Construction method of multi-wing centrifugal fan blade for controlling relative velocity distribution of blade passage

Abstract

The present invention belongs to the technical field related to fluid machinery fans, and discloses a construction method for multi-blade centrifugal fan blades that controls the relative velocity distribution in the blade passage. The method includes the following steps: S1 Calculate the air flow velocities at the flow-through cross-sections at the inlet and outlet of the impeller, and solve for the relative velocities at the inlet and outlet of the blade passage; S2 Construct the average air flow radial velocity distribution line in the radial direction of the impeller radius; solve for the relative velocity distribution curve of the air flow in the blade passage; S3 Divide the blade profile into multiple segments, and calculate the average air flow radial velocity c i corresponding to any point P ri and the relative air flow velocity w i , construct the relational expression of the angle between any point P i and the adjacent point P i+1 , and recursively determine the polar coordinates of any point on the blade profile based on this, thereby realizing the construction of the blade profile. Through the present invention, the problems of excessive flow loss in the blade passage and blade profile design in multi-blade centrifugal fan blades are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field related to fluid machinery fans, and more specifically, relates to a method for constructing blades of a multi-wing centrifugal fan for controlling the relative velocity distribution in the blade passage. Background Art

[0002] Most multi-wing centrifugal impellers adopt circular arc straight blades, and their shapes can be uniquely drawn with only a few geometric parameters. It is generally considered that a strongly forward-curved accelerating blade passage is beneficial to eliminating vortices in the blade passage and improving the fan efficiency. However, the curvature and thickness of a single circular arc blade are constant along the flow direction, and it is impossible to achieve segmented control of the air flow in the blade passage. Therefore, fans with higher performance requirements will adopt a blade profile with a slightly more complex shape, such as a double circular arc profile. This profile is formed by connecting two circular arcs, and the curvature of the blade passage can be adjusted in segments to achieve a better air flow acceleration effect.

[0003] Flow separation on the blade surface is one of the main flow losses in the blade passage. By calculating the thickness of the blade boundary layer and the corresponding losses under different load distribution methods, a more reasonable average velocity and suction surface velocity distribution model in the blade passage is derived, which greatly improves the fan performance. However, the suction surface separation of the forward-curved centrifugal fan is extremely serious, and the calculation formulas for the boundary layer thickness and losses cannot accurately predict the flow losses in the blade passage; and the average relative velocity in the forward-curved blade passage first decreases and then increases, rather than monotonically decreasing under normal circumstances. Therefore, it is still necessary to further discuss whether the above "load method" is applicable to forward-curved centrifugal fans.

[0004] Cheng Xinde proposed a design method for forward blades based on the deflection characteristics of the air flow direction. Aiming at the characteristics of the gradually turning air flow velocity in the forward blade passage, it is considered that there will be a radial inflection point in the air flow, and by grasping the characteristics of the relative velocity decreasing first and then increasing, a velocity distribution model for forward impellers is proposed. This method can achieve a more free curvature change than circular arc blades, is more in line with the flow characteristics of the forward blade passage than the "load method", and can obtain better fan aerodynamic performance without a large amount of numerical calculations. However, this method still has the following technical problems: 1) The compatibility with short blade passage forward blades of multi-wing centrifugal fans is insufficient, and the relative velocity in the blade passage generally increases rather than decreases; 2) The configuration description of the velocity distribution curve is not clear enough, resulting in the tangency relationship between the relative velocity curve and the radial velocity curve at the so-called inflection point and the smoothness of the relative velocity curve at the so-called inflection point cannot be guaranteed. Therefore, this "deflection model" and the recommended velocity distribution parameters cannot be directly applied to the design of multi-wing centrifugal fan blades. Summary of the Invention

[0005] Aiming at the above defects or improvement requirements of the prior art, the present invention provides a method for constructing blades of a multi-wing centrifugal fan for controlling the relative velocity distribution in the blade passage, and solves the problems of excessive flow losses in the blade passage and blade profile design of multi-wing centrifugal fan blades.

