CN106949095B - The optimization method of Low-pressure axial fan impeller blade - Google Patents

Abstract

The invention discloses an optimization method for impeller blades of a low-pressure axial flow fan. Low-pressure axial flow fans are widely used, but there are problems of low total pressure, large air volume, and low impeller efficiency. In the present invention, a blade of the impeller model to be optimized is divided into n sections along the radial direction of the impeller, and the chord length b _i , the outlet geometric angle β _2A(i) and the inlet airflow angle β _1(i) of the n sections are obtained. Draw a sketch, the sketch includes the first line segment, the second line segment, the third line segment, the fourth line segment, the fifth line segment, the sixth line segment, the first arc, the second arc, the seventh line segment and the eighth line segment. The first arc and the second arc form a new type of line. According to the new line, n new sections are obtained, and the optimized impeller model is obtained according to the n new sections. The present invention can optimize the performance of the low-pressure axial flow fan only by knowing the chord length of the blade section to be optimized, the inlet flow angle and the outlet geometric angle, greatly reducing the design time and cost.

Description

Optimization Method of Impeller Blades of Low Pressure Axial Flow Fan

technical field

The invention belongs to the technical field of fan impellers, and in particular relates to an optimization method for blades of a low-pressure axial flow fan impeller.

Background technique

Low-pressure axial flow fans are widely used as the main power of industrial equipment and household appliances such as ventilation, HVAC, cooling, air conditioning and transportation. The aerodynamic characteristics of the axial flow fan are low total pressure, large air volume, and low impeller efficiency. The reason is that there is a gap between the blade and the pipe, there is a secondary flow at the top of the blade, the blade root is connected to the hub, and the separation flow is also serious. There are a large number of vortices near the tip of the blade, and even backflow, causing a large flow loss.

In an axial flow fan, the pressure loss when the airflow passes through the blades is very complicated, and the pressure loss distribution along the height of the blades is uneven. At the average radius of the blade, the pressure loss is relatively small, and the pressure loss is mainly concentrated in a very narrow area in the wake of the blade; in the middle part of the blade path close to the average radius of the blade, the pressure loss is relatively small and relatively uniform; but Near the hub and casing, the area of pressure loss is enlarged, and the value of pressure loss also increases. That is because when the airflow flows through the blade passage, there is relative motion between the airflow and the blade, so there is a force between them, and the pressure on the concave surface of the blade is greater than the pressure on the convex surface of the blade. Therefore, between two adjacent blades, there is a lateral pressure gradient from the concave surface of one blade to the convex surface of the other blade, and this lateral pressure gradient increases with the increase of the lift coefficient. On the other hand, the airflow passes through the cascades in a curvilinear motion, which creates a centrifugal force directed from the convex surface of one blade to the concave surface of the adjacent blade. In the mid-section along the height of the blades, the lateral pressure gradient between adjacent blades is balanced by the centrifugal force of the airflow, so that the airflow does not flow in a lateral direction. However, the situation is different at the root and tip of the blade. For example, at the blade root, the airflow pressure in the boundary layer on the hub surface is the same as the airflow pressure outside the boundary layer, while the airflow velocity inside the boundary layer decreases as it approaches the hub surface and tends to zero. Therefore, there is a transverse pressure gradient in the boundary layer, but there is no or very little centrifugal force of the airflow, so the transverse gradient pressure in the boundary layer cannot be balanced, and the gas in the boundary layer will flow from the concave surface of one blade to the other. The lateral flow of the convex surface adjacent to the blade reduces the pressure in the boundary layer near the concave surface of the blade, while the pressure increases near the convex surface of the adjacent blade, thus forming a vortex. These eddies are carried away by the main air flow, and behind the blade tip, these eddies are gradually converted into heat energy loss, which occurs at the root and tip of the blade. Therefore, the design and optimization goal of the axial flow fan is to reduce the radial speed, make the axial speed more uniform, increase the axial speed at the hub and wheel cover, and improve the working ability of the blades, etc., so that the fan efficiency and All-in pressure is boosted.

