JP6064003B2 - Centrifugal fluid machine - Google Patents

Description

  The present invention relates to a centrifugal fluid machine having a centrifugal impeller, and more particularly to a blade shape of a centrifugal impeller.

  Centrifugal fluid machines having a rotating centrifugal impeller have been used in various plants, air conditioners, liquid pumps and the like. In response to increasing demands for reducing environmental impact in recent years, these centrifugal fluid machines are required to have higher efficiency and wider operating range than before.

  An example of a conventional centrifugal fluid machine will be described below with reference to FIG. FIG. 15 is a cross-sectional view of a conventional centrifugal fluid machine in a plane passing through an impeller rotating shaft. A conventional centrifugal fluid machine mainly includes a centrifugal impeller 1 for applying energy to a fluid by rotating, a rotating shaft 2 for rotating the impeller, and a radially outer side of the impeller. It comprises a diffuser 3 that converts the dynamic pressure of fluid flowing from the impeller outlet into static pressure, and a return channel 4 that is downstream of the diffuser and guides the fluid to the downstream flow path 6. The impeller 1 includes a disk (hub) 11 that is fastened to the main shaft, a side plate (shroud) 12 that faces the main shaft, and a plurality of blades 13 that are sandwiched between the hub and the shroud and arranged in the circumferential direction. , There may be no shroud. As for the diffuser 3, there are a vaned diffuser in which a plurality of blades arranged in the circumferential direction exist and a vaneless diffuser without a blade.

  In the centrifugal fluid machine, the fluid is sucked from the impeller suction port 5, and then is pressurized through the impeller, the diffuser, and the return channel, and is guided to the downstream flow path 6.

  An impeller plays a very important role in realizing high efficiency of centrifugal fluid machines. As for the higher efficiency of the impeller, the friction loss that occurs on the wall surface when fluid flows inside the impeller, and the relative flow velocity of the internal fluid decreases from the inlet to the outlet of the impeller, and the boundary layer of the flow near the wall surface. Deceleration loss caused by increased thickness, and secondary flow loss caused by low-velocity / low-energy fluid near the wall surface driven by a static pressure gradient in the cross section perpendicular to the main flow direction inside the impeller Need to be reduced.

  Various methods have been proposed to reduce the secondary flow loss among these losses. For example, as in Patent Document 1 below, the distribution of blade loads on the impeller of a centrifugal fluid machine is considered, the blade load on the shroud side is concentrated on the leading edge side of the blade, and the load on the hub side is concentrated on the trailing edge side of the blade As a result, the static pressure difference between the hub and the shroud near the blade trailing edge suction surface on the shroud side (see Fig. 16 to be described later) is reduced, and secondary flow loss is reduced. There is an example.

  In addition, as shown in Patent Document 1 or Patent Document 2 and Patent Document 3 below, the inclination of the blades in the circumferential direction is such that the hub side near the trailing edge of the impeller blades precedes the shroud side in the rotational direction of the impeller. There is an example in which the secondary flow loss is reduced by adding. By adopting such a shape near the blade trailing edge, the effect shown in FIG. 16B can be obtained. FIG. 16 shows a view of two adjacent wings in an impeller, excluding the shroud. The direction of the blade force F applied to the fluid flowing inside the impeller from the pressure surface 14 of each blade 13 (the blade surface on the side preceding the impeller rotation direction) is a direction perpendicular to the pressure surface 14 of the blade. Become. Therefore, for example, as shown in FIG. 16 (a), there is an inclination in the vicinity of the blade trailing edge opposite to these patent documents (that is, in the vicinity of the blade trailing edge 17, the rotation direction of the impeller with respect to the shroud side on the hub side). In the impeller (retracted), the static pressure on the blade pressure surface hub side 141, which normally increases, decreases in the shape shown in FIG. On the other hand, the static pressure on the blade suction surface shroud side 151, which normally decreases in the impeller as shown in FIG. 16A, increases in the shape shown in FIG. 16B. Therefore, in the blade as shown in FIG. 16A, the secondary flow formed to accumulate the low energy fluid on the suction surface shroud side 151 is suppressed in FIG. 16B, and the secondary flow loss is reduced. To do.

