Adjustable variable mach number wind tunnel nozzle structure and profile design method

Abstract

The invention discloses a variable mach number wind tunnel nozzle with a variable internal flow channel cross section area and a design method, and belongs to the technical field of hypersonic speed wind tunnel tests, and the structure comprises a nozzle shell, a conical support, an actuator, an adjustable center cone and a pre-tightening bolt. The molded surfaces of the nozzle shell and the adjustable central cone adopt integrated design of Witoszynski, Foelsch, characteristic lines, boundary layer correction, aerodynamic turbulence and the like, and aerodynamic characteristics and test requirements of an aircraft under different Mach numbers are truly simulated. The cone-type support is parallelly arranged at an inlet of the spray pipe, the actuator is arranged inside, the adjustable center cone coincides with the center line of an outlet of the spray pipe and is suspended, and the cone-type support can rectify wind tunnel airflow. According to the invention, a flow field has high symmetry, and meanwhile, the specific area of a core of an airflow region is larger; by controlling the moving range of the adjustable center cone, the real environment and testing conditions of equipment motion testing are simulated, and the device has the advantages of being high in applicability, simple in structure, wide in adjusting range and good in economical efficiency in engineering.

Description

Technical Field

[0001] The present invention belongs to the technical field of hypersonic wind tunnel tests, and relates to a variable Mach number wind tunnel nozzle structure and profile design method based on regulation, which can realize continuous adjustment of the Mach number in the test area during the test process, and effectively improve the working efficiency and structural complexity of wind tunnel tests. Background Art

[0002] Supersonic wind tunnel equipment is a crucial ground equipment for studying aerodynamics, and is used to simulate the aerodynamic characteristics of tip equipment at different altitudes, speeds and attitudes in the real environment. Especially for frontier technology fields such as supersonic aircraft, being able to continuously change the Mach number at the outlet of the wind tunnel nozzle is of extremely important significance for realizing accurate aerodynamic experiments. The essence of a wind tunnel is to utilize the relative motion principle and approximate criteria to simulate a specific airflow environment of an aircraft by artificially controlling the airflow size. However, as the core component of the wind tunnel, the main function of the nozzle is to control the expansion of high-pressure gas to meet the formation of a specific Mach number in the test area. In the field of hypersonic wind tunnel experiments in China, a specific Mach number of a uniform flow field is usually formed by using a traditional solid-wall nozzle. Although the solid-wall nozzle has the characteristics of high repeatability and smooth uniformity, its fixed nature limits the dynamic adjustment performance and experimental efficiency of the Mach number. If the Mach number at the inlet of the test section is changed, a nozzle with a corresponding profile needs to be replaced. This method has the disadvantages of low efficiency, long time consumption, high cost, and cannot continuously simulate the motion states of an aircraft and a propulsion system under certain specific conditions. For example, simulating the reciprocating start of a ramjet engine and the aerodynamic characteristics of a scramjet aircraft under different flight conditions. Therefore, being able to effectively realize the nozzle of the wind tunnel to change the Mach number in a smooth and continuous manner has gradually become a hot issue in the current research on wind tunnel nozzles.

[0003] At present, the research on continuously variable Mach number nozzles mainly focuses on flexible wall and profile rotation technologies. The flexible wall regulation technology adjusts the Mach number by using a hydraulic cylinder to act on the shape of the nozzle wall surface, and the profile rotation regulation technology adjusts the throat area by using a rotation fulcrum for rigid-flexible coupling of the wall surface. The above two methods have problems such as complex structure, high cost, and wall warping. Therefore, how to design a continuously variable Mach number nozzle structure with high precision, high flow field quality and simple structure has important scientific and engineering value for the aerodynamic characteristic test of hypersonic aircraft.

[0004] Based on the above listing and analysis of variable Mach number nozzle technologies, it can be seen that the main requirements of the current variable Mach number nozzle technologies are: having a simple structure, high-precision continuous adjustment, low cost, and uniform flow at the nozzle outlet. Therefore, the present invention proposes a variable Mach number wind tunnel nozzle structure and design method with a controllable flow channel area to solve the above problems. Summary of the Invention