Contents of the invention

The object of the present invention is to provide an optimization method for the impeller blades of a low-pressure axial flow fan aiming at the deficiencies of the prior art.

The steps of the present invention are specifically as follows:

Step 1: Establish the impeller model to be optimized. The distance between the hub side wall of the impeller and the outer end of the blade is n×s. Take n sections perpendicular to the radial direction of the impeller on one blade of the model and the corresponding profiles of the n sections, the distance between two adjacent sections is s, and the innermost section is tangent to the hub side wall, 3≤ n≤20. Measure the chord length b _i of n sections, i=1, 2, 3,..., n, and the outlet geometric angle β _2A(i) , i=1, 2, 3,..., n. Remove all chamfers and rounded corners in the model to obtain a simplified model. Use meshing software to mesh the simplified model and perform numerical simulation calculations to obtain the total pressure of the impeller model to be optimized and the three velocity components at the inlet of n sections; draw the velocity triangle according to the three velocity components to obtain n Inlet airflow angle β _1(i) of each section, i=1, 2, 3, . . . , n. Assign the full pressure value of the model to Z1.

Step 2. Assign 1 to i.

Step 3. Draw a sketch, the sketch includes the first line segment, the second line segment, the third line segment, the fourth line segment, the fifth line segment, the sixth line segment, the first arc, the second arc, the seventh line segment and the eighth line segment . The first line segment and the second line segment are parallel to each other, the endpoints of the third line segment are on the first line segment and the second line segment respectively, and the length of the third line segment is b _i . The fourth line segment and the sixth line segment are respectively arranged on both sides of the fifth line segment, and the end points of one end of the fourth line segment and the sixth line segment coincide with the end points of both ends of the third line segment respectively. The other end point of the fourth line segment is on the fifth line segment. The other endpoint of the sixth line segment coincides with the one end point of the fifth line segment, and the sixth line segment and the fifth line segment have the same length. The fifth line segment intersects the third line segment. The center of the first arc is the intersection point of the fourth line segment and the fifth line segment, and the two end points are non-coincident end points of the fourth line segment and the fifth line segment respectively. The center of the second circular arc is the intersection point of the fifth line segment and the sixth line segment, and the two end points are non-coincident end points of the fifth line segment and the sixth line segment respectively. The first arc is in the clockwise direction of the second arc. The seventh line segment coincides with the tangent of the first arc at the end point of the fourth line segment, the angle between the seventh line segment and the first line segment is β _1(i) , and the eighth line segment and the second arc are at the end point of the sixth line segment The tangents of are coincident, and the angle between the eighth line segment and the second line segment is β _2A(i) . The included angle between the seventh line segment and the eighth line segment is θ _c , and θ _c = β _{2A(i) -} β _{1(i) is} obtained. The angle between the fourth line segment and the fifth line segment is α ₁ , and α ₁ =0.6θ _c ; the angle between the sixth line segment and the fifth line segment is α ₂ , and α ₂ =0.4θ _c . The included angle between the third line segment and the seventh line segment is α ₁ , and the included angle between the third line segment and the eighth line segment is α ₂ .

Step 4: The first arc and the second arc form a new type of line. Superimpose the thickness value a of the new line, 1mm≤a≤6mm, to obtain a circular arc section; or select an airfoil from the airfoil database to obtain the thickness distribution of the airfoil section, and combine the thickness distribution of the airfoil section with the new line to obtain the airfoil type section. Record the resulting arc-shaped section or airfoil section as the i-th section.

Step 5, increase i by 1, if i≤n, repeat steps 3 and 4, the sections obtained in step 4 during the repetition process are all arc-shaped sections or airfoil sections. Otherwise, go to the next step.