Japanese Patent No. 3693121 Japanese Patent No. 2701604 Japanese Patent No. 2730396

  However, as in Patent Documents 1 to 3, when the hub side in the vicinity of the trailing edge of the impeller blades is inclined with respect to the shroud side in the circumferential direction such that the blades precede the rotation direction of the impeller, FIG. In the blade suction surface shroud side 151, the static pressure suddenly increases from the leading edge 16 in the flow direction. Therefore, the reverse pressure gradient of the static pressure with respect to the flow direction becomes large, particularly on the blade suction surface shroud side where the degree of deceleration of the relative flow velocity is large, and flow separation and stall occur near the leading edge of the blade suction surface shroud. As a result, there was a problem that the working range of the impeller was narrowed.

  The present invention solves the above-mentioned problems of the prior art, and reduces flow separation and stall in the vicinity of the leading edge of the impeller blade suction surface shroud when reducing the flow rate while reducing the secondary flow loss inside the impeller. An object of the present invention is to provide a centrifugal fluid machine having an impeller that can suppress and maintain an impeller operating range.

  In order to solve the above problems, in the present invention, when the impeller is viewed from the upstream direction (suction direction) of the rotating shaft, the shroud side is tilted backward from the hub side with respect to the rotating direction at the trailing edge of the impeller blade and adjacent A centrifugal fluid machine was constructed in which the shroud side of the blades behind the impeller rotation direction of the two blades had a blade in front of the rotation direction and a centrifugal impeller forming an overlap near the blade leading edge. It is characterized by.

  In addition, when the impeller shroud leading edge diameter is larger than the hub leading edge diameter and the impeller is viewed from the suction direction, the shroud side at the trailing edge of the impeller blade is tilted backward from the hub side with respect to the rotation direction. Furthermore, at the leading edge of the impeller blade, a centrifugal fluid machine having a centrifugal impeller in which the impeller shroud side is the same as or advanced from the hub side with respect to the rotation direction with respect to a line drawn in the radial direction from the impeller rotation center. It is characterized by comprising.

  Also, when the impeller is viewed from the suction direction, it has a centrifugal impeller in which the shroud side is tilted backward with respect to the rotational direction from the hub side at the blade trailing edge, and the impeller incident angle is 0 ° or less at the specification point. A centrifugal fluid machine is constructed.

  In any of the above centrifugal fluid machines, in the impeller, a plane passing through the impeller rotation center and parallel to the impeller rotation axis (the meridional plane) and the rear edge from the front edge of each hub and shroud on the meridian plane. The angle (Rake angle) formed by the lines (blade elements) connecting points on the hub and shroud in the same ratio between the edges, when the impeller rotation direction is positive, the flow direction from the blade leading edge The centrifugal fluid machine has an impeller that takes a maximum value up to the center and decreases on the downstream side of the blade and has an impeller of -5 ° to -35 ° at the blade outlet.

  According to the present invention, while reducing the secondary flow loss inside the impeller, the separation and stalling of the flow in the vicinity of the leading edge of the blade suction surface shroud of the impeller at the time of reducing the flow rate is suppressed and the impeller operating range is maintained. It is possible to provide a centrifugal fluid machine having an impeller having sufficient strength and manufacturability.

Sectional drawing in the plane which passes along the impeller rotating shaft of the centrifugal fluid machine in this invention Example 1. FIG. The figure which looked at the impeller of the centrifugal fluid machine in Example 1 of this invention from the rotating shaft upstream direction (suction direction). FIG. 3 is a radial flow velocity distribution diagram at the exit of an impeller derived by three-dimensional fluid analysis of the conventional centrifugal fluid machine according to the first embodiment of the present invention. Explanatory drawing regarding the overlap part of two adjacent wing | blades in the impeller of a centrifugal fluid machine. Flow direction distribution of blade surface static pressure value derived by three-dimensional fluid analysis when the size of the overlapping part of two adjacent blades is changed in an impeller of a centrifugal fluid machine. The performance test result comparison figure of the conventional centrifugal fluid machine in Example 1 of this invention and this invention. Explanatory drawing of wing element using meridional view of centrifugal impeller. Explanatory drawing of a Rake angle | corner. The Rake angle distribution map of the centrifugal fluid machine in Example 1 of the present invention. The impeller blade shape figure of the centrifugal fluid machine in this invention Example 2. FIG. An explanatory view of an impeller blade leading edge shape on a meridian plane of a centrifugal fluid machine, and an explanatory view of a meridional surface direction speed near the first half of an impeller blade. Comparison diagram of impeller inlet speed triangle when centrifugal impeller blade inlet hub side and shroud side diameters are different. FIG. 10 is a comparison diagram of blade hub side shapes when the diameters of the impeller blade inlet hub side and shroud side are different in the centrifugal fluid machine in the second embodiment. The impeller blade | wing shape figure of the centrifugal fluid machine in this invention Example 3. FIG. Sectional drawing in the surface parallel to the impeller rotating shaft of the conventional centrifugal fluid machine. Explanatory drawing of the characteristic of the static pressure distribution in the direction of the blade force which acts on the fluid which flows between the two adjacent blades in the impeller, drawn excluding the shroud.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the centrifugal fluid machine means, for example, a centrifugal blower or a centrifugal compressor.

  Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

  Constituent elements of the centrifugal fluid machine of the present embodiment are the centrifugal impeller 1 for imparting energy to the fluid mainly by rotating, as in the conventional centrifugal fluid machine shown in FIG. A rotary shaft 2 for rotating the vehicle, a diffuser 3 on the radially outer side of the impeller and converting the dynamic pressure of the fluid flowing from the impeller outlet into a static pressure, and a downstream flow channel downstream of the diffuser And a return channel 4 for guiding fluid to the The impeller 1 includes a disk (hub) 11 that is fastened to the main shaft, a side plate (shroud) 12 that faces the main shaft, and a plurality of blades 13 that are sandwiched between the hub and the shroud and arranged in the circumferential direction. , It may be an open impeller without a shroud. As for the diffuser 3, there are a vaned diffuser in which a plurality of blades arranged in the circumferential direction exist and a vaneless diffuser without a blade. In this figure, a single-stage centrifugal fluid machine is shown, but as shown in FIG. 1, a suction casing 7 for introducing a flow from the upstream pipe upstream of the impeller suction port, and a blade An inlet guide vane 8 for attaching a pre-turn to the vehicle suction flow may be attached. Further, as shown in FIG. 1, there may be a multistage centrifugal fluid machine in which a combination of impellers, diffusers, and return channels is combined in a plurality of stages. Further, as shown in FIG. 1, a discharge casing 9 may be provided at the return channel outlet on the most downstream side. In the present specification, the centrifugal fluid machine means, for example, a centrifugal blower or a centrifugal compressor.

  In the present embodiment, in the centrifugal fluid machine, as shown in FIG. 2, when the impeller is viewed from the upstream direction (suction direction) of the rotating shaft, the shroud side is set near the hub side near the trailing edge of the impeller blade. The shroud side of the blade 131 that is tilted backward with respect to the rotation direction and is behind the impeller rotation direction of the two adjacent blades is formed with the blade 132 that is forward of the rotation direction and the overlapping portion 21 in the vicinity of the blade leading edge. It is configured to have a centrifugal impeller.

  In this configuration, first, the shroud side is tilted backward with respect to the rotational direction from the hub side in the vicinity of the trailing edge of the impeller blades, and as described above, the direction of the blade force acting on the fluid changes, so The static pressure distribution changes, and the secondary flow that is normally formed to accumulate low-energy fluid on the shroud side of the suction surface of the blade is suppressed, and the secondary flow loss can be reduced.

FIG. 3A shows a case where the blade trailing edge shroud side is tilted forward with respect to the impeller rotation direction from the hub side, and FIG. 3B shows that the blade trailing edge shroud side is inclined from the hub side with respect to the impeller rotation direction. The distribution of the radial flow velocity Cr at the exit of the impeller, which is derived by performing a three-dimensional fluid analysis, respectively, when the vehicle is tilted backward. Note that Cr is dimensionless at the blade outlet peripheral speed U ₂ (= blade outlet radius R ₂ × impeller angular velocity ω). In FIG. 3A, a low-energy fluid is accumulated by the secondary flow, and a reverse flow region shown in black exists near the blade suction surface shroud side. On the other hand, in FIG.3 (b), it turns out that the backflow area seen in Fig.3 (a) lose | disappears, and the flow is equalized.

  Next, in the two adjacent blades of the impeller, the effect of forming an overlapping portion on the shroud side of the blade behind the rotation direction of the impeller and the blade at the front of the rotation direction in the vicinity of the leading edge of the blade, This will be described with reference to FIG. FIG. 4 shows a schematic diagram of the centrifugal impeller when the size of the overlapping portion of the two adjacent blades is gradually changed. In these three figures, the hatched area is the area between the blade cross sections defined as the plane where the distance between the two blades becomes the smallest at each position in the flow direction of the two adjacent blades near the leading edge of the blade. The throat surface 31 having the smallest cross-sectional area is shown. From the figure, it can be seen that the cross-sectional area of the inter-blade channel represented by the throat surface gradually increases as the overlapping portion is gradually reduced.