[0006] To achieve the above object, according to the present invention, there is provided a construction method for the blades of a multi-wing centrifugal fan for controlling the relative velocity distribution of the blade passage, and the method includes the following steps:

[0007] S1 Calculate the radial components c 1r and c 2r of the air flow velocity on the flow-through cross-sections at the inlet and outlet of the impeller, and solve for the relative velocities w1 and w2 at the inlet and outlet of the blade passage;

[0008] S2 Set the relative radius at the inner diameter of the impeller to 0 and the relative radius at the outer diameter to 1. According to the radial components c 1r and c 2r of the average air flow velocity at the inlet and outlet of the impeller determined in step S1, the distribution line of the average air flow radial velocity c r in the radial direction of the impeller radius can be constructed; according to the relative velocities w1 and w2 at the inlet and outlet of the impeller determined in step S1, the starting point A(0, w1) and the ending point B(1, w2) of the air flow relative velocity w distribution curve can be determined. Then, according to the characteristics of the air flow angle distribution of the blade, an inflection point C of the air flow velocity distribution is set on the average air flow radial velocity distribution line, and the points A, C, and B are connected in a specific manner using a Bezier curve to obtain the air flow relative velocity distribution curve in the blade passage;

[0009] S3 Divide the blade profile between the inner diameter and the outer diameter of the blade passage into multiple segments. The starting point and the ending point of the air flow velocity distribution curve respectively correspond to the starting point and the ending point of the blade profile. Calculate the average air flow radial velocity c i and the air flow relative velocity w ri corresponding to any point P i on the blade profile using the average air flow radial velocity distribution line and the air flow relative velocity distribution curve obtained in step S2. Construct the relationship formula of the included angle Δθ i between any point P i+1 and the adjacent point P i with respect to c ri and w i . Given the position of the starting point or the ending point of the blade profile, the polar coordinates of any point on the blade profile can be obtained by recursion, thereby realizing the construction of the blade profile.

[0010] Further preferably, in step S1, the radial components c 1r and c 2r of the air flow velocity on the flow-through cross-sections at the inlet and outlet are respectively calculated according to the following expressions:

[0011]

[0012]

[0013] Among them, Q v is the designed volumetric flow rate of the fan, R1 is the inner diameter of the impeller, R2 is the outer diameter of the impeller, b1 is the width at the impeller inlet, and b2 is the width at the impeller outlet.

[0014] Further preferably, in step S1, the relative velocities w1 and w2 at the inlet and outlet of the blade passage are calculated according to the following relational expressions:

[0015]

[0016]

[0017] Among them, β1 is the ideal air flow angle at the impeller inlet, and β2 is the ideal air flow angle at the impeller outlet.

[0018] Further preferably, before step S2, the ideal air flow angle β1 at the impeller inlet needs to be corrected. The corrected air flow angle β1' at the inlet is the sum of the ideal air flow angle β1 before correction and the pre-whirl angle. Among them, the value range of the pre-whirl angle is 10° to 50°. The coordinates of the starting point A of the air flow relative velocity distribution curve are updated to (0, w1') according to the corrected air flow angle β1'.

[0019] Further preferably, in step S2, the average air flow radial velocity distribution line is a straight line, with the starting point being L(0, c 1r ), and the end point being T(1, c 2r ).

[0020] Further preferably, in step S2, the inflection point C is on the average air flow radial velocity distribution line, which is obtained by interpolation, and its coordinates are ( c r,T ), and the best value range of its relative radius is 0.15 to 0.4.

[0021] Further preferably, in step S3, for any point P i the corresponding average air flow radial velocity c ri and the air flow relative velocity w i are obtained in the following manner: First, obtain the R i value corresponding to any point P i , then determine the corresponding c ri on the average air flow radial velocity distribution line, and finally determine the air flow velocity w i corresponding to the air flow relative velocity distribution curve at a radius of R i .

[0022] Further preferably, in step S3, the included angle Δθi Regarding c ri and w i The relational expression is as follows:

[0023]

[0024] where β bi is the angle between the connecting line between any point P i and P i+1 and the tangent line at any point P i on the outer contour of the blade, R i is the radius at any point P i ΔR i is the radius difference between any point P i and P i+1 .

[0025] Further preferably, the β bi is calculated according to the following relational expression:

[0026]

[0027] where R T is the radius value corresponding to the relative radius of the inflection point C.