[0005] The object of the present invention is to overcome the defects of the prior art, and provide a variable Mach number wind tunnel nozzle structure and design method with controllable flow channel area. By adopting the form of a combination of an adjustable center cone and an actuator, the flow channel gap is accurately changed on the basis of the inherent structure to achieve continuous change of the Mach number at the nozzle outlet. The nozzle structure includes: a nozzle housing, a conical support, an actuator, an adjustable center cone, and a pre-tightening bolt. Among them, the profiles of the nozzle housing and the adjustable center cone are integrally designed by using the Witoszynski, Foelsch, characteristic line, boundary layer correction, aerodynamic turbulence, and alternating line symmetry theory methods, and the idea of combining multiple theoretical symmetries is used to truly simulate the aerodynamic characteristics and test requirements of the aircraft at different Mach numbers. At the same time, the design theory of the variable Mach number nozzle is broadened. The conical supports are arranged in parallel at the nozzle inlet, and the actuators are arranged inside the central body, and the actuators are pre-tightened by means of pre-tightening bolts. The adjustable center cone coincides with the nozzle outlet center line and is placed in suspension. By changing the axial position of the adjustable center cone, continuous change of the Mach number at the nozzle outlet is achieved. In addition, the conical support can rectify the wind tunnel airflow, which helps to guide and adjust the flow rate to remain stable and reduce the occurrence of eddy current phenomena. The present invention can make the flow field have high symmetry, and at the same time, the core area ratio of the airflow region is larger. By controlling the movement range of the adjustable center cone, the real environment and test conditions of the simulation equipment movement test are simulated, and it has the advantages of strong applicability, simple structure, wide adjustment range, and good economy in engineering.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A controllable variable Mach number wind tunnel nozzle structure, which functions to control the flow channel area to achieve continuous change of the Mach number at the nozzle outlet, includes a nozzle outer wall 1, a conical support 2, a pre-tightening bolt 3, an actuator 4, and an adjustable central cone 5. The nozzle outer wall 1 serves as an air flow channel, with the left end face being the nozzle inlet area and the right end face being the nozzle outlet area. It not only supports all internal structures but also is tightly connected to the test section. The internal profile is divided into a contraction section I and a straight wall section, which can ensure air flow stability in a complex mechanical environment and effectively reduce turbulence and energy loss. The conical support 2 is arranged in parallel at the inlet of the nozzle outer wall 1. The front end is a conical structure, and the rear end is a cylindrical structure with four groups of streamlined blades. Both the front and rear end faces are equipped with mounting flanges for fastening connection with the nozzle outer wall 1. The actuator 4 is installed inside the cylindrical structure with four groups of streamlined blades. The control system inside the actuator 4 selects PID axial control. Its adjustment device is led out through the nozzle outer wall 1, and the actuator 4 is fixed using the pre-tightening screw 3. One end of the actuator 4 is fixed and constrained, and the other end is connected to the adjustable central cone 5. The adjustable central cone 5 is an overall rotating body structure, with the diameter increasing first and then decreasing from the front end to the end. It includes a contraction section II at the front end, an expansion section in the middle, a termination section at the end, and a conical rectifying section outside the nozzle outlet. This design helps to regulate the throat gap between the nozzle outer wall 1 and the adjustable central cone 5.

[0008] When continuous adjustment of the Mach number in the test section is required during the test process, the output displacement of the actuator 4 is controlled to change the throat gap, realizing continuous change of the Mach number at the nozzle outlet, so as to meet the requirements of different working conditions.

[0009] Furthermore, the nozzle outer wall 1 is a hollow rotating body structure and serves as the main air flow channel. The nozzle outer wall 1 and the conical support 2 are connected using flanges or pre-tightening bolts 3 to form a seamless connection to ensure sealing. Among them, the nozzle inlet radius is denoted as r0, the nozzle outlet radius is denoted as r e , the thickness of the nozzle outer wall 1 is denoted as t1, and the vertical distance from the highest point of the adjustable central cone 5 to the profile curve of the nozzle outer wall is denoted as the throat radius r t .

[0010] Furthermore, the conical support 2 is a composite structure, mainly composed of a flow splitting cone 2-1 and a streamlined support frame 2-2. The flow splitting cone 2-1 is located at the end of the structure and is integrally formed with the streamlined support frame 2-2. The upper outer wall of the streamlined support frame 2-2 is a circular ring structure, and multiple threaded holes are regularly arranged on its upper surface for fixed connection with the nozzle outer wall 1. The bottom surface of the streamlined support frame 2-2 is designed with an internal installation structure for connection with the actuator 4. The streamlined support frame 2-2 is arranged with four groups of streamlined blades in an integral connection manner. These blade structures are not only used to adjust the air flow at the wind tunnel inlet but also play a role in supporting other structures.