  Normally, the relative flow velocity of the fluid flowing inside the centrifugal impeller is the fastest at the leading edge of the blade, and the flow cross-sectional area between the blades increases as the radius increases downstream from the leading edge of the blade. Become. Here, when there is no overlap between two adjacent blades as shown in the rightmost diagram of FIG. 4, the flow between the blades in the front half of the blade, where flow separation and stalling are likely to occur, is particularly likely to occur inside the impeller. The area increase rate increases, and the relative flow velocity in the direction along the main flow inside the impeller is rapidly decelerated. Therefore, the reverse pressure gradient of the static pressure in the main flow direction also increases. Furthermore, in the present embodiment, the reverse pressure gradient of the static pressure with respect to the flow direction on the blade suction surface shroud side as described above is also obtained by tilting the shroud side backward from the hub side in the vicinity of the trailing edge of the impeller blade. growing. In combination with the above effects, if there is no overlap between adjacent two blades, flow separation and stall will occur on the large flow rate side, especially near the blade suction surface shroud leading edge. Will narrow.

  On the other hand, when two adjacent blades overlap each other as in this embodiment shown in FIG. 2, the cross-sectional area between the blades in the front half of the blade increases as shown in the leftmost diagram of FIG. The rate can be suppressed. Therefore, even if the shroud side is tilted backward with respect to the rotational direction from the hub side near the rear edge of the impeller blade, the reduction of the relative flow velocity in the direction along the main flow inside the impeller can be suppressed, resulting in the blade suction surface shroud. The reverse pressure gradient of the static pressure with respect to the flow direction on the side can be reduced.

Fig. 5 shows the flow direction distribution of the shroud-side blade surface static pressure when the size of the overlapping part of two adjacent blades is changed to three types as shown in Fig. 4 by conducting a three-dimensional fluid analysis. It is a comparison. The abscissa indicates the dimensionless flow direction position where the impeller leading edge is 0 and the trailing edge is 1. The vertical axis shows the amount of static pressure increase on the blade surface at each dimensionless flow direction relative to the blade leading edge static pressure value, and the dynamic pressure 1 / 2ρU ₂ ² (ρ: density) based on the impeller outlet peripheral speed U ₂ The dimensionless static pressure rise on the blade surface, which was made dimensionless by. In the figure, when the value of the throat area when the blade overlap portion is the largest is 1, the throat area values of two types of impellers having a smaller overlap portion are also shown. From the figure, as the overlapping part of the two blades becomes smaller (as the throat area becomes larger), the gradient with respect to the flow direction of the static pressure rise on the blade suction surface side in the first half of the blade increases, and the reverse pressure gradient It turns out that becomes severe. From the above, it is possible to suppress the reverse pressure gradient of static pressure in the main flow direction in the first half of the impeller, and to maintain and expand the operating range of the centrifugal fluid machine, as the overlap between the two adjacent blades increases. Become.

  FIG. 6 shows a performance test result comparison between the conventional centrifugal fluid machine and the centrifugal fluid machine described in the present embodiment. The horizontal axis shows the dimensionless flow rate with the specified flow rate as 1, and the vertical axis shows the heat insulation head and efficiency. The flow point on the lowest flow rate side of the adiabatic head curve, that is, the leftmost flow point of the adiabatic head curve is a surging flow rate at which the centrifugal fluid machine has a large pressure pulsation and cannot be operated. In the performance test, a vane diffuser designed by matching each of the conventional impeller and the impeller of this embodiment and a return channel are combined to constitute a single-stage centrifugal fluid machine. Carried out. From the figure, it can be seen that the centrifugal fluid machine described in the present embodiment is improved in both efficiency and operating range as compared with the prior art.

  In the centrifugal fluid machine of this example, the shroud front edge diameter of the impeller was made larger than the hub front edge diameter and the impeller was viewed from the suction direction as described in Example 2 described later. In this case, at the trailing edge of the impeller blade, the shroud side is tilted backward with respect to the rotation direction from the hub side, and at the leading edge of the impeller blade, the impeller shroud side is the hub on the radial line from the impeller rotation center. The impeller may be configured in combination with the same or advancing feature with respect to the rotational direction from the side. In this way, even if the shroud side is tilted backward from the rotation direction from the hub side near the trailing edge of the impeller blade, the reverse pressure of the static pressure on the blade suction surface shroud side in the direction along the main flow inside the impeller The gradient can be further relaxed. Details regarding this will be described in Example 2.

