CN115952604A - Centrifugal impeller blade generation method based on free-form surface blade neutral surface - Google Patents
Centrifugal impeller blade generation method based on free-form surface blade neutral surface Download PDFInfo
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Abstract
The invention discloses a centrifugal impeller blade generation method based on a free-form surface blade neutral surface, which comprises the steps of obtaining blade data, and extracting a plurality of curved surface structure lines as blade mean camber lines; calculating the meridian thickness distribution at the high position of each leaf; calculating the actual normal thickness corresponding to any point on the mean camber line of each blade; calculating the position interval of the ellipse-like head on the leaf-shaped line; dispersing the mean camber line into a plurality of coordinate points; drawing a thickness circle by taking the coordinate point as the center of a circle and the actual normal thickness as the diameter, and intersecting the thickness circle with the revolution surface of the corresponding camber line to obtain the coordinate points of the pressure surface and the suction surface at the corresponding leaf height; fitting coordinate points to obtain pressure surface and suction surface leaf-shaped lines; and constructing the NURBS curved surface to obtain a pressure surface and a suction surface. The shapes of the pressure surface and the suction surface of the generated blade are defined by the neutral surface, the ovality and the thickness of the blade, curved surface extension and construction are not needed, the blade angle of each position can be ensured to meet the design requirement, and the actual aerodynamic performance and the structural strength of the impeller are improved.
Description
Technical Field
The invention belongs to the technical field of aerospace, and relates to a centrifugal impeller blade generation method based on a free-form surface blade neutral surface.
Background
The centrifugal compressor is a rotary machine which uses fluid as a working medium to realize function conversion, is widely applied to the fields of petrifaction, metallurgy, civil air conditioning, aerospace and the like, and can bring considerable economic benefits by improving the performance. The centrifugal impeller is a core part of the centrifugal compressor, the compressor utilizes the high-speed rotation of the impeller to enable gas flowing through the impeller to flow at a high speed under the action of centrifugal force and blade forcing force to generate kinetic energy, the flow area of the gas is controlled through the predesigned blade shape, and the kinetic energy of the gas is converted into pressure energy, so that the pressure of the gas is improved. In the process, the blade takes on the main function conversion task, and the efficiency of converting mechanical energy into gas pressure energy is directly influenced by the shape of the blade.
The blades of a centrifugal impeller are mainly composed of a pressure surface and a suction surface, and when gas flows across the surface of the blade, the pressure on the pressure surface of the blade is usually higher than the pressure on the suction surface at the same position. When a designer initially designs the shape of the blade, in order to achieve performance estimation, the blade is usually simplified into a curved surface without thickness, and the shape of the curved surface is reasonably designed to make the performance of the impeller approach the design target, and the curved surface is called a blade neutral surface. After the design of the neutral surface of the blade is finished, in order to obtain the actual shape of the blade with a geometric solid, a pressure surface and a suction surface are generated on two sides of the neutral surface by utilizing the given thickness distribution of the blade. The pressure surface and the suction surface are blade profiles in actual contact with gas, the shapes of the pressure surface and the suction surface not only meet the design of a neutral surface of the blade, but also meet the rule of thickness distribution, and continuous and smooth surface shapes are required to reduce the air flow impact loss.
The existing blade generation technology is mainly suitable for a straight line element neutral plane with a simple shape and a thickness distribution rule with gentle change. For a more complex free-form surface blade neutral surface and a more steeply-changed thickness distribution rule, the existing blade generation technology is difficult to ensure the generation of a smooth and accurate blade pressure surface and suction surface, and particularly, the phenomenon of non-smooth connection of curved surfaces such as edges, folds and the like easily occurs because the front edge of the blade is rough, so that the actual aerodynamic performance and the structural strength of the impeller are seriously influenced.
