CN105673558A - Centrifugal blower vane designed based on load method - Google Patents

Abstract

The invention discloses a centrifugal blower vane designed based on a load method. A traditional design method for vane molded lines frequently depends on engineering experience, and blindness exists. According to the centrifugal blower vane, the load method is used for optimizing an original model vane and includes the steps that firstly, a proper average relative velocity curve is selected; then, multiple groups of load distribution functions are obtained by setting changes of loads at different positions; and afterwards, a vane molded line is determined according to load distribution. The performance of a blower can be improved through the obtained vane, a model with the middle load ratio being 0.7 is better in performance, especially under rated working conditions and small-flow working conditions, the efficiency under large-flow working conditions is gradually improved along with increasing of the load ratio, and the efficiency under the small-flow working conditions is reduced; flow in the optimized model is more stable than that in the original model, and no obvious flow separation and vortex exist; and in addition, due to the fact that no influence of separation exists, static pressure is stably increased in a vane channel, and a jet-wake structure at the position of an outlet of the vane channel is also improved.

Description

A Centrifugal Fan Blade Based on Load Method Design

technical field

The invention belongs to the field of fan equipment and relates to a centrifugal fan, in particular to a centrifugal fan blade designed based on a load method.

Background technique

As a kind of general machinery, centrifugal fans are widely used in industries such as iron and steel, cement, petroleum and petrochemical, and building ventilation. They are used in a huge amount and consume a lot of energy. Therefore, improving the efficiency of centrifugal fans can obtain very considerable economic and social benefits.

The centrifugal impeller is the core component of the centrifugal fan. The loss in the centrifugal fan is also the main source of loss in the centrifugal fan. The flow at the outlet of the centrifugal impeller will also affect the flow of the air in the volute and the pipe. It can be seen that improving the efficiency of the impeller is the key to improving the efficiency of the centrifugal fan. The efficiency of the impeller is closely related to the flow inside the impeller, and the blade profile is the key to the centrifugal impeller. The traditional design method often relies on engineering experience, which makes it difficult to improve the performance of the fan after it reaches a certain level, and the improvement methods of some blades are often blind.

Contents of the invention

The purpose of the present invention is to address the deficiencies in the prior art, obtain the velocity distribution function according to the impeller parameters in combination with the average relative velocity curve of the blade path center line and the boundary layer calculation formula, then adopt the load method to optimize the original model blade, first select a suitable The average relative velocity curve, and then get multiple sets of load distribution functions by setting the load changes at different positions, and then determine the blade shape line according to the load distribution. The blades obtained by the load distribution of the present invention can improve the performance of the fan, and the model with a middle load ratio of 0.7 has better performance, especially under rated working conditions and low flow working conditions, as the load ratio increases, at large The efficiency under the condition of flow increases gradually, while the efficiency decreases under the condition of small flow. The internal flow of the optimized model is more stable than the original model, and there is no obvious flow separation and vortex, and because it is not affected by the separation, the blade The static pressure in the tunnel increases stably, and the jet-wake structure at the exit of the blade tunnel is also improved.

The load calculation formula that the present invention adopts is:

δ=ρ·ω·Δω(1)

Among them, δ is the load; ρ is the fluid density in the flow direction, and ρ is a constant value for incompressible fluids; ω is the average relative velocity of the fluid on the centerline of the blade passage, and Δω is the average relative velocity difference between the suction surface and the pressure surface.

Since the average relative velocity of the blade path centerline is similar to the average relative velocity of the suction surface and the pressure surface, the formula (1) can be written as:

δ=ρ·S·ω ² (2)

$\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, S is the load coefficient, ω _s and ω _p are the average relative velocities of the fluid on the suction surface and the pressure surface, respectively.

Therefore, the corresponding load can be obtained by the average relative velocity of the fluid on the centerline of the blade passage and the load coefficient. Set the average relative velocity of the fluid at the centerline position L of the blade path, and set a maximum value position of the load as the position L=0.25, the load coefficient at L=0.25 is 0.9, and the other maximum value position of the load is L=0.7, the load factor at L=0.7 is 0.85. From this, the loads where L is 0.25 and 0.7 can be obtained.

Note that the load at L=0.7 is the base load, and the ratio of the position L to the base load is the load ratio; the minimum position of the set load is the load at L=0.5, that is, the middle load; the ratio of the middle load to the base load Four different values are taken to establish four load ratio distribution function models, and the load ratio distribution function is set as a three-section segmental function, and L is taken as 0.25 and 0.7 as the boundary positions corresponding to the load ratio distribution function; one of the load ratio distribution function models is The function of the second segment is the equation of a straight line connecting two maximum points; the first and third segments of the other three load ratio distribution function models are quadratic functions, and the second segment in the middle is a quartic function. The ratios of the middle load of the second segment function to the base load are respectively 0.8, 0.7, and 0.6; the coefficients of each load ratio distribution function are the load ratios where L is 0, 0.25, 0.5, 0.7, and 1, and the load ratios are at the minimum , and the boundary condition where the derivative at the maximum value is 0 is obtained.

