Vortex generator for improving flow capturing capacity of hypersonic air inlet channel

Abstract

The invention discloses a vortex generator for improving the flow capturing capacity of a hypersonic air inlet channel, and belongs to the field of flow control of the hypersonic air inlet channel. The slope-shaped tetrahedral structure is composed of two slope-shaped tetrahedral structures which are oppositely installed. The junction of the bottom face and the inclined face forms the front edge of the vortex generator, the junction of the two side faces forms the tail edge of the vortex generator and is highly perpendicular to the bottom face, the bottom face is a right triangle, and the right angle is located on the outer side of the vortex generator. On the basis of vortex dynamics, a vortex with the rotating direction opposite to that of a vortex induced by a traditional vortex generator is induced through the oppositely-arranged half-slope type vortex generator, so that the trend that a low-energy fluid in a boundary layer is conveyed to a main stream by the traditional vortex generator is converted into the trend that a high-energy fluid is conveyed to the boundary layer by the main stream; a thinner boundary layer is obtained, the adverse effect of boundary layer separation on air inlet channel flow capture is weakened, combustion of a ramjet engine is improved, and the thrust-drag ratio of a hypersonic aircraft is increased.

Description

Technical Field

[0001] The present invention belongs to the field of hypersonic inlet flow control and relates to a vortex generator for improving the flow capture capability of a hypersonic inlet and a design method thereof. Background Art

[0002] Air-breathing hypersonic propulsion is a current research hotspot in the aerospace field, and its development plays a crucial role in achieving hypersonic flight and improving aircraft performance. Ramjets are widely used due to their high specific impulse, simple structure, and suitability for high-speed flight. Combined cycle engines, such as RBCC and TBCC, derived from ramjets combined with rocket and turbine engines, organically combine the advantages of these propulsion units to maximize engine performance.

[0003] As one of the core components of a ramjet engine, the design and performance of the air inlet directly determine the efficiency of the engine and further affect the overall performance of the aircraft. The main function of a hypersonic air inlet is to capture high-speed incoming flow, decelerate and compress it, and provide the combustion chamber with a uniform airflow that meets certain pressure and Mach number requirements. The flow capture capability of the air inlet is one of the important indicators to measure its performance and plays a decisive role in the thrust of the engine. The boundary layer of the incoming flow in the air inlet of a traditional ramjet engine is relatively thin and has little effect on flow capture. However, for a combined engine with a ramjet engine as the core, the position and structural layout of the air inlet have changed, resulting in a significant thickening of the incoming flow boundary layer, and even blocking the entire height of the air inlet, which greatly weakens its flow capture capability and seriously restricts the overall performance of the engine.

[0004] Sloped vortex generators (VGs) are widely used in hypersonic flow separation control due to their simple and stable structure, high thermal protection, and economical performance. Their principle is to transport high-momentum fluid from the mainstream into the boundary layer, enhancing the boundary layer's resistance to adverse pressure gradients, thereby delaying or weakening separation. Existing VGs are primarily used for flow separation control, and new VG configurations designed to increase the captured flow in the downstream inlet have not yet been considered.

[0005] Under hypersonic incoming flow, conventional vortex generators usually induce a set of opposite main vortex pairs, such as Figure 1 As shown in a, the rotation directions of the left and right branches are counterclockwise and clockwise respectively. This counter-rotating vortex pair will transport more low-energy fluid in the boundary layer to the mainstream. Summary of the Invention

[0006] In order to solve the above-mentioned problems of the prior art, the purpose of the present invention is to provide a vortex generator that improves the flow capture capability of the hypersonic inlet. The vortex generator is a reverse-opposed semi-slope vortex generator, which induces a group of reverse main vortices and two streamwise vortices with smaller intensity and scale based on vortex dynamics. The reverse main vortex is generated on the inner side of the two semi-slope vortex generators. Different from the vortex pairs induced by traditional vortex generators, the rotation directions of the left and right branches are clockwise and counterclockwise respectively. The reverse main vortex pair strengthens the transport of the mainstream high-energy fluid to the boundary layer, thereby thinning the boundary layer thickness, weakening the adverse effects of boundary layer separation on the capture of the inlet flow, and improving the unit thrust and specific impulse of the combined engine.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The present invention discloses a vortex generator for improving the flow capture capability of a high-speed air inlet, which is composed of two oppositely mounted sloped tetrahedron structures; a single sloped tetrahedron includes an inclined surface, a left side surface, a right side surface and a bottom surface; the intersection of the bottom surface and the inclined surface constitutes the leading edge of the vortex generator, and the intersection line of the two side surfaces constitutes the trailing edge of the vortex generator; the height is perpendicular to the bottom surface, the bottom surface is a right triangle, and the right angle is on the outside of the vortex generator; the leading edge of the vortex generator is arranged in front of the hypersonic air inlet close to the direction of the incoming flow, and the vortex generator is used to improve the flow capture capability of the hypersonic air inlet.