Disclosure of Invention
The invention aims to solve the problems that when a complex free-form surface blade neutral plane is generated in the prior art, the front edge of the blade is processed roughly, the phenomenon of unsmooth connection of curved surfaces is easy to occur, and the actual aerodynamic performance and the structural strength of an impeller are affected, and provides a method for generating a centrifugal impeller blade based on the free-form surface blade neutral plane.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
a centrifugal impeller blade generation method based on a free-form surface blade neutral plane comprises the following steps:
acquiring free-form surface blade neutral plane data, extracting a plurality of curved surface structure lines on the blade neutral plane along the blade height direction, and taking the curved surface structure lines as blade mean camber lines;
calculating the blade mean camber line at each blade height through linear interpolation to obtain the meridional thickness distribution at the blade height;
calculating the actual normal thickness corresponding to any point on each blade mean camber line through the meridional thickness distribution and the corresponding blade mean camber line;
calculating the position interval of the ellipse-like head on the blade profile line through the actual normal thickness on the camber line of the blade and the given front edge ellipticity;
dispersing the camber line of the blade into a plurality of coordinate points, wherein the elliptical line is uniformly divided when the coordinate points of the discrete camber line of the blade corresponding to the elliptical head generate corresponding thickness points on the pressure surface or the suction surface;
drawing a thickness circle by taking the coordinate point obtained after dispersion as a circle center and the actual normal thickness of the coordinate point as a diameter, and obtaining the coordinate points of the pressure surface and the suction surface at the positions corresponding to the blade heights after intersection of the thickness circle and the revolution surface of the camber line in the corresponding blade;
fitting coordinate points of the pressure surface and the suction surface at each leaf height position by using a NURBS curve interpolation method to obtain a pressure surface leaf-shaped line and a suction surface leaf-shaped line corresponding to the leaf height position;
and taking the pressure surface leaf-shaped lines and the suction surface leaf-shaped lines at all the leaf height positions as NURBS curved surface structure lines, constructing a NURBS curved surface, and obtaining the pressure surface and the suction surface of the blade.
The invention is further improved in that:
the extraction of the curved surface structure line comprises the following steps:
the neutral surface of the free-form surface blade comprises four edges which are a blade root, a blade top, a front edge and a tail edge respectively; taking the direction from the leading edge to the trailing edge as the u direction of the curved surface, and taking the direction from the blade top to the blade root as the v direction of the curved surface; uniformly extracting U curved surface structure lines in the U direction along the v direction, wherein the v coordinate of each curved surface structure line is a fixed value; taking the curved surface structure line as a blade mean camber line corresponding to the blade height position, taking the blade top as the 0 th layer and the blade root as the U-1 th layer.
The meridian thickness distribution of She Gaochu is calculated by the blade root thickness distribution and the blade top thickness distribution, the blade root thickness distribution and the blade top thickness distribution are dispersed into k points at equal normalized meridian coordinate intervals, and the thickness value of the ith point of the ith layer is calculated according to linear interpolation, specifically expressed as:
thk_i(j)＝thk_shroud(j)+i×(thk_hub(j)-thk_shroud(j))/(U-1) (1)
wherein thk _ i (j) represents the thickness value of the ith layer j point, thk _ shroud (j) represents the thickness value of the jth point of the blade top, and thk _ hub (j) represents the thickness value of the jth point of the blade root.
The step of calculating the actual normal thickness corresponding to any point on the mean camber line of each blade specifically comprises the following steps:
projecting the camber line of the blade to an r-z meridian plane to obtain a meridian line corresponding to the camber line of the blade;
given a curve coordinate t on a blade mean camber line, obtaining coordinates (x (t), y (t), z (t)) of a corresponding point P on the blade mean camber line, projecting the point P to a r-z meridian plane to obtain P ', and solving a point P ' nearest to the point P ' on the meridian line by using a bisection method m And its corresponding normalized meridian coordinate t m ；
With t m As the normalized meridian coordinate of the point P, the actual normal thickness is obtained by interpolation calculation, as shown in formula (2):
n i (t)＝thk_i((k-1)×t m +1) (2)
wherein n is i Represents the actual normal thickness, t, corresponding to any point on the mean camber line of each blade m The normalized meridian coordinates of the corresponding points are represented.
The obtaining of the meridian corresponding to the blade mean camber line specifically comprises the following steps:
firstly, uniformly dispersing camber lines in the blades into N coordinate points;
calculating meridional coordinate values (r, z) from the coordinate values (x, y, z) of each coordinate point, projecting each of the N coordinate points onto an r-z meridional plane:
and finally fitting coordinate points on the r-z meridian plane by NURBS curve interpolation to obtain a meridian corresponding to the mean camber line of the blade.
The method specifically comprises the following steps of calculating the position interval of the ellipse-like head on the leaf-shaped line:
obtaining the total length of the camber line of the ith blade as l i The length of the ellipse-like head on the camber line of the blade is
According to the definition of ellipticity, the length of the ellipse-like head on the camber line of the blade is calculated by adopting a dichotomy method, the position interval of the ellipse-like head on the blade profile line is obtained, and the length of the ellipse-like head on the camber line of the blade satisfies the formula (4):
wherein e is p The ovality of the leading edge is shown,
the thickness of the joint position of the ellipse-like head and the blade is shown.
