from the nozzle, the shear layer initiation point, the method includes: Design a nozzle (21) with coaxial double-layer jets; The flow field quality of the open wind tunnel is improved by using the nozzle (21) with coaxial double-layer jets. The method for designing a nozzle (21) with a coaxial double-layer jet includes: A layer of outer jet (2) coaxial with the main jet (1) is wrapped around the main jet (1) of the nozzle (21), thereby forming a coaxial double-layer jet; the jet velocity of the outer jet (2) is lower than that of the main jet (1); The original contraction section and nozzle are used as the outer ring (101). An inner ring (102) is installed inside the outer ring (101). The inner ring (102) is connected to the outer ring (101) through several connecting plates (104). The outer ring (101) is fixed to the ground by a support. An inlet ring (103) is set at the inlet of the inner ring (102). According to different needs, the specific flow rates of the main jet (1) and the outer jet (2) are changed by changing the inlet ring (103) at different angles, thereby changing the flow rate ratio of the main jet (1) and the outer jet (2).

4. An open-face wind tunnel, comprising a stabilizing section (40), a contraction section (10), a sump chamber (20), and a first diffuser section (30) connected in sequence, wherein the contraction section (10) and the sump chamber (20) are connected via a nozzle (21), the sump chamber (20) and the first diffuser section (30) are connected via a collector (22), and a test section (23) is located between the nozzle (21) and the collector (22), characterized in that, In order to minimize the generation of large-scale vortex structures from the starting position of the shear layer at the nozzle, the nozzle (21) has a coaxial double-layer jet; The coaxial double-layer jet includes: a main jet (1); and an outer jet (2) that is coaxial with the main jet (1) and surrounds the main jet (1); the jet velocity of the outer jet (2) is lower than that of the main jet (1); The original contraction section (10) and nozzle (21) are used as the outer ring (101). An inner ring (102) is set inside the outer ring (101), and an inlet ring (103) is set at the inlet of the inner ring (102). The inner ring (102) and the outer ring (101) are fixedly connected by several connecting plates (104). According to different needs, the specific flow rates of the main jet (1) and the outer jet (2) are changed by changing the inlet ring (103) at different angles, thereby changing the flow rate ratio of the main jet (1) and the outer jet (2).

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