CN113536702B - Design method for wind tunnel contraction section with circular section torque-shaped section - Google Patents
Design method for wind tunnel contraction section with circular section torque-shaped section Download PDFInfo
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Abstract
The invention relates to the field of fluid mechanics, in particular to a wind tunnel contraction section design method with a circular section and a torque-shaped section, which comprises the following steps of 1: analyzing the model characteristics of the inlet and outlet shapes of the contraction section, and determining the mapping relation of the inlet and outlet shapes; step 2: setting control parameters of the flow direction control curve, and determining the flow direction control curve; and step 3: determining a shape function of a section from the inlet section to the outlet section in the flow direction by using a linear weighting mode according to the mapping relation determined in the step 1 and the flow direction control curve obtained in the step 2, and obtaining a three-dimensional shape discrete coordinate; and 4, step 4: and importing the obtained three-dimensional shape discrete coordinates into three-dimensional digital analog software for modeling to obtain the three-dimensional shape of the circular-section torque-shaped section contraction section. The invention can realize abundant appearance change, meet the appearance design of the contraction section of various requirements, and further realize the fine control of the three-dimensional appearance of the contraction section.
Description
Technical Field
The invention relates to the field of fluid mechanics, in particular to a design method of a wind tunnel contraction section with a circular section and a torque-shaped section.
Background
The wind tunnel is a pipeline-shaped device which simulates the airflow flowing condition around an aircraft or other objects by utilizing the principle of fluid mechanics similarity. During operation, air flow is generated and controlled from upstream in a manual mode, the action effect of the air flow on an entity is measured by utilizing measuring equipment, physical phenomena are observed, and the motion condition of an object in a real flow field is further obtained.
The wind tunnel is an indispensable important technology for developing aircrafts and power systems thereof, and is an important component for showing a national scientific and technical level. The wind tunnel method is used for testing, so that the economic cost can be greatly reduced, the experimental period can be greatly shortened, and the wind tunnel method plays an important role in national defense and military and national economy.
The transonic cascade wind tunnel generally comprises a high-pressure air source system, a diffuser, a stable section, a contraction section, a spray pipe section, an experimental section, an exhaust collector and a control system. In order to meet the requirements of cascade experiments, the spray pipe section generally adopts a binary-profile spray pipe, namely the cross section of the inlet of the spray pipe is a rectangular cross section. Upstream, however, the stabilization section needs to be designed as a flow channel of circular cross section because of structural and pneumatic requirements. Therefore, in the transonic cascade wind tunnel, the main function of the contraction section is to guide the airflow from the pressure stabilizing section into the inlet of the nozzle pipe and smoothly transition the circular section size of the pressure stabilizing section to the inlet section size of the nozzle pipe section. Namely, the shape is changed from a circular section to a rectangular section; and pneumatically guiding the incoming flow of the stabilizing section into the spray pipe to match the incoming flow requirement of the inlet of the spray pipe.
At present, no special design method related to the contraction section is introduced, and in practical design, the following two methods are mostly adopted: one method is that depending on the engineering experience of the designer, the experience is used for judging, and the experience shape is obtained through the transition mode of repeatedly adjusting the section; the other method is that the shape design is carried out by utilizing CAD design software depending on the development of the modern technology, the transition of the shape is mostly realized by a curved surface lofting mode, and the transition is realized by an algorithm built in software and is not easy to be finely controlled.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for designing a wind tunnel contraction section with a circular section and a torque-shaped section, which has the advantages that the transition of geometric shapes can be finely controlled, and the design requirements of various contraction sections are met. The effect diagram is shown in fig. 2, where the coordinate system is defined as the flow direction as x-axis, the longitudinal direction as y-axis, and the z-axis direction is given by the right-hand rule.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a design method for a wind tunnel contraction section with a circular cross section and a torque-shaped cross section comprises the following steps:
step 1: analyzing the model characteristics of the inlet and outlet shapes of the contraction section, and determining the mapping relation of the inlet and outlet shapes;
and 2, step: setting control parameters of the flow direction control curve, and determining the flow direction control curve;
and step 3: : determining a shape function of a section from the inlet section to the outlet section in the flow direction by using a linear weighting mode according to the mapping relation determined in the step 1 and the flow direction control curve obtained in the step 2, and obtaining a three-dimensional shape discrete coordinate;
and 4, step 4: and importing the obtained three-dimensional shape discrete coordinates into three-dimensional digital-analog software for modeling to obtain the three-dimensional shape of the circular-section torque-shaped section contraction section.