The discretizing of the blade mean camber line into the plurality of coordinate points comprises discretizing the blade mean camber line corresponding to the ellipse-like head and discretizing the blade mean camber line except for the leading edge part.
The discrete coordinate points of the camber line in the blade corresponding to the ellipse-like head are obtained through the following steps:
taking the mean camber line of the blade as an x axis and the normal direction of the mean camber line of the blade as a y axis, then the unilateral elliptical head-like parameter equation is defined as:
wherein the parameters
And when theta = pi, represents an ellipse-like head starting point, </or>
When, it represents the ellipse-like head end point;
calculating the total length of the unilateral elliptical head-like part according to a parametric equation
Dividing the unilateral elliptical head into N according to the length of the curve leading Each segment length is specifically expressed as
And calculating the coordinate value of each equant point on the ellipse-like head curve, taking the coordinate value of the x axis as a discrete point of the front edge part on the camber line of the ith blade, and taking the coordinate value of the y axis as a normal half thickness corresponding to the discrete point.
The camber lines of the blades except the front edge part are discrete, and the curves of the camber line of the ith blade except the front edge part are equally divided into N main And (3) the coordinates of the curve of each discrete point are expressed as:
wherein j = N leading +2,…,N leading +N main +1，t j Representing the coordinates of the curve for each discrete point.
The generation of the pressure surface leaf-shaped line and the suction surface leaf-shaped line at the leaf height position specifically comprises the following steps:
smoothly extending the ith mean camber line at two ends in a linear mode, then sweeping the extended mean camber line for 180 degrees around the rotating shaft of the impeller in the positive direction to obtain a suction side rotating surface, and then sweeping the mean camber line for 180 degrees in the negative direction to the rotating shaft of the impeller to obtain a pressure side rotating surface;
for each discrete point P except the leading edge point i j Finding out the tangent vector of the blade on the camber line
Then with P i j Is taken as a circle center and is combined with>
Is radius, is at and vector->
Drawing a thickness circle on a vertical plane;
intersecting the thickness circle with the suction side revolution surface, and performing NURBS curve interpolation on all intersection points including the leading edge point on the suction side revolution surface to obtain a suction side leaf-shaped line;
and intersecting the thickness circle with the pressure side revolution surface, and carrying out NURBS curve interpolation on all intersection points including the leading edge point on the pressure side revolution surface to obtain a pressure surface leaf line.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a centrifugal impeller blade generation method based on a free-form surface blade neutral surface, the shapes of a generated blade pressure surface and a generated blade suction surface are defined by the neutral surface, ovality and thickness of a blade, extension and construction of a curved surface are not needed, the blade pressure surface and the suction surface with a front edge elliptical head and a tail edge square head are accurately generated through specified meridian thickness distribution and ovality, the blade angle of each position can be accurately and effectively ensured to meet the design requirement, and the actual aerodynamic performance and the structural strength of an impeller are improved.
Furthermore, the positions of the modeling points can be reasonably distributed through the proposed ellipse-head-like parameter equation and the generation method, and the smoothness of the front edge can be ensured under the condition of strictly conforming to the shape change rule and the given ellipticity of the front edge of the neutral surface; meanwhile, the integrated modeling of the front edge of the blade and the blade main body can be realized, namely, no curved surface seam exists between the elliptical head and the blade main body, and the smooth connection between the elliptical head and the blade main body is ensured.
Drawings
In order to more clearly explain the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention, and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a flow chart of a method for generating a centrifugal impeller blade based on a free-form surface blade neutral plane according to the present invention;
FIG. 2 is a schematic view of a neutral plane of a free-form surface blade and its structure line according to the present invention;
FIG. 3 is a schematic view of the meridian thickness distribution and the interpolation of the intermediate layer thickness in the present invention;
FIG. 4 is a schematic view of a leading edge elliptical-like head of a blade according to the present invention;
FIG. 5 is a schematic view of a method of discretizing a camber line in a leading edge in accordance with the present invention;
FIG. 6 is a schematic view of a method for forming a blade profile at any blade height;
FIG. 7 is an enlarged view taken at a point a in FIG. 6;
FIG. 8 is an enlarged view of the point b in FIG. 6;
FIG. 9 is a schematic diagram of a method for forming a pressure/suction surface of a blade according to the present invention.
