A method for designing a scoop inlet with wall flow control and an inlet

Abstract

The application is a spoon-shaped air inlet design method with wall flow control and an air inlet, belonging to the technical field of aircrafts. The method steps are: determining the structure and axial length of the spoon-shaped air inlet according to the performance requirements of the aircraft propulsion system; determining the position of the inlet fairing section and the curved expansion section of the spoon-shaped air inlet according to the shape and axial length of the spoon-shaped air inlet; determining the position of the airflow turbulence on both sides of the wall according to the curved expansion section of the air inlet; designing the vortex generator according to the airflow mixing condition at the airflow turbulence position; the design of the vortex generator includes the outer contour size design and the cross-section curve design; obtaining the vortex generator capable of restraining the airflow direction, that is, completing the design of the spoon-shaped air inlet with wall flow control. The application solves the problem of flow loss caused by wall separation vortex due to the bending of the flow channel and the wall expansion of the existing spoon-shaped air inlet.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of aircraft technology, and particularly relates to a spoon-shaped inlet duct design method with wall flow control and an inlet duct. BACKGROUND

[0002] As an important part of the aircraft propulsion system, the performance of the inlet duct will directly affect the performance of the engine. For the air-breathing propeller aircraft, the front part of the aircraft has a biased gearbox, and the transmission shaft needs to pass through the center of the inlet duct, resulting in a special spoon-shaped structure of the inlet duct. This large bias of the special-shaped structure will inevitably cause a large flow loss of the inlet duct. Therefore, it is necessary to use flow control technology for the spoon-shaped inlet duct.

[0003] Current research on the performance of the spoon-shaped inlet system used in the aircraft shows that, with the bending of the flow passage of the curved section and the expansion of the two side walls, the wall separation vortex is generated on the two side walls, the separation vortex develops by mixing in the inlet duct, and flow loss is caused in the inlet duct. SUMMARY

[0004] The technical problem to be solved is:

[0005] In order to avoid the shortcomings of the prior art air-breathing propeller aircraft inlet duct, the present application provides a spoon-shaped inlet duct with wall flow control. By designing vortex generators on the two side walls of the inlet duct, the flow control of the two side walls is completed, the inhibition of the separation vortex on the two side walls of the spoon-shaped inlet duct is achieved, and the performance of the inlet duct is improved. The present application uses a local precise inhibition measure to achieve the inhibition of the separation vortex on the wall of the inlet duct without causing a large increase in the structure weight of the aircraft and a complex manufacturing process. The problem of flow loss caused by the wall separation vortex due to the bending of the flow passage and the expansion of the wall of the existing spoon-shaped inlet duct is solved.

[0006] The technical solution of the present application is: a spoon-shaped inlet duct design method with wall flow control, characterized by the following specific steps:

[0007] The structure and axial length of the spoon-shaped inlet duct are determined according to the performance requirements of the aircraft propulsion system;

[0008] The positions of the inlet fairing section and the curved expansion section of the spoon-shaped inlet duct are determined according to the shape and axial length of the spoon-shaped inlet duct;

[0009] The positions of the two side walls where the air flow is turbulent are determined according to the curved expansion section of the inlet duct;

[0010] The vortex generators are designed according to the air flow mixing condition of the air flow turbulence position; the design of the vortex generators includes the outer contour size design and the cross-sectional curve design;

[0011] Obtain the vortex generator capable of restraining the airflow flow direction, namely complete the design of the spoon-shaped air inlet channel with wall flow control.

[0012] Further technical solutions of the present application are that the structure of the spoon-shaped air inlet channel sequentially comprises an air inlet channel entrance rectification section, an air inlet channel curved expansion section and an air inlet channel end rectification section along the axial direction.

[0013] Further technical solutions of the present application are that the air inlet channel entrance rectification section is an equal cross-section pipeline, the axial length is 10% of the total length of the air inlet channel, the cross-section shape is a spoon shape, the cross-section expansion angle is 55 degrees, and the cross-section area formula is as follows:

[0014]

[0015] Wherein, W is the engine air flow, p0 is the static pressure, T0 is the static temperature, Ma0 is the flight Mach number, is the air inlet channel flow coefficient.