Step 6: Arranging the obtained n sections in parallel with a distance s between two adjacent sections, and placing them between two coaxial cylindrical surfaces with a radius difference of n×s. The geometric centers of the n sections are all on a straight line perpendicular to the n sections, and the straight line perpendicularly intersects the axes of the two cylindrical surfaces. The n sections are arranged in sequence according to the chord length, and the section with the longest chord length is located on the innermost side. The section with the longest chord is tangent to the cylindrical surface with the smaller diameter. The first line segments of the n sections are parallel to each other and perpendicular to the axes of the two cylindrical surfaces. The first line segments of the n sections are on the same side. Obtain the prototype of the blade according to the n sections. The two ends of the blade rudiment are extended so that the outer end of the blade rudiment completely passes through the larger-diameter cylindrical surface, and the inner end of the blade rudiment completely passes through the smaller-diameter cylindrical surface. The prototype of the blade between the two cylindrical surfaces is the optimized blade. Taking the axes of the two cylindrical surfaces as the array center, m blades are evenly distributed along the circumference, and 4≤m≤10. Draw the hub for m blades to obtain the optimized impeller model.

Step 7. On a blade of the model built in step 6, take n sections perpendicular to the radial direction of the impeller and the corresponding molding lines of the n sections. cut. Measure the chord length b _i of n sections, i=1, 2, 3,..., n, and the outlet geometric angle β _2A(i) , i=1, 2, 3,..., n. Remove all chamfers and rounded corners in the model built in step 6 to obtain a new simplified model. Use meshing software to mesh the new simplified model, and perform numerical simulation calculations to obtain the total pressure of the model built in step 6 and the three velocity components at the entrance of n sections; draw a velocity triangle according to the three velocity components, Thus, the inlet airflow angle β _1(i) of n sections is obtained, i=1, 2, 3, . . . , n. Assign the full pressure value of the model to Z2.

Step 8. If the value obtained by subtracting Z1 from Z2 is greater than k, and 3Pa≤k≤8Pa, assign the value of Z2 to Z1, and repeat steps 2, 3, 4, 5, 6 and 7. Otherwise, optimization ends.

The method of obtaining the prototype of the blade in step 6 is as follows: perform the "lofting surface" operation on the contour lines of n sections in solidworks, and generate the prototype of the blade with a smooth transition.

The method of extending both ends of the blade prototype in step six is as follows: perform the "surface extension" operation on the blade prototype in solidworks.

The airfoil selected in step 4 is NACA0012.

The value of k in step 8 is 5Pa.

The beneficial effects that the present invention has are:

1. The present invention combines fluid machinery, three-dimensional modeling and CFD, and can optimize the performance of the low-pressure axial flow fan through the chord length of the blade section, the inlet airflow angle and the outlet geometric angle, which greatly shortens the design time and cost .

2. The present invention has repeated optimization step units, and repeated execution of the optimization step units can complete multiple optimizations of the performance of the low-pressure axial flow fan.

3. When the present invention executes the optimization step unit for the first time, the total pressure of the low-pressure axial flow fan is greatly improved, but the efficiency is slightly reduced; when the follow-up optimization step unit is executed, the efficiency of the low-pressure axial flow fan remains basically unchanged, and the overall The pressure will continue to increase.

Description of drawings

Fig. 1 is the perspective view of impeller model to be optimized;

Fig. 2 is a sketch for drawing blade cross-section molding lines in the present invention.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

The specific steps of the optimization method for the impeller blades of the low-pressure axial flow fan are as follows:

Step 1: Establishing the impeller model to be optimized As shown in Figure 1, the distance between the hub side wall of the impeller and the outer end of the blade is 8s. On one blade of the model, eight sections vertical to the radial direction of the impeller and the corresponding molding lines of the eight sections are taken. The distance between adjacent sections is s, and the innermost section is tangent to the side wall of the hub. The chord lengths b _i of the eight sections are respectively measured, i=1, 2, 3,...,8, and the outlet geometric angle β _2A(i) , i=1, 2, 3,...,8. Remove all chamfers and rounded corners in the model to obtain a simplified model. The simplified model is meshed and numerically simulated by the meshing software, and the total pressure of the impeller model to be optimized and the three velocity components at the inlet of the eight sections are obtained; the velocity triangle is drawn according to the three velocity components, and the eight Inlet airflow angle β _1(i) of each section, i=1, 2, 3, . . . , 8. Assign the total pressure value of the impeller model to be optimized to Z1.