Wherein: 1-leading edge, 2-trailing edge, 3-blade tip, 4-blade root, 5-u direction structure line, 6-suction side revolution surface, 7-extension section, 8-ith blade middle arc line, 9-pressure side revolution surface, 10-pressure side blade profile line, 11-suction side blade profile line, 12-blade profile lines at different blade height positions, 13-pressure surface and 14-suction surface.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of protection of the present invention.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. are used for indicating the orientation or positional relationship based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship which is usually arranged when the product of the present invention is used, the description is merely for convenience and simplicity, and the indication or suggestion that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus, cannot be understood as limiting the present invention. Furthermore, the terms "first," "second," and the like are used solely to distinguish one from another, and are not to be construed as indicating or implying relative importance.
Furthermore, the term "horizontal", if present, does not mean that the component is required to be absolutely horizontal, but may be slightly inclined. For example, "horizontal" merely means that the direction is more horizontal than "vertical" and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.
In the description of the embodiments of the present invention, it should be further noted that unless otherwise explicitly stated or limited, the terms "disposed," "mounted," "connected," and "connected" should be broadly construed and interpreted as including, for example, fixed connections, detachable connections, or integral connections; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
The invention is described in further detail below with reference to the accompanying drawings:
referring to fig. 1, a flow chart of a method for generating a centrifugal impeller blade based on a neutral plane of a free-form surface blade according to the present invention is shown, and the method specifically includes the following steps:
s1, acquiring neutral plane data of a free-form surface blade, extracting a plurality of curved surface structure lines on the neutral plane of the blade along the blade height direction, and taking the curved surface structure lines as a blade mean camber line.
The neutral surface of the free-form surface blade comprises four edges which are a blade root, a blade top, a front edge and a tail edge respectively; taking the direction from the front edge to the tail edge as the u direction of the curved surface, and taking the direction from the blade top to the blade root as the v direction of the curved surface; uniformly extracting U curved surface structure lines in the U direction along the v direction, wherein the v coordinate of each curved surface structure line is a fixed value; and taking the curved surface structure line as a blade mean camber line corresponding to the blade height position, taking the blade top as the 0 th layer and the blade root as the U-1 th layer.
And S2, calculating the camber line of each blade at each blade height through linear interpolation to obtain the meridional thickness distribution at the blade height.
She Gaochu, calculating the blade root thickness distribution and the blade tip thickness distribution, dispersing the blade root thickness distribution and the blade tip thickness distribution into k points at equal normalized meridian coordinate intervals, and calculating the thickness value of the jth point of the ith layer according to linear interpolation, specifically expressed as:
thk_i(j)＝thk_shroud(j)+i×(thk_hub(j)-thk_shroud(j))/(U-1) (1)
wherein thk _ i (j) represents the thickness value of the ith layer j point, thk _ shroud (j) represents the thickness value of the jth point of the blade top, and thk _ hub (j) represents the thickness value of the jth point of the blade root.
And S3, calculating the actual normal thickness corresponding to any point on each blade mean camber line through the meridian thickness distribution and the corresponding blade mean camber line.
S3.1, uniformly dispersing camber lines in the blade into N coordinate points, calculating meridian coordinate values (r, z) according to the coordinate values (x, y, z) of each coordinate point, and projecting the N coordinate points to an r-z meridian plane:
and fitting coordinate points on the r-z meridian plane by NURBS curve interpolation to obtain a meridian corresponding to the blade mean camber line.
S3.2, a curve coordinate t on the mean camber line of the blade is given, coordinates (x (t), y (t) and z (t)) of a corresponding point P on the mean camber line of the blade are obtained, the point P is projected to an r-z meridian plane to obtain P ', and a point P ' nearest to the point P ' on the meridian line is obtained by using a bisection method m And its corresponding normalized meridian coordinate t m ；
S3.3, in t m As the normalized meridian coordinate of the point P, the actual normal thickness is obtained through interpolation calculation, as shown in formula (2):
n i (t)＝thk_i((k-1)×t m +1) (2)
wherein n is i Represents the actual normal thickness, t, corresponding to any point on the mean camber line of each blade m Normalized meridian representing corresponding pointsAnd (4) coordinates.
