CN1022584C - thick blade centrifugal impeller - Google Patents

Abstract

A centrifugal impeller with thick blades, consisting of at least two blades, the thickness of the blades is increased so that the plugging function K _(r) at different radii r must be r ₁ ≤ r ≤ 0.8(r ₂ -r ₁ )+r ₁ Within the radius range of K _(r) ≥min[1, r/2(rr ₁ )], and it is required that r ₂ /r ₁ >1.7, the first half of the flow channel should satisfy r ₁ ≤r≤r _m , select appropriately K _(r) prevents the channel from expanding, and the second half should satisfy r _m <r≤r, and allow the channel to diffuse slightly. In the formula, r ₁ , r ₂ , and r _m are the average radii of the blade leading edge, blade trailing edge, and blade, respectively. The invention can reduce and eliminate the flow separation area and the recirculation area near the pressure surface of the blade, thereby significantly improving the efficiency. Since the blade thickens rapidly from the leading edge and there is no expansion at the inlet of the flow channel, the high-efficiency working area of the impeller is relatively wide.

Description

The invention relates to an impeller of a centrifugal fluid machine, especially a thick blade centrifugal impeller.

In the prior art, centrifugal fluid machines such as centrifugal pumps, centrifugal compressors and centrifugal blowers have low impeller efficiency. The flow field in the wheel flow channel is strongly swirling; secondly, due to the thinner blades of the conventional design, the flow channel between the blades expands from the inlet to most of the flow channel area, so the side of the pressure surface of the blade must be There are large areas of flow separation or recirculation, and these flow areas consume a lot of energy, which is the key to the low efficiency of the impeller. Taking centrifugal water pumps as an example, the impeller efficiency generally does not exceed 80%, making it difficult for the overall pump efficiency to exceed 70%.

In 1981, in order to eliminate the vortex in the flow channel formed by adjacent blades, Eiichi Sugiura proposed the idea of thickening the blades to gradually narrow the width of the flow channel from the inlet to the outlet for the axially equal-thickness multi-blade centrifugal pump impeller, and applied for it in the United States. Patent, Patent No. 4,253,798.

The purpose of the present invention is, no matter whether the axial direction is equal or not, to reduce or eliminate the reflux vortex in the flow channel formed by adjacent blades, the degree of diffusion of the flow channel must be controlled, and the flow channel should be kept non-diffused in the first half of the flow channel. In order to make the liquid (gas) flow into the volute more smoothly, which is beneficial to restore the pressure, the flow channel is allowed to spread slightly.

In order to illustrate the profile of the thick blade impeller of the present invention, the concept of plugging function is first proposed, as shown in Figure 1, the blocking function K _(r) is defined as follows:

${\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; (\; r\; )</span>}}\mathrm{<span\; class="notranslate">\; =</span>}\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; (\; r\; )</span>}}\mathrm{<span\; class="notranslate">\; m</span>}}{{\mathrm{<span\; class="notranslate">\; (r\; -\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; )\; 2\; \pi </span>}}$

In the formula:

L _(r) - the circumferential width of the blade at different radii r;

m - the number of leaves;

r ₁ - polar radius at the leading edge of the blade.

The larger the circumferential width L _(r) of the blade, the greater the plugging function K _(r) , because the circumferential width S _(r) of the flow channel between adjacent blades is:

S _(r) = (2πr)/(m) -L _(r)

Therefore, when K _(r) is constant at 1, the circumferential width of the flow channel will not change, that is to say, the flow channel will not be diffuse. When K _(r) <1, the channel is diffuse, and the smaller its value, the greater the degree of diffusion.

The technical solution of the present invention is: it consists of at least two or more blades, and the thickness of the blades on the impeller is increased to make the blockage function K _(r) in the range of r ₁ ≤ r ≤ 0.8 (r ₂ -r ₁ )+r ₁ Inside is K _(r) ≥min〔1, (r)/(2(rr ₁ ))〕When making the above definition, it is required that r ₂ /r ₁ >1.7, and the meaning of min in formula (3) is to take the minimum value . r ₂ - radius in polar coordinates at the trailing edge of the blade.

When the first half of the flow channel satisfies: r ₁ ≤ r ≤ r _m , properly select K _(r) so that the flow channel is not in a diffuse shape. For example, for the commonly used backward curved impeller, this can be guaranteed as long as K _(r) = 1. where r _m =0.5(r ₁ +r ₂ ).

In the second half of the flow channel, that is, in the range of r _m < r ≤ r ₂ , K _(r) is taken as:

K _(r) = (K ₂ -1)/((r ₂ -r _m )) (rr _m )+1

In the formula, K ₂ =K _(r2) is the blockage function at the outlet, which is generally required to be large enough to ensure that the conditions expressed by (3) are satisfied, but K ₂ is not greater than 1.

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

Figure 1. Cutaway view of thick blade centrifugal impeller blade;

Figure 2. Axial channel flow diagram of centrifugal impeller of fluid machinery;

Figure 3. Axial structure diagram of centrifugal impeller of fluid machinery.

The impeller of the present invention consists of a disc with a wheel shell 1 in the center, on one or both sides of the disc (one side is single suction type, both sides are double suction type, as shown in Figure 1 to Figure 3 is single suction type) There are specially designed thick blades evenly distributed, together with the cover plate 2 with a central hole, the center of the impeller has a through hole, and the impeller can be installed on the rotating shaft.