Preferably, in the above-mentioned step 1,
step 101: dividing the rectangular surface of the outlet into four areas, determining that four inflection points and four curves exist, and dividing the circular surface of the inlet into four areas, wherein the four inflection points and the four curves of the area are to be determined;
step 102: establishing a mapping relation from an inlet area to an outlet area according to model characteristics of the shapes of the inlet and the outlet of the contraction section;
step 103: from the four "corners" and the four-segment curve of the outlet that have been determined in step 101, four corners and four-segment curve of the inlet are determined using either area mapping or angle mapping.
Preferably, according to step 101, the circular surface of the inlet is divided into region No. 1, region No. 2, region No. 3 and region No. 4 through the center of the circle, and the rectangular surface of the outlet is divided into region No. 1 ', region No. 2', region No. 3 'and region No. 4' along the diagonal.
Preferably, in the step 103, the area mapping comprises the following steps:
step 2101: according to the geometric principle, the areas of the No. 1 'area, the No. 2' area, the No. 3 'area and the No. 4' area of the outlet are equal, and the areas of the No. 1 area, the No. 2 area, the No. 3 area and the No. 4 area of the inlet are determined to be equal;
step 2102: setting the radius of the circle as R, and the diagonals of the four areas obtained according to the step 1, wherein the diagonal of the inlet forms an angle theta with the z axisc1The diagonal of the outlet forms an angle theta with the z-axisc2；
Step 2103: according to the equally divided circle, the following can be obtained: thetac1Pi/4, which can be derived from the rectangular geometry: thetac2In an entry-to-exit mapping, the mapping angle varies linearly, i.e. θ (b/a)c＝θc1+(θc2-θc1)x/L，θcThe angle along the x direction is shown, x represents the abscissa along the flow direction, L represents the length of the flow channel, and then the mapping relation of 4 curves of the inlet and 4 curves of the outlet is established.
Preferably, in the step 103, the angle mapping comprises the following steps:
step 2201: setting the angle of the outlet partition region to thetad2According to the rectangular diagonal principle, the method comprises the following steps: theta.theta.d2＝arctan(b/a)；
Step 2202: setting the angle of the inlet partition region to θd1According to the condition that the angle formed by the inlet 4 dividing points to the diagonal line is equal to the angle formed by the outlet 4 turning points, the method can obtainThe inlet angle also satisfies thetad1And establishing a mapping relation between 4 curves at the inlet and 4 curves at the outlet.
Preferably, in step 2, the weight is given when the entrance function and the exit function are linearly weighted, and the weight factor is controlled by using 4 points, i.e. c1(0,0)，c2(0,p1)，c3(p21) and c4(1,1) wherein 0 < p1＜p2< 1, for c1c2Control point, adjust p1Can control the speed of the change of the shape of the cross section of the inlet, and for c3c4Control point, adjust p2The value of (2) can control the speed of the change of the shape of the cross section of the outlet.
Preferably, in step 3, a shape function of the inlet cross section to the outlet cross section in the flow direction is established by means of linear weighting:
f(x,y,z)＝[1-k(x)]·fin(x,y,z)+k(x)·fout(x,y,z)
where f (x, y, z) represents the systolic profile function, k (x) represents the weighting factor, i.e. the flow control function, fin(x, y, z) represents the inlet cross-sectional shape, fout(x, y, z) represents the influence of the outlet cross section, the weight factor satisfies 0 ≦ k (x ≦ 1, x ∈ [0, L ]]。
Preferably, a three-dimensional coordinate function is determined according to the established shape function, first, the respective 4 segments of curves of the inlet and the outlet are discretized, the centroid of the inlet is taken as the origin of a coordinate system, and the inlet is marked as: (0, y)in(s,j),zin(s, j)), the exit is noted: (L, y)out(s,j),zout(s, j)), wherein s is 1,2,3,4 represents a curve number, j is 1,2, and N represents the number of discrete points, and the three-dimensional shape coordinates of the discrete points of the contraction section are obtained by using a linear weighting method:
X(i,j)＝L·x(i)
Y(i,j)＝[1-k(i)]·yin(i,j)+k(i)·yout(i,j)
Z(i,j)＝[1-k(i)]·zin(i,j)+k(i)·zout(i,j)
where i 1,2, where M represents the number of discrete points of the flow control curve.
