阅读说明：本技术 一种蜗壳型线生成方法、蜗壳、风机系统及吸油烟机 (Volute profile generation method, volute, fan system and range hood ) 是由 吴灵辉 于 2020-07-06 设计创作，主要内容包括：本发明公开了一种蜗壳型线生成方法,包括如下步骤：1)确定圆心至少三个具有特征意义的定位点,所述特征意义为蜗舌定位、蜗壳高度或蜗壳宽度；2)以圆心为原点,根据各定位点的坐标、通过曲线拟合的方式确定蜗壳型线；3)各定位点确定后,通过反向推导阿基米德或对数螺旋线的系数m,再用光滑曲线通过各定位点所对应的m值、拟合出关于m-<Image he="23" wi="13" file="DEST_PATH_IMAGE002.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>的曲线图,其中<Image he="23" wi="13" file="600341DEST_PATH_IMAGE002.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>为这一点与蜗壳起始径向截面形成的夹角；4)再通过阿基米德或对数螺旋线公式：<Image he="39" wi="85" file="DEST_PATH_IMAGE004.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>,进行计算得到不同<Image he="23" wi="13" file="529114DEST_PATH_IMAGE002.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>值下的<Image he="32" wi="20" file="DEST_PATH_IMAGE006.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>值,得到相应修正后的蜗壳型线。还公开了根据上述方法生成的蜗壳,应用有上述蜗壳的风机系统,以及应用有上述风机系统的吸油烟机。(The invention discloses a volute profile generation method, which comprises the following steps: 1) determining at least three positioning points with characteristic meanings of circle centers, wherein the characteristic meanings are volute tongue positioning, volute height or volute width; 2) determining the molded line of the volute by a curve fitting mode according to the coordinates of each positioning point by taking the circle center as an origin; 3) after each positioning point is determined, the coefficient m of Archimedes or logarithmic spiral is deduced reversely, and then a smooth curve is used for fitting the m-value corresponding to each positioning point A graph of (1), wherein The included angle formed by the point and the initial radial section of the volute; 4) then through Archimedes or logarithmic spiral formula: is calculated to obtain differences Value of And obtaining the corresponding corrected volute profile. The volute generated according to the method, the fan system applying the volute and the range hood applying the fan system are further disclosed.)

1. A volute profile generation method is characterized by comprising the following steps: the method comprises the following steps:

1) determining a circle center (O) and at least three positioning points with characteristic meanings, wherein the characteristic meanings are volute tongue positioning, volute height or volute width;

2) determining the volute profile by taking the circle center (O) as an origin point and according to the coordinates of each positioning point in a curve fitting manner;

3) after each positioning point is determined, the coefficient m of Archimedes or logarithmic spiral is deduced reversely, and then a smooth curve is used for fitting the m-value corresponding to each positioning pointA graph of (1), whereinThe included angle formed by the point and the initial radial section of the volute;

4) then through Archimedes or logarithmic spiral formula:is calculated to obtain differencesValue ofValue, obtained after corresponding correctionThe volute profile of (1), whereinThe distance between a certain point on the molded line of the volute and the origin is，Is the diameter of the impeller of the fan system to which the volute is applied.

2. The volute profile generating method of claim 1, wherein: the positioning point comprises a first positioning point (N1) serving as a volute tongue positioning point, and the coordinates of the first positioning point (N1) are (A),) By the following formula，，After determining the coordinates of the first location point (N1), the corresponding coordinates can be obtainedtAndwhereintIs a clearance between the volute tongues,starting a radial section of the first location point (N1) from the volute profileThe angle formed by the faces according totAndthe corresponding m value for the first anchor site (N1) was obtained.

3. The volute profile generating method of claim 2, wherein: the positioning point comprises a second positioning point (N2) as a first width positioning point of the volute, the coordinates of the second positioning point (N2) being (N2),) The second positioning point (N2) determines the distance of the volute height in the positive direction, and the opening degree at the second positioning point (N2) is，，Is a coefficient of proportionality that is,the value range is 1.0-1.2 according toAnd obtaining the corresponding m value of the second positioning point (N2).