[0028] Further preferably, in step S2, the Bezier curve connecting points A, C, and B is composed of two second-order Bezier curves. On the average airflow radial velocity distribution line, points P1 and Q1 are constructed between points L and C, and between points C and T. Among them, A, P1, C form the first second-order Bezier curve, and C, Q1, B form the second second-order Bezier curve. The two curves are smoothly connected at point C, and points P1 and Q1 satisfy the following relationships:

[0029]

[0030] where a2 is the distance from point P1 to point C, b1 is the distance from point Q1 to point C, h P is the projection distance from the starting point A to the average airflow radial velocity distribution line, h Q is the projection distance from the ending point B to the average airflow radial velocity distribution line.

[0031] Generally speaking, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

[0032] 1. The method for constructing the blades of a multi-wing centrifugal fan that controls the relative velocity distribution of the air flow in the present invention belongs to a forward blade modeling method. Based on the given parameters, the blade shape can be quickly formed. When these parameters are within the preferred range, the obtained blade shape can ensure better aerodynamic performance, eliminating the iterative optimization process of multiple calculations and multiple tests. Moreover, the blade shape designed by the present invention also has obvious performance advantages compared with the traditional single-arc blade;

[0033] 2. The "inflection point model" of the prior art does not predict the actual flow impact at the blade inlet, resulting in its design results being inapplicable to multi-wing centrifugal fans. The correction of the blade inlet angle in the present invention, on the one hand, makes the inlet air flow state during design closer to reality, and the inlet impact loss is pre-estimated and weakened as much as possible. At the same time, the blade is not overly bent, reducing the separation loss caused by excessive blade bending;

[0034] 3. The preferred value range of the relative radius of the inflection point C in the present invention is 0.15 - 0.4, located in the middle and front section of the blade. This inflection point position fully conforms to the motion characteristic that the relative velocity of the air flow in the multi-wing centrifugal fan passage first decreases and then increases after the correction of the inlet angle, and the outlet velocity is not lower than the inlet velocity. The inflection point position set according to this preferred parameter makes the blade have a more flexible and continuous curvature change along the passage flow direction compared with the circular arc blade, having a better guiding and accelerating effect on the air flow in the passage. It not only helps to reduce the energy loss during the flow-through process but also improves the load distribution of the blade, and the overall work capacity of the blade is increased;

[0035] 4. In the present invention, two sections of second-order Bezier curves are used to construct the relative velocity distribution curve of the air flow, which can more flexibly control the shape of the curve. By controlling the intermediate control points to satisfy a certain positional relationship, on the one hand, the curve can be made to be completely tangent to the average air flow radial velocity distribution curve at the inflection point C, ensuring the correct calculation and construction of the subsequent blade profile. On the other hand, the curve has quadratic smoothness at the inflection point C, making the constructed blade profile have a continuous curvature change and reducing the flow loss. Description of the Drawings

[0036] Figure 1 is a schematic structural diagram of the blade to be constructed on the impeller constructed according to the preferred embodiment of the present invention;

[0037] Figure 2 is a schematic diagram of the design parameters of a typical blade modeling - single-arc blade of a multi-wing centrifugal fan;

[0038] Figure 3 is a schematic diagram of the ideal and actual passage flow states of a multi-wing centrifugal fan;

[0039] Figure 4It is a schematic diagram of the angular velocity triangles at the inlet and outlet of the centrifugal cascade of a multi-wing centrifugal fan;

[0040] Figure 5 It is a schematic diagram of the "pre-whirl" treatment during the inlet angle design constructed according to the preferred embodiment of the present invention;

[0041] Figure 6 It is a velocity distribution curve constructed according to the preferred embodiment of the present invention;

[0042] Figure 7 It is a relative velocity distribution curve composed of two sections of second-order Bezier curves constructed according to the preferred embodiment of the present invention;

[0043] Figure 8 It is a schematic diagram of the blade profile drawing process constructed according to the preferred embodiment of the present invention;

[0044] Figure 9 It is the difference between the relative velocity distribution curve of the flow in the blade passage constructed according to the preferred embodiment of the present invention and the design result of the prior art;

[0045] Figure 10 It is a comparison of the blade profiles of the blade constructed according to the preferred embodiment of the present invention and a single-arc blade with the same inlet and outlet angles;

[0046] Figure 11 It is a comparison of the measured aerodynamic performance of the fan when the blade constructed according to the preferred embodiment of the present invention and a single-arc blade with the same inlet and outlet angles are applied to the same fan, where: (a) is the total pressure - flow performance curve of the fan, (b) is the total pressure efficiency - flow performance curve of the fan, (c) is the power - flow performance curve of the fan, and (d) is the A-weighted noise - flow performance curve of the fan.