  By the way, in the centrifugal fluid machine of the present embodiment, as shown in FIG. 2, the inclination of the impeller blade with respect to the circumferential direction increases. Therefore, a large bending stress is generated especially at the blade leading edge where the fluid begins to push away and at the blade root near the blade trailing edge where the shroud side is inclined backward from the hub side with respect to the rotation direction of the impeller. End up. Further, if the degree of tilting the shroud side backward with respect to the rotational direction from the hub side at the blade trailing edge is too large, it becomes very difficult to manufacture the impeller blade. Therefore, it is necessary to appropriately set the degree of inclination of the impeller blades.

  Therefore, in the centrifugal fluid machine in this embodiment, in the impeller, the Rake angle formed by the meridian plane and the blade element is between the blade leading edge and the flow direction center when the impeller rotation direction is positive. Take the maximum value and decrease it downstream, and set it to -5 ° to -35 ° at the blade outlet. Details will be described below.

  FIG. 7 is a diagram in which the blades of the centrifugal impeller are projected onto the meridian plane (the plane passing through the impeller rotation axis and parallel to the rotation axis). The dotted lines drawn on the wings in the figure connect the points on the hub and shroud that have the same flow direction position between the front and rear edges of each hub and shroud on the meridian plane. This is defined as a wing element 41.

  FIG. 8 is an explanatory diagram relating to the Rake angle. As shown in the figure, the Rake angle 51 is a line in which each meridian plane intersects with each part of the wing when the meridian plane 52 passing through each of the wing elements and a point on the hub side of the wing element is created. Is defined as the angle between A case where the blade element is moving forward in the impeller rotation direction with respect to the meridian plane is defined as a positive Rake angle, and a case where the blade element is moving backward is defined as a negative Rake angle.

  In the present embodiment, the Rake angle defined above has a maximum value between the blade leading edge and the center in the flow direction as shown in FIG. 9, and is further decreased from the maximum value on the downstream side. FIG. 9 shows a Rake angle distribution in the flow direction. The abscissa indicates the dimensionless flow direction position on the meridian plane, where the blade leading edge is 0 and the blade trailing edge is 1. On the other hand, the value of the Rake angle is shown on the vertical axis. In the present embodiment, such a Rake angle distribution has the following effects.

  As described above, a large bending stress acts on the blade root of the leading edge of the impeller in this embodiment. The bending stress increases as the blade inclination increases, that is, as the absolute value of the Rake angle increases. Therefore, each value of Rake at the blade leading edge should be as small as possible. On the other hand, in order to increase the overlap between the two adjacent blades of the impeller with the aim of causing separation and stall of the internal flow of the impeller as low as possible, the positive Rake angle of the front half of the impeller is increased as much as possible. Good to do. In consideration of the above, as shown in FIG. 9, if the Rake angle is set to a maximum value between the blade leading edge and the flow direction center, the Rake angle at the blade leading edge where the bending stress increases. Can be kept relatively small, and at the same time, by increasing the value of the positive Rake angle on the downstream side, the overlapping portion of the two adjacent blades can be increased. Therefore, it is possible to achieve both the effect of maintaining the blade leading edge strength and the effect of suppressing separation and stall of the internal flow of the impeller.

  In the present embodiment, as described above, the impeller blades are formed so as to reduce the Rake angle gradually and take a negative value in the latter half of the impeller with the aim of reducing the secondary flow loss in the impeller. At this time, considering the manufacturability in the vicinity of the trailing edge of the blade and the bending stress, the range of the Rake angle where the secondary flow loss reduction effect can be obtained was examined by numerical analysis. As a result, the Rake angle of the trailing edge of the impeller blade was set to -5 ° to -35 °.

  As described above, in this embodiment, while maintaining the impeller operating range by reducing the secondary flow loss inside the impeller and suppressing the flow separation and stall in the vicinity of the leading edge of the blade suction surface shroud of the impeller when the flow rate is reduced. It is possible to provide a centrifugal fluid machine having an impeller having sufficient strength and manufacturability.