[0011] Further, the actuator 4 mainly consists of an ultra-precision electric cylinder 4-1, a rear flange internal thread connector 4-2, a front flange connector 4-3, and an axially displaced system controlled by PID, and is installed inside the streamlined support frame 2-2. The ultra-precision electric cylinder 4-1 converts the rotational motion of the motor into linear motion to achieve high-precision displacement control. The rear flange internal thread connector 4-2 is of a rectangular body structure, and 12 threaded holes are equidistantly arranged on its surface for fixing the position of the ultra-precision electric cylinder 4-1 to ensure its stability and reliability. The front flange connector 4-3 is also of a rectangular body structure, and 4 threaded holes are equidistantly arranged on its surface for connecting with the motor of the ultra-precision electric cylinder 4-1, playing a role in bearing and dispersing force to ensure the strength and stability of the overall structure. The above design uses a displacement system controlled by PID to accurately achieve displacement adjustment.

[0012] Further, the main body structure of the adjustable center cone 5 is streamlined, and the diameter of the front end first increases and then decreases, aiming to adjust the throat distance from the outer wall of the nozzle. The front end face of the device has a connecting hole with internal threads and is fixedly connected to the actuator 4 using an adapter flange. The tail is designed as a tapered structure with a curved connection, which can reduce the impact and resistance of the fluid and avoid the aggravation of turbulent flow and eddy current phenomena. The critical point between the expansion section and the termination section of the adjustable center cone 5 is set as point B, and the angle between point B and the horizontal plane is expressed as the maximum expansion angle β B , the curve BN represents the profile curve of the termination section of the adjustable center cone 5, the angle between each moving point on the curve BN and the horizontal plane is expressed as β, and the diameter of the tapered fairing section outside the nozzle outlet is R c , the length of the contraction section is l0, and the length of the expansion section is l B , the length of the termination section is l c .

[0013] A design method for a controllable variable Mach number wind tunnel nozzle structure includes the following steps:

[0014] The first step is to design the profile curve of the nozzle outer wall 1;

[0015] 1.1) According to the designed range of the required outlet Mach number (Ma1, Ma2), the nozzle inlet diameter R0, and the nozzle outlet diameter R e , combined with the specific relationship of the nozzle sonic speed section, use the gas isentropic flow formula to determine the ratio of the nozzle outlet radius to the throat radius;

[0016] 1.2) According to the design requirements of the wind tunnel nozzle, the profile curve of the front contraction section Ⅰ of the nozzle outer wall 1 adopts the method of optimizing the shift of the Witoszynski curve, and the profile of the rear straight wall section adopts the design method of linear connection. Therefore, only the profile curves of the two limit values of Ma1 and Ma2 need to be calculated.

[0017] 1.3) Since the profile curve of the contraction section Ⅰ is closely related to the design of the nozzle throat, it is necessary to ensure that the radius of curvature of the nozzle throat is greater than the end during the design process. Therefore, the maximum limit value of the Mach number Ma2 at the nozzle outlet is used as the design basis to ensure that the variable Mach number wind tunnel nozzle structure designed by the present invention has excellent performance and flow field quality under high Mach number conditions.

[0018] In the second step, based on the profile curves corresponding to the two limit values (Ma1 and Ma2) of the Mach number at the outlet of the variable Mach number wind tunnel nozzle structure, the adjustment range of the throat radius between the adjustable center cone 5 and the straight wall section is determined. By converting the adjustment range into the movement range of the actuator 4, precise adjustment of the throat radius is achieved.

[0019] In the third step, based on the design method of the first step, an axisymmetric form is adopted to make the profile curve of the contraction section Ⅱ of the adjustable center cone 5 symmetrical with the contraction section Ⅰ of the nozzle outer wall 1. By ensuring the symmetrical layout, the flow of the air in the contraction section is made more stable, further improving the flow field quality of the wind tunnel nozzle structure under different Mach number conditions.

[0020] In the fourth step, the profile curve of the expansion section at the end of the adjustable center cone 5 is designed

[0021] 4.1) Since the flow channel between the middle expansion section of the adjustable center cone and the nozzle outer wall 1 is a single-wave zone, the radial expansion waves generated on the wall surface will not cause crossing and reflection phenomena, and the profile curve of the expansion section of the adjustable center cone can be designed according to the profile curve of the traditional Laval nozzle.