[0016] Further technical solutions of the present application are that the curved expansion section of the air inlet channel takes the end of the entrance rectification section as the starting point, and accounts for 70% of the total length of the air inlet channel; the flow channel is curved upwards from the starting point, the cross-section expansion angle gradually increases along the path from 55 degrees to 360 degrees, and the cross-section area gradually increases, the airflow is further decelerated and expanded, and separation tendency is generated on the two side walls, the inlet and outlet slope of the curved expansion section is 0; the flow channel design formula is as follows:

[0017]

[0018] Wherein, Delta y represents the difference value of the longitudinal coordinates of the inlet and outlet, L represents the difference value of the transverse coordinates of the inlet and outlet; y represents the longitudinal coordinate of the flow channel profile, and x represents the transverse coordinate of the flow channel profile.

[0019] Further technical solutions of the present application are that the position of the two side walls of the curved expansion section of the air inlet channel where the airflow is disturbed is 60% of the total length of the air inlet channel from the air inlet, that is, the position is determined as the position of the vortex generator.

[0020] Further technical solutions of the present application are that the outer contour size of the vortex generator is respectively 1.5% of the total length of the air inlet channel in the axial characteristic length, 50% of the axial characteristic length in the height, 20% of the axial characteristic length in the width, and the distance between the adjacent two vortex generators is 50% of the axial characteristic length.

[0021] Further technical solutions of the present application are that the cross-section shape of the vortex generator is designed as a streamline shape by an improved category shape function, and the specific formula is as follows:

[0022] ξ(ψ) = C(ψ)S(ψ) + ψΔξ te

[0023]

[0024]

[0025] wherein C(ψ) represents a category function, defining the basic shape of the aerodynamic profile; S(ψ) represents a shape function, further modifying the basic aerodynamic profile defined by the category function; c represents the length of the curve; ξ is the dimensionless processing of y coordinate; ψ is the dimensionless processing of x coordinate; Δξ represents the difference of the vertical coordinates of the starting point and the ending point of the curve, in the present application, the vertical coordinates of the starting point and the ending point of the curve are the same, and the term of ψΔξ is zero.

[0026] The category function is:

[0027]

[0028] wherein N1 and N2 are indexes, N1 takes the value of 0.5, and N2 takes the value of 1.0;

[0029] The shape function is:

[0030] S = Δξ(A×ψ 2 +B×ψ 3 +C×ψ 4 )

[0031]

[0032] wherein ψ0 represents the value of the independent variable when S''=0, that is, the value of ψ0 can control the configuration of the entire aerodynamic profile.

[0033] A spoon-shaped air inlet with wall flow control, characterized by: sequentially divided into an air inlet entrance flow regulating section, an air inlet curved expansion section, and an air inlet terminal flow regulating section along the axial direction, a plurality of vortex generators are arranged on the two side walls of the air inlet curved expansion section along the radial direction, and the distance between the vortex generators and the air inlet is 60% of the total length of the air inlet, which can constrain the direction of airflow.

[0034] A further technical solution of the present application is that the length of the air inlet entrance flow regulating section is 10% of the total length of the air inlet, and the length of the air inlet curved expansion section is 70% of the total length of the air inlet.

[0035] A further technical solution of the present application is that the axial characteristic length of the vortex generator is 1.5% of the total length of the air inlet, the height is 50% of the axial characteristic length, the width is 20% of the axial characteristic length, and the distance between adjacent two vortex generators is 50% of the axial characteristic length.

[0036] Beneficial effects

[0037] The beneficial effects of the present application are that: the scoop inlet of the existing air-breathing propeller aircraft, under the combined action of the flow channel bending and wall expansion, the airflow separates at the two side walls, producing wall separation vortex, which mixes and develops in the inlet, causing the flow loss of the inlet to increase. The scoop inlet with wall flow control technology of the present application installs vortex generators on both sides of the position where the airflow in the curved expansion section of the inlet has a tendency to separate, which straightens the airflow, restricts the flow direction of the airflow, reduces the intensity of lateral mixing of the airflow, and reduces the flow loss of the two side walls.