The profiles of thick blades must meet:

The blade reference line AB obtained by conventional design (Fig. 1), the circumferential thickening △L _(r) at different radii to obtain the blade suction surface shape line

${\mathrm{<span\; class="notranslate">\; △\; L</span>}}_{\mathrm{<span\; class="notranslate">\; (\; r\; )</span>}}\mathrm{<span\; class="notranslate">\; =</span>}\frac{{\mathrm{<span\; class="notranslate">\; r\; ·\; L</span>}}_{}}{}$ 2 (r - r 1 ) 2r 2 (r 2 -r 1 )

In the formula: L ₂ - the circumferential width of the blade at the radius r ₂ , namely

L ₂ =K ₂ (r ₂ -r ₁ ) (2π)/(m)

Blade circumferential width at different radii:

L _(r) = K _(r) (rr ₁ ) (2π)/(m)

为基准得出压力面型线

。From this it can be determined from the suction surface profile

Derived from the pressure surface profile

.

在F点以及

在A点均为折线，必须在F及A点处作成适当光滑，即可得出最后叶片型线。because

at point F and

Point A is a broken line, and it must be properly smoothed at points F and A to obtain the final blade shape.

为旋成面上的叶型在以转轴中心线

为中心的极座标平面上的投影。同理，本发明中提及的叶片前缘处半径r₁，一般是指任一轴面设计流 线旋成面上的叶片前缘处A点的极座标半径值。但当该轴面设计线在叶片前缘A点处与转轴中心线 的轴面夹角γ₁小于45°时，则把该轴设计流线与转轴中心线

的轴面夹角γ等于45°处的极座标半径定义为r₁，在这种情况下，本设计只用于半径r≥r₁的叶型部份。The above-mentioned airfoil is a two-dimensional geometric shape described by polar coordinates (that is, an axial equal-thickness impeller). For centrifugal impellers with non-two-dimensional blades (that is, axial unequal thickness impellers) caused by axial water (or air intake) and other reasons, as shown in Figure 2, the blade shape refers to the design of the axial surface Streamline

The airfoil on the rotating surface is centered on the centerline of the rotating shaft

Projection on a polar coordinate plane centered on . Similarly, the radius r ₁ at the leading edge of the blade mentioned in the present invention generally refers to the polar coordinate radius value of point A at the leading edge of the blade on any axial design streamline rotation surface. However, when the design line of the axial surface is at the point A of the leading edge of the blade and the centerline of the rotating shaft When the included angle γ ₁ of the shaft surface is less than 45°, the design streamline of the shaft and the center line of the shaft

The polar coordinate radius at which the axial plane angle γ is equal to 45° is defined as r ₁ , in this case, this design is only used for the airfoil part with radius r≥r ₁ .

Compared with the impeller of the centrifugal fluid machine in the prior art, the present invention has the following advantages:

(1) High efficiency. Since the flow channel is basically not expanded in the first half, the diffusion amount is reduced in the second half, which can reduce and eliminate the flow separation zone and recirculation zone near the pressure surface of the blade, thereby reducing the internal consumption of energy and significantly improving the efficiency. The design efficiency can reach more than 90%.

(2) Since the blades of the impeller thicken rapidly from the leading edge, and the flow channel has no expansion at the inlet and has a convergent section. The impeller is more adaptable to the change of the speed triangle area caused by the flow change at the inlet, so it can still maintain a wide and efficient working area when it deviates from the design point.

(3) The cavitation condition of the water pump is improved. Since this design reduces the expansion of the flow channel by thickening the blade instead of reducing the ratio of r ₂ /r ₁ , it is possible to properly reduce r ₁ while maintaining the r ₂ determined by the design lift, so that the leading edge of the blade can work at In a lower peripheral velocity environment, this will help improve cavitation.

Claims (3)

1, a kind of thick blade centrifugal vane wheel is made up of the blade more than two at least, and feature of the present invention is: the obstruction function K that vane thickness is increased to make different radii _(r)Must be at r ₁≤ r≤0.8 (r ₂-r ₁)+r ₁Radius be K _(r)〉=min[1, r/2 (r-r ₁)], and require r ₂/ r ₁〉=1.7, preceding half section of formed runner should be satisfied r between adjacent blades ₁≤ r≤r _m, choose K _(r)Make runner not be expansion shape, second half section r _m＜r≤r ₂, choose K _(r)=(K ₂-1)/((r ₂-r _m)) (r-r _m)+1, and allow runner diffusion to be arranged slightly, K in the formula ₂For stopping up function in the outlet port, can be by r=0.8 (r ₂-r ₁)+r ₁The K at place _(r)Value is tried to achieve K ₂, and K ₂Be not more than 1, the runner between adjacent blades is at the circumferential width S at different radii r place _(r)=2 π r/m-L _(r), blade is at the circumferential width L at different radii r place _(r)=K _(r)2 π (r-r ₁)/m, r in the formula ₁The polar coordinates radius at-blade inlet edge place, r ₂The polar coordinates radius at-trailing edge place, the m-number of blade, r _m-be r ₁, r ₂Mean radius.

2, thick blade centrifugal vane wheel according to claim 1 is characterized in that: to the centrifugal impeller of non-two-dimentional blade profile, its blade profile is meant the axial plane design path

Revolve into blade profile on the face with shaft centerline

Be the projection on the polar coordinates plane at center, blade inlet edge place radius r ₁Be meant that a certain axial plane design path revolves into the polar coordinates radius value at the blade inlet edge A point place on the face.

3, thick blade centrifugal vane wheel according to claim 1 and 2 is characterized in that: when the axial plane design path

At blade inlet edge A point place and shaft centerline

Axial plane angle γ ₁During less than 45 °, then this design path

With shaft centerline

Axial plane angle γ equal 45 ° of polar coordinates radiuses of locating and be defined as r ₁, and only be used for radius r 〉=r ₁Blade profile partly.

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