JP4880952B2 - Axial pump impeller - Google Patents

Description

  The present invention relates to an impeller of an axial flow pump.

  Various types of axial pumps are widely used. For example, Patent Document 1 describes a drain pump for a pump gate and an axial pump used as a so-called inline pump interposed in a pipe (for example, see Patent Document 1).

  In the design of the impeller blades of an axial flow pump, NACA (National Advisory Committee on Aeronautics) 65 series airfoils are widely adopted. The NACA65 type airfoil and its selection method are widely known, and are described in Non-Patent Document 1, for example. In addition, with regard to the NACA65 series airfoil, a large amount of cascade test data and design data are accumulated and available. Furthermore, the NACA65 type airfoil is actually widely used for impeller blades and has high reliability.

  However, since the NACA65 type airfoil is originally a compressor airfoil, it is not a shape considering cavitation performance. For this reason, in an impeller employing a NACA65 type airfoil as a blade, cavitation tends to occur particularly on the leading edge side of the blade. In addition, as a design of the impeller blades, a method of three-dimensionally stacking two-dimensional blade rows obtained by inverse analysis or the like is known. However, it is difficult to obtain a smooth three-dimensional curved surface by this method, and there is no accumulation of experimental data and design data such as NACA65 type airfoil.

JP 2002-129539 A Kensaku Imaichi et al., “Basics of Pump Design”, Nihon Kogyo Publishing Co., Ltd.

  In view of the above-described conventional problems, the present invention provides an impeller of an axial flow pump that can prevent the generation of a cavity and can effectively use a large amount of experimental data and design data related to a NACA65-based airfoil. Let it be an issue.

  According to a first aspect of the present invention, in the impeller of the axial flow pump, the plurality of blades included in the impeller are obtained by applying a conversion function to the coordinate value in the chord length direction of the NACA65 series airfoil camber line. The conversion function has a one-to-one correspondence between the coordinate value in the chord length direction before conversion and the coordinate value in the chord length direction after conversion, and the chord length direction before the conversion at the leading edge of the blade. Is equal to the coordinate value after conversion, the coordinate value in the chord length direction before conversion is equal to the coordinate value after conversion at the trailing edge of the blade, and the chord length direction before conversion is An impeller of an axial flow pump is provided which is an upwardly convex and monotonically increasing function in an orthogonal coordinate system having a coordinate value as a horizontal axis and a coordinate axis in the chord length direction after conversion as a vertical axis.

  Only the position of the maximum sled in the chord length direction can be shifted to the exit side of the blade while maintaining the NACA65-based airfoil for the inflow angle, the outflow angle, and the maximum warp of the blade. As a result, compared to the original NACA65 type airfoil, the pressure on the suction surface is higher (the vacuum degree is lower) on the leading edge side than the center in the chord length direction of the blade, so that the generation of the cavity is effectively performed. Can be suppressed. Further, since the inflow angle, the outflow angle, and the maximum warp of the blade are the same as those of the original NACA65 airfoil, it is possible to effectively use a great amount of design data related to the NACA65 airfoil.

  For example, the conversion function is a function defined by the following formula (1).

  2nd invention is an axial-flow pump provided with the said impeller.

  The impeller of the axial flow pump according to the present invention can effectively suppress the generation of cavities and can effectively use a great amount of design data related to the NACA65-based airfoil.

  FIG. 1 shows an axial pump 2 having an impeller 1 according to an embodiment of the present invention. This axial flow pump 2 includes an outer casing 4 having a cylindrical shape with openings at both ends constituting the flow path 3, a fixed vane 5 extending into the flow path 3, and a bearing portion 6 supported by the fixed vane 5. And. A boss portion 8 of the impeller 1 is fixed to a tip end of a rotating shaft 7 that extends in the horizontal direction and is rotatably supported by the bearing portion 6. The base end side of the plurality of blades 9 is fixed to the boss portion 8. The rotational output of the prime mover 10 is transmitted to the rotary shaft 7 through the sealing device. The blades 9 of the impeller 1 rotating with the rotary shaft 7 give lift to the water in the flow path 3, thereby generating pressure.

The blade 9 of the impeller 1 has a shape designed by the following procedure described with reference to FIG. In FIG. 3, R is the direction of rotation of the blade 9, FL _in is the direction of water flow at the leading edge 9 a that is the inlet of the blade 9, and FL _out is the direction of water flow at the trailing edge 9 b that is the outlet of the blade 9. Show. Moreover, the code | symbol 9c shows the positive pressure surface (abdominal surface) of the blade | wing 9, and the code | symbol 9d shows a negative pressure surface (back surface). Further, the orthogonal coordinate system set in FIG. 3 sets the x axis in the chord length direction with the leading edge of the blade 9 as the origin, and sets the direction orthogonal to the chord length direction, that is, the warp direction as the y axis. ing.