And S4, calculating the position interval of the ellipse-like head on the blade profile line through the actual normal thickness on the camber line of the blade and the given ovality of the front edge.
S4.1, acquiring that the total length of the camber line of the ith blade is l i The length of the ellipse-like head on the camber line of the blade is
S4.2, calculating the length of the ellipse-like head on the camber line of the blade by adopting a dichotomy according to the definition of ellipticity to obtain the position interval of the ellipse-like head on the blade profile line, wherein the length of the ellipse-like head on the camber line of the blade meets the formula (4):
wherein e is p The ovality of the leading edge is shown,
the thickness of the joint of the ellipse-like head and the blade is shown.
And S5, dispersing the camber line of the blade into a plurality of coordinate points, wherein the blade camber line corresponding to the ellipse-like head is dispersed, and the blade camber line except the front edge part is dispersed, and the ellipse-like line is uniformly divided when the corresponding thickness point is generated on the pressure surface or the suction surface by the discrete coordinate point of the camber line of the blade corresponding to the ellipse-like head.
Discrete coordinate points of the camber line in the blade corresponding to the ellipse-like head are obtained through the following steps:
taking the mean camber line of the blade as an x-axis and the normal direction of the mean camber line of the blade as a y-axis, defining a unilateral elliptical head-like parameter equation as follows:
wherein the parameters
And when theta = pi, represents an ellipse-like head starting point, </or>
When, it represents the ellipse-like head end point;
calculating the total length of the unilateral elliptical head according to a parameter equation
Equally dividing the unilateral elliptical heads into N according to the length of the curve leading Parts, each segment length being specified as
And calculating the coordinate value of each equant point on the ellipse-like head curve, taking the coordinate value of the x axis as a discrete point of the front edge part on the camber line of the ith blade, and taking the coordinate value of the y axis as a normal half thickness corresponding to the discrete point.
The mean camber lines of the blades except the front edge part are discrete, and the curves of the mean camber line of the ith blade except the front edge part are equally divided into N main And (3) the coordinates of the curve of each discrete point are expressed as:
wherein j = N leading +2,…,N leading +N main +1，t j Representing the coordinates of the curve for each discrete point.
And S6, drawing a thickness circle by taking the coordinate points obtained after dispersion as the circle center and the actual normal thickness of the coordinate points as the diameter, and obtaining the coordinate points of the pressure surface and the suction surface at the positions corresponding to the blade heights after intersecting the thickness circle with the revolution surface of the pitch arc of the corresponding blade.
S7, fitting coordinate points of the pressure surface and the suction surface at each leaf height position by using a NURBS curve interpolation method to obtain a pressure surface leaf-shaped line and a suction surface leaf-shaped line corresponding to the leaf height position.
S7.1, smoothly extending the ith camber line at two ends in a straight line manner, then sweeping the extended camber line for 180 degrees around the rotating shaft of the impeller in the positive direction to obtain a suction side rotating surface, and then sweeping for 180 degrees in the reverse direction of the rotating shaft of the impeller to obtain a pressure side rotating surface;
s7.2, for each discrete point P except the leading edge point i j Finding out the tangent vector of the blade on the camber line
Then with P i j Is taken as a circle center and is combined with>
Is radius, is at and vector->
Drawing a thickness circle on a vertical plane;
s7.3, intersecting the thickness circle with the suction side revolution surface, and performing NURBS curve interpolation on all intersection points including the leading edge point on the suction side revolution surface to obtain a suction side leaf-shaped line;
s7.4, intersecting the thickness circle with the pressure side revolution surface, and carrying out NURBS curve interpolation on all intersection points including the leading edge point on the pressure side revolution surface to obtain a pressure surface leaf line.
And S8, taking the pressure surface leaf-shaped lines and the suction surface leaf-shaped lines at all the leaf height positions as NURBS curved surface structure lines, and constructing a NURBS curved surface to obtain the pressure surface and the suction surface of the blade.