[0009] Furthermore, the half-angle of the vertex angle of the right triangle of the bottom surface is Ap=40°-50°, and the length of the hypotenuse L is 6-7 times the boundary layer thickness τ when the leading edge position of the vortex generator is not controlled.

[0010] Furthermore, the height H is 1-2 times the boundary layer thickness τ when the leading edge position of the vortex generator is not controlled.

[0011] Furthermore, the distance between the trailing edge of the vortex generator and the hypersonic inlet entrance is 12 times the boundary layer thickness τ when the leading edge position of the vortex generator is not controlled.

[0012] The present invention discloses a method for designing a vortex generator for improving the flow capture capability of a hypersonic inlet, which is used to design the vortex generator for improving the flow capture capability of a hypersonic inlet. The method for designing a vortex generator for improving the flow capture capability of a hypersonic inlet comprises the following steps:

[0013] Step 1: Generate the mesh of the hypersonic inlet model and use numerical simulation to simulate the known incoming flow conditions to obtain the local boundary layer thickness τ at the leading edge of the vortex generator installation area;

[0014] Step 2: Based on the τ obtained in step 1, a ramp vortex generator model is constructed;

[0015] Step 3: Generate an inlet model grid with a vortex generator and perform numerical simulation under known incoming flow conditions to obtain the flow field structure and aerodynamic performance; the flow field structure includes the shock wave system, vortex structure and boundary layer thickness; the aerodynamic performance includes the streamwise vorticity distribution, flow velocity profile and inlet inlet flow rate;

[0016] Step 4: Based on the flow field structure and aerodynamic performance obtained in Step 3, the ramp-type vortex generator model of Step 2 is modified multiple times to maximize the flow rate at the inlet inlet section and determine the optimal installation spacing d of the semi-slope vortex generators.

[0017] Step 5: Based on H, L and Ap obtained in step 2, and d obtained in step 4, the optimal structure of the vortex generator is obtained.

[0018] Furthermore, during the grid generation process in step 1, the height of the first layer of wall grid needs to be set small enough to ensure that Y plus ≤ 1.

[0019] Furthermore, the geometric configuration of the sloped vortex generator model in step 2 is represented by three parameters, namely, the vortex generator height H, the base triangle half angle Ap, and the base triangle hypotenuse length L; the three parameters satisfy the following relationship:

[0020] H xp =100%-200%τ. L xp =6-7*τ. A xp =40°-50°.

[0021] Furthermore, the specific implementation method of step four is: cutting the slope-type vortex generator, and installing the cut half-slope vortex generators opposite to each other, to construct a reverse vortex generator combination structure with a gain effect on convective flow capture. The vortex induced by this structure is called a vortex structure; by analyzing the vortex structure, the range of the installation spacing d of the two half-slope vortex generators is obtained, and the optimal spacing between the two oppositely installed half-slope vortex generators is determined through multiple modifications.

[0022] Furthermore, the installation spacing d of the two semi-slope vortex generators in step 4 ranges from 0.057τ to 0.1τ.

[0023] Beneficial effects:

[0024] 1. The present invention discloses a vortex generator and a design method for improving the flow capture capability of a hypersonic inlet. To address the problem of insufficient flow capture caused by the thickening of the incoming flow boundary layer in the inlet of a hypersonic aircraft, which may even block the entire inlet, the invention combines a vortex generator for suppressing separation with flow enhancement, and proposes a new vortex generator configuration. The new configuration consists of two opposing sloped tetrahedral structures. The intersection of the bottom surface and the slope constitutes the leading edge of the vortex generator, and the intersection of the two side surfaces constitutes the trailing edge of the vortex generator. The height is perpendicular to the bottom surface, and the bottom surface is a right triangle with the right angle on the outside of the vortex generator. The leading edge of the vortex generator is arranged in front of the hypersonic inlet, close to the direction of the incoming flow, and can transport the mainstream high-energy fluid into the boundary layer for mixing with the low-energy fluid inside the boundary layer, thereby improving the flow capture of the hypersonic inlet and ensuring more complete combustion in the ramjet engine. Under the conditions of an incoming flow Mach number of 8 and a local boundary layer thickness of 17 mm, the opposed semi-slope vortex generators can increase the inlet flow capture by 277%.

