JPH09317692A - Centrifugal impeller of rotational fluid machinery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To collect motive power from a leaking flow flowing in a clearance between a shroud disc and a casing of a centrifugal impeller and to reduce leakage itself. SOLUTION: A turbine blade 4 having a blade angle in the opposite direction of a main blade 3 is installed on a back surface facing a casing 2 of a shroud disc 1, and motive power is collected by generating torque on the turbine blade 4 by a leaking flow flowing between the shroud disc 1 and the casing 2. Additionally, leakage is reduced by lowering pressure of the leaking flow at the time when it passes the turbine blade 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a centrifugal blade of a rotary fluid machine such as a centrifugal compressor, a centrifugal blower and a centrifugal pump.

[0002]

2. Description of the Related Art In conventional centrifugal compressors, centrifugal blowers, centrifugal pumps, and other closed type centrifugal impellers, the back surface of the shroud disk is a smooth surface with nothing attached. That is, as shown in FIG. 4, a main blade 3 that is rotated by a main shaft 10 to pressurize or move a fluid is attached to a shroud disk 1 arranged in a casing 2, and the main blade 3 is in a main flow path in an impeller. It is located in.
The rear surface of the shroud disk 1 facing the casing 2 and not having the main blade 3 attached thereto was a smooth surface having nothing attached. Reference numeral 5 in FIG. 4 denotes a labyrinth provided between the casing 2 and the upstream end of the shroud disc 1.

[0003]

In the conventional centrifugal impeller described above, the leakage flow leaking through the gap between the shroud disk and the casing is about 10 to 20% of the main flow rate in the small flow impeller. , This leakage flow flows from the impeller outlet through the gap between the shroud disc and the casing, joins the impeller inlet, and creates reflux between the impeller outlet and inlet, and the same ratio as the main flow rate ratio to the impeller. About 10-2
The required power of 0% was increased.

It is the labyrinth at the upstream end of the shroud disk that limits the leakage flow. However, if the clearance of the labyrinth is reduced to reduce the leakage flow, the excitation force generated in the labyrinth increases. Moreover, the risk of vibration amplification due to contact increases, which is not desirable.

The present invention is intended to provide a centrifugal impeller of a rotary fluid machine capable of solving the above problems.

[0006]

In a centrifugal impeller of a rotary fluid machine according to the present invention, a turbine blade having a blade angle opposite to a blade for pressurizing a fluid is provided on a rear surface of a shroud disk facing a casing. It is characterized by

According to the present invention, since the turbine blade having the blade angle opposite to the blade that pressurizes or moves the fluid is attached to the back surface of the shroud disk facing the casing, the clearance between the shroud disk and the casing is set. In the resulting leak flow, the turbine blades will be placed and a torque will be generated in the shroud disc in the direction of rotation. As a result, the torque applied to the entire impeller in the counter-rotational direction can be reduced, and the required power of the centrifugal impeller can be reduced.

Further, as the leak flow passes through the turbine blade, the pressure drops and the leak amount itself also decreases.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. In the present embodiment, in the centrifugal impeller shown in FIG. 4, on the rear surface of the shroud disk 1 facing the casing 2 and on the side opposite to the side on which the main blade 3 is attached, blades in the direction opposite to the main blade 3 are provided. A plurality of angled turbine blades 4 are attached at equal intervals.

As shown in FIG. 2, the turbine blade 4 has an impeller outlet turning amount Cu ₂ , which corresponds to a turbine inlet,
The inlet blade angle is calculated from the outlet peripheral velocity U ₂ and the leakage flow velocity Cm ₂ .
It is efficient to calculate the outlet blade angle so that the turning amount is 0 at the turbine outlet and form a curved blade shape, but a straight line may be used for ease of manufacturing. Also, W _{2 in} FIG.
Is the turbine inlet relative flow velocity, C ₂ is the turbine inlet absolute flow velocity, W ₁ is the turbine outlet relative flow velocity U ₁ is the turbine outlet peripheral velocity, Cm ₁ is the leakage flow velocity at the turbine outlet, and the turbine blade 4 has a curved blade shape. In this case, the turbine inlet blade angle is set close to the direction of W ₁ , and the turbine outlet blade angle is set so that the outlet direction is in the W ₂ direction. However,
When making the turbine blade 4 into a straight blade shape, the turbine inlet blade angle is merely directed toward the direction of W ₁ .

In the present embodiment configured as described above, when the impeller starts rotating, the leakage flow returning from the impeller outlet to the impeller inlet in the gap between the back surface of the shroud disk 1 and the casing 2. Occurs. This leakage flow passes between the turbine blades 4 attached to the shroud disk 1, and causes a torque in the rotating direction in the impeller to reduce the required shaft power.

In the impeller for a small flow rate of the centrifugal impeller, the leakage flow is 10 to 20% of the main flow, which directly increases the required shaft power, but in the present embodiment, it is shown in FIG. Thus, even for the same amount of leakage, the power is recovered and the shaft power is reduced to improve the efficiency of the impeller. (The efficiency is the flow rate x head / shaft power, so the denominator of the efficiency is reduced and the efficiency is increased by reducing the shaft power.) The dotted line in Fig. 3 is the conventional centrifugal impeller, and the solid line is the present embodiment. The morphology is shown.

Further, the leakage flow is caused by the turbine blade 4
As a result of the passage between the two, the pressure drops, the differential pressure before and after the labyrinth 5 decreases, and the leak amount itself also decreases.

[0014]

The centrifugal impeller of the rotary fluid machine of the present invention is
Since a turbine blade having a blade angle in the opposite direction to the blade that pressurizes or moves the fluid is attached to the back surface facing the casing of the shroud disk, the torque required by the turbine blade reduces the power required for the centrifugal impeller. In addition, the leakage flow passes through the turbine blades, so that the pressure drops and the leakage amount can be reduced.

[Brief description of drawings]

FIG. 1 is a meridional sectional view of a centrifugal impeller according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view (cross section in the circumferential direction) taken along the line AA of FIG.

FIG. 3 is a performance curve diagram showing an effect of the same embodiment.

FIG. 4 is a meridional sectional view showing a conventional centrifugal impeller.

[Explanation of symbols]

 1 Shroud disk 2 Casing 3 Main blade 4 Turbine blade 5 Labyrinth 10 Spindle

Claims (1)

[Claims] 1. A centrifugal impeller of a rotary fluid machine, wherein a turbine blade having a blade angle in a direction opposite to a blade for pressurizing or moving a fluid is attached to a back surface of the shroud disk facing the casing.