[0022] 4.2) By adopting the Foelsch curve calculation method, the maximum expansion angle β of the critical point B of the expansion section curve of the adjustable center cone can be determined B (the angle between the end of the expansion section curve and the horizontal plane) and the relationship with the nozzle outlet radius. The radius of curvature of the critical point B, the abscissa and ordinate (x B , y B ) of the critical point B, and the profile curve of the expansion section of the adjustable center cone 5 can be expressed as:

[0023]

[0024] Among them, β B represents the maximum expansion angle; v1 represents the Prandtl-Meyer angle corresponding to the designed Mach number of the nozzle; r t represents the nozzle throat radius; r e represents the nozzle outlet radius; r B represents the nozzle radius at the position of point B; Ma BIt represents the Mach number at point B; k represents the specific heat ratio coefficient of the applied gas; r represents the nozzle curvature radius corresponding to x; x represents the abscissa of the profile curve of the adjustable center cone surface;

[0025] 4.3) Combining the above formulas, the expansion section profile curves under the limit Mach numbers Ma1 and Ma2 working conditions are obtained by using the analytical method. If a non - minimum Mach number is selected as the design condition, it will lead to incomplete performance of the shock - absorbing wall surface and generate compression waves. Therefore, Ma2 is selected as the design Mach number of the expansion section of the adjustable center cone 5 to optimize the nozzle performance.

[0026] In the fifth step, according to the known technical solution of the supersonic nozzle, in the design of the termination section, the characteristic line and the Mach line can be regarded as coincident. The curve BN is divided into an infinite number of short broken lines by using the differential limit theorem. Based on the relationship between the Prandtl - Meyer function and the Mach number of the air flow, the angle β between each moving point on the curve BN and the horizontal plane is used as the design variable, and the coordinate relationship between different MN lengths and point N is matched, so as to obtain a continuous termination section profile curve.

[0027] In the sixth step, verify by finite - element simulation of fluid mechanics;

[0028] 6.1) Import the profile curves of the designed contraction section Ⅰ, contraction section Ⅱ, straight wall section, expansion section, termination section and conical fairing section into the finite - element simulation software, and assign the material parameters of the variable - Mach - number wind tunnel nozzle structure.

[0029] 6.2) Use the k - ε turbulence model in the high - Mach - number fluid physical field to simulate the gas flow state, and set the specific heat ratio and the inlet temperature to ensure the reliability of the simulation conditions.

[0030] 6.3) Set the boundary conditions in the fluid mechanics physical field, select the nozzle inlet and outlet, set the nozzle inlet flow velocity and the nozzle outlet pressure, and define the adjustable center cone 1 and the splitter cone 2 as solid regions.

[0031] 6.4) After completing the setting of the fluid mechanics physical field, divide the mesh and perform finite - element analysis.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] (1) For the variable - Mach - number wind tunnel nozzle designed by the present invention, the reciprocating axial movement of the adjustable center cone is realized by using a high - precision actuator installed inside the conical bracket.

[0034] (2) By cross - integrating the Witoszynski, Foelsch, alternating symmetry, and numerical optimization theories, the present invention derives the optimal profile curve parameters of the variable - Mach - number nozzle and forms a complete set of closed - loop nozzle profile curves.

[0035] (3) Each unit of the variable Mach number wind tunnel nozzle designed by the present invention has the characteristics of high precision, simple structure, and controllable smooth quality. At the same time, a conical fairing section is combined to reduce the eddy current phenomenon of the outlet air flow.

[0036] (4) The variable Mach number wind tunnel nozzle designed by the present invention breaks through the problem that it is difficult to regulate the outlet Mach number of traditional solid wall nozzles, greatly improves the test efficiency and structural complexity of wind tunnel tests, so that a continuous change in Mach number is obtained at the nozzle outlet. Brief Description of the Drawings

[0037] Figure 1 It is a flow chart of the design method of the variable Mach number wind tunnel nozzle.

[0038] Figure 2 It is a schematic diagram of the structural decomposition of the variable Mach number wind tunnel nozzle of the present invention example.

[0039] Figure 3 It is a schematic diagram of the working principle of the variable Mach number wind tunnel nozzle of the present invention example.

[0040] Figure 4 It is a schematic diagram of the conical support structure of the present invention example.