4. The volute profile generating method of claim 3, wherein: the positioning point comprises a third positioning point (N3) as a first width positioning point of the volute, the coordinates of the third positioning point (N3) being (N3),) The third positioning point (N3) determines the distance of the width of the volute in the positive direction, and the opening degree at the third positioning point (N3) is，，Is a coefficient of proportionality that is,according toThe corresponding m value of the third anchor point (N3) is obtained.

5. The volute profile generating method of claim 4, wherein: the positioning point comprises a fourth positioning point (N4) being a second height positioning point of the volute, the coordinates of the fourth positioning point (N4) being,) The fourth positioning point (N4) determines the distance of the volute height in the negative direction, and the opening degree at the fourth positioning point (N4) is，，Is a coefficient of proportionality that is,according toAnd obtaining a corresponding m value of the fourth positioning point.

6. The volute profile generating method of claim 5, wherein: the positioning points comprise a fifth positioning point (N5) as a second width positioning point of the volute, and the coordinates of the fifth positioning point (N5) are,) The fifth positioning point (N5) determines the distance of the width of the volute in the negative direction, and the opening degree at the fifth positioning point (N5) is，，Is a coefficient of proportionality that is,the value range is (0.2,1), according toThe corresponding m value of the fifth anchor point (N5) is obtained.

7. The volute profile generating method of claim 6, wherein: the positioning points comprise a sixth positioning point (N6), the coordinates of the sixth positioning point (N6) being,) Said sixth positioning point (N6) being the decision point of the final height of the volute,，and obtaining the corresponding m value of the sixth positioning point (N6) according to the coordinates of the sixth positioning point (N6).

8. The volute profile generating method of claim 7, wherein: in the step 2), the width L of an air outlet (16) of the volute and the radius r of the volute tongue are combined,，thereby determining the volute profile.

9. A volute generated by the volute profile generating method according to any one of claims 1-8, comprising a front cover plate (11), a rear cover plate (12), and a ring wall (13) disposed between the front cover plate (11) and the rear cover plate (12), wherein: the inner contour line of the annular wall (13) forms the volute contour line.

10. A fan system employing the volute of claim 9, wherein: the fan system comprises an impeller (2) arranged in the volute and a motor (3) used for driving the impeller (2) to rotate, and the axis of the impeller (2) passes through a circle center (O).

11. A range hood, its characterized in that: use of a fan system according to claim 10.

Technical Field

The invention relates to a power system, in particular to a volute generating method, a volute obtained by the method, a fan system applying the volute and a range hood applying the fan system.

Background

Centrifugal fans generally consist of a volute, a motor, an impeller, etc. The working principle of the centrifugal fan is that the motor drives the impeller to rotate to apply work to airflow and the airflow is discharged from the radial direction through the diffusion effect of the volute.

In the volute of the existing centrifugal fan, the volute molded line is designed by adopting the conventional concept of logarithmic spiral and Archimedes spiral. The volute of the range hood disclosed in chinese patent application No. 201510135345.2 includes a front volute plate, a rear volute plate, a flange, and a shroud plate connecting the front volute plate and the rear volute plate, wherein the shroud plate connects the front volute plate and the rear volute plate together via an approximate archimedes spiral curve. Also, for example, the volute disclosed in chinese patent application No. 201911266506.6 for a centrifugal fan includes a volute top plate, a volute surrounding plate, and a volute bottom plate, where the volute surrounding plate is connected between the volute top plate and the volute bottom plate, and a cross-section peripheral profile of the volute surrounding plate includes a logarithmic spiral diffusion profile, a logarithmic spiral profile, a volute tongue profile, and a volute tongue diffusion profile, which are sequentially and smoothly connected in an anticlockwise order.

In the above traditional design methods, assuming that the flow parameters on the inlet circumference are uniformly distributed and the airflow momentum moment in the volute is not changed, the pneumatic performance and noise performance of the fan system using the design idea on the range hood are not good; in addition, the relevance of all sizes on the volute type line is too strong, the height is necessarily influenced when the width is increased, the outlet size is necessarily influenced by the change of the volute tongue clearance, and the sizes of all dimensions of the volute cannot be reasonably limited according to the limitation requirements of the box body (the height and the width are often limited), so that the optimal performance is achieved.

Disclosure of Invention

The first technical problem to be solved by the present invention is to provide a method for generating a volute profile, which can improve the flow condition of the air flow in the volute, increase the air volume and air pressure of the fan system, and reduce noise.