[0047] In all the drawings, the same reference numerals are used to represent the same elements or structures, where:

[0048] 1 - front disc of the impeller, 2 - blade, 3 - disc of the impeller. Detailed implementation manners

[0049] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0050] A blade shape with good aerodynamic performance can do work on gas more efficiently, so the blade profile design is the key in impeller design. For some multi-wing centrifugal fans made of metal, in order to facilitate manufacturing, arc-shaped blades are often used, and there is still room for further improvement in their aerodynamic performance.

[0051] Such as Figure 2 is a design schematic diagram of the single-arc blade profile of a multi-wing centrifugal fan. The main design parameters include the inner radius R1, the outer radius R2, the inlet installation angle β 1b , the outlet installation angle β 2b , the arc radius R k the arc central angle δ and the radius R0 where the arc center is located. However, these parameters are not independent of each other. Generally, only 4 of them need to be determined, and the remaining two can be uniquely determined.

[0052] The present invention mainly relates to a design process of a non-circular arc-shaped blade profile with better aerodynamic performance. Such as Figure 1 shown, the blades 2 to be constructed in the figure are evenly distributed along the circumference of the impeller. Its two ends are connected to and fixed with the impeller front disc 1 and the wheel disc 3 to form the impeller as a whole. The present invention proposes a method for designing the blade profile after determining the main parameters of a fan impeller such as the inner radius R1, the outer radius R2, the width b, and the outlet installation angle β 2b The present invention relates to the correction of the inlet angle β 1b , so the relevant calculation process of the inlet angle is briefly described.

[0053] The blade profile design of the present invention includes the following steps:

[0054] Step 1: Calculate the inlet and outlet parameters of the blade

[0055] Such as Figure 3 shown is the flow state of the blade passage in the ideal state where the blade has no thickness and the flow has no separation. The air flow flows evenly along the designed path (i.e., the blade profile). The air passing through the blade is in an incompressible state, so its volume flow rate satisfies the continuity hypothesis and is a constant value. Taking different radius toroidal surfaces as the flow-through cross-sections, the flow rates passing through these cross-sections should be equal, and the flow rate on each flow-through cross-section can be expressed as the product of the cross-sectional area and the air flow velocity component perpendicular to the cross-section. Since the flow-through cross-section is a toroidal surface, the air flow velocity component perpendicular to the cross-section is along the radial direction, that is, the radial component c r , c r is unevenly distributed on the cross-section, but we can calculate the average c r on this cross-section according to formula (1):

[0056] 2πR·b·c, = Q v (I)

[0057] In the formula, Q vis the designed volume flow rate of the fan.

[0058] The impeller inlet and outlet of the multi-wing centrifugal fan have the same width, i.e., b1 = b2 = b. The corresponding c at the impeller inlet and outlet can be obtained with the corresponding inlet and outlet parameters r , which are respectively denoted as c 1r and c 2r .

[0059] Such as Figure 4 is the inlet and outlet velocity triangles on the developed blade cascade of the multi-wing centrifugal fan. In the figure, the air flow is from bottom to top, and the lower part of the blade cascade is the inlet velocity triangle of the blade passage. The vector is the absolute velocity of the air flow; the vector is the circumferential velocity at the impeller inlet, and its value can be obtained from the impeller speed n; the vector is the relative velocity of the air flow. Since there is no guide vane for the blade, the inlet air velocity is perpendicular to the rotation direction in the ideal state, that is, only along the radial direction, so c1 = c 1r . From formula (1), the circumferentially averaged c1 can be obtained from the design flow rate Q v , the inner diameter D1, and the blade width b1 at the impeller inlet:

[0060]

[0061] Such as Figure 4 where u1 is the circumferential velocity at the impeller inlet and can be obtained from the impeller speed n, then the ideal air flow angle at the impeller inlet is:

[0062]