Step 2. Assign 1 to i.

Step 3, as shown in Figure 2, draw a sketch, the sketch includes the first line segment 1, the second line segment 2, the third line segment 3, the fourth line segment 4, the fifth line segment 5, the sixth line segment 6, and the first arc 7 -1, the second arc 7-2, the seventh line segment 8 and the eighth line segment 9. The first line segment 1 and the second line segment 2 are parallel lines to each other, the endpoints of the third line segment 3 are on the first line segment 1 and the second line segment 2 respectively, and the length of the third line segment 3 is b _i . The fourth line segment 4 and the sixth line segment 6 are arranged on both sides of the fifth line segment 5 respectively, and one end point of the fourth line segment 4 and sixth line segment 6 coincides with two end points of the third line segment 3 respectively. The other end point of the fourth line segment 4 is on the fifth line segment 5 . The other end point of the sixth line segment 6 coincides with one end point of the fifth line segment 5 , and the sixth line segment 6 is equal in length to the fifth line segment 5 . The fifth line segment 5 intersects the third line segment 3 . The center of the first arc 7 - 1 is the intersection point of the fourth line segment 4 and the fifth line segment 5 , and the two ends are the non-coincident endpoints of the fourth line segment 4 and the fifth line segment 5 respectively. The center of the second arc 7 - 2 is the intersection point of the fifth line segment 5 and the sixth line segment 6 , and the two ends are the non-overlapping endpoints of the fifth line segment 5 and the sixth line segment 6 respectively. The first arc 7-1 is in the clockwise direction of the second arc 7-2. The seventh line segment 8 coincides with the tangent of the first arc 7-1 on the end point of the fourth line segment 4, the angle between the seventh line segment 8 and the first line segment 1 is β _1(i) , the eighth line segment 9 and the second The tangents of the arc 7-2 on the endpoint of the sixth line segment 6 coincide, and the included angle between the eighth line segment 9 and the second line segment 2 is β _2A(i) . The included angle between the seventh line segment 8 and the eighth line segment 9 is θ _c , and θ _c = β _{2A(i) -} β _{1(i) is} obtained. The angle between the fourth line segment 4 and the fifth line segment 5 is α ₁ , which is α ₁ =0.6θ _c ; the angle between the sixth line segment 6 and the fifth line segment 5 is α ₂ , and α ₂ =0.4θ _c . The included angle between the third line segment 3 and the seventh line segment 8 is α ₁ , and the included angle between the third line segment 3 and the eighth line segment 9 is α ₂ .

Step 4, the first circular arc 7-1 and the second circular arc 7-2 form a new type of line. For the new line superimposed thickness value a, the value of a is 4mm to obtain a circular arc section; or select an airfoil in the airfoil database, and the selected airfoil is NACA0012 to obtain the thickness distribution of the airfoil section, and the airfoil section The airfoil section is obtained by combining the thickness distribution with the novel line, and the obtained arc-shaped section or airfoil section is recorded as the i-th section.

Step 5, increase i by 1, if i≤8, repeat steps 3 and 4, the sections obtained in step 4 during the repetition process are all arc-shaped sections or airfoil sections. Otherwise, go to the next step.

Step 6: Arrange the obtained eight cross-sections in parallel with the distance s between two adjacent cross-sections, and place them between two coaxial cylindrical surfaces with a radius difference of 8s. The geometric centers of the eight sections are all on a straight line perpendicular to the eight sections, and the straight line perpendicularly intersects the axes of the two cylindrical surfaces. The eight sections are arranged in sequence according to the chord length, and the section with the longest chord length is located on the innermost side. The section with the longest chord is tangent to the cylindrical surface with the smaller diameter. The first line segments 1 of the eight sections are parallel to each other and perpendicular to the axes of the two cylindrical surfaces. The first line segments 1 of the eight sections are all located on the same side. Perform the "lofting surface" operation on the contour lines of the eight sections in solidworks, and make a smooth transition to generate the prototype of the blade. Perform the "surface extension" operation on the blade prototype in solidworks, so that the outer end of the blade prototype completely passes through the larger-diameter cylindrical surface, and the inner end of the blade prototype completely passes through the smaller-diameter cylindrical surface. The prototype of the blade between the two cylindrical surfaces is the optimized blade. With the axes of the two cylinders as the array center and 60° as the array angle, six blades are arrayed in a circle. Draw the hub for six blades to get the optimized impeller model. The first circular arc of the blade section profile is close to the inlet of the impeller model, and the second circular arc is close to the outlet of the impeller model.