According to the momentum moment theorem, we can get:

dM=Zδpbrdr=ρQd(rC _u ) (4)

In the formula, d is the differential operator, M is the moment, r is the radius of the impeller, Z is the number of blades, b is the width of the blade path, p is the fluid pressure, _Cu is the circumferential velocity of the fluid, and Q is the volume flow.

which is:

$\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&rho;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; rC</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&rho;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

From the velocity triangle vector relation at any radius inside the impeller, it can be obtained:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; 30</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

In the formula, n is the rotational speed, u is the linear velocity at the _radius of the impeller, β is the blade angle, and Cr is the radial velocity of the fluid.

From this, the relationship between the blade outlet angle and the blade load can be obtained:

$\frac{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 15</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{\mathrm{<span\; class="notranslate">\; b</span>}}\frac{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; b</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; k</span>}}\frac{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{{\mathrm{<span\; class="notranslate">\; \&rho;Q\&psi;C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

In the formula, ψ is the pressure coefficient.

Four sets of blade centerlines corresponding to different load distributions are obtained from formula (7). Since the upper and lower contours are parallel, the upper and lower contours of the blade can be obtained only by giving the blade centerline and blade thickness.

The three-dimensional model of the centrifugal fan is established for the four blade profiles, and the numerical simulation of the three-dimensional model is carried out by CFD software. A three-dimensional model whose flow coefficient has a greater total pressure efficiency than the original model within the operating range of the original model and has the highest average value of the total pressure efficiency within the original model’s operating range is selected as the best model. Establish a coordinate system with the impeller rotation center as the coordinate origin, select discrete points on the blade midline line corresponding to the best model, and record the abscissa and ordinate of each discrete point, that is, the design of the centrifugal fan based on the load calculation formula is completed blade.

The beneficial effect that the present invention has:

1. The blades obtained according to the load distribution of the present invention can improve the performance of the fan, and the model with a middle load ratio of 0.7 has better performance, especially under rated working conditions and small flow conditions, as the load ratio increases, The efficiency gradually increases under the condition of large flow rate, while the efficiency decreases under the condition of small flow rate;

2. The internal flow of the improved model of the present invention is more stable than the original model, and there is no obvious flow separation and vortex, and because it is not affected by the separation, the static pressure growth in the blade passage is stable, and the jet-wake structure at the outlet of the blade passage is also stable. Improved.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Figure 2 is a graph showing the relationship between the position of the fluid on the centerline of the blade passage and the average relative velocity;

Figure 3 is a curve diagram of the relationship between the position of the center line of the blade path and the distribution of the load ratio;

Fig. 4 is the line diagram of the leaf path center line of the present invention;

Fig. 5 is the relationship diagram between the total pressure coefficient and the flow coefficient of each model in the embodiment of the present invention;

Fig. 6 is a graph showing the relationship between the total pressure efficiency and the flow coefficient of each model in the embodiment of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

A centrifugal fan blade designed based on the load method, the load calculation formula used is:

δ=ρ·ω·Δω(1)

Among them, δ is the load; ρ is the fluid density in the flow direction, and since the research scope belongs to incompressible fluid, ρ is a constant value; ω is the average relative velocity of the fluid on the centerline of the blade passage, and Δω is the fluid density on the suction surface and the pressure surface Average relative velocity difference.

Since the average relative velocity of the blade path centerline is similar to the average relative velocity of the suction surface and the pressure surface, the formula (1) can be written as:

δ=ρ·S·ω ² (2)

$\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, S is the load coefficient, ω _s and ω _p are the average relative velocities of the fluid on the suction surface and the pressure surface, respectively.

Therefore, the corresponding load can be obtained through the average relative velocity of the fluid on the centerline of the blade passage and the load coefficient. Set the average relative velocity of the fluid at the centerline position L of the blade path as shown in Figure 2, and set a maximum value position of the load at the position L=0.25, the load coefficient at L=0.25 is 0.9, and the load Another maximum position is L=0.7, and the load factor at L=0.7 is 0.85. From this, the loads where L is 0.25 and 0.7 can be obtained.