Compared with the prior art, the invention has the beneficial effects that:
1. aiming at the three-dimensional shape design of the torque-shaped section contraction section with the circular section, the invention provides the contraction section shape design which can realize rich shape change and meet various requirements by determining the mapping relation and giving the weight factor control parameter.
2. Compared with the existing design method, the invention can realize the fine control of the three-dimensional shape of the contraction section.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
In the drawings:
FIG. 1 is a schematic view of a main body of a test stand.
FIG. 2 is a schematic view of a transonic cascade wind tunnel constriction.
FIG. 3 is a schematic view of a constriction shape map.
FIG. 4 is a schematic diagram of an area mapping relationship.
FIG. 5 is a schematic view of an angle mapping relationship.
Fig. 6 is a schematic view of a flow control curve based on a B-spline curve.
Figure 7 the round section torque-shaped section constrictor design of example 1.
Figure 8 the round section torque section constriction design of example 2.
Wherein: 1. the system comprises a quick valve, 2 a pressure regulating valve, 3 an expansion joint, 4 a diffuser, 5 a pressure stabilizing section, 6 a contraction section, 7 a spray pipe section and 8 a test section.
Detailed Description
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
As shown in fig. 1, which is a schematic diagram of a main body of a test bed of a transonic cascade wind tunnel, the test bed is provided with a quick valve 1, a pressure regulating valve 2, an expansion joint 3, a diffuser 4, a pressure stabilizing section 5, a contraction section 6, a jet pipe section 7 and a test section 8 from left to right in sequence, and the contraction section 6 mainly functions to guide airflow from the pressure stabilizing section 5 into an inlet of the jet pipe section 7 and smoothly transition the circular cross-sectional dimension of the pressure stabilizing section 5 to the inlet cross-sectional dimension of the jet pipe section 7. Namely, the shape is changed from a circular section to a rectangular section; and pneumatically guiding the incoming flow of the pressure stabilizing section 5 into the nozzle section 7 to match the incoming flow requirement of the inlet of the nozzle section 7.
A wind tunnel contraction section design method with a circular section torque-shaped section is characterized in that a contraction section effect diagram is shown in figure 2, a coordinate system of the wind tunnel contraction section effect diagram is defined as that a flow direction is an x axis, a longitudinal direction is a y axis, and a z axis direction is given by a right-hand rule. The specific design comprises the following steps.
Step 1: and analyzing the model characteristics of the inlet and outlet shapes of the contraction section, and determining the mapping relation of the inlet and outlet shapes. As shown in fig. 3, according to the shape characteristic analysis of the inlet and the outlet, the inlet is a smooth circular curve, and the outlet is a non-smooth curve with right angles, i.e. the outlet has four inflection points to divide the outlet into four continuous smooth straight lines, and since the contraction section is gradually transited from the circular section to the rectangular section, the inlet should also have four continuous smooth curves corresponding to the four continuous smooth curves of the outlet. The method comprises the following specific steps:
step 101: as shown in fig. 3, the circular surface of the inlet is divided into a region No. 1, a region No. 2, a region No. 3 and a region No. 4, four 'inflection points' and four curves of the inlet are undetermined, the rectangular surface of the outlet is divided into a region No. 1 ', a region No. 2', a region No. 3 'and a region No. 4' along the diagonal, and four inflection points and four sections of curves are determined;
step 102: according to the model characteristics of the shapes of the inlet and the outlet of the contraction section, namely the inlet is a smooth circular curve, the outlet is a non-smooth curve with right angles, and the mapping relation from the area No. 1, the area No. 2, the area No. 3 and the area No. 4 at the inlet to the area No. 1 ', the area No. 2 ', the area No. 3 ' and the area No. 4 at the outlet is established;
step 103: according to the four 'inflection points' and the four-segment curve of the outlet which are determined in the step 102, the four-segment curve of the inlet is determined by adopting area mapping or angle mapping, namely the four inflection points of the inlet are determined, and the mapping relation with the four-segment curve of the outlet is further ensured.