  The second embodiment of the centrifugal fluid machine in the present invention will be described below.

  In the centrifugal fluid machine in the present embodiment, in the centrifugal fluid machine having the same components (impeller, diffuser, return channel, etc.) as in the first embodiment, as shown in FIG. When the leading edge diameter 121 is larger than the hub leading edge diameter 111 and the impeller is viewed from the upstream direction (suction direction) of the rotating shaft as shown in FIG. Then, the shroud side is tilted backward with respect to the rotational direction from the hub side. Further, at the leading edge of the impeller blade, the impeller shroud side is rotated from the hub side to the rotational direction with respect to the line 61 drawn radially from the impeller rotational center. It is configured to have the same or advancing impeller.

  In this configuration, first, the shroud side is tilted backward with respect to the rotational direction from the hub side in the vicinity of the trailing edge of the impeller blades, and as described above, the direction of the blade force acting on the fluid changes, so The static pressure distribution changes, and the secondary flow that is normally formed to accumulate low-energy fluid on the shroud side of the suction surface of the blade is suppressed, and the secondary flow loss can be reduced.

  Next, the shroud leading edge diameter of the impeller is made larger than the hub leading edge diameter, and the impeller blade leading edge is located on the impeller shroud side with respect to the rotational direction with respect to the line drawn radially from the impeller rotation center. The effect of the same or advancing from the hub side will be described below.

  First, the effect of making the impeller blade leading edge shroud side the same or moving forward from the blade leading edge hub side with respect to the rotation direction with respect to the line drawn in the radial direction from the impeller rotation center will be described. By doing so, the blade length on the shroud side can be increased. Therefore, the blade load per unit blade length is reduced, and the blade surface static pressure increase per unit blade length is reduced. From the above, even if the shroud side is inclined backward from the hub side in the vicinity of the impeller blade trailing edge, the reverse pressure gradient of the static pressure on the blade suction surface shroud side in the direction along the main flow inside the impeller is This makes it possible to relax and maintain and expand the operating range of centrifugal fluid machinery.

  However, in the state where the shroud diameter and the hub diameter of the blade leading edge are substantially equal as in, for example, Patent Document 2 or Patent Document 3 which are known examples, the impeller shroud side on the blade leading edge as in the present embodiment Even if it is the same or advanced in the rotational direction from the hub side, there is a possibility of performance degradation as shown below.

  FIG. 11 is an explanatory diagram relating to the meridional surface direction velocity in the vicinity of the first half of the impeller blades on the impeller meridian surface. As can be seen from the figure, in the first half of the blade, the meridional curvature of the shroud side blade shape is larger than that of the hub side, and centrifugal force acts in the direction indicated by symbol 71 in the drawing on the impeller inflow. Therefore, the static pressure on the hub side near the impeller inlet increases, and therefore the meridional speed decreases. On the other hand, on the impeller inlet shroud side, the static pressure decreases and the meridional speed increases.

  FIG. 12 shows speed triangles on the impeller blade inlet shroud side and the hub side, which are obtained in consideration of the velocity distribution in the meridian plane near the impeller inlet. FIG. 12A shows an inlet speed triangle when the blade leading edge shroud diameter and the hub diameter of the impeller are made substantially equal (corresponding to the blade leading edge 161 in FIG. 11). On the other hand, FIG. 12B shows an inlet speed triangle when the blade leading edge shroud diameter of the impeller is larger than the hub diameter (corresponding to the blade leading edge 162 in FIG. 11).

As shown in FIG. 12A, when the blade leading edge shroud diameter and the hub diameter of the impeller are substantially equal, the blade inlet peripheral speed U _1s on the shroud side and the blade inlet peripheral speed U _1h on the hub side Are approximately equal. However, with respect to the inlet meridional velocity, the shroud-side value Cm _1s is larger than the hub-side value Cm _{1h as} described above. Accordingly, as shown in FIG. 12A, the relative flow angle β _{1h with} respect to the impeller on the hub side is significantly smaller than the relative flow angle β _{1s with} respect to the impeller on the shroud side.