Note that the load at the L=0.7 place is the base load, and the ratio of the position L and the base load is the load ratio δ*; the present invention mainly studies the impact of the load distribution in the middle of the blade (L=0.5) on the performance of the centrifugal fan, and the setting load The position of the minimum value is the load at L=0.5, that is, the middle load; the ratio of the middle load to the base load takes four different values, and four load ratio distribution function models are established, and the load ratio distribution function is set as a three-section segmental function, L takes 0.25 and 0.7 as the boundary position corresponding to the load ratio distribution function; the second segment function of the load ratio distribution function model A is the straight line equation connecting two maximum points; the load ratio distribution function models B, C, and D The first and third sections are both quadratic functions, and the second section in the middle is a quartic function. The ratios of the middle load of the second section of the function to the base load are respectively 0.8, 0.7, and 0.6; the distribution functions of each load ratio The coefficients are obtained from the load ratios where L is 0, 0.25, 0.5, 0.7, and 1, and the boundary conditions where the derivative of the load ratio is 0 at the minimum and maximum values. The load ratio distribution curve drawn according to the load distribution function is shown in the figure 3.

According to the momentum moment theorem, we can get:

dM=Zδpbrdr=ρQd(rC _u ) (4)

In the formula, d is the differential operator, M is the moment, r is the radius of the impeller, Z is the number of blades, b is the width of the blade path, p is the fluid pressure, _Cu is the circumferential velocity of the fluid, and Q is the volume flow.

which is:

$\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&rho;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; rC</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&rho;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

According to the velocity triangle vector relation at any radius inside the impeller, it can be obtained:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; 30</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

In the formula, n is the rotational speed, u is the linear velocity at the _radius of the impeller, β is the blade angle, and Cr is the radial velocity of the fluid.

From this, the relationship between the blade outlet angle and the blade load can be obtained:

$\frac{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 15</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{\mathrm{<span\; class="notranslate">\; b</span>}}\frac{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; b</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; k</span>}}\frac{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{{\mathrm{<span\; class="notranslate">\; \&rho;Q\&psi;C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

In the formula, ψ is the pressure coefficient.

Then four sets of blade centerlines corresponding to different load distributions are obtained, as shown in Fig. 4. Since the upper line and the lower line are parallel, the upper line and the lower line of the blade can be obtained only by giving the centerline and thickness of the blade; here, the thickness of the blade is taken as 4.5mm.

The three-dimensional model of the centrifugal fan is established for the four blade profiles, and the numerical simulation of the three-dimensional model is carried out by the CFD software Fluent. It can be seen from Figure 5 that the total pressure coefficients of models A and B are higher than those of the original model O, the total pressure coefficient of model C is not much different from that of the original model, and the total pressure coefficient of model D is lower than that of the original model . It can be seen from Figure 6 that the total pressure efficiency after the improvement is higher than that of the original model, and the efficiency of model C is obviously higher than that of other models near the rated working condition of the original model (flow coefficient is 0.23), but in large Under flow conditions, the total pressure efficiency of model A and model B is higher than that of models C and D. This is due to the influence of the load distribution in the middle, and the blade outlet angle of model A and model B is larger, so in large flow The total pressure coefficient and total pressure efficiency under working conditions are higher. Since the performance of the centrifugal fan is more important in the case of small flow, model C is considered to be the best model on the whole. A coordinate system is established with the center of rotation of the impeller as the coordinate origin, and 101 discrete points are selected on the blade center line corresponding to model C for subsequent analysis and processing (the blade processed in this embodiment is shown in Figure 1), each discrete The abscissa xu and ordinate yu of the point are listed in the following table, that is, the designed centrifugal fan blade based on the load calculation formula:

In the original model, there is an obvious low-pressure area near the suction side, and the static pressure contour starts at the blade inlet, extends to near the blade tail and then returns, and ends at the middle of the blade. This low-pressure area coincides with the position of the vortex in the blade passage, which is due to the formation of the vortex in the blade passage and affects the pressure growth. In the improved model, the static pressure increases relatively uniformly in the leaf duct, and there is no obvious low pressure area. Both the original model and the improved model C have a low-pressure area on the side of the wheel cover near the inlet, but the location is different. The low-pressure area of the original model is a little behind, while the low-pressure area of the improved model is in the front, and the improved model C This low-pressure area is small, which is formed due to the impact of the airflow at the inlet, and has no effect on the static pressure distribution behind. The larger area of the original model also directly affects the subsequent static pressure distribution, which is due to the impact of flow separation on static pressure. The improved model C has a better effect on the static pressure distribution on the blade.