In the step 103, the area mapping is shown in fig. 4, and specifically includes the following steps:
step 2101: according to the rectangular geometric principle, the areas of the No. 1 'area, the No. 2' area, the No. 3 'area and the No. 4' area of the outlet are equal, and the areas of the No. 1 area, the No. 2 area, the No. 3 area and the No. 4 area of the inlet are determined to be equal;
step 2102: setting the radius of the circle as R, and obtaining the diagonals of the four areas according to the step 1, wherein the angle formed by the diagonal of the inlet and the z axis is thetac1The diagonal of the outlet forms an angle theta with the z-axisc2；
Step 2103: according to the equally divided circle, the following can be obtained: theta.theta.c1Pi/4, which can be derived from the rectangular geometry: thetac2In an entry-to-exit mapping, the mapping angle changes linearly, i.e., θ (b/a)c＝θc1+(θc2-θc1)x/L，θcThe angle along the x direction is shown, x represents the abscissa along the flow direction, and L represents the length of the flow channel, so that the mapping relation between 4 curves at the inlet and 4 curves at the outlet is established.
In the step 103, the angle mapping is shown in fig. 5, and specifically includes the following steps:
step 2201: setting the angle of the outlet partition region to thetad2According to the rectangular diagonal principle, the method comprises the following steps: thetad2＝arctan(b/a)；
Step 2202: setting the angle of the inlet partition region to thetad1According to the condition that the angle formed by the corner lines of the 4 boundary points at the inlet is equal to the angle formed by the diagonal lines of the 4 corner points at the outlet, the inlet angle also satisfies thetad1And (4) establishing a mapping relation between the 4 curves at the inlet and the 4 curves at the outlet.
Step 2: and setting control parameters of the flow direction control curve, and determining the flow direction control curve. The flow control curve is used to control the weighting factor, which gives the magnitude of the weight when the entry and exit functions are linearly weighted. The invention describes the weight factor by using a 3-time quasi-uniform rational B-spline curve, wherein the B-spline curve is a very mature geometric modeling tool, the basic principle of the B-spline curve is not repeated here, and the invention only provides specific control parameters of the B-spline curve.
As shown in FIG. 6, a schematic diagram of a flow direction control curve based on a quasi-uniform 3-order rational B-spline curve in a normalized coordinate system is given, and a total of 4 points are adopted to control the weight factors, namely c1(0,0)，c2(0,p1)，c3(p21) and c4(1,1) wherein 0 < p1＜p2< 1, for c1c2Control point, adjust p1Can control the speed of the change of the shape of the cross section of the inlet, and for c3c4Control point, adjust p2The value of (2) can control the speed of the change of the shape of the cross section of the outlet.
And 3, step 3: determining the mapping relation of the inlet and the outlet according to the area mapping or the angle mapping in the step 1, obtaining a control function of the weight factor in the flow direction in the step 2, and establishing a shape function from the inlet section to the outlet section in the flow direction by using a linear weighting mode as follows:
f(x,y,z)＝[1-k(x)]·fin(x,y,z)+k(x)·fout(x,y,z)
where f (x, y, z) represents the systolic profile function, k (x) represents the weighting factor, i.e. the flow control function, fin(x, y, z) represents the inlet cross-sectional shape, fout(x, y, z) represents the influence of the outlet cross section, the weight factor satisfies k is more than or equal to 0 and less than or equal to 1 (x), and x belongs to [0, L ]]。
Determining a three-dimensional coordinate function according to the established shape function, specifically, when the algorithm is implemented, firstly dispersing 4 sections of curves of the inlet and the outlet respectively, taking the inlet centroid as the origin of a coordinate system,
the entry is noted as: (0, y)in(s,j),zin(s,j))，
The outlet is noted as: (L, y)out(s,j),zout(s,j))，
Where s is 1,2,3,4 denotes a curve number, and j is 1,2, so, N denotes the number of discrete points, and the three-dimensional shape coordinates of the discrete points of the contraction section are obtained by using a linear weighting method:
X(i,j)＝L·x(i)
Y(i,j)＝[1-k(i)]·yin(i,j)+k(i)·yout(i,j)
Z(i,j)＝[1-k(i)]·zin(i,j)+k(i)·zout(i,j)
where i 1,2, M represents the number of discrete points of the flow control curve.
