Design method of internal waverider inlet based on circumferential azimuth pressure gradient correction

Abstract

The present invention discloses a design method of an internal waverider inlet based on circumferential azimuthal pressure gradient correction, comprising the following steps: adopting the concept of osculating axisymmetric flow to design the internal waverider inlet, using the Euler incompressible flow equation to calculate the circumferential velocity term between all osculating planes, the equation using the circumferential velocity to represent the azimuthal pressure gradient, adding the circumferential velocity term to the original design method to consider the influence of the azimuthal pressure gradient, and then adopting the streamline tracing method to obtain a new type of surface of the internal waverider inlet. Finally, the new surface of the internal waverider inlet is smoothed to avoid surface deformity caused by sudden changes in the azimuthal pressure gradient, thereby solving the azimuthal pressure gradient problem of the three-dimensional internal waverider inlet and making the internal waverider inlet after the circumferential pressure gradient correction show better performance in terms of total pressure recovery and flow uniformity.

Description

Technical Field

[0001] The present invention relates to the field of aircraft technology, in particular to supersonic and hypersonic air-breathing aircraft, and specifically to a design method for an internal waverider inlet based on circumferential azimuth pressure gradient correction. Background Art

[0002] Research shows that hypersonic inlets have a significant impact on the performance of engines and aircraft, among which the inlet plays a major role in the thrust of the engine and directly affects the lift-to-drag ratio. The design objectives of an efficient hypersonic inlet are to capture and compress air, properly adjust the uniformity of the flow field, provide thermodynamically effective air to the combustion chamber at a predictable mass flow rate, and minimize the degradation of the inlet performance and ensure stable operation under non-design conditions.

[0003] In the process of inlet design, when the inlet and outlet shapes are specified in advance, the idea of ​​cross-sectional transition is adopted to obtain the REST inlet shape. Although the REST inlet satisfies the shape transition, it does not satisfy the aerodynamic transition. Although streamline tracing inlets such as the Busemann inlet can satisfy the aerodynamic transition, the inlet and outlet shapes cannot be obtained at the same time. Only one of them can be selected, and then the other is formed according to streamline tracing. The three-dimensional internal waverider inlet SCIW with controllable cross-section, also known as the internal waverider inlet IWI, can meet the complex geometric shape transition and achieve acceptable aerodynamic transition. Although the SCIW inlet successfully achieves the goal of cross-sectional geometric shape transition and fully captures the upstream flow, its total pressure recovery is lower than that of the Busemann inlet because the design method adopted ignores the lateral flow effect. Since total pressure recovery plays a vital role in the thrust and efficiency of the aircraft, the lower the total pressure recovery, the lower the thrust, so it is the most important parameter in the inlet design.

[0004] The concept of the internal waverider inlet is basically a combination of the osculating axisymmetric flow method and the streamline tracing method. This idea relies on the characteristics provided by the waverider vehicle design process, with a shock wave attached to the inlet entrance, the shape riding on the shock wave, and its lower surface completely attached to the shock wave. Although the inlet is a pressurized component, the captured streamlines will not leak out by sealing the inlet entrance with the shock wave; this maximizes the flow capture rate of the inlet, making it close to 1.

[0005] The concept of osculating axisymmetric flow is introduced as a generalization of the concept of osculating cone, where the concept of osculating axisymmetric flow is referred to as OA and the osculating cone is referred to as OC, which is used for the design of curved shock waves in waverider design. The concept of osculating axisymmetric flow transforms the three-dimensional inlet into a series of local two-dimensional slices or osculating planes, and the flow in the plane is a local two-dimensional flow. The streamline tracing method is used on each osculating plane to form the wall. The OA method is an approximate method that ignores the influence of the lateral flow between adjacent planes on the circumferential direction and introduces the azimuthal pressure gradient problem that has a negative effect on the inlet performance. Summary of the invention

[0006] The present invention provides an internal waverider inlet design method based on circumferential azimuth pressure gradient correction to solve the azimuth pressure gradient problem of a three-dimensional internal waverider inlet.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for designing an inner waverider inlet based on circumferential azimuth pressure gradient correction, comprising the following steps:

