A method for designing a variable-mach-number static wind tunnel nozzle

Abstract

The application discloses a variable Mach number static wind tunnel nozzle design method, and belongs to the technical field of wind tunnel test. According to the nozzle design theory, the Sivells method is adopted to design the nozzle expansion section curve in combination with the structure form of the static wind tunnel nozzle, and the expansion section between the throat to the downstream source flow curve conical wall surface is replaced; the CQCQ (cylinder-quartic-cone-quartic) curve is adopted to design the nozzle contraction section, and the contraction section between the conical section to the throat is replaced. The throat size and the profile at the suction groove are designed and modified, so that the Mach number at the nozzle outlet is changed. The application provides a method for changing the flow field Mach number of the static wind tunnel.

Description

Technical Field

[0001] This invention relates to a method for designing a static wind tunnel nozzle with variable Mach number, belonging to the field of wind tunnel testing technology. Background Technology

[0002] With the continuous development of high-speed aircraft, wide-range flight is an essential capability for new aircraft. Changes in Mach number lead to changes in flight performance, and to obtain accurate experimental data, ground simulation equipment needs to be capable of operating at multiple Mach numbers. In supersonic nozzles, different Mach numbers correspond to different expansion ratios, which are the ratio of the nozzle exit area to the throat area.

[0003] In a still wind tunnel, the core component that generates a still flow field is the still nozzle. The still nozzle is designed with features such as suction channels, slow expansion, and a highly smooth inner surface to minimize noise at the nozzle exit and maintain laminar flow at the exit boundary layer. Due to the extremely high requirements for nozzle profile machining and surface roughness, a single nozzle is very expensive. Designing it like a conventional high-speed wind tunnel, where the Mach number is changed by replacing the entire nozzle, would be prohibitively costly. Furthermore, because of the requirements for the nozzle's internal profile and flow field quality, and its structure differing from conventional nozzles, replacing the throat in a still wind tunnel, like in a shock tunnel, requires careful redesign of the relevant profiles and structure. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a method for designing a static wind tunnel nozzle with a variable Mach number. By replacing fewer parts of the nozzle, the Mach number at the exit of the static nozzle can be changed while maintaining the same flow field quality.

[0005] The technical solution of this invention is: a method for designing a variable Mach number static wind tunnel nozzle, comprising:

[0006] (1) Determine the expansion section curve of the three-dimensional axisymmetric nozzle based on the nozzle exit Mach number and exit diameter; calculate the suction groove width based on the throat size and design the suction volume; determine the contraction section curve based on the inlet size of the contraction section.

[0007] (2) Design and segment the nozzle structure, with the segmentation located at the conical section of the contraction and expansion sections;

[0008] (3) Calculate the new throat size according to the required change of the outlet Mach number, design the suction volume based on the new throat size and calculate the suction slit width;

[0009] (4) Divide the static wind tunnel nozzle from the upstream inlet to the downstream outlet into a contraction section, a throat section, and a divergence section. The contraction section is further divided from the inlet into a cylindrical section, a quartic curve section, a conical section, and a quartic curve section, denoted as ab, bc, cd, and de, respectively. The divergence section is divided from left to right into a characteristic line solution region, a source region, and a characteristic line solution region, denoted as TIEG, GEBA, and ABCD, respectively. The wall profile from the throat to the nozzle outlet is divided into TG, GA, and AD by points T, G, A, and D, respectively. The segment, where GA is the conical segment, is divided into segments IE, EB, and BC on the nozzle axis from the throat to the outlet by points I, E, B, and C respectively. TI, GE, AB, and DC are all characteristic lines. The Mach number at point I is 1, and the Mach numbers at points C and D are the same, both being the nozzle outlet Mach number. A new quartic curve for segment de is designed based on the suction slot width, connected upstream to segment cd, maintaining a consistent slope. The length of segment cd is adjusted to ensure the suction slot width, so that the ratio of the suction slot area to the throat area is within a preset range.

[0010] (5) Design the Mach number at point B according to the required change of the exit Mach number, and calculate the Mach numbers at points G and E;

[0011] (6) Design a new velocity distribution for the IE segment, calculate the characteristic line of the TIEG region, solve the new curve of the TG segment, adjust the length of the GA segment according to the calculation results, change the position of point G and the characteristic line parameters of the GE segment along the GA segment, and repeat the iteration to obtain a smooth connection between the TG segment and the GA segment.

[0012] (7) Design stop joints at the segmentation points to ensure smooth and continuous inner surfaces and complete the design.