[0063] Such as Figure 4 The upper part of the blade cascade is the outlet velocity triangle of the blade passage. The vector is the absolute velocity of the air flow; the vector is the circumferential velocity at the impeller inlet, and its value can be obtained from the impeller speed n; the vector is the relative velocity of the air flow. Assuming that the air flow flowing out of the blade passage has been fully guided by the curved blade, the relative velocity of the outlet air flow is along the tangential direction of the blade outlet, that is, the air flow angle β2 is equal to the blade outlet installation angle β 2b . Since the blade outlet installation angle of the multi-wing centrifugal blade is often greater than 90°, the magnitude of the average relative velocity at the blade passage outlet can be obtained according to the velocity triangle at this time:

[0064]

[0065] Step 2: Inlet installation angle correction

[0066] Under normal circumstances, the inlet installation angle of the blade should be designed to be the same as the air flow direction (i.e., β 1b = β1, and the inlet incidence angle is zero), so that the impact of the air flow on the blade when entering the blade passage and the resulting flow separation will be relatively small.

[0067] However, the inner diameter of the multi-wing centrifugal impeller is generally not much smaller than the outer diameter, and the widths of the impeller inlet and outlet are equal. This often results in the circumferential velocity u1 at the inlet being much greater than the radial component c of the air flow velocity 1r . If the inlet installation angle of the blade is still designed according to the concept of zero incidence angle at this time, the obtained inlet angle β 1b will often be very small. Research shows that too small an inlet angle will lead to too large a bending degree of the blade, resulting in increased flow separation on the blade surface and reduced blade performance.

[0068] The blade design method of the present invention corrects it by adding a certain "pre-whirl angle" on the basis of the inlet angle obtained by the "zero incidence angle" design. As Figure 5 shown in the schematic diagram of the design method of the "pre-whirl angle" in the present invention. The ideal inlet velocity triangle is shown by the dotted line in the figure, while the corrected inlet velocity triangle is shown by the solid line, and the corrected velocity components are indicated by superscript '.

[0069] The "pre-whirl" method of the present invention is to directly move the arrow representing the inlet circumferential velocity along the rotation direction, then the absolute velocity and the relative velocity will both change direction accordingly, forming a certain angle with the velocity vector corresponding to the ideal velocity triangle. The included angle δ between the relative velocities before and after pre-whirl is the "pre-whirl angle" of the present invention. The best value range of the pre-whirl angle δ is approximately between 10° and 50°, depending on the calculation result of the "zero incidence angle" inlet angle β 1b in step one: when β 1b is relatively small, the pre-whirl angle δ can be relatively large, taking the upper limit in the range; while when β 1b is relatively large, the pre-whirl angle δ should be relatively small, taking the lower limit in the range.

[0070] Step three: Drawing the air flow velocity distribution curve

[0071] Based on c 1r and c 2r calculated in step one, the distribution of the radial velocity along the radius can be drawn. As Figure 6 shown, the abscissa in the figure is the dimensionless radius representing the inner diameter position, and represents the outer diameter of the impeller, which can be calculated by the following formula:

[0072]

[0073] The average radial velocity c of the air flow at any radius can be obtained from Equation (1), r and its radial distribution curve can be obtained. Since the ratio of the inner diameter to the outer diameter of the multi-wing centrifugal fan is very large (0.8 - 0.9), then the curvature of the c r distribution curve will be very small and can be approximately simplified to a straight line. Therefore, connecting the inlet and outlet points L(0, c 1r ) and T(1, c 2r ) can obtain the approximate c r radial distribution (straight) line.

[0074] Based on the relative velocities at the inlet and outlet calculated in Steps 1 and 2 (denoted as w1' and w2 respectively), then points with physical meanings A(0, w1') and B(1, w2) can be plotted accordingly as shown in Figure 6 .

[0075] For forward blades, the blade air flow angle ranges from less than 90° to greater than 90° at the outlet, and there must be an inflection point in the middle of the blade passage where the air flow is completely radial, and at this time w = c r . This indicates that there is an intersection point between the c r radial distribution line and the radial distribution line of the relative velocity w at this point. Then the position of the inflection point C can be obtained by interpolation on the c r line, and then point C( c c r,T ) can be plotted. The optimal value range of the relative radius where the inflection point C is located is between 0.15 and 0.4. If a higher blade pressure is desired, then is taken to be about 0.2. If both the blade efficiency and the blade pressure are desired to be considered, then is taken between 0.2 and 0.3.