[0041] Figure 5 It is a schematic diagram of the actuator structure of the present invention example.

[0042] Figure 6 It is a schematic diagram of the design of the curve of the outer wall contraction section Ⅰ of the nozzle of the present invention example.

[0043] Figure 7 It is a schematic diagram of the profile curve design of the adjustable center cone expansion section and the termination section.

[0044] Figure 8 It is a schematic diagram of the Mach number distribution of the flow field when the outlet Mach number of the nozzle of the present invention example is 1.8.

[0045] Figure 9 It is a schematic diagram of the pressure distribution of the flow field when the outlet Mach number of the nozzle of the present invention example is 1.8.

[0046] Figure 10 It is a schematic diagram of the flow field when the outlet Mach number of the nozzle of the present invention example is 2.2.

[0047] Figure 11 It is a schematic diagram of the pressure distribution of the flow field when the outlet Mach number of the nozzle of the present invention example is 2.2. Detailed Description of the Invention

[0048] The following combines the drawings and technical solutions to detail the specific implementation manners of the present invention.

[0049] The design process based on the structure of the variable Mach number wind tunnel nozzle is as Figure 1As shown, the method for regulating the Mach number is implemented based on the wind tunnel nozzle structure, including the following steps:

[0050] First step: Design of the profile curve of the outer wall 1 of the variable Mach number wind tunnel nozzle

[0051] Referring to Figure 2 、 Figure 3 , the present invention designs a variable Mach number wind tunnel nozzle structure suitable for a controllable cross-sectional area of the flow channel. The outer wall of the nozzle serves as the air flow channel, with the left end face being the nozzle inlet area and the right end face being the nozzle outlet area. It not only supports all the internal structures but also is closely connected to the test section. The internal profile is divided into a contraction section and a straight wall section, which can ensure the air flow stability under complex mechanical environments and effectively reduce turbulence and energy loss. Assuming the nozzle inlet radius is 400 mm, the outlet radius is 160 mm, and the diameter of the conical fairing section outside the nozzle outlet is 40 mm. The outer wall 1 of the nozzle is connected to the conical support 2 by a flange or a pre-tightening bolt 3 to form a seamless connection to ensure tightness. The conical support 2 is a composite structure, mainly composed of a flow splitting cone 2-1 and a streamlined support frame 2-2, as shown in Figure 4 . The flow splitting cone 2-1 is located at the end of the structure and is integrally formed with the support frame 2-2. The inner ring diameter is 800 mm, which can rectify the air flow at the wind tunnel inlet to ensure the guidance and flow stability of the air flow. The upper outer wall of the streamlined support frame 2-2 is a circular ring structure, and a plurality of threaded holes are regularly arranged on its upper surface, and the outer surface is closely attached to the nozzle housing 1.

[0052] According to the known parameters such as the nozzle outer wall inlet radius, outlet radius, and the diameter of the conical fairing section outside the nozzle outlet, the range of the nozzle outlet limit Mach number is selected as 1.8 Ma - 2.2 Ma, and combined with the specific relationship of the nozzle sonic speed section, the ratio of the nozzle outlet radius to the throat radius is determined using the gas isentropic flow formula. The profile curve of the front-end contraction section Ⅰ of the nozzle outer wall adopts the method of optimizing the shift of the Witoszynski curve, and the rear end is connected by a straight line section to calculate the profile curves of the two limit values of 1.8 Ma and 2.2 Ma, as shown in Figure 6 . Since the profile curve of the contraction section Ⅰ is closely related to the design of the nozzle throat radius, it is necessary to ensure that the curvature radius of the throat is greater than the end during the design process. Therefore, the maximum limit value of the outlet Mach number, 2.2 Ma, is used as the design basis to ensure that the nozzle has excellent performance and flow field quality at other Mach numbers.

[0053] Second step, based on the profile curves corresponding to the contraction sections of 1.8 Ma and 2.2 Ma, the variation range of the nozzle throat radius is determined. By converting this regulation range into the movement range of the actuator, precise adjustment of the throat radius is achieved. From the calculation results, it can be seen that the controllable range of the throat radius is from 71.3 mm to 80.5 mm, and the moving distance of the actuator can be obtained as 125 mm.