[0038] Referring to Figure 4 The streamline diagram of the conventional inlet end wall is shown, and the distance from the marked cross-section position to the inlet of the inlet is 60% of the total length of the inlet. As can be seen, before the vortex generator is installed, the airflow begins to mix laterally at this point, and the outermost airflow is deflected inward under the action of angular momentum, mixed with the inner airflow, and interferes with the flow of the inner airflow. After this cross-section, the mixing phenomenon intensifies, forming vortex and separation, so it is necessary to straighten the airflow at this point, restrict the flow direction of the airflow, and weaken the lateral mixing phenomenon of the airflow. The technical solution of the present application is to install a vortex generator at this point, the axial characteristic length of a single vortex generator is 1.5% of the total length of the inlet, the height is 50% of the axial characteristic length, and the width is 20% of the axial characteristic length. The distance between the adjacent two vortex generators is 50% to 80% of the axial characteristic length. The axial characteristic length of the vortex generator affects the straightening effect, and the weight of the inlet installation is also considered. If the vortex generator is too short, it cannot have good straightening effect, and if it is too long, it will increase the flow loss due to wall shear and increase the weight of the inlet installation, so the axial length of 1.5% of the total length of the inlet is more appropriate. In addition, the distance between the adjacent two vortex generators is also a key factor affecting the flow. If the distance between the vortex generators is too large (more than one characteristic length of the vortex generator), flow separation will occur in the channel due to the adverse pressure gradient, which cannot achieve the straightening effect. If the distance is too narrow (less than 30% of the characteristic length of the vortex generator), it will increase the weight of the entire inlet system, and too dense vortex generators are not easy to process, which is not conducive to actual engineering application. Considering the present application technology, the distance between the adjacent two vortex generators is 50% of the axial characteristic length.

[0039] Referring to Figure 5The wall streamline diagram after the vortex generator is added to the application can be seen that at the installation position of the vortex generator, the transverse mixing of the airflow is obviously weakened, most of the outermost airflow still flows along the outer wall under constraint, only a small proportion of the airflow deflects inward and mixes with the inner airflow. Compared with the conventional design of the inlet duct, the airflow flow is obviously improved, and the precise control of separation is realized. Without complex mechanisms and control systems, the flow loss in the inlet duct is reduced, thereby improving the working performance of the air-breathing propeller engine, and solving the problem of large flow loss of the existing large-curvature spoon-shaped inlet duct. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The application is a spoon-shaped inlet duct structure with wall flow control.

[0041] Figure 2 The application is an inlet duct cross-sectional shape schematic diagram.

[0042] Figure 3 The application is a vortex generator structure schematic diagram.

[0043] Figure 4 The application is a conventional inlet duct side wall streamline diagram.

[0044] Figure 5 The application is an inlet duct side wall streamline diagram using the technical solution of the application.

[0045] Figure 6 The application is an improved category shape function aerodynamic profile schematic diagram

[0046] Figure 7 The application is a conventional inlet duct total pressure distribution at a 60% inlet duct length cross-sectional position.

[0047] Figure 8 The application is a total pressure distribution after the vortex generator using the technical solution of the application.

[0048] The application is an inlet duct inlet fairing section, 2. an inlet duct curved expansion section, 3. a wall vortex generator, 4. an inlet duct end fairing section, 5. an inlet duct 60% length position cross section. DETAILED DESCRIPTION

[0049] The embodiments described below with reference to the drawings are exemplary and are intended to explain the application, but cannot be understood as a limitation of the application.

[0050] Based on the existing spoon-shaped inlet system, the flow channel of the curved section is curved, and the two side walls are expanded, the wall separation vortex is generated on the two side walls, the separation vortex develops by mixing in the inlet duct, causing flow loss and other problems in the inlet duct. The application provides a spoon-shaped inlet duct design method with wall flow control, and the specific steps are as follows:

[0051] Step 1: Determine the structure and axial length of the scoop inlet according to the performance requirements of the aircraft propulsion system;

[0052] Step 2: Determine the position of the inlet fairing section and curved expansion section of the scoop inlet according to the shape and axial length of the scoop inlet;

[0053] Step 3: Determine the position of the airflow turbulence on both sides of the curved expansion section of the inlet;

[0054] Step 4: Design vortex generators according to the airflow mixing situation at the airflow turbulence position; the design of the vortex generators includes outer contour size design and cross-sectional curve design;

[0055] Step 5: Obtain vortex generators that can constrain the direction of airflow, i.e., complete the design of the scoop inlet with wall flow control.