The second technical problem to be solved by the present invention is to provide a volute obtained by the above-mentioned profile generating method.

The third technical problem to be solved by the invention is to provide a fan system applying the volute.

The fourth technical problem to be solved by the invention is to provide a range hood with the fan system.

The technical scheme adopted by the invention for solving the first technical problem is as follows: a volute profile generation method is characterized by comprising the following steps: the method comprises the following steps:

1) determining at least three positioning points with characteristic meanings of circle centers, wherein the characteristic meanings are volute tongue positioning, volute height or volute width;

2) determining the molded line of the volute by a curve fitting mode according to the coordinates of each positioning point by taking the circle center as an origin;

3) after each positioning point is determined, the coefficient m of Archimedes or logarithmic spiral is deduced reversely, and then a smooth curve is used for fitting the m-value corresponding to each positioning pointA graph of (1), whereinThe included angle formed by the point and the initial radial section of the volute;

4) then through Archimedes or logarithmic spiral formula:is calculated to obtain differencesValue ofValue, obtaining a corresponding corrected volute profile, whereinThe distance between a certain point on the molded line of the volute and the center O is，Is the diameter of the impeller of the fan system to which the volute is applied.

Preferably, the positioning point includes a first positioning point as a positioning point of the volute tongue, and the coordinate of the first positioning point is (,) By the following formula，，After determining the coordinates of the first fixed position point, the corresponding coordinates can be obtainedtAndwhereintIs a clearance between the volute tongues,the included angle formed by the first fixed point and the initial radial section of the volute profile is determined according totAndobtaining the corresponding m value of the first positioning site.

Preferably, the positioning point includes a second positioning point which is a first width positioning point of the scroll casing, and the coordinates of the second positioning point are (a),) The second positioning point determines the distance of the volute height in the positive direction, and the opening degree of the second positioning point (N2) is，，Is a coefficient of proportionality that is,the value range is 1.0-1.2 according toAnd obtaining the corresponding m value of the second positioning point.

Preferably, the positioning point includes a third positioning point which is a first width positioning point of the volute, and the coordinate of the third positioning point is (a),) The third positioning point determines that the width of the volute is positiveThe distance of the direction, the opening degree at the third positioning point is，，Is a coefficient of proportionality that is,according toAnd obtaining the corresponding m value of the third positioning point.

Preferably, the positioning point includes a fourth positioning point serving as a second height positioning point of the volute, and the coordinates of the fourth positioning point are,) The fourth positioning point determines the distance of the volute height in the negative direction, and the opening degree of the fourth positioning point is，，Is a coefficient of proportionality that is,according toAnd obtaining a corresponding m value of the fourth positioning point.

Preferably, the positioning point includes a fifth positioning point serving as a second width positioning point of the volute, and the coordinates of the fifth positioning point are,) The fifth positioning point determines the distance of the width of the volute in the negative direction, and the opening degree of the fifth positioning point is，，Is a coefficient of proportionality that is,the value range is (0.2,1), according toAnd obtaining the corresponding m value of the fifth positioning point.

Preferably, the positioning points include a sixth positioning point, and the coordinates of the sixth positioning point are,) The sixth positioning point is a decision point of the final height of the volute,，and obtaining the m value corresponding to the sixth positioning point according to the coordinates of the sixth positioning point.

In order to determine the molded line of the volute, in step 2), the width L of the air outlet of the volute and the radius r of the volute tongue are combined,，thereby determining the volute profile.

The technical scheme adopted by the invention for solving the second technical problem is as follows: a volute generated according to the volute profile generating method described above, including a front cover plate, a back cover plate, and a ring wall disposed between the front cover plate and the back cover plate, wherein: the inner contour line of the annular wall forms the volute profile line.

The technical scheme adopted by the invention for solving the third technical problem is as follows: a fan system that uses the spiral case as above characterized in that: the fan system comprises an impeller arranged in the volute and a motor used for driving the impeller to rotate, and the axis of the impeller passes through the circle center.

The technical scheme adopted by the invention for solving the fourth technical problem is as follows: a range hood, its characterized in that: a fan system as described above is applied.