Examples
And 2, calculating the meridian thickness distribution of the ith layer according to the distribution of the given meridian thickness on the blade root and the blade top. Referring to the meridional thickness distribution in fig. 3 as an example, the root thickness distribution and the tip thickness distribution are dispersed into k points at equal normalized meridional coordinate intervals, where k =101 in this embodiment. According to a linear interpolation method, the thickness value of any j point of the ith layer is calculated as:
thk_i(j)＝thk_shroud(j)+i×(thk_hub(j)-thk_shroud(j))/(U-1)
the ith layer thickness profile in fig. 3 was calculated.
step 3.1, projecting the blade mean camber line to an r-z meridian plane to obtain a meridian corresponding to the blade mean camber line, uniformly dispersing the mean camber line into N coordinate points, where N =1000 in this embodiment, and calculating (r, z) coordinates according to (x, y, z) coordinates of each coordinate point:
and projecting the N coordinate points to an r-z meridian plane, and fitting the coordinate points on the meridian plane by NURBS curve interpolation to obtain a meridian corresponding to the camber line.
Step 3.2, given on the mean camber lineAnd (3) obtaining the three-dimensional coordinates (x (t), y (t), z (t)) of the corresponding point P on the curve according to the parameter equation of the camber line of the blade. This point is projected onto the meridian plane to obtain point P'. Using dichotomy to find the nearest point P 'to the point P' on the meridian m And its corresponding normalized meridian curve coordinate t m 。
Step 3.3, with t m As the normalized meridian coordinate of the point P, the actual normal thickness n is obtained by interpolation according to the ith layer of sub-meridian thickness distribution thk _ i calculated in the step 2 i (t)＝thk_i((k-1)×t m +1)。
And 5, for the ith mean arc line, dispersing the mean arc line part corresponding to the elliptical head. Due to the fact that the length of the ellipse-like head is compared with the mean camber lineThe curvature change of the camber line is small in the range, and the camber line can be simplified into a straight line when the ellipse-like head curve length estimation is carried out, and the calculation is carried out under a rectangular coordinate system. As shown in FIG. 5, the camber line of the leading edge portion is approximated to be the x-axis, the normal to the camber line is defined as the y-axis, and is defined according to the one-sided elliptical head-like curve parameter equation, which is used to calculate the total length of the one-sided elliptical head
In actual calculation, the following discrete form can be adopted for calculation:
then dividing the unilateral elliptical head into N according to the length of the curve leading Portion, in this example, take N leading =10, each segment length is
And (3) solving the x coordinate and the y coordinate of each bisector (including an end point) on the ellipse-like head curve. Taking the x coordinates as discrete points of the front edge part on the ith mean camber line, wherein the corresponding curve normalization parameters on the mean camber line are as follows: t is t j ＝x j /l i Where j =1,2, …, N leading +1, and j =1, t 1 ＝0，j＝N leading +1 time, based on the measured signal strength>
The y coordinate is taken as the normal half thickness corresponding to the discrete point: />
And 6, for the ith mean camber line,dividing the curves except the leading edge portion equally into N main Portion, in this example, take N main =102, the curve coordinates for each discrete point (including curve end points) may be expressed as:
wherein j = N leading +2,…,N leading +N main +1。
step 7.1, as shown in fig. 6, first, the ith mean camber line is extended smoothly at both ends in a straight line form, in this embodiment, 15mm is taken, and the extension distance can be roughly adjusted according to the thickness of the blade, so as to ensure the following intersection process. Then, the lengthened mean camber line is swept by 180 degrees around the z axis (the rotating shaft of the impeller) in the positive direction to obtain a suction side revolution surface, and then swept by 180 degrees in the reverse direction of the z axis to obtain a pressure side revolution surface.
Step 7.2, as shown in FIGS. 7 and 8, for each discrete point P, except the leading edge point i j Finding out its tangent vector on the mean camber line
Then with P i j Is taken as a circle center and is combined with>
Is radius, is at and vector->
A thickness circle is drawn on the vertical plane.
And 7.3, drawing a thickness circle for all discrete points (except the front edge point), and intersecting the thickness circle with the suction side revolution surface and the pressure side revolution surface respectively. NURBS curve interpolation is carried out on all the intersection points (including leading edge points) on the suction side revolution surface to obtain suction side blade profile lines, and NURBS curve interpolation is carried out on all the intersection points (including leading edge points) on the pressure side revolution surface to obtain pressure side blade profile lines.