[0054] In the third step, based on the design method of the first step, by adopting the way of alternating symmetry of the axis and the surface, the type-II surface curve of the adjustable central cone contraction section is made symmetrical with part of the 2.2Ma shifted-axis optimization, and combined with the symmetrical layout to ensure that the air flow after flow division is more stable. Through the above design method, the uniformity of the air flow distribution is optimized, the turbulence and separation phenomena are reduced, and the air flow stability under different working conditions is further improved.

[0055] In the fourth step, design the surface curve of the adjustable central cone expansion section

[0056] Since the flow channel between the middle expansion section of the adjustable central cone and the outer wall 1 of the nozzle is a single-wave zone, selecting the minimum limit Mach number 1.8Ma at the nozzle exit as the design condition will result in incomplete performance of the shock wave wall surface and the generation of compression waves. Therefore, the calculation method of the Foelsch curve is adopted, and 2.2Ma is used as the design condition for the expansion section to optimize the nozzle performance. The surface curve of its expansion section is as Figure 7 (a) shown.

[0057] In the fifth step, according to the known technical solution of the supersonic nozzle, the characteristic line and the Mach line can be regarded as coincident in the termination section design. The surface curve BN of the adjustable central cone termination section is divided into an infinite number of short broken lines by using the differential limit theorem. Based on the relationship between the Prandtl-Meyer function and the air flow Mach number, the angle β between each moving point on the curve BN and the horizontal plane is used as the design variable, and it is made to change within a specific range (0 ≤ β ≤ β B °), and the size parameters of the termination section surface curve and the coordinate set of point N at different β angles can be calculated. The surface curve of its termination section is as Figure 7 (b) shown.

[0058] In the sixth step, verify by finite element simulation of fluid mechanics

[0059] Import the designed surface curve into the finite element simulation software and assign the material parameters of the variable Mach number wind tunnel nozzle structure. Use the k-ε turbulence model in the high Mach number fluid physical field to simulate the gas flow state, set the specific heat ratio to 1.4, and the inlet temperature to 300K. Define the adjustable central cone and the flow division cone as solid regions in the fluid mechanics physical field, set the inlet flow velocity to 136m / s, and the axial movement range of the adjustable central cone to 0mm - 125mm. When the designed Mach number at the nozzle exit is 1.8, the adjustable central cone is in the non-elongated state, and the throat area of the variable Mach number nozzle is at its maximum limit value. Under this working condition, the Mach number distribution and pressure nephogram of the flow field obtained by numerical simulation are respectively as Figure 8 and Figure 9As shown, the adjustable center cone is axially moved by an actuator, causing its throat radius to change in the direction of the minimum Mach number limit value of 1.8 Ma. During this process, compared with the throat cross-sectional area corresponding to the initial Mach number, the flow channel area of the variable Mach number nozzle gradually decreases, thereby achieving continuous adjustment of the Mach number at the nozzle outlet. When the designed Mach number is 2.2 Ma, the simulation results of the Mach number distribution and pressure contour in the flow field are as shown in Figure 10 and Figure 11 shown.

[0060] In summary, the various solutions provided by the present invention can achieve continuous change of the Mach number at the nozzle outlet, meet the performance requirements of wind tunnel nozzle experiments, and have the characteristics of high efficiency, simple structure, and low cost. Although the present invention has been described in detail, it is not only applicable to the above situation.

[0061] Those skilled in the art can make changes without departing from the scope of the present invention upon understanding the present invention. This method can also be used for the structural design of traditional solid-wall nozzles with different Mach numbers, and only the nozzle inlet and outlet radii, profile conversion relationship, and actuator electric adjustment need to be changed. Therefore, the additions made to the technology and the replacements of some similar contents in the art should all fall within the protection scope of the present invention.