Compared with the prior art, the invention has the advantages that: 1) the size of the gap between the volute tongue and the impeller can be adjusted, and reasonable outlet size and outlet airflow angle are ensured; 2) the independence of dimensions in two directions of the width and the height of the volute is realized, the dimensions can be deformed and strengthened, the volute volume can be reasonably designed according to the dimensions of an external box body, if the height of the range hood is low, the proper width of the volute is ensured, the height dimension of the volute is reduced, and vice versa; 3) the volute of this design can improve the interior air current flow situation of volute according to the characteristics of the inside air current of range hood box through molded lines optimization, promotes range hood's amount of wind, wind pressure, full pressure efficiency and noise reduction, can control the size of each direction of volute, satisfies the demand of range hood different dimension volume (height, width).

Drawings

FIG. 1 is a schematic front view of a blower system according to an embodiment of the invention;

FIG. 2 is a schematic rear view of a blower system according to an embodiment of the invention;

FIG. 3 is a volute profile schematic of a fan system (with an impeller shown) according to an embodiment of the invention;

FIG. 4 is a prior art volute profile schematic (with the impeller shown);

figure 5 is a comparative illustration of a volute profile of an embodiment of the present invention and a volute profile of the prior art.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar functions.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the present invention and to simplify the description, but are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and that the directional terms are used for purposes of illustration and are not to be construed as limiting, for example, because the disclosed embodiments of the present invention may be oriented in different directions, "lower" is not necessarily limited to a direction opposite to or coincident with the direction of gravity. Furthermore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

Referring to fig. 1 and 2, a fan system, which is a centrifugal fan, may be used in a range hood. Comprises a volute 1, an impeller 2 arranged in the volute 1 and a motor 3 for driving the impeller 2 to rotate.

The volute 1 comprises a front cover plate 11, a rear cover plate 12 and a ring wall 13 arranged between the front cover plate 11 and the rear cover plate 12, wherein a first air inlet 14 is formed in the front cover plate 11, and an air inlet ring (not shown) is arranged at the first air inlet 14. The front cover plate 11, the rear cover plate 12 and the annular wall 13 jointly enclose to form an air outlet 16, and a flange 17 is arranged at the air outlet 16 and used for being connected and fixed with other parts of the range hood, such as a fan frame. The rear cover plate 12 is provided with a second air inlet 18. Thereby forming a double-air-inlet fan system.

The motor 3 penetrates into the impeller 2 from the second air inlet 18, and the motor 3 and the rear cover plate 12 are fixedly connected through a motor bracket 31. The output shaft of the motor 3 and the impeller 2 are fixedly connected through a lock nut 4, so that when the motor 3 is started, the impeller 2 can be driven to rotate.

The inner contour of the circumferential wall 13 constitutes a volute contour. Referring to fig. 4, the volute profile generally includes a first straight line segment AB, a circular arc segment BC, a fitting curve segment CD, and a second straight line segment DE, which are sequentially connected in an end-to-end manner and smoothly transited. A. E corresponds to the air outlet 16, and the arc section BC corresponds to the volute tongue. In the prior art, the fitting curve segment CD is a logarithmic spiral or an archimedean spiral, and the center of the first air inlet 14 (or the second air inlet 18) is taken as a center O point (the center is on the axis of the impeller 2). The distance between a certain point on the fitting curve segment CD and the circle center O isThe calculation method is as follows:

，

whereinIs the diameter of the impeller 2 and,mfor coefficients related to impeller parameters, rated design flow and the like,this point, to which the curve segment CD is fitted, forms an angle with the initial radial cross-section (horizontal plane shown in figure 3) of the volute 1.

The curve section CD designed by the method is fitted, the correlation between the height and the width of the curve is large, the maximum height is determined after the maximum width is determined, and vice versa, meanwhile, the change of the gap between the volute tongue and the impeller 2 can directly influence the related size of the air outlet 16, and the design idea follows the assumption that the flow parameters on the circumference of the air inlet are uniformly distributed and the airflow momentum moment in the volute 1 is unchanged, so the curve design is not reasonable.

In order to solve the above problem, a multi-point positioning manner is required, and referring to fig. 3, a plurality of positioning points having a characteristic meaning are selected on the entire volute type line, where the number of the positioning points is not less than 3, and six positioning points are selected in this embodiment, and are respectively a first positioning point N1, i.e., a volute tongue positioning point, a second positioning point N2, i.e., a first height positioning point, a third positioning point N3, i.e., a first width positioning point, a fourth positioning point N4, i.e., a second height positioning point, a fifth positioning point N5, i.e., a second width positioning point, and a sixth positioning point N6, i.e., a third height positioning point.