[0056] Specifically, the scoop inlet includes an inlet fairing section, a curved expansion section, a wall vortex generator, and an end fairing section. The present application is mainly applied to air-breathing propeller aircraft. The transmission shaft passes through the middle of the scoop inlet to drive the propeller. The high-speed incoming flow is decelerated and rammed at the inlet fairing section, then enters the curved expansion section, the wall vortex generator is arranged on both sides of the curved expansion section, and the airflow is collected into the engine at the end fairing section after completing the flow around.

[0057] Specifically, the inlet fairing section of the inlet is a section of equal cross-sectional area pipeline, the cross-sectional shape is scoop-shaped, and the cross-sectional area is calculated according to the design point flight state of the aircraft. The length of this fairing section is 10% of the total length of the inlet.

[0058] Specifically, the curved expansion section of the inlet starts to expand outward on both sides, and at the same time, due to the longitudinal offset of the inlet and outlet, the flow passage starts to bend upward, the cross-sectional area of the inlet, and the expansion angle of each section gradually increase, and the length of the curved expansion section is 70% of the total length of the inlet.

[0059] Specifically, the vortex generator is arranged in the curved expansion section of the inlet, the distance from the inlet is 60% of the total length of the inlet, the axial characteristic length of a single vortex generator is 1.5% of the total length of the inlet, the height is 50% of the axial length, the width is 20% of the axial length, the distance between adjacent two vortex generators is 50% of the axial characteristic length, and the cross-sectional shape is designed as a streamlined shape by improving the category shape function curve.

[0060] High-speed free flow enters the intake duct. Due to the ram effect of the intake duct, it is initially decelerated and pressurized in the inlet rectification section. Then it enters the bending expansion section, where the two side walls expand outward and the expansion angle gradually increases. Under the combined effect of the flow channel bending and wall expansion, the airflow on the two side walls gradually becomes turbulent and tends to separate. At this time, the vortex generators on the two side walls rectify the airflow, constrain the airflow direction, reduce the lateral mixing intensity of the airflow, and minimize the flow loss of the airflow on the two side walls. The airflow finally mixes in the terminal rectification section and enters the engine.

[0061] The above technical solution will be further explained below with reference to the accompanying drawings:

[0062] Reference Figure 1 As shown, this embodiment of a spoon-shaped air intake with wall flow control includes: an inlet rectifying section 1, an inlet bending expansion section 2, a wall vortex generator 3, and an inlet end rectifying section 4. High-speed free flow enters the air intake. Due to the ram effect of the air intake, it initially decelerates and pressurizes in the inlet rectifying section, then enters the bending expansion section. The two side walls expand outwards, and the expansion angle gradually increases. Under the combined effect of the flow channel bending and wall expansion, the airflow on both side walls gradually becomes turbulent and tends to separate. At this time, the vortex generators on both walls rectify the airflow, constrain the airflow direction, reduce the lateral mixing intensity of the airflow, and minimize the flow loss of the airflow on both side walls. The airflow finally mixes in the end rectifying section and enters the engine.

[0063] Reference Figure 2 As shown, the intake duct inlet rectifying section is a pipe with a constant cross-section, where the airflow is initially rectified and slowed down. Its length is 10% of the total intake duct length, and its cross-sectional shape is spoon-shaped. Figure 2 As shown, the cross-sectional expansion angle θ = 55°, and the cross-sectional area is determined by the engine airflow W, static pressure p0, static temperature T0, flight Mach number Ma0, and inlet flow coefficient under design conditions. It is calculated according to the following formula.

[0064]

[0065] Reference Figure 1 As shown, the airflow enters the curved expansion section after passing through the inlet rectification section. At this time, the flow channel bends upward, and the cross-sectional expansion angle gradually increases along the flow, from 55° to 360°. The cross-sectional area also gradually increases, and the airflow further decelerates and expands, and a separation tendency is generated on both sides of the wall. The flow channel is designed according to the following formula, and its inlet and outlet slopes are 0.