[0076] Draw a Bezier curve to smoothly connect points A, C, and B, and make it tangent to the c r line at point C, then the radial distribution curve of the air flow relative velocity w can be obtained. The equation of the k-th order Bezier curve is:

[0077]

[0078] where P i represents the i-th control point:

[0079]

[0080] As shown in Figure 7This is a method for drawing the radial distribution curve of the relative air velocity w based on the Bezier curve. The Bezier curve is composed of two second-order Bezier curves connected at point C, such as the curves P0P1P2 and Q0Q1Q2 shown. Among them, point P0 and point Q2 are the head and tail of the w curve, that is, the aforementioned points A(0, w1’) and B(1, w2). P2 and Q0 are the same point, which is the point C where the relative velocity curve coincides with the c Figure 7 line. As shown. Therefore, the shapes of the first Bezier curve and the second Bezier curve can be adjusted by the intermediate control points P1 and Q1 between their distributions. The characteristic of the second-order Bezier curve is that the tangential direction at its endpoints is the direction of the line connecting the endpoints and the upper (lower) control point. Therefore, as long as the control points P1 and Q1 are on the c r line, the two curves are smoothly connected at point C, and both are tangent to the c c r,T line at point C. r The relative positions of the intermediate control points P1 and Q1 are defined by the scale factors k1 and k2, as shown in r Figure 7 . k1 represents the ratio of the distance between P1 and P2 to the total distance between 0 and

[0081] , while k2 represents the ratio of the distance between point Q0 and Q1 to the distance between Figure 7 and 1. The optimal value range of the coefficient k1 is 0.5 - 1, which is related to the inflection point position : when is larger and close to 0.5, k1 takes the lower limit within the optimal range; when is smaller and close to 0, k1 takes the upper limit within the optimal range; For the w curve drawn according to the Bezier curve, its advantage is that the radial distribution curve of the relative velocity w not only has basic first-order continuity at point C, but also satisfies second-order continuity.

[0082] As shown in

[0083] Figure 7 , draw a straight line l0 perpendicular to the c Figure 7 line through point C. Then, the distance distributions of the distances between P0 and P1 and between Q1 and Q2 projected onto the line l0 are denoted as h r and h P and h Q . Then, the values of k1 and k2 should be such that the distance a2 between P1 and P2 and the distance b between Q0 and Q1 satisfy:

[0084]

[0085] Step Four: Solve the mean camber line of the blade

[0086] As shown inFigure 8 Schematic diagram for calculating the mean camber line of the blade based on the determined design parameters and the velocity distribution curve. The blade radius is evenly divided into m segments from R1 to R2, and the radius of the i-th (i = 0, 2,..., m) point is:

[0087]

[0088] Subsequently, a series of circular rings are drawn based on the radius R i Assume that this series of circular rings intersect the mean camber line of the blade at P i (i = 0, 2,..., m). Based on the assumption of an infinite number of blades and the assumption that the air flow fills the blade passage, the air flow completely follows the blade. The absolute air flow velocity c i at point P ri and the relative air flow velocity w i can be obtained by interpolation on the velocity radial distribution curve drawn in the previous step. The air flow angle at point P i can be calculated as follows:

[0089]

[0090] When m approaches infinity, the curve between point P i and point P i+1 can be approximated as a straight line segment, and the included angle between it and the included angle in the reverse circumferential distance direction is β bi . Then its length dl, radial distance dR, and the phase distance Rdθ between the two points can approximately form a right triangle. According to the Pythagorean theorem:

[0091]

[0092] Then the phase difference between point P i and point P i+1 can be given in the form of a difference:

[0093]

[0094] If the phase of the leading edge point of the blade, i.e., P0, is defined as zero: θ0 = 0°. Then the phase of the next point can be calculated successively according to the above formula until the trailing edge point P m (Conversely, after determining the trailing edge point, the coordinates of all points can also be obtained by reverse recursion). Smoothly connecting points P0, P1,..., to P m can obtain the shape of the mean camber line of the blade designed by this method.