[0013] Furthermore, the method for determining the three-dimensional axisymmetric nozzle expansion segment curve is the Sivells method.

[0014] Furthermore, the contraction segment includes a cylindrical segment, a first curve segment with an outer contour line of a quartic curve, a conical segment, and a second curve segment with an outer contour line of a quartic curve, with smooth connections between each segment and continuous curvature.

[0015] Furthermore, the static wind tunnel nozzle includes a suction slit located between the contraction section and the throat section, with a preset range of 0.4 to 1.

[0016] Furthermore, the nozzle contraction section, throat section, and expansion section are processed in segments. The contraction section is further segmented in its conic section, and the expansion section is further segmented in its source flow region conic section.

[0017] Furthermore, the replacement segment is a conic section from a contraction segment to an expansion segment.

[0018] Furthermore, the nozzle changes its Mach number by altering the profile between the two conical sections. The Mach number is determined by the throat area and the exit area. Among them, A 出 A is the nozzle exit area. 喉 γ is the nozzle throat area, Ma is the nozzle exit Mach number, and γ is the air specific heat ratio.

[0019] Furthermore, the maximum expansion angle of the expansion section is fixed, that is, the slope of the conical section GA is fixed. The Mach number at point E is calculated based on the exit Mach number, and a new velocity distribution for the IE section is set to calculate the curve for the TG section.

[0020] Furthermore, the slope of the conic curve in the contraction section remains unchanged, and a new fourth-order curve is connected to the conic curve, while ensuring the suction slit width.

[0021] Furthermore, the replacement section and the original nozzle section are positioned by a stop, the flange is tightened, and the sealing ring is used for sealing. There is no reverse airflow step at the interface, and the forward airflow step is less than 0.02mm.

[0022] The advantages of this invention compared to the prior art are:

[0023] (1) The present invention adopts a cylindrical-quadrupole-cone-quadrupole curve design for the shrinkage section, and performs segmentation and replacement of the shrinkage section at the conical curve to achieve continuous curvature of the shrinkage section, easy adjustment of the profile, and ensure the width of the suction seam;

[0024] (2) This invention achieves continuous curvature of the expansion section profile, reasonable Mach number distribution of the flow field, easy processing at the segmentation point, and controllable installation step by designing the conic curve of the source flow region of the expansion section using the Sivells method, readjusting the Mach number distribution of the IE section, and calculating the curve of the TG section.

[0025] (3) This invention reduces the nozzle processing cost and improves the flow field quality after the throat is replaced by replacing the nozzle throat with a suction slit and adjusting the Mach number of the nozzle in the still wind tunnel. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the static wind tunnel nozzle of the present invention;

[0027] Among them, 1. contraction section, 2. suction groove, 3. throat, 4. dilation section;

[0028] Figure 2 This is a schematic diagram of the inner surface of the nozzle of the present invention. Detailed Implementation

[0029] To better understand the above technical solutions, the technical solutions of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.

[0030] The following description, in conjunction with the accompanying drawings, provides a more detailed explanation of a variable Mach number static wind tunnel nozzle design method provided in this application. Specific implementation methods may include (e.g.) Figures 1-2 As shown):

[0031] The static nozzle adopts an axisymmetric nozzle design; the contraction section uses a CQCQ curve design, and the expansion section uses the Sivells method design. First, based on a target Mach number, the nozzle is designed using the method described in the scheme. The nozzle is segmented at the conical sections of the contraction and expansion sections, and a suction groove is designed based on the throat diameter. Depending on the required Mach number and nozzle exit size, the throat area and diameter of the new nozzle are calculated. The suction groove lip is designed based on the new throat diameter and suction volume. A new quartic curve is designed upstream of the throat as the upper surface curve of the suction groove, smoothly connecting to the original conical section. Downstream of the throat, based on the Sivells method design principle, the Mach number distribution along the IE segment axis is redesigned, and the TIEG characteristic line region is calculated using the method of characteristics to solve for the TG segment curve.

[0032] The present invention specifically includes the following steps:

[0033] (1) Determine the expansion section curve of the three-dimensional axisymmetric nozzle based on the nozzle exit Mach number and exit diameter; calculate the suction groove width based on the throat size and design the suction volume; determine the contraction section curve based on the inlet size of the contraction section.