First, a temporary camber line C _pre that is a NACA65-based airfoil camber line is determined. In particular, a beta ₁ (the angle between the inflow direction FL _in the rotating shaft and water at the leading edge 9a) inflow angle, the outflow direction in the direction of the trailing edge 9b of the inflow direction FL _in the turning angle theta (front edge 9a The angle formed with the direction of FL _out ; θ = β ₁ −β ₂ ) is determined based on the specifications of the impeller 9 and the like. 2A and 2B, a chord which is a ratio of a pitch t (t = πD / N; π is a circumference ratio, D is a diameter of a cylinder on a blade cross section, N is the number of blades), and a chord length L. Determine the node ratio L / t. When the inflow angle β ₁ , the turning angle θ, and the chordal ratio L / t are determined, a temporary camber line C _pre is given from the NACA65-based camber selection carpet diagram. FIG. 4 shows a temporary camber line C _pre .

If the camber line C _pre is used as it is in the conventional method and the shape of the blade 9 is determined by determining the stagger angle ξ, the blade thickness w, etc., in particular, the center of the blade 9 in the chord length direction (L / 2 ), The pressure on the negative pressure surface 9d is lower (the degree of vacuum is higher) on the front edge 9a side, so that a cavity is easily generated. Therefore, in the present invention, the temporary camber line C _pre is corrected so as to shift the maximum warp position toward the rear edge 9b, thereby increasing the pressure of the suction surface 9d on the front edge 9a side of the blade 9 (decreasing the degree of vacuum). ) 4 shows a maximum camber position of the camber line _{C pre} tentative by symbol _{ML pre.} On the other hand, by correcting the temporary camber line C _pre , any one of the camber line gradient at the leading edge 9a, the camber line gradient at the trailing edge 9a, and the maximum warp (denoted by C _max in FIG. 4) If it changes, the closeness with the NACA65 system airfoil will be lost to the extent that the experimental data and design data related to the NACA65 system cannot be used. From the above points, in the present invention, the temporary camber line C _pre is corrected so as to satisfy the following two conditions. That is, the first condition is that the maximum warp position is shifted toward the trailing edge 9b. The second condition is that the camber line gradient at the leading edge 9a, the camber line gradient at the trailing edge 9b, and the maximum warp do not change.

In order to correct the temporary camber line C _pre so as to satisfy the first and second conditions, the coordinate values in the chord length direction of the temporary camber line C _pre (the x-axis value of FIG. 3 and FIG. 4). The conversion function x ′ = F (x) is applied to the value on the horizontal axis). An example of the conversion function F (x) is shown by the solid line in FIG. In the orthogonal coordinate system of FIG. 5, the horizontal axis represents the coordinate value x in the chord length direction before conversion, and the vertical axis represents the coordinate value x ′ in the chord length direction after conversion. The origin corresponds to the leading edge 9a, and x = L corresponds to the trailing edge 9b. In order to satisfy the first and second conditions, the conversion function F (x) needs to be a function having the following characteristics (1) to (4).
(1) The coordinate value x in the chord length direction before conversion and the coordinate value x ′ in the chord length direction after conversion have a one-to-one correspondence.
(2) At the leading edge 9a of the blade 9 (x = 0), the coordinate value x in the chord length direction before conversion and the coordinate value in the chord length direction after conversion are equal.
(3) At the trailing edge 9b of the blade 9 (x = L), the coordinate value x in the chord length direction before conversion and the coordinate value in the chord length direction after conversion are equal.
(4) Convex upward in the orthogonal coordinate system set as shown in FIG. 5 and monotonously increasing.

  The transformation function F (x) illustrated in FIG. 5 defined by the following formula (2) is 45 degrees in the counterclockwise direction around the origin in FIG. It is a function rotated by degrees.

  When it is confirmed that the conversion function F (x) in FIG. 5 has all the above-mentioned characteristics (1) to (4), the coordinate values x and x ′ before and after conversion are clearly one-to-one for (1). It corresponds to. Next, for (2), when x = 0 (the leading edge 9a), x ′ = 0. As for (3), when x = L (rear edge 9b), x '= L. Furthermore, (4) is also clearly upward and monotonically increasing. Further, when this function F (x) is expressed by Expression (2), x ′ = x (45 shown by a broken line in FIG. 5 at x = 0 (front edge 9a) and x = L (rear edge 9b). A straight line with a slope of °.