[0025] 2. Unlike ramp-shaped vortex generators, the vortex generator and its design method disclosed in the present invention for improving hypersonic inlet flow capture capabilities utilize opposed semi-ramped vortex generators. Under identical incoming flow conditions and geometric parameters, the opposed semi-ramped vortex generators can generate a pair of opposing vortex pairs that intersect in the downwash zone and enhance the downwash velocity, thereby achieving a stronger ability to transport the mainstream high-energy fluid into the boundary layer. A pair of weaker streamwise vortices are generated on either side of the opposed semi-ramped vortex generators, which transport the mainstream high-energy fluid into the boundary layer, thereby widening the range of flow control by the vortex generator. Under conditions of an incoming flow Mach number of 8 and a local boundary layer thickness of 17 mm, the opposed semi-ramped vortex generators increase inlet capture flow by 179% compared to conventional ramp-shaped vortex generators.

[0026] 3. The vortex generator and design method disclosed in the present invention for improving the flow capture capability of the hypersonic inlet adopt opposed semi-slope vortex generators, which are a passive control method. Compared with active control methods such as boundary layer suction, passive control has lower cost and higher feasibility, and exhibits stronger stability in extreme hypersonic environments.

[0027] 4. The vortex generator and its design method disclosed in the present invention are intended to improve the flow capture capability of the hypersonic inlet duct. The opposed semi-slope vortex generators have a larger bottom contact area and stronger structural stability. Compared with the wing-shaped vortex generators, they show stronger adaptability and reliability in hypersonic conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1Schematic diagram of the rotation direction and rear boundary layer of the vortex induced by the opposed semi-slope vortex generator of the present invention and the traditional slope vortex generator;

[0029] Figure 2 This is a schematic structural diagram of a group of semi-slope vortex generators according to the present invention;

[0030] Figure 3 This is a schematic structural diagram of a single semi-slope vortex generator according to the present invention;

[0031] Figure 4 A schematic diagram of an asymmetric semi-ramp vortex generator installed upstream of the combined engine intake duct to control intake flow;

[0032] Figure 5 The design process of the opposed semi-slope vortex generator;

[0033] Figure 6 The geometric configuration of the ramp-shaped vortex generator includes an oblique view, a top view, and a side view;

[0034] Figure 7 Dimensional parameter diagram of the semi-slope vortex generator structure of the present invention, wherein (A) is a top view and (B) is a front view;

[0035] Figure 8 A schematic diagram of an asymmetric semi-slope vortex generator installed on a flat plate with an air inlet to control the intake flow rate;

[0036] Figure 9 Comparison of the mass flow rate average density flow of an inlet without vortex generators, an inlet with traditional ramp-shaped vortex generators, and an inlet with the opposed semi-ramp-shaped vortex generators of the present invention;

[0037] Among them, 1 is the inclined surface of the sloped vortex generator, 2 is the left side of the sloped vortex generator, 3 is the right side of the sloped vortex generator, 4 is the bottom surface of the sloped vortex generator, 5 is the area on the flat plate surface where the vortex generator is installed, and 6 is the cross-section of the air inlet inlet behind the flat plate. DETAILED DESCRIPTION

[0038] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0039] In order to verify the superiority of the present invention in improving the flow capture capability of the hypersonic inlet, the TBCC combined engine inlet and its upstream components (whose geometric shape is as follows) installed on the hypersonic aircraft are used. Figure 8The geometric parameters (see Table 1) were used as the research object. Furthermore, to simplify the calculation, only the upstream portion of the inlet was considered, and structures that had no significant impact on aerodynamic performance were removed, thus simplifying the aircraft structure to a flat-plate model. The boundary conditions were as follows: an incoming Mach number of 5-8, an angle of attack of 8°, and an altitude of 40 km.