[0034] (2) Design and segment the nozzle structure, with the segmentation located at the conical section of the contraction and expansion sections;

[0035] (3) Calculate the new throat size according to the required change of the outlet Mach number, and calculate the suction volume and suction slit width from the new throat size;

[0036] (4) Divide the static wind tunnel nozzle from the upstream inlet to the downstream outlet into a contraction section, a throat section, and an expansion section; the contraction section is divided into a cylindrical section, a quartic curve section, a conical section, and a quartic curve section from the inlet, denoted as 'ab', 'bc', 'cd', and 'de' sections respectively; the expansion section is divided into a characteristic line solution area, a source flow area, and a characteristic line solution area from left to right, denoted as 'TIEG', 'GEBA', and 'ABCD' areas respectively; design a new quartic curve for the 'de' section based on the suction slot width, connect it upstream to the 'cd' section, maintain a consistent slope, adjust the length of the 'cd' section to ensure the suction slot width, so that the ratio of the suction slot area to the throat area is within a preset range;

[0037] (5) Design the Mach number at point B according to the required change of the exit Mach number, and calculate the Mach numbers at points G and E;

[0038] (6) Design a new velocity distribution for the IE segment, calculate the characteristic line of the TIEG region, solve the new curve of the TG segment, adjust the length of the GA segment according to the calculation results, change the position of point G and the characteristic line parameters of the GE segment along the GA segment, and repeat the iteration to obtain a smooth connection between the TG segment and the GA segment.

[0039] (7) Design stop joints at the segmentation points to ensure smooth and continuous inner surfaces and complete the design.

[0040] Optionally, the method for determining the three-dimensional axisymmetric nozzle expansion segment curve is the Sivells method.

[0041] Furthermore, the curve for determining the contraction segment is a cylindrical-quartic-conical-quartic curve, with smooth connections between segments and continuous curvature.

[0042] Furthermore, in one possible implementation, the static wind tunnel nozzle includes a suction slit located between the contraction section and the throat section, with the preset range being 0.4 to 1.

[0043] In one possible implementation, the nozzle contraction section, throat section, and expansion section are segmented, with the contraction section further segmented in its conic section and the expansion section further segmented in its source flow region conic section.

[0044] Optionally, in one possible implementation, the replacement segment is a conic section transitioning from a contraction segment to an expansion segment.

[0045] Furthermore, in one possible implementation, the nozzle changes its Mach number by altering the profile between two conical sections, the Mach number being determined by the throat area and the exit area. Among them, A 出 A is the nozzle exit area. 喉 γ is the nozzle throat area, Ma is the nozzle exit Mach number, and γ is the air specific heat ratio.

[0046] In one possible implementation, the maximum expansion angle of the expansion segment is constant, i.e. the slope of the conical segment GA is constant. The Mach number at point E is calculated based on the exit Mach number, and a new velocity distribution for the IE segment is set to calculate the curve for the TG segment.

[0047] In one possible implementation, the slope of the conic section remains unchanged, and a new quartic curve is designed to connect to the conic section while ensuring the suction slit width.

[0048] Optionally, the replacement section and the original nozzle section are positioned by a stop, the flange is tightened, and the sealing ring is used for sealing. There is no reverse airflow step at the interface, and the forward airflow step is less than 0.02mm.

[0049] The steps in the solution provided in this application embodiment are as follows:

[0050] (1) Based on the nozzle exit Mach number and exit diameter, the Sivells method is used to design the three-dimensional axisymmetric nozzle expansion section curve, the suction volume is designed based on the throat size, the suction groove width is calculated, and the contraction section curve is designed based on the inlet size of the contraction section.

[0051] (2) Design and segment the nozzle structure, with the segmentation located at the conical section of the contraction and expansion sections;

[0052] (3) Calculate the new throat size according to the required change of the outlet Mach number, and calculate the suction slit width based on the new throat size to design the suction volume;

[0053] (4) Design a new 'de' segment quartic curve based on the seam width, with the upstream end connected to the 'cd' segment, maintaining a consistent slope, and appropriately adjusting the length of the 'cd' segment to ensure the suction seam width;

[0054] (5) Based on the new exit Mach number, design the Mach number at point B, and calculate the Mach number at point G based on the source region assumption.

[0055] (6) Design a new velocity distribution for the IE segment, calculate the characteristic line of the TIEG region, solve the new curve of the TG segment, adjust the length of the GA segment according to the calculation results, change the position of point G and the characteristic line parameters of the GE segment along the GA segment, and repeat the iteration to obtain a smooth connection between the TG segment and the GA segment.

[0056] (7) After the design is completed, stop joints are designed at the segment points to ensure that the inner surface is smooth and continuous.