[0066]

[0067] Where Δy represents the difference between the inlet and outlet vertical coordinates, and L represents the difference between the inlet and outlet horizontal coordinates; y represents the vertical coordinate of the flow channel profile, and x represents the horizontal coordinate of the flow channel profile.

[0068] Referring to Figure 3 Figure 1, the vortex generator is arranged on the two side walls of the curved expansion section of the air inlet channel, the distance to the inlet of the air inlet channel is 60% of the total length of the air inlet channel, the axial characteristic length of a single vortex generator is 1.5% of the total length of the air inlet channel, the height is 50% of the axial length, the width is 20% of the axial length, and the distance between two adjacent vortex generators is 50% of the axial characteristic length, as shown in Figure 3 Figure 2.

[0069] The vortex generator is installed in the adverse pressure gradient flow field, and the aerodynamic profile thereof is required to be continuous, smooth and compact, so as to ensure that the airflow will not generate additional flow loss due to the vortex generator profile design problem of the profile. The cross-sectional shape of the vortex generator in the technical scheme is designed as a streamline by an improved category shape function, the aerodynamic profile is represented as the product of the category function and the shape function, and the product of the difference between the tail edge function value and the front edge function value and the independent variable is added, as follows.

[0070] ξ(ψ)=C(ψ)S(ψ)+ψΔξ te

[0071]

[0072]

[0073] Wherein, C(ψ) represents a category function, which defines the basic shape of the aerodynamic profile; S(ψ) represents a shape function, which further corrects the basic aerodynamic profile defined by the category function; c represents the length of the curve; ξ is the dimensionless processing of the y coordinate; ψ is the dimensionless processing of the x coordinate; Δξ represents the difference between the starting point and the ending point of the curve, and it is worth noting that the y coordinates of the starting point and the ending point of the curve are the same in the present application, and the term ψΔξ is zero.

[0074] The function formula of the category function is as follows, which represents a family of curves, and the curve shape represented by the category function is different according to the values of the exponents N1 and N2. In the technical scheme of the present application, according to the aerodynamic profile requirements proposed by the working state of the vortex generator, N1 is 0.5 and N2 is 1.0.

[0075]

[0076] The shape function is selected by the user according to the actual demand. The function in the technical scheme of the present application can realize high-order curvature continuity and flexible adjustment, and the specific function formula is as follows:

[0077] S=Δξ(A×ψ 2 +B×ψ 3 +C×ψ 4 )

[0078]

[0079] Wherein ψ0 represents the value of the independent variable when S" = 0, that is, the value of ψ0 can control the configuration of the entire aerodynamic profile.

[0080] In actual profile design, the front and rear sections are designed separately. The constraint conditions in the design of the front section curve include the curvature radius of the leading edge point, the position and slope of the intermediate extreme point, and the slope of the trailing edge point. The constraint conditions in the design of the rear section curve mainly include the curvature radius of the leading edge point, the position, slope, second derivative and third derivative of the intermediate extreme point, and the slope and curvature of the trailing edge point, and the like. Figure 6 The profile design is shown. The advantage of such design is to ensure that the vortex generator profile is fully smooth, while meeting the second-order curvature continuity, so that the airflow can flow along the wall in the adverse pressure gradient flow field without causing additional flow loss.