[0008] S1. The original osculating axisymmetric flow method is used to design the internal waverider inlet. The basic flow field is osculated along the azimuth direction to generate the three-dimensional geometric shape of the internal waverider inlet, and finally the flow information of all points on the osculating plane is obtained;

[0009] S2. Use the Euler incompressible flow equation to calculate the circumferential velocity terms between all osculating planes and use the circumferential velocity to represent the azimuthal pressure gradient, where the Euler incompressible flow equation is:

[0010] dV 2 =-2dp / ρ

[0011] Among them, p is pressure, ρ is density, and V is velocity;

[0012] S3. Add the circumferential velocity term to the original design method to consider the influence of the azimuthal pressure gradient, and use the velocity correction vector to convert the ICFC+ flow field axial velocity U and R velocity V used in the original osculating axisymmetric flow method. R Update and calculate the corrected velocity u, v, w of point J in XYZ coordinates;

[0013] S4, for each osculating plane J, use the new velocities u, v and w to apply the streamline tracing method along the flow direction i to obtain the internal waverider inlet after pressure gradient correction;

[0014] S5. The new surface of the inner waverider inlet is smoothed to avoid surface deformity caused by sudden changes in azimuthal pressure gradients, thus forming a new inlet shape.

[0015] Preferably, in step S1, the inner waverider inlet flow field includes streamlines extracted from the ICFC+ basic flow, and the truncated Busemann and ICFA basic flow fields are generated using the characteristic line method, and then the Busemann compression surface is pushed down using the streamline function.

[0016] Preferably, in step S1 , the shapes of the inlet and outlet of the air intake passage are pre-specified as a circle and a semi-rectangle having the same internal contraction ratio.

[0017] Preferably, in step S1, a series of local two-dimensional streamline slices extracted from the ICFC+ basic flow field are used as osculating planes and converted into three-dimensional inlet duct profiles using a streamline tracing method.

[0018] Preferably, the method for calculating the speed correction vector comprises the following steps:

[0019] 1) After obtaining the flow information of all points on the osculating plane through step S1, calculate the velocity correction between the considered point J and its two adjacent points J+1 and J-1 in each osculating plane slice, with the flow direction being the i direction and the circumferential direction being the J direction;

[0020] 2) Project the velocity correction onto the ZY and XY planes and calculate the velocity components;

[0021] 3) Project the velocity correction vector onto the considered osculating plane J, with directions R and R N , where R is the normal direction, and on the azimuth plane ZY, the velocity correction vector is calculated.

[0022] Preferably, in step S2, an osculating plane is included, wherein the local flow is a two-dimensional flow, and the position of the point and the flow information are known.

[0023] Preferably, in step S4, the speed at the new coordinates is calculated by using an inverse distance weighted interpolation method.

[0024] Preferably, in step S5, the original point positions of all osculating planes in each azimuth J direction are updated by adopting a maximum radius correction and an average angle correction in the J direction.

[0025] Compared with the prior art, the present invention has the following beneficial effects: the present invention adopts the Euler incompressible flow equation to calculate the lateral flow velocity and corrects the azimuthal pressure gradient to the original design level; then, the three-dimensional streamlines are replaced by the two-dimensional streamlines of the osculating plane; in addition, the comparison with the original internal waverider inlet shows that the internal waverider inlet with the circumferential pressure gradient corrected shows better performance in total pressure recovery and flow uniformity; the present invention can eliminate the circumferential pressure difference between the osculating surfaces through the pressure gradient correction, thereby avoiding the circumferential migration of the low-energy flow near the wall and further enhancing the flow distortion in the inlet. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0027] In the attached picture:

[0028] Figure 1 It is a schematic diagram of the circumferential pressure gradient corrected osculating axisymmetric flow method of the present invention;

[0029] Figure 2 is a simplified theoretical diagram of the osculating axisymmetric inner waverider inlet of the present invention;

[0030] Figure 3 It is a diagram of three local points (i to i+1) on the shock wave surface generated by the osculating plane of a line segment of the present invention;