Claims

1. A controllable variable Mach number wind tunnel nozzle structure, which functions to control the flow channel area to achieve continuous change of the Mach number at the nozzle outlet, is characterized in that, The variable Mach number wind tunnel nozzle structure includes a nozzle outer wall (1), a conical support (2), a pre-tightening bolt (3), an actuator (4), and an adjustable center cone (5); The nozzle outer wall (1) serves as an air flow channel, with its left end face being the nozzle inlet area, its right end face being the nozzle outlet area, and it is connected to the test section. The internal profile is divided into a contraction section I and a straight wall section; The conical support (2) is arranged in parallel at the inlet of the nozzle outer wall (1). Its front end is a conical structure, and its rear end is a cylindrical structure with four groups of streamlined blades. Both the front and rear end faces are equipped with mounting flanges for fastening connection with the nozzle outer wall (1); The actuator (4) is installed inside the cylindrical structure with four groups of streamlined blades. The control system inside the actuator (4) selects PID axial control. Its adjustment device is led out through the nozzle outer wall (1), and the actuator (4) is fixed using a pre-tightening screw (3); one end of the actuator (4) is fixed and constrained, and the other end is connected to the adjustable center cone (5); The adjustable center cone (5) is an overall rotating body structure. Its diameter increases first and then decreases from the front end to the end. It includes a contraction section II at the front end, an expansion section in the middle, a termination section at the end, and a conical fairing section outside the nozzle outlet, which is used to regulate the throat gap between the nozzle outer wall (1) and the adjustable center cone (5); When continuous adjustment of the Mach number in the test section is required during the test process, the output displacement of the actuator (4) is controlled to change the throat gap, realizing continuous change of the Mach number at the nozzle outlet and meeting the requirements of different working conditions.

2. The adjustable variable Mach number wind tunnel nozzle structure according to claim 1, characterized in that, The nozzle outer wall (1) is a hollow rotating body structure and serves as the main air flow channel; the nozzle outer wall (1) is connected to the conical support (2) using a flange or a pre-tightening bolt (3) to form a seamless connection to ensure tightness.

3. A controllable variable Mach number wind tunnel nozzle structure according to claim 1, characterized in that, The conical support (2) is a composite structure, mainly composed of a flow dividing cone (2-1) and a streamlined support frame (2-2); the flow dividing cone (2-1) is located at the end of the structure and is integrally formed with the streamlined support frame (2-2); the outer wall of the upper end of the streamlined support frame (2-2) is a circular ring structure, and multiple threaded holes are regularly arranged on its upper surface for fixed connection with the nozzle outer wall (1); the bottom surface of the streamlined support frame (2-2) is designed with an internal installation structure for connection with the actuator (4); the streamlined support frame (2-2) is arranged with four groups of streamlined blades in an integral connection manner.

4. A controllable variable Mach number wind tunnel nozzle structure according to claim 1, characterized in that, The actuator (4) is mainly composed of an ultra-precision electric cylinder (4-1), a rear flange internal thread connecting piece (4-2), a front flange connecting piece (4-3), and an axially displaced system controlled by PID, and is installed inside the streamlined support frame (2-2).

5. A controllable variable Mach number wind tunnel nozzle structure according to claim 1, characterized in that, The main structure of the adjustable center cone (5) is streamlined, and its front diameter increases first and then decreases, which is used to adjust the throat distance from the nozzle outer wall; the front end face has a connecting hole with internal threads and is fixed to the actuator (4) using an adapter flange; the tail is designed as a tapered structure with a curved connection.