In the original model, near the inlet of the blade, there is a position with high static pressure on both the suction surface and the pressure surface, and then the static pressure drops rapidly, and the static pressure on the pressure surface begins to gradually increase until L is around 0.2 , which is due to the fact that the fluid near this location is squeezed by the flow separation on the suction side of the nearby blade, thereby affecting the pressure growth. And at the blade outlet, the static pressure drop is larger. In the improved model C, the static pressure began to increase steadily after only a brief drop in the initial stage, and the pressure drop at the outlet was also significantly smaller than that of the original model. There is a clear jet-wake structure in the original model. The jet-wake structure is due to the thickening and separation of the boundary layer of the suction surface, which affects the flow of the main flow and reduces the relative velocity close to the suction surface. The low-velocity area near the suction surface becomes a wake, and the high-speed area formed by extrusion becomes a jet. In the original model, the flow separation on the suction surface is obvious, resulting in an obvious jet-wake structure, while in the improved model C, the load distribution is reasonable to suppress the flow separation, and the jet-wake structure is also improved.

Claims (1)

1. A centrifugal fan blade designed based on load method, characterized in that: the load calculation formula adopted is: δ=ρ·ω·Δω(1) Among them, δ is the load; ρ is the fluid density in the flow direction, and ρ is a constant value for incompressible fluid; ω is the average relative velocity of the fluid on the centerline of the blade passage, and Δω is the average relative velocity difference between the suction surface and the pressure surface; Since the average relative velocity of the blade path centerline is similar to the average relative velocity of the suction surface and the pressure surface, the formula (1) can be written as: δ=ρ·S·ω ² (2) $\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ Among them, S is the load coefficient, ω _s and ω _p are the average relative velocity of the fluid on the suction surface and the pressure surface, respectively; Therefore, the corresponding load can be obtained through the average relative velocity value and load coefficient of the fluid at the centerline of the blade path; set the average relative velocity of the fluid at the position L of the centerline of the blade path, and set a maximum value position of the load as L= At the position of 0.25, the load factor at L=0.25 is 0.9, and the other maximum position of the load is L=0.7, and the load factor at L=0.7 is 0.85; thus, the load at L=0.25 and 0.7 can be obtained; Note that the load at L=0.7 is the base load, and the ratio of the position L to the base load is the load ratio; the minimum position of the set load is the load at L=0.5, that is, the middle load; the ratio of the middle load to the base load Four different values are taken to establish four load ratio distribution function models, and the load ratio distribution function is set as a three-section segmental function, and L is taken as 0.25 and 0.7 as the boundary positions corresponding to the load ratio distribution function; one of the load ratio distribution function models is The function of the second segment is the equation of a straight line connecting two maximum points; the first and third segments of the other three load ratio distribution function models are quadratic functions, and the second segment in the middle is a quartic function. The ratios of the middle load of the second segment function to the base load are respectively 0.8, 0.7, and 0.6; the coefficients of each load ratio distribution function are the load ratios where L is 0, 0.25, 0.5, 0.7, and 1, and the load ratios are at the minimum , obtained from the boundary condition where the derivative at the maximum value is 0; According to the momentum moment theorem, we can get: dM=Zδpbrdr=ρQd(rC _u ) (4) In the formula, d is the differential operator, M is the moment, r is the radius of the impeller, Z is the number of blades, b is the width of the blade path, p is the fluid pressure, _Cu is the circumferential velocity of the fluid, and Q is the volume flow; which is: $\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&rho;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; rC</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&rho;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$ According to the velocity triangle vector relation at any radius inside the impeller, it can be obtained: ${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; 30</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$ In the formula, n is the rotational speed, u is the linear velocity at the radius of the impeller, β is the blade angle, C _r is the radial velocity of the fluid; From this, the relationship between the blade outlet angle and the blade load can be obtained: $\frac{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 15</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; cot</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}{\mathrm{<span\; class="notranslate">\; b</span>}}\frac{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; b</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}}{{\mathrm{<span\; class="notranslate">\; \&rho;Q\&psi;C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$ In the formula, ψ is the pressure coefficient; Four sets of blade centerlines corresponding to different load distributions are obtained from formula (7). Since the upper and lower contours are parallel, the upper and lower blades can be obtained only by giving the blade centerline and blade thickness; Establish a three-dimensional model of the centrifugal fan for the four types of blades and use CFD software to numerically simulate the three-dimensional model; the total pressure efficiency of the flow coefficient within the operating range of the original model is greater than that of the original model, and within the operating range of the original model A three-dimensional model with the highest average value of total pressure efficiency is selected as the best model; a coordinate system is established with the impeller rotation center as the coordinate origin, discrete points are selected on the blade midline line corresponding to the best model, and the abscissa of each discrete point is recorded With the ordinate, the design is completed based on the load calculation formula of the centrifugal fan blades.