RU2406880C2 - Blade diffuser of centrifugal machine - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: recommended value of this angle depends on lead angle of blades, on output radius of diffuser and input radius ratio, and also on input width of diffuser and output width ratio. Loss of head decreases, because recommended value of output angle of blades ensures absence of cross non-uniformity of rate of working medium in between-blade channels of the diffuser.

EFFECT: decrease of working medium loss of head in diffuser due to optimisation of output angle of blades.

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Description

The invention relates to energy turbomachines and can be used in scapular diffusers of centrifugal compressors, blowers, fans and pumps.

Vane diffusers are known in which the output angle of the blades is set depending on the input angle of the blades, namely, it is taken 5 ... 20 ° more than the last (p. 160 in the book of Seleznev KP and Galerkin Yu.B. Centrifugal compressors. Leningrad, Mechanical Engineering , 1982). The disadvantage of such diffusers is the large uncertainty of the outlet angle of the blades: the absolute range of this angle is 15 °, and the relative range is 68% (with an average input angle of the blades 17 °).

The noted drawback is partially eliminated in the blade diffusers having a smaller recommended range of the outlet angle of the blades. The known blade diffuser of a centrifugal turbomachine (SU 1134795 A1, 01/15/1985) contains end walls and vanes located between them. The output angle of the blades is 90 ... 100 °, that is, the absolute range of this angle is 10 °, and the relative 9%.

A disadvantage of the known blade diffuser is the increased pressure loss of the working medium in the diffuser. The reason for the increased losses is the non-optimal output angle of the blades, which does not ensure the absence of transverse unevenness of the speed of the working medium in the interscapular channels.

The objective of the present invention is to reduce the pressure loss in the blade diffuser by setting such an outlet angle of the blades, which ensures the absence of transverse unevenness of the speed of the working medium in the interscapular channels.

,Technical result is achieved by that in the known centrifugal bladed diffuser turbomachine comprising end walls and the vanes extending therebetween, according to the invention the exit angle α _O vanes is determined from the equation

,

wherein

R _o - the output radius of the diffuser;

R _in - the input radius of the diffuser;

b _in - input width of the diffuser;

b _o - output width of the diffuser;

α _I - the input angle of the blades.

The present invention, unlike the prior art determines the output angle of the blades and allows for uniquely angle dependence of the three parameters diffusers (R _O / R _Bx, b _Rin / b and α _{O Rin).}

Figure 1 shows the scapular diffuser of a centrifugal turbomachine, a meridional section; figure 2 is a radial section aa in figure 1; figure 3 - section aa in figure 1 with blades that do not affect the flow of the working medium; figure 4 is a section aa in figure 1 with a zero angle of curvature of the blades.

The spatula diffuser contains end walls 1, 2 and vanes 3 located between them. The vanes 3 are depicted as non-profiled, but can also be profiled, according to any law. The blades 3 and the end walls 1, 2 interblade channels form a diffuser 4. The output angle α blades _O 3 corresponds to the invention.

Spatula diffuser operates as follows.

The working medium moves along the interscapular channels 4 in the direction from the input circle 5 to the output circle 6. Moreover, since the interscapular channels 4 are diffuser, the kinetic energy of the working medium decreases, and the pressure of the working medium in accordance with Bernoulli’s law increases. The movement of the medium along the interscapular channels 4 is accompanied by pressure losses due to the friction of the working medium on the blades 3 and the inner surfaces 7 and 8 of the end walls 1 and 2.

The pressure loss is less, the smaller the transverse unevenness of the speed of the working medium in the interscapular channels 4. Due to the fact that the output angle α of the _outgoing blades 3 corresponds to the invention, there is no transverse unevenness of the speed of the working medium in the interscapular channels 4. This ensures a minimum pressure loss. The fact that the invention ensures the absence of lateral velocity unevenness is explained as follows.

), где

- поточный угол на выходе из диффузора, соответствующий таким лопаткам, которые не оказывают воздействия на поток рабочей среды, то есть соответствует отсутствию лопаток. При этом согласно общеизвестным данным гидравлики и промышленной аэродинамики угол и обусловливает увеличение скорости рабочей среды поперек канала в направлении к центру кривизны канала (фиг.3). Согласно данным исследований лопаточных диффузоров разность (α_вых -

) обусловливает увеличение скорости в противоположном направлении (фиг.4). Отсюда следует условие отсутствия поперечной неравномерности скорости рабочей среды в межлопаточных каналах лопаточного диффузора:The nature of the change in the speed of the working medium across the interscapular channel of the scapular diffuser depends on two factors: a) on the angle of curvature of the interscapular channel, or, which is the same thing, on the angle and curvature of the blades; b) the difference (α _out -

), where

- the flow angle at the outlet of the diffuser, corresponding to such blades that do not affect the flow of the working medium, that is, corresponds to the absence of blades. Moreover, according to well-known data of hydraulics and industrial aerodynamics, the angle and causes an increase in the speed of the working medium across the channel in the direction to the center of curvature of the channel (Fig. 3). According to studies of blade diffusers, the difference (α _out -

) causes an increase in speed in the opposite direction (figure 4). This implies the condition for the absence of transverse unevenness of the speed of the working medium in the interscapular channels of the blade diffuser:

Based on the formula 3.42 in the book Rice V.F. Centrifugal compressor machines. Leningrad, Mechanical Engineering, 1982

and, therefore, (1) takes the form

The angle υ that appears here, not being a free parameter of the diffuser, depends on its other parameters. Communication with the independent parameters of the diffuser can be set in figure 2.

From the OVS triangle by the sine theorem

From figure 2:

OC = R _out

OB = R _I

β = δ + α _in = 90 ^o -0.5υ + α _in

γ = δ-α _out = 90 ^o -0.5υ-α _out

Substituting these equalities into (3), we have

From (2)

Substitution

this expression in (4) and elementary algebraic transformations give the equation

,

,

which appears in the invention.

Claims (1)

Vaned diffuser centrifugal turbomachine comprising end walls and disposed between the blade, characterized in that the exit angle α _O vanes is determined from the equation

in which R _o - the output radius of the diffuser;
R _in - the input radius of the diffuser;
b _in - input width of the diffuser;
b _o - output width of the diffuser;
α _I - the input angle of the blades.

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