And 4, step 4: and importing the discrete coordinates of the calculated appearance into three-dimensional digital-analog software for three-dimensional modeling to obtain the three-dimensional appearance of the circular-section torque-shaped section contraction section. And finally obtaining the circular-section torque-shaped section contraction section.
Example 1:
a method for designing a wind tunnel contraction section with a circular section and a torque-shaped section is characterized in that a contraction section effect diagram is shown in figure 2, a coordinate system of the method is defined as that a flow direction is an x axis, a longitudinal direction is a y axis, and a z axis direction is given by a right-hand rule. The specific design comprises the following steps.
Step 1: and analyzing the model characteristics of the inlet and outlet shapes of the contraction section, and determining the mapping relation of the inlet and outlet shapes. As shown in fig. 3, according to the shape characteristic analysis of the inlet and the outlet, the inlet is a smooth circular curve, and the outlet is a non-smooth curve with right angles, i.e. the outlet has four inflection points to divide the outlet into four continuous smooth straight lines, and since the contraction section is gradually transited from the circular section to the rectangular section, the inlet should also have four continuous smooth curves corresponding to the four continuous smooth curves of the outlet. The method comprises the following specific steps:
step 101: as shown in fig. 3, the rectangular surface of the outlet is divided into a region No. 1 ', a region No. 2', a region No. 3 'and a region No. 4' along the diagonal, four inflection points and four curves are determined, the circular surface of the inlet is divided into a region No. 1, a region No. 2, a region No. 3 and a region No. 4, and the four "inflection points" and the four curves of the region are undetermined;
step 102: according to the model characteristics of the shapes of the inlet and the outlet of the contraction section, namely the inlet is a smooth circular curve, the outlet is a non-smooth curve with a right angle, and the mapping relation from the area No. 1, the area No. 2, the area No. 3 and the area No. 4 at the inlet to the area No. 1, the area No. 2, the area No. 3 and the area No. 4 at the outlet is established;
step 103: according to the four inflection points and four-segment curves of the outlet which are determined in the step 102, the four inflection points and four-segment curves of the inlet are determined by adopting area mapping so as to ensure that a mapping relation is established with the four-segment curves of the outlet.
In the step 103, the area mapping is shown in fig. 4, and specifically includes the following steps:
step 2101: according to the rectangular geometric principle, the areas of the No. 1 'area, the No. 2' area, the No. 3 'area and the No. 4' area of the outlet are equal, and the areas of the No. 1 area, the No. 2 area, the No. 3 area and the No. 4 area of the inlet are determined to be equal;
step 2102: the radius of the circle is set to be R, R is 450mm, and the area of one area is set to be thetac1The length b of the rectangle is set to 200mm, the width a is set to 100mm, and the area of one of the regions is set to θc2The length L of the flow direction is 800 mm;
step 2103: according to the equally divided circumference, the following can be obtained: thetac1Pi/4, obtained according to the rectangular geometry principle: thetac2In an entry-to-exit mapping, the mapping angle varies linearly, i.e. θ (2)c＝θc1+(θc2-θc1)x/L，θcThe angle along the x direction is shown, and then the mapping relation of 4 curves of the inlet and 4 curves of the outlet is established.
And 2, step: and setting the control parameters of the flow direction control curve, and determining the flow direction control curve. The flow control curve is used to control the weighting factor, which gives the magnitude of the weight when the entry and exit functions are linearly weighted. In this embodiment, the weighting factor is described by using a 3-time quasi-uniform rational B-spline curve, which is a very mature geometric modeling tool, and the basic principle is not described herein, and only the specific control parameters are given in the present invention.