Taking the circle center O as the origin of coordinates, the six positioning points respectively satisfy the following relations:

the coordinate of the first positioning point N1 is (,) The first fixed point N1 determines the volute tongue gap (gap between volute tongue and impeller)tAnd the distance | x of the volute tongue from the center of the impeller 2₁| gap between volute tongue，，. The first positioning point N1 can be determined through the relational expression, the volute tongue gap can be reasonably adjusted according to needs, and the outflow is not influenced by the change of the size of an outlet caused by the deviation distance of the volute tongue from the impeller and the influence of the outflow in the traditional design thought. After the coordinate of the first positioning point N1 is determined, the corresponding volute tongue clearance can be obtainedtAnd(the included angle formed by the first positioning point N1 and the initial radial section of the volute profile line) passes through the volute tongue clearanceThe first positioning site N1 is obtained() The corresponding m value can be obtained by the Archimedes spiral formula (or logarithmic spiral formula) and is marked as m₁。

The coordinate of the second positioning point N2 is (,) The second positioning point N2 determines the distance of the volute height in the positive direction (the upward direction of the circle center O in FIG. 3) and the opening degree at the second positioning point N2 is，，Is a scale factor, conventional logarithmScrew thread slaveToThe opening degree of the fan system is continuously increased in a mode of continuously superposing gas flows, and the gas flows in the fan system are not distributed unevenly in the range hood and are not increased in the mode, so the fan system is provided with a proportional coefficientDetermining，The value range is 1.0-1.2, the lower the rated flow of the range hood,the smaller the suggested value is, based onThe second positioning point N2 can be obtained()，At 90 deg., the corresponding m value can be obtained by using the Archimedes' spiral formula (or logarithmic spiral formula) and is marked as m₂。

The coordinate of the third positioning point N3 is (,) The third positioning point N3 determines the distance of the width of the volute in the positive direction (the circle center O in the right direction in FIG. 3) and the opening degree at the third positioning point N3 is，The increasing rate from the second positioning point N2 to the third positioning point N3 is increased relative to the increasing rate from the first positioning point N1 to the second positioning point N2, and a proportionality coefficient is set，Smaller scale factorCan have smaller volute width and needs to ensurePreventing the gap from being too small here. According toThe third positioning point N3 can be obtained()，Is 180 deg. according toThe corresponding m value can be obtained by the Archimedes spiral formula (or logarithmic spiral formula) and recordedIs m₃。

The coordinates of the fourth positioning point N4 are,) The fourth positioning point N4 determines the distance in the negative direction (downward in fig. 3) of the height of the scroll casing, and the opening degree at the fourth positioning point N4 is set to，The air inlet of the fan system in the range hood is mainly concentrated at the lower part of the fan system, and compared with the conventional spiral line, the range hood needs to be enlarged as much as possible, and the setting proportionality coefficient，. According toThe fourth positioning point N4 can be obtained()，Is 270 deg. according toThe corresponding m value can be obtained by the Archimedes spiral formula (or logarithmic spiral formula) and is marked as m₄。

The coordinates of the fifth positioning point N5 are,) The fifth positioning point N5 determines the distance of the volute width in the negative direction (the center O in FIG. 3 is negative towards the left), and the opening degree at the fifth positioning point N5 is，，On one hand, the width of the volute needs to be controlled, on the other hand, the volute cannot be shrunk too tightly, so that the airflow cannot be effectively expanded, dynamic pressure is collected as static pressure,is a coefficient of proportionality that is,the value range is (0.2, 1). According toThe fourth positioning point N4 can be obtained()，Is 360 degrees according toThe same Archimedes' spiral formula (or logarithmic spiral formula) can be used to solveGiving out the corresponding m value, and recording as m₅。

The coordinates of the sixth positioning point N6 are,) The sixth positioning point N6 is the final height determining point of the volute and also determines the inclination angle of the left side of the volute (opposite to the volute tongue),，ensuring that the effective outflow and the outflow gas have proper inclination angles. From the coordinates of the sixth locating point N6 (i.e. determining the coordinates of this point)And) The above-mentioned Archimedes' spiral formula (or logarithmic spiral formula) can be used to obtain the corresponding m value, which is recorded as m₆。