[0031] Figure 4 It is the osculating plane projection diagram and the velocity projection diagram on the ZY plane of the present invention: wherein (a) is the osculating plane projection diagram, and (b) is the velocity projection diagram;

[0032] Figure 5 It is a schematic diagram of new surface points after the circumferential pressure gradient correction of the osculating plane J generated by the present invention;

[0033] Figure 6 It is a flow chart of the algorithm for the present invention to execute the method of the present invention;

[0034] Figure 7 It is an algorithm flow chart of the method of the present invention;

[0035] Figure 8 It is a schematic structural diagram of an inner waverider air inlet with a rectangular inlet and outlet according to the present invention;

[0036] Fig. 9 It is a diagram of a pressure-corrected inner waverider inlet (PWI) and an original inner waverider inlet (OWI) of a three-dimensional structure of the present invention;

[0037] Fig.10 It is a diagram of a pressure-corrected inner waverider inlet (PWI) and an original inner waverider inlet (OWI) of a two-dimensional structure of the present invention;

[0038] Fig.11 It is a schematic structural diagram of an inner waverider air inlet with a circular inlet and outlet according to the present invention;

[0039] Fig.12 It is a diagram of a pressure-corrected inner waverider inlet (PWI) and an original inner waverider inlet (OWI) of the three-dimensional structure of the present invention. DETAILED DESCRIPTION

[0040] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0041] The present invention provides a design method for an internal waverider inlet based on circumferential azimuth pressure gradient correction. The method incorporates the azimuth pressure gradient effect into the concept of osculating axisymmetric flow of the internal waverider inlet by considering the lateral flow between osculating planes caused by the pressure difference in the azimuth direction, and then compensates it to the velocity of the profile by a streamline tracing method; in order to achieve this purpose, at each local point, the influence of the azimuth pressure gradient is converted into velocity by using the Euler incompressible flow equation, wherein the Euler incompressible flow equation is:

[0042] dV 2 =-2dp / ρ

[0043] Where p is pressure, ρ is density, and V is velocity. Since the ICFC+ basic flow field that generates the internal waverider inlet is inviscid, the Euler incompressible flow equation is used. Therefore, Figure 1 As shown, the present invention adopts the following technical steps:

[0044] 1. The original osculating axisymmetric flow method is used to design the internal waverider inlet. The basic flow field is osculated along the azimuth direction to generate a three-dimensional geometric shape and obtain the flow information of all points on the osculating plane, such as Figure 2 As shown;

[0045] 2. After obtaining the flow information of all points on the osculating plane through step 1, calculate the velocity correction between the considered point J and its two adjacent points J+1 and J-1 in each osculating plane slice, as follows: Figure 3 As shown. This figure shows three points of a line (i and i+1) on three osculating plane slices in the flow direction i. The three points are located in the azimuth direction J, and the point considered here is point J on the osculating plane J. The present invention applies the Euler incompressible flow equation dV between point J, J+1 and point J, J-1 respectively. 2 =-2dp / ρ, and gives the formula:

[0046]

[0047]

[0048] 3. Project the velocity correction onto the ZY and XY planes, such as Figure 3 As shown, use:

[0049]

[0050]

[0051] 4. The velocity correction vector is projected on the considered osculating plane J, with directions R and R N , where R is the normal direction; on the azimuth plane ZY plane, the velocity correction vector is given, such as Figure 4 As shown;

[0052]

[0053]

[0054] 5. Consider the U and V of the point R The speed is updated to:

[0055]

[0056] Speed ​​U and V R are the axial and R-direction velocities of the ICFC+ flow field used in the original osculating axisymmetric flow method; these velocities are updated separately with the influence of the pressure gradient and then the new velocities in the XYZ coordinates, i.e., u, v, and w, are obtained. Other variables are calculated according to the following relationship:

[0057]

[0058] 6. Apply the streamline tracing method along the flow direction i for each osculating plane J using the new velocities u, v and w to obtain a new surface of the inner waverider inlet; Figure 5 As shown, the new y and z coordinates of each point are calculated as follows:

[0059] (a) After this step, the new velocities u, v, w are assigned to point i-1 at the original xyz position;

[0060] (b) At the new xyz position, use inverse distance weighted interpolation between points (i-2; i-1 (new) and i-1 (old)) to determine the velocity of point i-1;

[0061]

[0062] in is the calculated value, is a known value, d is the distance from n data points to the estimated n points, and p = 2.