In the design of a blade of a normal impeller, the value obtained by subtracting the inlet relative flow angle β ₁ from the blade inlet angle β _1b , that is, the blade incident angle i ₁ is often set to be approximately equal on the hub side and the shroud side. Therefore, when the blade leading edge shroud diameter and the hub diameter of the impeller are made substantially equal, the hub side blade inlet angle β _1bh is significantly smaller than the shroud side blade inlet angle β _1bs . In addition, when the blade leading edge shroud diameter of the impeller and the hub diameter are substantially equal, the radial length of the hub side blade is shortened. For this reason, as shown in FIG. 13, if the shroud side of the impeller is made substantially equal to the hub shroud diameter and the shroud side is inclined backward from the hub side with respect to the rotation direction in the vicinity of the trailing edge of the impeller blade, On the hub side, as shown in the middle 112, there is a portion where the blade angle increases sharply on the downstream side with respect to the blade leading edge having a small blade angle and facing substantially in the circumferential direction. In the part where the blade angle increases rapidly, the fluid flowing inside the impeller is rapidly decelerated in the direction along the blade, and the flow is separated at the blade suction surface without overcoming the pressure gradient in the flow direction. descend. Further, as shown in FIG. 11, in the front half of the blade, the hub side has a higher static pressure value than the shroud side, so the fluid near the blade surface that has lost kinetic energy in the sudden deceleration region is in the direction of this static pressure gradient. In other words, it will flow from the hub side toward the shroud side. As a result, the accumulation of low-energy fluid on the blade shroud suction surface is promoted, and even if the impeller blade leading edge shroud side is the same or advanced in the rotational direction from the blade leading edge hub side, the blade length on the shroud side is increased. Even if it is made longer, it becomes difficult to obtain the effect of suppressing the occurrence of flow separation and stall near the leading edge of the blade suction surface shroud.

On the other hand, as shown in FIG. 12B, when the blade leading edge shroud diameter of the impeller is larger than the hub diameter, the blade inlet peripheral speed U _1s on the shroud side is greater than the blade inlet peripheral speed U on the hub side. _Greater than _1h . As for the inlet meridional direction speed, the shroud side value Cm _1s is larger than the hub side value Cm _1h as described above. Accordingly, as shown in FIG. 12B, there is no significant difference between the relative flow angle β _1s for the impeller on the shroud side and the relative flow angle β _1h for the impeller on the hub side, and the hub side blade inlet angle β _1bh And the shroud side blade inlet angle β _1bs are not so different. Further, in this case, since the length in the radial direction of the hub side blade is increased, as shown by 113 in FIG. 13, there is no portion where the blade angle rapidly increases downstream from the leading edge of the hub side blade. Accordingly, separation of the suction surface on the blade front half hub side is suppressed and the impeller efficiency is maintained, and at the same time, accumulation of low-energy fluid on the blade shroud suction surface is also suppressed. As a result, the effect of suppressing the occurrence of flow separation and stall in the vicinity of the blade suction surface shroud leading edge by moving the impeller blade leading edge shroud side the same or advancing with respect to the rotation direction from the blade leading edge hub side is sufficient. It is possible to demonstrate.

  Further, in the centrifugal fluid machine in the present embodiment, as in the case described in the first embodiment, when the Rake angle formed by the meridian plane and the blade element in the impeller is positive in the impeller rotation direction, It may be configured in combination with a feature that takes a maximum value from the leading edge to the center in the flow direction and decreases downstream thereof, and is set to −5 ° to −35 ° at the blade outlet.

  The third embodiment of the centrifugal fluid machine in the present invention will be described below.

In the centrifugal fluid machine in the present embodiment, the centrifugal fluid machine having the same components (impeller, diffuser, return channel, etc.) as in the first embodiment and the second embodiment is shown in FIG. In the vicinity of the trailing edge of the blade, a centrifugal impeller in which the shroud side is inclined backward with respect to the rotational direction from the hub side and the impeller incident angle i _{1 is set} to 0 ° or less as shown in FIG. It is comprised so that it may have.

  In this embodiment, first, the shroud side is tilted backward with respect to the rotational direction from the hub side in the vicinity of the trailing edge of the impeller blades, and as described above, the direction of the blade force acting on the fluid changes, so The static pressure distribution changes, and the secondary flow that is normally formed to accumulate low-energy fluid on the shroud side of the suction surface of the blade is suppressed, and the secondary flow loss can be reduced.

On the other hand, by setting the impeller incident angle i ₁ to 0 ° or less at the specification point, the following effects are produced.