As shown in FIG. 6, a schematic diagram of a flow direction control curve based on a quasi-uniform 3-order rational B-spline curve in a normalized coordinate system is given, and a total of 4 points are adopted to control a weight factor, namely c1(0,0)，c2(0,p1)，c3(p21) and c4(1,1) wherein 0 < p1＜p2< 1, setting p1＝0.2，p1＝0.8。
And step 3: determining the mapping relation between an inlet and an outlet according to the area mapping, obtaining a control function of the weight factor in the flow direction, and establishing a shape function from the inlet section to the outlet section in the flow direction by using a linear weighting mode as follows:
f(x,y,z)＝[1-k(x)]·fin(x,y,z)+k(x)·fout(x,y,z)
where f (x, y, z) represents the systolic profile function, k (x) represents the weighting factor, i.e. the flow control function, fin(x, y, z) represents the inlet cross-sectional shape, fout(x, y, z) represents the influence of the outlet cross section, the weight factor satisfies k is more than or equal to 0 and less than or equal to 1 (x), and x belongs to [0, L ]]。
Determining a three-dimensional coordinate function according to the established shape function, specifically, in the implementation of the algorithm, firstly dispersing 4 sections of curves of the inlet and the outlet respectively, taking the centroid of the inlet as the origin of a coordinate system,
the entry is noted as: (0, y)in(s,j),zin(s,j))，
The outlet is noted as: (L, y)out(s,j),zout(s,j))，
Wherein s is 1,2,3,4 represents a curve number, j is 1,2, and N represents the number of discrete points, and a linear weighting method is used to obtain the three-dimensional outline coordinates of the discrete points of the contraction section:
X(i,j)＝L·x(i)
Y(i,j)＝[1-k(i)]·yin(i,j)+k(i)·yout(i,j)
Z(i,j)＝[1-k(i)]·zin(i,j)+k(i)·zout(i,j)
where i 1,2, M represents the number of discrete points of the flow control curve.
And 4, step 4: and (3) importing the discrete coordinates of the calculated appearance into three-dimensional digital analog software SolidWorks for three-dimensional modeling to obtain the three-dimensional appearance of the circular-section torque-shaped section contraction section. The resultant torque-shaped cross-sectional narrowing section layout of circular cross-section is shown in fig. 7.
Example 2:
a wind tunnel contraction section design method with a circular section torque-shaped section is characterized in that a contraction section effect diagram is shown in figure 2, a coordinate system of the wind tunnel contraction section effect diagram is defined as that a flow direction is an x axis, a longitudinal direction is a y axis, and a z axis direction is given by a right-hand rule. The specific design comprises the following steps.
Step 1: and analyzing the model characteristics of the inlet and outlet shapes of the contraction section, and determining the mapping relation of the inlet and outlet shapes. As shown in fig. 3, according to the shape characteristic analysis of the inlet and the outlet, the inlet is a smooth circular curve, and the outlet is a non-smooth curve with right angles, i.e. the outlet has four inflection points to divide the outlet into four continuous smooth straight lines, and since the contraction section is gradually transited from the circular section to the rectangular section, the inlet should also have four continuous smooth curves corresponding to the four continuous smooth curves of the outlet. The method comprises the following specific steps:
step 101: as shown in fig. 3, the rectangular surface of the outlet is divided into a region No. 1 ', a region No. 2', a region No. 3 'and a region No. 4' along the diagonal, four inflection points and four curves are determined, the circular surface of the inlet is divided into a region No. 1, a region No. 2, a region No. 3 and a region No. 4, and the four "inflection points" and four curves of the inlet are undetermined;
step 102: according to the model characteristics of the shapes of the inlet and the outlet of the contraction section, namely the inlet is a smooth circular curve, the outlet is a non-smooth curve with a right angle, and the mapping relation from the area No. 1, the area No. 2, the area No. 3 and the area No. 4 at the inlet to the area No. 1, the area No. 2, the area No. 3 and the area No. 4 at the outlet is established;
step 103: according to the four inflection points and four-segment curve of the outlet which are determined in the step 102, the four inflection points and four-segment curve of the inlet are determined by adopting angle mapping so as to ensure that a mapping relation is established with the four-segment curve of the outlet.
In the step 103, the angle mapping is shown in fig. 5, and specifically includes the following steps:
step 2201: the radius of the circle R is 450mm, the length of the rectangle b is 200mm, the width a is 100mm, and the flow direction length L is 800 mm.
Setting the angle of the outlet partition region to θd2According to the principle of rectangular diagonal line: thetad2＝arctan(b/a)；
Step 2202: setting the angle of the inlet partition region to thetad1According to the condition that the angle formed by the corner lines of the 4 boundary points at the inlet is equal to the angle formed by the diagonal lines of the 4 corner points at the outlet, the inlet angle also satisfies thetad1And establishing a mapping relation between 4 curves at the inlet and 4 curves at the outlet.