[0095] As Figure 9The differences between the relative velocity w distribution curve of the blade passage drawn by the blade design method of the present invention and the relative velocity w distribution curve drawn by the prior art. Since the present invention newly integrates the "pre-whirl" treatment of the blade inlet parameters, the starting point A of the w curve will be significantly lower, even lower than the end point B. This also results in the fact that the optimal inflection point position of the curve drawn by the method of the present invention is earlier than 0.5, while the inflection point position recommended by the prior art is later than 0.5, being 0.55 - 0.7.

[0096] As Figure 10 shown is the comparison between the blade profile designed according to the method of the present invention and the traditional single-arc blade profile under the same inlet and outlet installation angles. The main parameters of the impeller are as follows: outer diameter 600 mm, inner diameter 504 mm, inlet installation angle 59.4°, outlet installation angle 148.1°, number of blades 44, and blade height 275 mm. When the trailing edge points of the two profiles coincide, the leading edge point of the blade designed by the present method is more backward, the airflow angle of the front section of the blade changes faster and the rear section is relatively smoother; the chord length of the new blade is 54.9 mm, slightly longer than the chord length of the original single-arc blade, which is 50.3 mm.

[0097] As Figure 11 shown in (a) - (d) is the measured performance curve of the fan equipped with the blade designed by the method of the present invention and the traditional single-arc blade. First, the pressure-flow curve of the new scheme broadens to the right, and the total pressure of the fan under the same air volume also increases significantly, and the increase amplitude continues to increase with the increase of the air volume. The efficiency curve of the fan equipped with the blade designed by the method of the present invention moves to the right compared with the original machine curve. For most working conditions, the efficiency improvement amplitude is relatively obvious, and the increase amplitude also increases continuously with the increase of the flow rate.

[0098] The power curve of the fan equipped with the blade designed by the method of the present invention also moves to the right, but the impeller power under the same air volume does not increase significantly. The A-weighted sound level noise curve of the fan equipped with the blade designed by the method of the present invention is not higher than the original curve, and the noise at several working condition points in the middle is significantly lower than that of the original fan, indicating that the blade designed by the method of the present invention also has certain advantages in terms of noise.

[0099] In summary, the multi-wing centrifugal blade design method of the present invention significantly enhances the work capacity of the fan by reasonably planning the direction and velocity change of the air flow in the blade passage; at the same time, it reduces the flow loss in the blade passage and improves the fan efficiency. The power of the fan under the same air volume does not increase significantly, and the noise is also improved.

[0100] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A construction method of multi-wing centrifugal fan blades for controlling the relative velocity distribution of the blade passage, characterized in that, The method includes the following steps: S1 Calculate the radial components of the average gas flow velocities at the flow-through cross-sections at the inlet and outlet of the impeller c 1r and c 2r to solve for the relative velocities at the inlet and outlet of the blade passage w 1 and w 2; Set the relative radius at the inner diameter of the impeller to 0 and the relative radius at the outer diameter to 1. According to the radial components of the average air velocities at the impeller inlet and outlet determined in step S1 c 1r and c 2r , construct the distribution line of the average air radial velocity in the impeller radius direction; According to the respective relative velocities w 1 and w 2 at the impeller inlet and outlet determined in step S1, determine the starting point A(0, w 1) and the ending point B(1, w 2) of the air relative velocity distribution curve. Then, set the inflection point C of the air velocity distribution on the average air radial velocity distribution line according to the characteristics of the blade air flow angle distribution. Connect the points A, C, and B with a Bezier curve to obtain the air relative velocity distribution curve in the blade passage; S3 divides the blade profile set between the inner diameter and the outer diameter of the blade passage into multiple segments. The starting point and the ending point of the air flow velocity distribution curve respectively correspond to the starting point and the ending point of the blade profile. The average air flow radial velocity distribution line and the air flow relative velocity distribution curve obtained in step S2 are used to calculate the average air flow radial velocity i corresponding to any point P on the blade profile c ri and the air flow relative velocity w i , and an included angle Δ i between any point P i+1 and the adjacent point P θ i is constructed with respect to c ri and w i . The polar coordinates of any point on the blade profile are obtained by recursion according to the position of the starting point or the ending point of the blade profile, and thus the construction of the blade profile is realized.