As can be seen from the impeller inlet velocity triangle shown in FIG. 14B, the blade inlet meridional surface velocity Cm ₁ is proportional to the inlet volume flow rate Q ₁ , so that Cm ₁ decreases as the flow rate decreases. On the other hand, since the blade inlet peripheral speed U ₁ is constant, the direction of the blade inlet relative speed W ₁ gradually changes as the flow rate decreases, and the blade inlet relative flow angle β ₁ decreases as the flow rate decreases. Accordingly, as the flow rate decreases, the incident angle i ₁ (= β _1b −β ₁ ) of the fluid flowing into the blade increases, that is, the inlet relative flow angle β _1b gradually decreases with respect to the blade inlet angle β _1b . Therefore, as the flow rate decreases, the fluid flowing into the blade flows from the direction that does not follow the leading edge of the blade, and at a certain flow point on the lower flow rate side than the specification point, the inflow may eventually flow along the blade suction surface. It becomes impossible to peel off near the suction surface leading edge.

The flow rate at which the flow separation near the blade suction surface front edge can be shifted to the low flow rate side by reducing the incident angle i ₁ at the specification point. Therefore, if the impeller incident angle i ₁ is set to 0 ° or less at the specification point, even if the shroud side is inclined backward from the hub side with respect to the rotation direction near the trailing edge of the impeller blade, the blade suction surface shroud side Since the flow rate of flow separation and stall near the leading edge can be shifted to the low flow rate side, the impeller operating range can be maintained.

  In the centrifugal fluid machine of this embodiment, the shroud front edge diameter of the impeller is made larger than the hub front edge diameter and the impeller is viewed from the suction direction in the same manner as described in the first and second embodiments. In this case, the shroud side at the trailing edge of the impeller blade is tilted backward from the hub side with respect to the rotation direction, and at the leading edge of the impeller blade, the impeller shroud side is located on the radial line from the impeller rotation center. The impeller may be configured in combination with the same or advancing feature with respect to the rotation direction from the hub side.

  Further, in the centrifugal fluid machine in the present embodiment, the Rake angle formed by the meridional surface and the blade element in the impeller is positive in the impeller rotation direction, as in the contents described in the first and second embodiments. In some cases, the maximum value from the leading edge of the blade to the center in the flow direction may be obtained, and the value may be decreased downstream, and may be configured in combination with the feature set at -5 ° to -35 ° at the blade outlet. .

DESCRIPTION OF SYMBOLS 1 Centrifugal impeller 2 Rotating shaft 3 Diffuser 4 Return channel 5 Impeller inlet 6 Downstream flow path 7 Suction casing 8 Inlet guide vane 9 Discharge casing 11 Hub 12 Shroud 13, 131, 132 Impeller blade 14 Blade pressure surface 15 Blade negative Pressure surface 16, 161, 162 Blade leading edge 17 Blade trailing edge 18 Blade force 21 Overlapping portion 31 of adjacent blades of impeller Impeller blade throat surface 41 Blade element 51 Rake angle 52 Meridian surface 61 Pulled radially from impeller rotation center Wire 71 Centrifugal force 111 Hub leading edge diameter 112,113 Hub side blade shape 121 Shroud leading edge diameter 141 Blade pressure surface hub side 151 Blade suction surface shroud side

Claims (1)

In centrifugal fluid machinery,
When the impeller is viewed from the suction direction upstream of the rotation axis, the shroud side is tilted backward from the hub side with respect to the rotation direction at the trailing edge of the impeller blade.
And the shroud side of the blade leading edge of the blade that is rearward with respect to the impeller rotation direction in two adjacent impeller blades forms an overlapping portion that precedes the hub side of the blade that is forward with respect to the rotation direction ;
The impeller shroud leading edge diameter is larger than the hub leading edge diameter;
When the impeller is viewed from the suction direction, the impeller blade shroud side at the leading edge of the impeller blade is the same as or advanced from the hub side with respect to the rotation direction with respect to the line drawn in the radial direction from the impeller rotation center.
A meridian plane that is a plane passing through the impeller rotation center and parallel to the impeller rotation axis, and a hub having a flow direction position at the same ratio between the front edge and the rear edge of each of the hub and the shroud on the meridional plane; When a line connecting the points on the shroud and a meridian plane passing through the hub-side point of the line are created, the Rake angle, which is the angle formed by the meridian plane and the line, is positive for the impeller rotation direction. In this case, the centrifugal turbine is characterized by having an impeller that takes a maximum value from the leading edge of the blade to the center in the flow direction, decreases on the downstream side, and becomes −5 ° to −35 ° at the blade outlet. Fluid machine.

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