Step 2: and setting the control parameters of the flow direction control curve, and determining the flow direction control curve. The line control curve is used to control the weighting factor, giving the magnitude of the weight when the entry and exit functions are linearly weighted. In this embodiment, the weighting factors are described by using a B-spline curve, which is a very mature geometric modeling tool, and the basic principle thereof is not described herein, and only specific control parameters thereof are given in the present invention.
As shown in FIG. 6, a schematic diagram of a flow direction control curve based on a B-spline curve in a normalized coordinate system is given, and a total of 4 points are adopted to control the weight factors, namely c1(0,0)，c2(0,p1)，c3(p21) and c4(1,1) wherein 0 < p1＜p2< 1, p1＝0.2，p1＝0.5。
And step 3: determining the mapping relation between an inlet and an outlet according to the area mapping, obtaining a control function of the weight factor in the flow direction, and establishing a shape function from the inlet section to the outlet section in the flow direction by using a linear weighting mode as follows:
f(x,y,z)＝[1-k(x)]·fin(x,y,z)+k(x)·fout(x,y,z)
where f (x, y, z) represents the systolic profile function, k (x) represents the weighting factor, i.e. the flow control function, fin(x, y, z) represents the inlet cross-sectional shape, fout(x, y, z) represents the influence of the outlet cross section, the weight factor satisfies k is more than or equal to 0 and less than or equal to 1 (x), and x belongs to [0, L ]]。
Determining a three-dimensional coordinate function according to the established shape function, specifically, when the algorithm is implemented, firstly dispersing 4 sections of curves of the inlet and the outlet respectively, taking the inlet centroid as the origin of a coordinate system,
the entry is noted as: (0, y)in(s,j),zin(s,j))，
The outlet is noted as: (L, y)out(s,j),zout(s,j))，
Where s is 1,2,3,4 denotes a curve number, and j is 1,2, so, N denotes the number of discrete points, and the three-dimensional shape coordinates of the discrete points of the contraction section are obtained by using a linear weighting method:
X(i,j)＝L·x(i)
Y(i,j)＝[1-k(i)]·yin(i,j)+k(i)·yout(i,j)
Z(i,j)＝[1-k(i)]·zin(i,j)+k(i)·zout(i,j)
where i 1,2, where M represents the number of discrete points of the flow control curve.
And 4, step 4: and (4) importing the appearance discrete coordinates obtained by calculation into three-dimensional digital-analog software SolidWorks for three-dimensional modeling to obtain the three-dimensional appearance of the circular section torque-shaped section contraction section. The resultant torque-shaped cross-sectional narrowing section layout of circular cross-section is shown in fig. 7.
The foregoing shows and describes the general principles, principal features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (7)
1. A wind tunnel contraction section design method with a circular section torque-shaped section is characterized in that: the method comprises the following steps:
step 1: analyzing the model characteristics of the shapes of the inlet and the outlet of the contraction section, and determining the mapping relation of the shapes of the inlet and the outlet;
and 2, step: setting control parameters of the flow direction control curve, and determining the flow direction control curve;
and 3, step 3: determining a shape function of a section from the inlet section to the outlet section in the flow direction by using a linear weighting mode according to the mapping relation determined in the step 1 and the flow direction control curve obtained in the step 2, and obtaining a three-dimensional shape discrete coordinate;
and 4, step 4: importing the obtained three-dimensional shape discrete coordinates into three-dimensional digital analog software for modeling to obtain the three-dimensional shape of the circular section torque-shaped section contraction section;
in the step 1, the process is carried out,
step 101: dividing the rectangular surface of the outlet into four regions, determining that four inflection points and four curves exist, and dividing the circular surface of the inlet into four regions, wherein the four inflection points and the four curves of the region are undetermined;
step 102: establishing a mapping relation from an inlet area to an outlet area according to the model characteristics of the inlet and outlet shapes of the contraction section;
step 103: having determined four inflection points and four-segment curves for the exit at step 101, four "inflection points" and four-segment curves for the entrance are determined using either an area map or an angle map.
2. The method for designing the wind tunnel contraction section with the circular-section torque-shaped section according to claim 1, wherein the method comprises the following steps: in step 101, the circular surface of the inlet is divided into a region No. 1, a region No. 2, a region No. 3 and a region No. 4 through the center of a circle, and the rectangular surface of the outlet is divided into a region No. 1 ', a region No. 2', a region No. 3 'and a region No. 4' along the diagonal.