[0040] Table 1 Main geometric and aerodynamic parameters of hypersonic flat-plate aircraft

[0041]

[0042] like Figure 1 As shown, the embodiment discloses a vortex generator for improving the flow capture capability of a hypersonic inlet, which is composed of two oppositely mounted sloped tetrahedron structures. Figure 1 As shown, a single slope-shaped tetrahedron is formed. Figure 2 and Figure 3 As shown, it includes: an inclined surface 1, a left side surface 2, a right side surface 3 and a bottom surface 4. The intersection of the bottom surface and the inclined surface constitutes the leading edge of the vortex generator, and the intersection line of the two side surfaces constitutes the trailing edge of the vortex generator. The height is perpendicular to the bottom surface. The bottom surface is a right triangle, and the right angle is on the outside of the vortex generator. The vortex generator is as shown in FIG. Figure 4 In the manner shown, the leading edge is arranged in front of the hypersonic inlet close to the incoming flow, and the vortex generator is used to improve the flow capture capability of the hypersonic inlet.

[0043] The vortex generator design method disclosed in this embodiment for improving the flow capture capability of a hypersonic inlet is specifically implemented in the following steps:

[0044] Step 1: Take the front part of the hypersonic aircraft's air inlet as the research object and simplify its geometric model as follows: Figure 8 For the plate shown in the figure, geometric modeling is first carried out. Secondly, a high-quality 3D mesh is generated. According to formula (1), the first layer mesh height Y = 0.007 mm is given in the wall normal direction to ensure the dimensionless distance Y plus ≤1 to accurately capture the boundary layer flow. Numerical simulation is performed under given design flow conditions, such as Figure 8 As shown, the local boundary layer thickness at the leading edge of the vortex generator installation area 5 is obtained by velocity profile. Under the condition of an incoming flow Mach number of 8, the local boundary layer thickness τ = 17 mm. The mass flow average dense flow at the inlet inlet face 6 is used to represent the flow captured by the inlet.

[0045] The calculation formula for the first layer grid height Y in the wall normal direction is:

[0046]

[0047] Where ρ is the density, Yplus is the dimensionless distance normal to the wall, μ is the dynamic viscosity, u t is the friction velocity near the wall, and its value is obtained from formula (2).

[0048]

[0049] Where, t w is the wall shear stress.

[0050] The average density flow expression of mass flow is:

[0051]

[0052] Where ρ and v are density and velocity, respectively, ρv is the density flow, and A is the area of ​​the airway inlet surface. The mass flow average takes into account the momentum and flow rate of the fluid, while the surface average only considers the distribution of the physical quantity on the cross section. Therefore, the mass flow average is suitable for dynamic flow analysis. Under the condition of an incoming flow Mach number of 8, the average mass flow rate at the inlet of the airway is 0.3049 kg·m -2 ·s -1 .

[0053] Step 2: Based on the local boundary layer thickness τ, the geometric parameter values ​​of the ramp vortex generator are obtained and modeled. The geometric model of the ramp vortex generator is as follows: Figure 6 The geometric parameter values ​​are shown in Table 2.

[0054] Table 2 Main geometric parameters of ramp-shaped vortex generator

[0055]

[0056] Step 3: Generate a mesh for the flat plate model with a ramp-shaped vortex generator and perform numerical simulation under the same incoming flow conditions to obtain the required flow field structure (vortex structure and velocity profile) and performance parameters. The average mass flow rate at the outlet section is 0.4648 kg·m -2 ·s -1 .

[0057] Step 4: Based on the flow field structure of the ramp-shaped vortex generator model, adjust the vortex generator configuration to meet the following two requirements: On the one hand, the vortex generator generates tangential reverse vortex pairs in the downwash area, which enhance the downwash velocity. On the other hand, the strength of the tangential vortex pairs in the upwash area is weakened. The geometry of the modified design is as follows: Figure 7 As shown, by cutting the ramp-shaped vortex generator in half, the following Figure 1The semi-sloped vortex generators shown in the figure are installed opposite each other with a certain spacing d, resulting in several groups of vortex generators with different spacings d. To ensure sufficient interaction between the opposing vortex pairs, a certain spacing should be maintained between the two semi-sloped vortex generators. Too long a spacing will prevent the vortices from being tangential, thus weakening the interaction. Too short a spacing will cause the vortices to dissipate due to mutual interference. Therefore, the spacing d is selected to range from 0.057τ to 0.1τ.

[0058] Step 5: Generate meshes for opposed semi-sloped vortex generators with different spacings d and perform numerical simulations to compare their effects on the inlet flow capture capability. The optimal spacing d = 0.88τ is ultimately determined. The average mass flow rate of the inlet with the flat plate installed is 0.832 kg·m -2 ·s -1 The flow rates of the inlet planes of the flat plate without vortex generators, the flat plate with ramp-shaped vortex generators, and the flat plate with opposed semi-slope-shaped vortex generators are as follows: Figure 9 As shown in Figure 3, the designed vortex generator can capture 277% of the flow rate of the flat inlet without vortex generator.