[0057] Figure 2 In the diagram, segment ab is a cylinder; segment bc is a quartic curve; segment cd is a cone, which is divided into two parts for replacement and connection; segment de is a quartic curve; segment NST is the suction groove lip; segment TG is a profile, calculated based on the TIEG region feature lines; segment GA is a cone, which is divided into two parts for replacement and connection; segment AD is a profile, calculated based on the ABCD region feature lines.

[0058] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

[0059] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method of designing a variable Mach number static wind tunnel nozzle, characterized by, include: (1) Determine the expansion section curve of the three-dimensional axisymmetric nozzle based on the nozzle exit Mach number and exit diameter; Calculate the suction groove width based on the throat size and design the suction volume; determine the contraction section curve based on the inlet size of the contraction section. (2) Design and segment the nozzle structure, with the segmentation points located at the conical sections of the contraction and expansion sections; (3) Calculate the new throat size according to the required change of the outlet Mach number, design the suction volume based on the new throat size and calculate the suction slit width; (4) Divide the static wind tunnel nozzle from the upstream inlet to the downstream outlet into a contraction section, a throat section, and an expansion section; the contraction section is further divided from the inlet into a cylindrical section, a quartic curve section, a conical section, and a quartic curve section, denoted as ab, bc, cd, and de, respectively; the expansion section is divided from left to right into a characteristic line solution region, a source flow region, and a characteristic line solution region, denoted as TIEG, GEBA, and ABCD, respectively; the wall profile from the throat to the nozzle outlet is divided into TG, GA, and AD by points T, G, A, and D, respectively. The segment, where GA is the conical segment, is divided into segments IE, EB, and BC on the nozzle axis from the throat to the outlet by points I, E, B, and C respectively. TI, GE, AB, and DC are all characteristic lines. The Mach number at point I is 1, and the Mach numbers at points C and D are the same, both being the nozzle outlet Mach number. A new quartic curve for segment de is designed based on the suction slot width, connected upstream to segment cd, maintaining a consistent slope. The length of segment cd is adjusted to ensure the suction slot width, so that the ratio of the suction slot area to the throat area is within a preset range. (5) Design the Mach number at point B according to the required change of the exit Mach number, and calculate the Mach numbers at points G and E; (6) Design a new velocity distribution for the IE segment, calculate the characteristic line of the TIEG region, solve the new curve of the TG segment, adjust the length of the GA segment according to the calculation results, change the position of point G and the characteristic line parameters of the GE segment along the GA segment, and repeat the iteration to obtain a smooth connection between the TG segment and the GA segment. (7) Design stop joints at the segmentation points to ensure smooth and continuous inner surfaces, thus completing the design; The nozzle changes the Mach number by changing the profile between the two conic sections, the Mach number being determined by the throat area and the exit area, ; wherein is the exit area of the nozzle, is the throat area of the nozzle, is the exit Mach number of the nozzle, is the air specific heat ratio; The maximum expansion angle of the expansion section is constant, that is, the slope of the conical section GA is constant. The Mach number at point E is calculated based on the exit Mach number, and a new velocity distribution in the IE section is set to calculate the curve of the TG section. The slope of the conic curve in the contraction section remains unchanged, and a new fourth-order curve is designed to connect to the conic curve while ensuring the suction slit width.

2. The method of designing a variable Mach number static tunnel nozzle according to claim 1, wherein: The method for determining the expansion segment curve of a three-dimensional axisymmetric nozzle is the Sivells method.

3. The method of designing a variable Mach number static tunnel nozzle of claim 1, wherein: The contraction segment includes a cylindrical segment, a first curve segment with an outer contour line of quartic curve, a conical segment, and a second curve segment with an outer contour line of quartic curve. The segments are smoothly connected and have continuous curvature.

4. The method for designing a variable Mach number static wind tunnel nozzle according to claim 1, characterized in that: The static wind tunnel nozzle includes a suction slit located between the contraction section and the throat section, with a preset range of 0.4 to 1.

5. The method for designing a variable Mach number static wind tunnel nozzle according to claim 1, characterized in that: The contraction section, throat section, and expansion section are processed in segments. The contraction section is further segmented in its conic section, and the expansion section is further segmented in its source region conic section.

6. The method for designing a variable Mach number static wind tunnel nozzle according to claim 1, characterized in that: The replacement segment is a conic section that changes from a contraction segment to an expansion segment.

7. The method for designing a variable Mach number static wind tunnel nozzle according to claim 6, characterized in that: The replacement section and the original nozzle section are positioned by a stop, the flange is tightened, and the sealing ring is used for sealing. There is no reverse airflow step at the interface, and the forward airflow step is less than 0.02mm.

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