3. The method for designing the wind tunnel contraction section with the circular-section torque-shaped section according to claim 2, wherein the method comprises the following steps: in the above step 103, the area mapping includes the following steps:
step 2101: according to the geometric principle, the areas of the No. 1 'area, the No. 2' area, the No. 3 'area and the No. 4' area of the outlet are equal, and the areas of the No. 1 area, the No. 2 area, the No. 3 area and the No. 4 area of the inlet are determined to be equal;
step 2102: set to be circularRadius R, diagonal lines of the four regions obtained in step 1, wherein the diagonal line of the inlet forms an angle theta with the z-axisc1The diagonal of the outlet forms an angle theta with the z-axisc2；
Step 2103: according to the equally divided circumference, the following can be obtained: theta.theta.c1Pi/4, which can be derived from the rectangular geometry: thetac2Where b is the length of the rectangle and a is the width of the rectangle, the mapping angle varies linearly, i.e. θ, in the entry-to-exit mappingc＝θc1+(θc2-θc1)x/L，θcThe angle along the x direction is shown, x represents the abscissa along the flow direction, L represents the length of the flow channel, and then the mapping relation of 4 curves of the inlet and 4 curves of the outlet is established.
4. The method for designing the wind tunnel contraction section with the circular-section torque-shaped section according to claim 3, wherein: in the above step 103, the angle mapping includes the following steps:
step 2201: setting the angle of the outlet partition region to θd2According to the rectangular diagonal principle, the method comprises the following steps: theta.theta.d2＝arctan(b/a)；
Step 2202: setting the angle of the inlet partition region to θd1According to the condition that the angle formed by the inlet 4 boundary points on the corner line is equal to the diagonal angle formed by the outlet 4 corner points, the obtained inlet angle also satisfies thetad1And establishing a mapping relation between 4 curves at the inlet and 4 curves at the outlet.
5. The method for designing the wind tunnel contraction section with the circular-section torque-shaped section according to claim 4, wherein the method comprises the following steps: giving weight when linear weighting is carried out on the entrance function and the exit function, and adopting 4 points to control the weight factor, namely c1(0，0)，c2(0，p1)，c3(p21) and c4(1,1) wherein 0 < p1＜p2< 1, for c1c2Control point, adjust p1Can control the speed of the change of the shape of the cross section of the inlet, forc3c4Control point, adjust p2The value of (2) can control the speed of the change of the shape of the cross section of the outlet.
6. The method for designing the wind tunnel contraction section with the circular-section torque-shaped section according to claim 5, wherein the method comprises the following steps: in step 3, a shape function of the inlet cross section to the outlet cross section in the flow direction is established by means of linear weighting:
f(x，y，z)＝[1-k(x)]·fin(x，y，z)+k(x)·fout(x，y，z)
where f (x, y, z) represents the systolic profile function, k (x) represents the weighting factor, i.e. the flow control function, fin(x, y, z) represents the inlet cross-sectional shape, fout(x, y, z) represents the cross-sectional shape of the outlet, the weighting factor is 0 ≦ k (x ≦ 1), and x ∈ [0, L ]]。
7. The method for designing the wind tunnel contraction section with the circular-section torque-shaped section according to claim 6, wherein the method comprises the following steps: determining a three-dimensional coordinate function according to the established shape function, firstly dispersing 4 sections of curves of an inlet and an outlet, taking an inlet centroid as a coordinate system origin, and marking the inlet as: (0, y)in(s，j)，zin(s, j)), the exit is noted: (L, y)out(s，j)，zout(s, j)), wherein s is 1,2,3,4 represents a curve number, j is 1,2, and N represents the number of discrete points, and the three-dimensional shape coordinates of the discrete points of the contraction section are obtained by using a linear weighting method:
X(i，j)＝L·x(i)
Y(i，j)＝[1-k(i)]·yin(i，j)+k(i)·yout(i，j)
Z(i，j)＝[1-k(i)]·zin(i，j)+k(i)·zout(i，j)
where i 1, 2.., M denotes the number of discrete points of the flow direction control curve, x (i) denotes the normalized coordinates in the flow direction, and k (i) denotes the weighting factor.
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