6. A design method for the adjustable variable Mach number wind tunnel nozzle structure according to any one of claims 1-5, characterized in that, The design method includes the following steps: The first step is to design the profile curve of the nozzle outer wall (1); 1.1) Design the range Ma1, Ma2 of the required exit Mach number, the inlet diameter R0 of the nozzle, and the outlet diameter R of the nozzle e , and determine the ratio of the nozzle outlet radius to the throat radius in combination with the specific relationship in the sonic section of the nozzle; 1.2) According to the design requirements of the wind tunnel nozzle, the curve of the front-end contraction section type I surface of the outer wall (1) of the nozzle adopts the method of optimizing the shift of the Witoszynski curve, and the type surface of the rear-end straight wall section adopts the design method of straight line connection. Therefore, only the type surface curves of two limit values, Ma1 and Ma2, need to be calculated; 1.3) The type surface curve of the contraction section I is related to the throat of the nozzle. During the design process, ensure that the curvature radius of the nozzle throat is greater than the end; use the maximum limit value Ma2 of the Mach number at the nozzle outlet as the design basis; Second step, based on the type surface curves corresponding to the two limit values of the Mach number at the outlet of the variable Mach number wind tunnel nozzle structure, determine the adjustment range of the throat radius between the adjustable center cone (5) and the straight wall section; by converting the adjustment range into the movement range of the actuator (4), achieve precise adjustment of the throat radius; Third step, based on the design method of the first step, adopt an axisymmetric form to make the type surface curve of the contraction section II of the adjustable center cone (5) symmetric with the contraction section I of the outer wall (1) of the nozzle; Fourth step, design the type surface curve of the expansion section at the end of the adjustable center cone (5); 4.1) The flow channel between the middle expansion section of the adjustable center cone and the outer wall (1) of the nozzle is a single-wave zone. Design according to the type surface curve of the traditional Laval nozzle to obtain the type surface curve of the expansion section of the adjustable center cone; 4.2) By adopting the Foelsch curve calculation method, determine the maximum expansion angle β of the critical point B of the adjustable center cone expansion section curve B and the relationship with the nozzle exit radius; Define the critical point between the expansion section and the termination section of the adjustable center cone (5) as point B, and the angle between point B and the horizontal plane is denoted as the maximum expansion angle β. B , the curve BN represents the profile curve of the termination section of the adjustable center cone (5), the angle between each moving point on the curve BN and the horizontal plane is denoted as β, and the diameter of the conical fairing section outside the nozzle exit is R. c , the length of the contraction section is l0, and the length of the expansion section is l. B , the length of the termination section is l. c ; Define the radius of the nozzle inlet as r0 and the radius of the nozzle outlet as r. e , the thickness of the nozzle outer wall (1) is denoted as t1, and the vertical distance from the highest point of the adjustable center cone (5) to the profile curve of the nozzle outer wall is denoted as the throat radius r. t ; Then, represent the radius of curvature of critical point B, the abscissa and ordinate of critical point B (x B , y B ), and the profile curve of the expansion section of the adjustable center cone (5) as follows: Among them, β B represents the maximum expansion angle; v1 represents the Prandtl-Meyer angle corresponding to the nozzle design Mach number; r t represents the nozzle throat radius; r e represents the nozzle exit radius; r B represents the nozzle radius at the position of point B; Ma B represents the Mach number at point B; k represents the specific heat ratio coefficient of the applied gas; r represents the nozzle curvature radius corresponding to x; x represents the abscissa of the profile of the adjustable center cone surface; 4.3) Solve to obtain the type surface curves of the expansion section under the limit Mach numbers Ma1 and Ma2 conditions, and select Ma2 as the design Mach number of the expansion section of the adjustable center cone (5) to optimize the performance of the nozzle; Fifth step, design the type surface curve of the termination section. Specifically: In the design of the termination section, the characteristic line and the Mach line are regarded as coincident. Divide the curve BN into an infinite number of short broken lines. Take the angle β between each moving point on the curve BN and the horizontal plane as the design variable, and match the coordinate relationship between different MN lengths and point N to obtain a continuous type surface curve of the termination section; Sixth step, verify by finite element simulation of fluid mechanics.

7. A design method for a controllable variable Mach number wind tunnel nozzle structure according to claim 6, characterized in that, The two limit values in the second step are Ma1 and Ma2.

8. A design method for a controllable variable Mach number wind tunnel nozzle structure according to claim 6, characterized in that, In the fourth step 4.3), use the analytical method to obtain the type surface curves of the expansion section under the limit Mach numbers Ma1 and Ma2 conditions.

9. The design method of an adjustable variable Mach number wind tunnel nozzle structure according to claim 6, characterized in that, The fifth step is specifically: According to the known technical solution of the supersonic nozzle, in the design of the termination section, the characteristic line and the Mach line can be regarded as coincident. Use the differential limit theorem to divide the curve BN into an infinite number of short broken lines; based on the relationship between the Prandtl-Meyer function and the Mach number of the air flow, take the angle β between each moving point on the curve BN and the horizontal plane as the design variable, and match the coordinate relationship between different MN lengths and point N to obtain a continuous type surface curve of the termination section.

10. A design method for a controllable variable Mach number wind tunnel nozzle structure according to claim 6, characterized in that, The sixth step is specifically: 6.1) Import the type surface curves of the designed contraction section I, contraction section II, straight wall section, expansion section, termination section, and conical fairing section into the finite element simulation software, and assign the material parameters of the variable Mach number wind tunnel nozzle structure; 6.2) Use the k-ε turbulence model in the high Mach number fluid physical field to simulate the gas flow state, and set the specific heat ratio and the inlet temperature; 6.3) Set the boundary conditions in the fluid mechanics physical field, select the nozzle inlet and outlet, set the nozzle inlet flow velocity and the nozzle outlet pressure, and define the adjustable center cone 1 and the splitter cone 2 as solid regions; 6.4) After completing the setting of the physical field of fluid mechanics, divide the mesh and perform finite element analysis.

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