[0081] The technical scheme of the embodiment and the existing conventional spoon-shaped inlet duct are respectively subjected to numerical simulation calculation, and performance data of the technical scheme are obtained. In the application example, the total length of the inlet duct is 2000mm, the corresponding vortex generator axial characteristic length is 30mm, the height is 15mm, the width is 6mm, the spacing between two adjacent vortex generators is 15mm, and 9 vortex generators are arranged on one side according to the wall width of the inlet duct. Figure 7 and Figure 8 The total pressure recovery coefficient distribution of the conventional inlet duct and the inlet duct adopting the technical scheme of the present application at the 60% position cross section is respectively shown, the red color represents good airflow quality, the blue color represents poor airflow quality, and the large blue color aggregation represents flow separation. It can be seen that the existing conventional spoon-shaped inlet duct has a large amount of blue area aggregation on both side walls at the position of 60% of the total length of the inlet duct from the inlet of the inlet duct, indicating that the airflow has flow separation at this position, wall separation vortex is generated, and inlet loss is increased. This wall flow separation is caused by transverse mixing of the airflow and flow field turbulence. The inlet duct adopting the technical scheme of the present application has a significant reduction in the blue area at the same position, and no aggregation, indicating that the airflow does not separate after flowing through the vortex generator, and therefore no wall separation vortex is generated. A small amount of low-energy flow at the end wall is caused by the development of the inlet duct boundary layer and cannot be avoided. It can be seen that the present application solves the problem of increased flow loss caused by the change of the flow passage profile of the existing conventional spoon-shaped inlet duct. The total pressure recovery coefficient and distortion index of the present application and the existing spoon-shaped inlet duct are improved, and the specific comparison is shown in the following table. Figure 7

[0082] Cruise total pressure recovery coefficient Cruise distortion index Ground total pressure recovery coefficient Ground distortion index Prior art 0.980 0.115 0.976 0.159 The invention 0.982 0.081 0.979 0.113

[0083] ​Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that changes, modifications, substitutions and variations can be made by those skilled in the art without departing from the spirit and scope of the present application.

Claims

1. A design method for a spoon-shaped air intake with wall flow control, characterized in that... The specific steps are as follows: The structure and axial length of the spoon-shaped air intake are determined based on the performance requirements of the aircraft's propulsion system. The structure of the spoon-shaped air intake includes, along the axial direction, an air intake inlet rectifying section, an air intake bending and expanding section, and an air intake end rectifying section. The intake duct inlet rectifying section is a constant cross-section pipe with an axial length of 10% of the total intake duct length. Its cross-sectional shape is spoon-shaped, and its cross-sectional expansion angle is... The formula for cross-sectional area is as follows: in, For engine airflow, For static pressure, For static temperature, For the flight Mach number, This refers to the intake manifold flow coefficient. The curved expansion section of the intake duct starts at the end of the inlet rectifier section and accounts for 70% of the total length of the intake duct. Its flow path curves upwards from the starting point, with the cross-sectional expansion angle gradually increasing from 55° to 360° along the path. Simultaneously, the cross-sectional area gradually increases, further decelerating and expanding the airflow, and creating a separation tendency on both side walls. The inlet and outlet slopes of the curved expansion section are 0. The flow path design formula is as follows: in, This represents the difference between the import and export vertical axes. L The x-coordinate represents the difference between the inlet and outlet x-coordinates; y represents the ordinate of the flow channel profile, and x represents the abscissa of the flow channel profile. The distance from the location where airflow turbulence occurs on both sides of the curved expansion section of the air intake to the air intake inlet is 60% of the total length of the air intake, which is the location of the vortex generator. A vortex generator is designed based on the airflow mixing conditions at the location of airflow turbulence; the design of the vortex generator includes the design of its outer contour dimensions and cross-sectional curve. The outer contour dimensions of the vortex generator are as follows: axial characteristic length is 1.5% of the total length of the intake duct, height is 50% of the axial characteristic length, width is 20% of the axial characteristic length, and the distance between two adjacent vortex generators is 50% of the axial characteristic length. The cross-sectional shape of the eddy current generator is designed to be streamlined using an improved category shape function, as shown in the following formula: in, The category function represents the basic shape of the aerodynamic profile; For example, to represent the shape function, the basic aerodynamic profile defined by the category function is further modified; c represents the length of the curve; It is a dimensionless processing of the y-coordinate; It is a dimensionless processing of the x-coordinate; This represents the difference in the ordinates between the start and end points of the curve; The category function is: in, N 1 and N 2 is the exponent. N 1 takes the value 0.

5. N 2 takes the value 1.0; The shape function is: in, express S ’’ =0 The value of the independent variable at time, i.e., the control The value of can control the configuration of the entire aerodynamic profile; Obtain a vortex generator that can constrain the direction of airflow, thus completing the design of a spoon-shaped air intake with wall flow control.

2. A spoon-shaped air intake with wall flow control, characterized in that: It is designed by the spoon-shaped air intake design method with wall flow control as described in claim 1.

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