Step 7. On a blade of the model built in step 6, take eight sections perpendicular to the radial direction of the impeller and the corresponding molding lines of the eight sections. The distance between two adjacent sections is s, and the innermost section and the hub side wall tangent. The chord lengths b _i of the eight sections are respectively measured, i=1, 2, 3,...,8, and the outlet geometric angle β _2A(i) , i=1, 2, 3,...,8. Remove all chamfers and rounded corners in the model built in step 6 to obtain a new simplified model. Use meshing software to mesh the new simplified model, and perform numerical simulation calculations to obtain the total pressure of the model built in step 6 and the three velocity components at the entrance of the eight sections; draw the velocity triangle according to the three velocity components, Thus, the inlet airflow angles β _1(i) of eight sections are obtained, i=1, 2, 3, . . . , 8. Assign the full pressure value of the model built in step 6 to Z2.

Step 8. If the value obtained by subtracting Z1 from Z2 is greater than 5Pa, assign the value of Z2 to Z1, and repeat steps 2, 3, 4, 5, 6 and 7. Otherwise, optimization ends.

Claims (5)

1. The optimization method of low-pressure axial fan impeller blade is characterized in that: step 1, set up the impeller model to be optimized; The distance between the hub sidewall of impeller and the blade outer end is n * s; A blade in this model Take n sections perpendicular to the radial direction of the impeller and the corresponding profiles of the n sections, the distance between two adjacent sections is s, and the innermost section is tangent to the side wall of the hub, 3≤n≤20; The chord length b _i of n sections, i=1, 2, 3,..., n, and the outlet geometric angle β _2A(i) , i=1, 2, 3,..., n; All the chamfers and rounded corners are simplified to obtain a simplified model; the simplified model is meshed and numerically simulated using meshing software to obtain the total pressure of the impeller model to be optimized and the three velocity components at the inlet of n sections; according to Draw a velocity triangle for the three velocity components, thereby obtaining the inlet flow angle β _1(i) of n sections, i=1, 2, 3,..., n; assign the total pressure value of the model to Z1; Step 2. Assign 1 to i; Step 3. Draw a sketch, the sketch includes the first line segment, the second line segment, the third line segment, the fourth line segment, the fifth line segment, the sixth line segment, the first arc, the second arc, the seventh line segment and the eighth line segment ; The first line segment and the second line segment are mutually parallel lines, the endpoints of the two ends of the third line segment are respectively on the first line segment and the second line segment, and the length of the third line segment is b _i ; the fourth line segment and the sixth line segment are respectively Set on both sides of the fifth line segment, one end point of the fourth line segment, the sixth line segment coincides with the two end points of the third line segment; the other end point of the fourth line segment is on the fifth line segment; the other end point of the sixth line segment coincides with one end point of the fifth line segment, and the sixth line segment is equal to the fifth line segment; the fifth line segment intersects the third line segment; the center of the first arc is the intersection point of the fourth line segment and the fifth line segment, and the two ends are respectively The non-coinciding endpoints of the fourth line segment and the fifth line segment; the center of the second arc is the intersection point of the fifth line segment and the sixth line segment, and the two ends are the non-coinciding endpoints of the fifth line segment and the sixth line segment; the first arc is at In the clockwise direction of the second arc; the seventh line segment coincides with the tangent line of the first arc at the endpoint of the fourth line segment, the angle between the seventh line segment and the first line segment is β _1(i) , the eighth line segment and The tangent of the second arc on the endpoint of the sixth line segment coincides, the angle between the eighth line segment and the second line segment is β _2A(i) ; the angle between the seventh line segment and the eighth line segment is θ _c , and θ _c = β _2A(i) -β _1(i) ; the angle between the fourth line segment and