2. The construction method of the multi-wing centrifugal fan blade for controlling the relative velocity distribution of the blade passage as claimed in claim 1, wherein, In step S1, the radial components of the air flow velocity at the inlet and outlet through-flow cross-sections c 1r and c 2r are calculated respectively according to the following expressions: Among them, Q v is the designed volumetric flow rate of the fan, R 1 is the inner diameter of the impeller, R 2 is the outer diameter of the impeller, b 1 is the width at the impeller inlet, b 2 is the width at the impeller outlet.

3. A construction method of a multi-wing centrifugal fan blade for controlling the relative velocity distribution of the blade passage, as claimed in claim 1 or 2, characterized in that In step S1, the relative velocities w 1 and w 2 at the inlet and outlet of the blade passage are calculated according to the following relationship: w 1 and w 2 are calculated according to the following relationship: Among them, β 1 is the ideal air flow angle at the impeller inlet, β 2 is the ideal air flow angle at the impeller outlet.

4. A method for constructing a multi-wing centrifugal fan blade for controlling the relative velocity distribution of a blade passage, as claimed in claim 1 or 2, characterized in that, Before step S2, it is also necessary to correct the ideal airflow angle at the impeller inlet β 1. The corrected ideal airflow angle β 1' at the inlet is the sum of the ideal airflow angle β 1 before correction and the pre-whirl angle. The value range of the pre-whirl angle is 10° to 50°. The coordinates of the starting point A of the airflow relative velocity distribution curve are updated to (0, β according to the corrected airflow angle w 1').

5. A method for constructing a multi-wing centrifugal fan blade for controlling the relative velocity distribution of the blade passage, as claimed in claim 1 or 2, characterized in that, In step S2, the average air flow radial velocity distribution line is a straight line, starting from L(0, c 1r ), and ending at T(1, c 2r ).

6. A method for constructing a multi-wing centrifugal fan blade for controlling the relative velocity distribution of the blade passage, as claimed in claim 1 or 2, characterized in that In step S2, the inflection point C is on the average gas flow radial velocity distribution line, which is obtained by interpolation and has coordinates ( , c r,T ). The optimal value range of its relative radius is 0.15 to 0.

4.

7. A construction method of a multi-wing centrifugal fan blade for controlling the relative velocity distribution of the blade passage, as claimed in claim 1 or 2, characterized in that In step S3, any point P i The average radial air velocity corresponding to the point c ri And the relative air velocity w i Are obtained in the following manner: First, obtain the i Corresponding R i Value, then determine the corresponding c ri On the average radial air velocity distribution curve, and finally determine the relative air velocity corresponding to the relative air velocity distribution curve at a radius of R i w i .​ 8. The construction method of a multi-wing centrifugal fan blade for controlling the relative velocity distribution of the blade passage as claimed in claim 1, wherein In step S3, the included angle Δ θ i Regarding c ri And w i The relational expression is as follows: Among them, β bi is the connection line between an arbitrary point P i and P i+1 and the included angle between the tangent line at any point P i on the outer contour of the blade, R i is the radius at an arbitrary point P i , Δ R i is the radius difference between an arbitrary point P i and P i+1 。 9. The construction method of the multi-wing centrifugal fan blade for controlling the relative velocity distribution of the blade passage as claimed in claim 8, wherein, The β bi is calculated according to the following relational expression: Among them, is the radius value corresponding to the inflection point C of the relative velocity curve.

10. A method for constructing a multi-wing centrifugal fan blade for controlling the relative velocity distribution of a blade passage, as described in claim 5, characterized in that, In step S2, the Bezier curve connecting the points A, C, and B consists of two second-order Bezier curves. On the average airflow radial velocity distribution line, points P1 and Q1 are constructed between point L and point C, and between point C and point T. Among them, A, P1, C form the first second-order Bezier curve, and C, Q1, B form the second second-order Bezier curve. The two curves are smoothly connected at point C, and points P1 and Q1 satisfy the following relationship: Among them, a 2 is the distance from point P1 to point C, b 1 is the distance from point Q1 to point C, h P is the projection distance from the starting point A to the average airflow radial velocity distribution line, h Q is the projection distance from the ending point B to the average airflow radial velocity distribution line.

Images