When the conversion function F (x) in FIG. 5 is applied to the coordinate values in the chord length direction of the temporary camber line C _pre shown in FIG. 4, a corrected camber line C is obtained. In this example, the constant a in the above-described equation (2) is set to 0.05. As apparent from FIG. 4, the maximum warp position ML _pre of the temporary camber line C _pre is approximately 0.5L, whereas the maximum warp position ML of the corrected camber line C is approximately 0.7L. It is shifted to the edge 9b side. The maximum warp C _max is the same for the camber lines C _pre and C before and after correction. Further, the camber line slopes at the leading edge 9a and the trailing edge 9b are the same in the camber lines C _pre and C. As described above, by using the conversion function F (x) in FIG. 5, the temporary camber line C _pre can be corrected so as to satisfy the above-described first and second conditions.

By changing the value of the constant a in Expression (2), it is possible to set how much the maximum sled position ML is shifted from the original maximum sled position ML _pre . Specifically, as the value of the constant a is larger, the maximum sled position ML is shifted to the trailing edge 9b side. If the constant a is 0, the camber line C is not corrected and the original NACA65-based camber line is maintained.

After the corrected camber line C is obtained, the stagger angle ξ is calculated from the corrected camber line C, the chordal ratio L / t, and the inflow angle β _{1 using the} NACA65 system attack angle selection carpet diagram. decide. Finally, the blade thickness w is determined in consideration of the strength and the like.

6 shows the pressure distributions P ₊ ′ and P ₋ ′ in the chord length direction on the pressure surface 9c and the suction surface 9d of the blade 9 whose shape has been determined using the camber line C _pre of the NACA 65 before correction, and FIG. The pressure distribution P ₊ , P in the chord length direction on the pressure surface 9c and the suction surface 9d of the blade 9 whose shape is determined using the camber line C corrected by the function F (x) (constant a is set to 0.05) _-Is shown. As apparent from FIG. 6, the corrected camber line C is used to shift the maximum warp position toward the trailing edge 9 b, so that compared with the case where the camber line C _pre before correction is used, the blade 9 The pressure on the suction surface 9d is higher (the degree of vacuum is lower) on the front edge 9a side than the center (L / 2) in the chord length direction. Therefore, by determining the shape of the blade 9 using the corrected camber line C, the generation of a cavity can be effectively prevented.

The camber line C modified as described above has the same camber line slope and maximum warp C _{max at the} leading edge 9a and trailing edge 9b, so the modified camber line C is the same as the original NACA65 airfoil. With respect to the impeller 6 including the blade 9 whose shape is determined by use, a great amount of design data related to the NACA65-based airfoil can be effectively used.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the conversion function used for correcting the camber line is not limited to the one exemplified in the embodiment, and any function having the above-described characteristics (1) to (4) may be used.

The longitudinal section showing the axial flow pump which has the impeller concerning the embodiment of the present invention. A typical sectional view for explaining pitch and chord length ratio. The principal part expanded view of FIG. 2A. Sectional drawing in the III-III line of FIG. The diagram which shows distribution of the camber line sled with respect to the coordinate value of a chord length direction. The diagram which shows an example of a conversion function. The diagram which shows the blade surface pressure in a positive pressure surface and a negative pressure surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Impeller 2 Axial flow pump 3 Flow path 4 Outer casing 5 Fixed vane 6 Bearing part 7 Rotating shaft 8 Boss part 9 Blade 9a Front edge 9b Rear edge 9c Positive pressure surface 9d Negative pressure surface 10 Motor | power_engine

Claims (3)

In the impeller of an axial flow pump,
The plurality of blades included in the impeller have a camber line obtained by applying a conversion function to the coordinate value in the chord length direction of the NACA65 series airfoil camber line,
In the conversion function, the coordinate value in the chord length direction before the conversion and the coordinate value in the chord length direction after the conversion correspond one-to-one, and the coordinate value in the chord length direction before the conversion and the conversion at the leading edge of the blade The coordinate value in the chord length direction before conversion and the coordinate value after conversion at the trailing edge of the blade are equal, and the coordinate value in the chord length direction before conversion is the horizontal axis. An impeller for an axial flow pump, wherein the impeller is an upwardly convex and monotonically increasing function in an orthogonal coordinate system with the coordinate axis in the chord length direction after conversion as a vertical axis. The impeller of the axial flow pump according to claim 1, wherein the conversion function is defined by the following equation.

  An axial-flow pump provided with the impeller of any one of Claim 1 or Claim 2.

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