[0063] (c) After calculating the velocities u, v, and w at point i-1, according to the streamline equation Calculate the position of point i;

[0064]

[0065] (d) Repeat the previous steps to calculate all points on the osculating plane J;

[0066] (e) For each osculating plane, the leading edge point is connected to the shock wave. Since the intensity of the shock wave is constant, there is no pressure gradient at this point, so the calculation starts from this point.

[0067] 7. Repeat the entire method for all osculating planes along the azimuth J direction; Figure 6 A new internal waverider inlet design algorithm is outlined.

[0068] 8. The pressure gradient correction must include some processing to avoid any sudden changes in the profile caused by the interaction of the reflected shock wave and the pressure changes on the lower surface near the throat caused by the flow reflection. Therefore, in order to obtain a smooth surface, the maximum radius correction (ΔR max ) and the average angle correction (Δθ av ) Update the original point positions y and z of all osculating planes in the J direction. Repeat this process for all osculating plane slices along the downstream direction i. Since the correction to the azimuthal pressure gradient will produce a lateral velocity component, the streamlines regenerated by the streamline tracing method will have lateral displacements, unlike the original method that occurs on the same constant osculating plane, thus forming three-dimensional streamlines.

[0069]

[0070]

[0071] in θ=tan -1 (y / z) is the radius and angle of the point on the osculating plane slice, such as Figure 4 a. The subscripts “old” and “new” indicate the values ​​obtained using the original design method and the values ​​obtained using the current method, respectively.

[0072] 9. Finally, the new surface point of the pressure gradient corrected inner waverider inlet is calculated by the following formula:

[0073]

[0074]

[0075]

[0076] Example 1: Figure 7 As shown, the technical method for designing a hypersonic internal waverider inlet adopted by the present invention is as follows:

[0077] (1) Select the design conditions: inflow Mach number 6.0, static pressure 1170 Pa, static temperature 225.25 K;

[0078] (2) Generate the truncated Busemann flow field and ICFA basic flow field using the characteristic line method;

[0079] (3) On the basis of limiting the matching of the truncated Busemann flow field angle with the single ray angle of the ICFA flow field, the truncated Busemann flow field is merged with the ICFA base flow field to create the ICFC reference flow field;

[0080] (4) Use the line function to push down the Busmann compression surface so that the characteristic lines of the ICFC flow field converge to the incident point, and improve the ICFC basic flow field to the ICFC+ basic flow field;

[0081] (5) After 2D CFD numerical simulation, the ICFC+ basic flow field streamlines are extracted;

[0082] (6) The selected inlet and outlet planes are as follows Figure 8 As shown;

[0083] (7) Using the osculating axisymmetric flow method to obtain osculating plane points and flow information;

[0084] (8) Using the pressure and density at each point on the osculating plane, calculate the new velocity component, i.e., the circumferential velocity in the azimuth direction between the osculating planes;

[0085] (9) Update the velocity of each point on the osculating plane;

[0086] (10) Use the inverse distance weighted interpolation method to calculate the velocity at the new coordinates;

[0087] (11) Determine the geometry of the hypersonic internal waverider inlet using streamline tracing;

[0088] (12) Smooth the created geometric configuration to avoid geometric deformity;

[0089] (13) Fig. 9 and Fig.10 As shown, the final three-dimensional geometric design of the hypersonic internal waverider inlet is obtained;

[0090] (14) CFD simulation was performed on the designed hypersonic internal waverider inlet, and the results are shown in the following table:

[0091] Table: Average performance parameters of waverider inlet mass flow rate in the outlet section (M e ,π e ,σ e ,φ%,and A σ % are Mach number, pressure ratio, total pressure recovery, flow coefficient ratio, and area ratio of the outlet section with total pressure recovery σ>0.7:

[0092]

[0093] Example 2: As a verification, the method of the present invention is applied to a circular air inlet, and it is found that the shape of the air inlet does not change as expected compared with the air inlet designed by the original method. Since the circular air inlet has no circumferential pressure gradient, the method of the present invention is verified. The technical design method is as follows:

[0094] (1) Repeat the design steps (1) to (5) in Example 1;

[0095] (2) The inlet and outlet planes of the circular inlet are selected, such as Fig.11 As shown;

[0096] (3) Repeat the design steps (7) to (12) in Example 1;

[0097] (4) Obtain the final three-dimensional geometric design of the hypersonic internal waverider inlet, such as Fig.12 shown.

[0098] Finally, it should be noted that the above description is only a preferred example of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Design method of internal waverider inlet based on circumferential azimuth pressure gradient correction, It is characterized in that The following steps are involved: S1. The original osculating axisymmetric flow method is used to design the internal waverider inlet. The basic flow field is osculated along the azimuth direction to generate the three-dimensional geometric shape of the internal waverider inlet, and finally the flow information of all points on the osculating plane is obtained; S2. Using the Euler incompressible flow equation, calculate the circumferential velocity terms between all osculating planes and express the azimuthal pressure gradient in terms of the circumferential velocity; S3. Add the circumferential velocity term to the original design method to consider the influence of the azimuthal pressure gradient, and use the velocity correction vector to convert the ICFC+ flow field axial velocity U and R velocity V used in the original osculating axisymmetric flow method. R Update and calculate the corrected velocity u, v, w of point J in XYZ coordinates; S4, for each osculating plane J, use the new velocities u, v and w to apply the streamline tracing method along the flow direction i to obtain the internal waverider inlet after pressure gradient correction; S5. The new surface of the inner waverider inlet is smoothed to avoid surface deformity caused by sudden changes in azimuthal pressure gradients, thus forming a new inlet shape.

2. The inner waverider inlet design method based on circumferential azimuth pressure gradient correction according to claim 1, Features: In step S1, the inner waverider inlet flow field includes streamlines extracted from the ICFC+ basic flow, and the truncated Busemann and ICFA basic flow fields are generated using the characteristic line method, and then the Busemann compression surface is pushed down using the streamline function.

3. The inner waverider inlet design method based on circumferential azimuth pressure gradient correction according to claim 1, Features: In step S1 , the shapes of the inlet and outlet of the air intake duct are pre-specified as a circle and a semi-rectangle having the same inner contraction ratio.

4. The internal waverider inlet design method based on circumferential azimuth pressure gradient correction according to claim 1, Features: In step S1, a series of local two-dimensional streamline slices extracted from the ICFC+ basic flow field are used as osculating planes and converted into three-dimensional inlet duct profiles using the streamline tracing method.

5. The inner waverider inlet design method based on circumferential azimuth pressure gradient correction according to claim 1, It is characterized in that The method for calculating the speed correction vector comprises the following steps: 1) After obtaining the flow information of all points on the osculating plane through step S1, calculate the velocity correction between the considered point J and its two adjacent points J+1 and J-1 in each osculating plane slice, with the flow direction being the i direction and the circumferential direction being the J direction; 2) Project the velocity correction onto the ZY and XY planes and calculate the velocity components; 3) Project the velocity correction vector onto the considered osculating plane J, with directions R and R N , where R is the normal direction, and on the azimuth plane ZY, the velocity correction vector is calculated.

6. The inner waverider inlet design method based on circumferential azimuth pressure gradient correction according to claim 1, Features: In step S2, an osculating plane is included, where the local flow is a two-dimensional flow, and the position and flow information of the points are known.

7. The inner waverider inlet design method based on circumferential azimuth pressure gradient correction according to claim 1, Features: In step S4, the velocity at the new coordinates is calculated by using an inverse distance weighted interpolation method.

8. The method for designing an inner waverider inlet based on circumferential azimuth pressure gradient correction according to claim 1, Features: In step S5, the original point positions of all osculating planes in each azimuth J direction are updated by using the maximum radius correction and the average angle correction.

Images