the fifth line segment is α ₁ , take α ₁ =0.6θ _c ; the angle between the sixth line segment and the fifth line segment is α ₂ , take α ₂ =0.4θ _c ; the angle between the third line segment and the seventh line segment is α ₁ , and the angle between the third line segment and the eighth line segment is α ₂ ; Step 4: The first circular arc and the second circular arc form a new type of line; superimpose the thickness value a on the new type of line, 1mm≤a≤6mm, to obtain a circular arc cross section; or select an airfoil in the airfoil database to obtain the airfoil The thickness distribution of the section, the thickness distribution of the airfoil section is combined with the new line to obtain the airfoil section; the arc-shaped section or airfoil section obtained is recorded as the i-th section; Step 5, increase i by 1, if i≤n, repeat steps 3 and 4, the sections obtained in step 4 are all arc-shaped sections or airfoil sections during the repeating process; otherwise, go to the next step; Step 6. Set the obtained n sections in parallel with the distance s between two adjacent sections, and place them between two coaxial cylindrical surfaces with a radius difference of n×s; the geometric centers of the n sections are all on a vertical line On the straight line of n sections, and the straight line perpendicularly intersects the axes of the two cylindrical surfaces; the n sections are arranged in sequence according to the size of the chord length, and the section with the longest chord length is located on the innermost side; the section with the longest chord length and the diameter The smaller cylindrical surface is tangent; the first line segments of the n sections are parallel to each other and perpendicular to the axes of the two cylindrical surfaces; the first line segments of the n sections are located on the same side; the blade prototype is obtained according to the n sections; the blade prototype is extended Both ends, so that the outer end of the blade prototype completely passes through the larger-diameter cylindrical surface, and the inner end of the blade prototype completely passes through the smaller-diameter cylindrical surface; the blade prototype between the two cylindrical surfaces is the optimized blade; the two cylindrical surfaces The axis is the center of the array, and m blades are evenly distributed along the circumference, 4≤m≤10; the hub is drawn for the m blades, and the optimized impeller model is obtained; Step 7. On a blade of the model built in step 6, take n sections perpendicular to the radial direction of the impeller and the corresponding molding lines of the n sections. cut; respectively measure the chord length b _i of n sections, i=1, 2, 3,..., n, and the outlet geometric angle β _2A(i) , i=1, 2, 3,..., n; Remove all the chamfers and rounded corners in the model built in step 6 to obtain a new simplified model; use meshing software to mesh the new simplified model, and perform numerical simulation calculations to obtain the total pressure of the model built in step 6 and the three velocity components at the entrance of n sections; draw a velocity triangle according to the three velocity components, so as to obtain the inlet airflow angle β _1(i) of n sections, i=1, 2, 3,..., n ;Assign the full pressure value of the model to Z2; Step 8. If the value obtained by subtracting Z1 from Z2 is greater than k, and 3Pa≤k≤8Pa, assign the value of Z2 to Z1, and repeat steps 2, 3, 4, 5, 6 and 7; otherwise, the optimization ends. 2. The optimization method of the low-pressure axial fan impeller blade according to claim 1, characterized in that: the method of obtaining the blade prototype in step 6 is as follows: the contour lines of n sections are carried out in solidworks to "loft out the curved surface" Operation, the smooth transition generates the prototype of the blade. 3. The method for optimizing the impeller blades of a low-pressure axial flow fan according to claim 1, wherein the method for extending both ends of the blade prototype in step 6 is as follows: the blade prototype is subjected to a "curved surface extension" operation in solidworks. 4. The method for optimizing the impeller blades of a low-pressure axial flow fan according to claim 1, wherein the airfoil selected in step 4 is NACA0012. 5. The method for optimizing the impeller blades of a low-pressure axial flow fan according to claim 1, wherein the value of k in step 8 is 5Pa.