[0059] The above specific description further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A vortex generator for improving the flow capture capability of a high-speed inlet, characterized by: It consists of two oppositely mounted sloped tetrahedron structures; a single sloped tetrahedron includes an inclined surface, a left side surface, a right side surface and a bottom surface; the intersection of the bottom surface and the inclined surface constitutes the leading edge of the vortex generator, and the intersection line of the two side surfaces constitutes the trailing edge of the vortex generator; the height is perpendicular to the bottom surface, the bottom surface is a right triangle, and the right angle is on the outside of the vortex generator; the leading edge of the vortex generator is arranged in front of the hypersonic inlet close to the direction of the incoming flow, and the vortex generator is used to improve the flow capture capability of the hypersonic inlet.

2. A vortex generator for improving the flow capture capability of a hypersonic inlet according to claim 1, characterized in that: The half-angle of the vertex angle of the right triangle of the bottom surface is Ap=24°, and the length of the hypotenuse L is 6.5 times the boundary layer thickness τ when the leading edge position of the vortex generator is not controlled.

3. The vortex generator for improving the flow capture capability of a hypersonic inlet according to claim 1, characterized in that: The height H is 1.35 times the boundary layer thickness τ when the leading edge position of the vortex generator is not controlled.

4. The vortex generator for improving the flow capture capability of a hypersonic inlet according to claim 1, characterized in that: The distance between the trailing edge of the vortex generator and the hypersonic inlet entrance is 12 times the boundary layer thickness τ when the leading edge position of the vortex generator is not controlled.

5. A method for designing a vortex generator for improving the flow capture capability of a hypersonic inlet, the method being used to design a vortex generator for improving the flow capture capability of a hypersonic inlet as claimed in claim 1, 2, 3 or 4, characterized in that: The steps include: Step 1: Generate the mesh of the hypersonic inlet model and use numerical simulation to simulate the known incoming flow conditions to obtain the local boundary layer thickness τ at the leading edge of the vortex generator installation area; Step 2: Based on the τ obtained in step 1, a ramp vortex generator model is constructed; Step 3: Generate an inlet model grid with a vortex generator and perform numerical simulation under known incoming flow conditions to obtain the flow field structure and aerodynamic performance; the flow field structure includes the shock wave system, vortex structure and boundary layer thickness; the aerodynamic performance includes the streamwise vorticity distribution, flow velocity profile and inlet inlet flow rate; Step 4: Based on the flow field structure and aerodynamic performance obtained in Step 3, the ramp-type vortex generator model of Step 2 is modified multiple times to maximize the flow rate at the inlet inlet section and determine the optimal installation spacing d of the semi-slope vortex generators. Step 5: Based on H, L and Ap obtained in step 2, and d obtained in step 4, the optimal structure of the vortex generator is obtained.

6. The method for designing a vortex generator for improving the flow capture capability of a hypersonic inlet according to claim 5, characterized in that: During the mesh generation process in step 1, the height of the first layer of wall mesh needs to be set small enough to ensure Yplus≤1.

7. The method for designing a vortex generator for improving the flow capture capability of a hypersonic inlet according to claim 5, characterized in that: The geometric configuration of the ramp-type vortex generator model in step 2 is represented by three parameters, namely, the vortex generator height H, the base triangle half angle Ap, and the base triangle hypotenuse length L; the three parameters satisfy the following relationship: H=135%τ; L=6.5*τ; Ap=24°.

8. The method for designing a vortex generator for improving the flow capture capability of a hypersonic inlet according to claim 5, characterized in that: The specific implementation method of step four is: split the slope-type vortex generator, and install the split half-slope vortex generators opposite to each other to construct a reverse vortex generator combination structure with a gain effect on convective flow capture. The vortex induced by this structure is called a vortex structure; by analyzing the vortex structure, the range of the installation spacing d of the two half-slope vortex generators is obtained, and the optimal spacing between the two oppositely installed half-slope vortex generators is determined through multiple modifications.

9. The method for designing a vortex generator for improving the flow capture capability of a hypersonic inlet according to claim 8, characterized in that: The installation distance d between the two semi-slope vortex generators in step 4 ranges from 0.057τ to 0.1τ.

Images