And 8, finishing the steps 2-7 on the camber lines of all the U blades to obtain blade profile lines of the pressure/suction sides at all the high positions of the blades, as shown in fig. 9. And generating a blade pressure surface by taking all the pressure side blade shape lines as curved surface structure lines and performing NURBS curved surface interpolation, and generating a blade suction surface by taking all the suction side blade shape lines as curved surface structure lines in the same way.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A centrifugal impeller blade generation method based on a free-form surface blade neutral plane is characterized by comprising the following steps:
acquiring free-form surface blade neutral plane data, extracting a plurality of curved surface structure lines on the blade neutral plane along the blade height direction, and taking the curved surface structure lines as blade mean camber lines;
calculating the blade mean camber line at each blade height through linear interpolation to obtain the meridional thickness distribution at the blade height;
calculating the actual normal thickness corresponding to any point on each blade mean camber line through the meridian thickness distribution and the corresponding blade mean camber line;
calculating the position interval of the ellipse-like head on the blade profile line through the actual normal thickness on the camber line of the blade and the given ovality of the leading edge;
dispersing the camber lines of the blades into a plurality of coordinate points, wherein the elliptic lines are uniformly divided when the discrete coordinate points of the camber lines of the blades corresponding to the elliptic heads generate corresponding thickness points on the pressure surface or the suction surface;
drawing a thickness circle by taking the coordinate point obtained after dispersion as a circle center and the actual normal thickness of the coordinate point as a diameter, and obtaining the coordinate points of the pressure surface and the suction surface at the positions corresponding to the blade heights after intersection of the thickness circle and the revolution surface of the camber line in the corresponding blade;
fitting coordinate points of the pressure surface and the suction surface at each leaf height position by using a NURBS curve interpolation method to obtain a pressure surface leaf-shaped line and a suction surface leaf-shaped line corresponding to the leaf height position;
and (3) taking the pressure surface leaf-shaped lines and the suction surface leaf-shaped lines at all the leaf height positions as NURBS curved surface structure lines, constructing a NURBS curved surface, and obtaining the pressure surface and the suction surface of the leaf.
2. The method of claim 1, wherein the extraction of the curved structure line comprises the steps of:
the neutral surface of the free-form surface blade comprises four edges which are a blade root, a blade top, a leading edge and a trailing edge respectively; taking the direction from the leading edge to the trailing edge as the u direction of the curved surface, and taking the direction from the blade top to the blade root as the v direction of the curved surface; uniformly extracting U curved surface structure lines in the U direction along the v direction, wherein the v coordinate of each curved surface structure line is a fixed value; and taking the curved surface structure line as a blade mean camber line corresponding to the blade height position, taking the blade top as the 0 th layer and the blade root as the U-1 th layer.
3. The method for generating a centrifugal impeller blade based on a free-form surface blade neutral plane according to claim 1, wherein the radial thickness distribution of She Gaochu is obtained by calculating a blade root thickness distribution and a blade tip thickness distribution, dispersing the blade root thickness distribution and the blade tip thickness distribution into k points at equal normalized radial coordinate intervals, and calculating the thickness value of the jth point of the ith layer according to linear interpolation, specifically represented as:
thk_i(j)＝thk_shroud(j)+i×(thk_hub(j)-thk_shroud(j))/(U-1) (1)
wherein thk _ i (j) represents the thickness value of the ith layer j point, thk _ shroud (j) represents the thickness value of the jth point of the blade top, and thk _ hub (j) represents the thickness value of the jth point of the blade root.
4. The method as claimed in claim 1, wherein the step of calculating the actual normal thickness corresponding to any point on the mean camber line of each blade comprises the following steps:
projecting the camber line of the blade to an r-z meridian plane to obtain a meridian line corresponding to the camber line of the blade;
given a curve coordinate t on a blade mean camber line, obtaining coordinates (x (t), y (t), z (t)) of a corresponding point P on the blade mean camber line, projecting the point P to a r-z meridian plane to obtain P ', and solving a point P ' nearest to the point P ' on the meridian line by using a bisection method m And its corresponding normalized meridian coordinate t m ；
With t m As the normalized meridian coordinate of the point P, the actual normal thickness is obtained by interpolation calculation, as shown in formula (2):
n i (t)＝thk_i((k-1)×t m +1) (2)
wherein n is i Represents the actual normal thickness, t, corresponding to any point on the mean camber line of each blade m The normalized meridional coordinates of the corresponding points are represented.
5. The method for generating a centrifugal impeller blade based on a free-form surface blade neutral plane according to claim 4, wherein the obtaining of the meridian corresponding to the blade mean camber line is specifically performed by:
firstly, uniformly dispersing camber lines in the blades into N coordinate points;
calculating meridional coordinate values (r, z) from the coordinate values (x, y, z) of each coordinate point, projecting each of the N coordinate points onto an r-z meridional plane:
and finally fitting coordinate points on the r-z meridian plane by NURBS curve interpolation to obtain a meridian corresponding to the blade mean camber line.