The molded line of the volute can be basically determined by curve fitting according to the six points, the width L of the air outlet 16 and the radius r of the volute tongue are additionally required to be given,，。

after the six main positioning points are determined, the curve fitting mode is used for reversely deducing the m value of Archimedes or logarithmic spiral, and then a smooth curve is used for passing through the m value (m) of the six points₁、m_2……m₆) Fitting to obtain the value of m-The curve diagram of (A) is calculated by an Archimedes or logarithmic spiral formula to obtain different curvesValue ofThe value is obtained. Preferably, it is calculatedFrom 60 degrees to 400 degreesAnd finally, obtaining a corresponding modified volute profile according to the coordinates of the point N6 of the sixth positioning point, the value L and the value r.

In summary, the volute profile generating method of the present invention includes the following steps:

1) determining at least three locating points with characteristic significance;

2) determining the volute profile according to the coordinates of each positioning point in a curve fitting mode;

3) after each positioning point is determined, the coefficient m of Archimedes or logarithmic spiral is deduced reversely, and then a smooth curve is used for fitting the m-value corresponding to each positioning pointA graph of (a);

4) then through Archimedes or logarithmic spiral formula:is calculated to obtain differencesValue ofAnd obtaining the corresponding corrected volute profile.

In fig. 5, a schematic comparison of the profile (dashed line) of a conventional logarithmic spiral (m =0.0735) and the volute profile (solid line) after a six-point localization method (N1(-33.1,123.6), N2(0,130), N3(140,0), N4(0, -170), N5(-182.5,0), N6(-155,155)) is shown. Actually measuring according to the test: the fan system adopting the six-point positioning method volute molded line can improve 10% of static pressure in the range hood, reduce 1dB of noise, has smaller volute width and can be placed into a narrower box body.

According to the volute profile generation method, firstly, the volute volume is controllable, and the volute profile generation method can adapt to the size of a box body of a range hood (or other fields). The coordinate values of the third positioning point N3 and the fifth positioning point N5 are customized to realize the controllable width of the volute, and the coordinate values of the second positioning point N2, the fourth positioning point N4 and the sixth positioning point N6 are customized to realize the controllable height of the volute. For example, in the case of limited box width and sufficient height, taking a small value in the coefficient value interval of k2 and k4 can reduce the distance from the coordinate origin to the third positioning point N3 and the fifth positioning point N5, and reduce the width of the volute, taking a large value in the coefficient value interval of k1 and k3 to change the distance from the coordinate origin to the third positioning point N3, the fifth positioning point N5 and the sixth positioning point N6 can keep the size of the volute high, so that the kinetic energy of the air flow can be converted into static pressure in the interval, and the dynamic pressure loss inside the volute can be reduced. And the height of the volute is synchronously reduced along with the reduction of the width of the volute, and vice versa, in the volute designed by the conventional logarithmic spiral or Archimedes spiral.

Secondly, the volute tongue clearance and the volute outlet can be reasonably adjusted. The first straight line segment AB is deviated rightwards due to the larger outlet of the volute, if the molded line formed by only one logarithmic spiral line can increase the volute tongue clearance, the airflow at the volute tongue can flow back due to the larger volute tongue clearance, the first positioning point N1 is set, the independence of the outlet size and the volute tongue clearance can be realized, and the reasonable volute tongue clearance value can be set even if the outlet size is large, so that the backflow is reduced.

Finally, the overall flow conditions inside the volute can be improved. The spiral case of traditional logarithmic spiral line or Archimedes spiral design is based on the assumption that the air current evenly flows along the impeller export, and the air current does not evenly flow along the impeller export among the actual range hood centrifugal fan, the place that impeller export air current outflow is big needs the great spiral case runner of synchronous match, can also be through adjusting the coefficient value of the coordinate value of each definition point to local size adjustment in this design thinking, and each point passes through the logarithmic spiral and fits, the local big value of getting of air flow, prevent that the local air flow velocity of flow is too fast, the place that the air flow is little then dwindles, prevent to expand suddenly and produce local vortex.