6. The method for generating the centrifugal impeller blade based on the free-form surface blade neutral plane as claimed in claim 1, wherein the step of calculating the position interval of the ellipse-like head on the blade profile line is specifically performed by the following steps:
obtaining the total length of a mean camber line of the ith blade as l i The length of the ellipse-like head on the camber line of the blade is
According to the definition of ellipticity, the length of the ellipse-like head on the camber line of the blade is calculated by adopting a dichotomy method, the position interval of the ellipse-like head on the blade profile line is obtained, and the length of the ellipse-like head on the camber line of the blade satisfies the formula (4):
wherein e is p The ovality of the leading edge is shown,
the thickness of the joint position of the ellipse-like head and the blade is shown.
7. The method of claim 1, wherein said discretizing the mean camber line of the blade into a plurality of coordinate points comprises discretizing the mean camber line of the blade corresponding to the ellipse-like head and discretizing the mean camber line of the blade except for a leading edge portion.
8. The method as claimed in claim 7, wherein the discrete coordinate points of the camber line of the blade corresponding to the ellipse-like head are obtained by the following steps:
taking the mean camber line of the blade as an x axis and the normal direction of the mean camber line of the blade as a y axis, then the unilateral elliptical head-like parameter equation is defined as:
wherein the parameters
And when theta = pi, represents the ellipse-like head starting point, </or>
When, it represents the ellipse-like head end point;
calculating the total length of the unilateral elliptical head-like part according to a parametric equation
Dividing the unilateral elliptical head into N according to the length of the curve leading Each segment length is specifically expressed as
And calculating the coordinate value of each equant point on the ellipse-like head curve, taking the coordinate value of the x axis as a discrete point of the front edge part on the camber line of the ith blade, and taking the coordinate value of the y axis as a normal half thickness corresponding to the discrete point.
9. The method of claim 7, wherein the camber lines of the blades other than the leading edge are discrete, and the curves of the ith camber line of the blade other than the leading edge are divided into N main And (3) the coordinates of the curve of each discrete point are expressed as:
wherein j = N leading +2,…,N leading +N main +1，t j Representing the coordinates of the curve for each discrete point.
10. The method for generating a centrifugal impeller blade based on a free-form surface blade neutral plane as claimed in claim 1, wherein the generation of the pressure surface profile line and the suction surface profile line at the blade height position specifically comprises the following steps:
smoothly extending the ith camber line at two ends in a linear mode, then sweeping the extended camber line for 180 degrees around the rotating shaft of the impeller in the forward direction to obtain a suction side rotating surface, and then sweeping for 180 degrees in the reverse direction of the rotating shaft of the impeller to obtain a pressure side rotating surface;
for each discrete point P except the leading edge point i j Finding out the tangent vector of the blade on the camber line
And then to +>
Is taken as a circle center and is combined with>
Is radius, is in and vector>
Drawing a thickness circle on a vertical plane;
intersecting the thickness circle with the suction side revolution surface, and carrying out NURBS curve interpolation on all intersection points including the leading edge point on the suction side revolution surface to obtain a suction side leaf line;
and intersecting the thickness circle with the pressure side revolution surface, and carrying out NURBS curve interpolation on all intersection points including the leading edge point on the pressure side revolution surface to obtain a pressure surface leaf line.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117171924A (en) * | 2023-11-03 | 2023-12-05 | 陕西空天信息技术有限公司 | Blade design method, device, equipment and computer storage medium |
| CN117171923A (en) * | 2023-11-02 | 2023-12-05 | 陕西空天信息技术有限公司 | Blade design method, device, equipment and computer storage medium |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117171923A (en) * | 2023-11-02 | 2023-12-05 | 陕西空天信息技术有限公司 | Blade design method, device, equipment and computer storage medium |
| CN117171923B (en) * | 2023-11-02 | 2024-03-22 | 陕西空天信息技术有限公司 | Blade design method, device, equipment and computer storage medium |
| CN117171924A (en) * | 2023-11-03 | 2023-12-05 | 陕西空天信息技术有限公司 | Blade design method, device, equipment and computer storage medium |
| CN117171924B (en) * | 2023-11-03 | 2024-01-09 | 陕西空天信息技术有限公司 | Blade design method, device, equipment and computer storage medium |
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