RU2612309C1 - Centripetal turbine - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: centripetal turbine comprising a casing, radial-axial turbine impeller provided with a blading is proposed. A collar spanning the gap between the casing and the impeller blades is made on the centripetal turbine casing on the working medium outlet from the blading radial-axial impeller. The distance between blade system tailing edge and the collar on the centripetal turbine casing is less than the gap between the periphery of the blade system and the centripetal turbine casing. On the output side of the working medium the collar may be formed with a flat surface disposed normally to the oncoming flow of working fluid.

EFFECT: reduction of the working medium fluid leaks through the gap between the impeller blade and the housing, and increase turbine efficiency.

2 cl, 1 dwg

Description

The invention relates to energy, transport and aircraft engines and can be used in technical facilities, where it is advisable to use a high-temperature high-speed centripetal turbine of low power with a small volumetric flow rate of the working fluid as an energy source.

A known design, designed to reduce leakage of the working fluid [1], which includes the impeller of a centripetal turbine with a cover disk. A non-contact labyrinth seal is installed between the turbine casing and the cover disk to reduce leaks, which is a set of annular protrusions (sealing ridges) located on the rotor and stator so that the protrusions overlap and form a labyrinth. Due to the hydraulic resistance created by the maze, the flow rate of the working fluid through the gaps is markedly reduced.

This design has a number of significant limitations for its use in high-temperature high-speed radial-axial turbines. The presence of a cover disk significantly increases the stresses in the material of the impeller caused by centrifugal forces and uneven thermal expansion.

Closest to the technical nature of the present invention is the design of a centrifugal turbine designed to minimize the gaps between the housing and the blade apparatus of the impeller [2], adopted as a prototype. The design includes a radial-axial impeller and a housing (stator), coated on the inside with a special soft material that has such mechanical properties that when it comes in contact with the blades of the wheel, it rapidly deteriorates without damaging the blade system of the wheel. Thus, during the operation of the turbine, the smallest possible clearance between the rotor and stator in the flow part is established.

However, the use of this design has a number of significant limitations. It can be used without sacrificing reliability only if the estimated thickness of the layer of soft material that is abraded during the running-in of the rotor and stator does not exceed 0.1-0.3 millimeters, which is typical for turbines with a rigid shaft (operating at a frequency rotation below the first critical) and moderate thermal expansions of the impeller.

For a high-speed turbine, it is often not possible to produce a rigid shaft. During the passage of the critical frequency, the precession amplitude can reach a significant value, which will lead to excessive load on the impeller vanes during the development of a large thickness (more than 0.5 mm) of the abrasive layer on the casing and an emergency.

=0,05-0,07 (

, где δ - зазор,

- высота лопатки по выходной кромке) (см. чертеж).The gap between the impeller vanes and the casing must be at least 1-1.5 mm, in terms of reliability (in order to avoid impacting the rotor on the stator at all operating and transient modes), while the relative size of the gap is

= 0.05-0.07 (

where δ is the gap

- blade height along the outlet edge) (see drawing).

This problem is especially relevant for high-speed turbines of small power, where magnetic bearings or bearings with gas lubrication are used as bearings, which have a noticeably greater flexibility compared to ball bearings or liquid friction bearings.

The turbine rotor on such supports during the passage of resonant frequencies during acceleration and shutdown can reach significant amplitudes of the precession, which can lead to grazing of the rotor on the stator and an emergency situation.

For high-temperature centripetal turbines, significant thermal deformations of the turbine impeller do not allow reducing the gaps in the flow part to an acceptable value. The use of a cover disk is also unacceptable due to additional stresses due to centrifugal forces and uneven heating and expansion of the material of the cover disk and blades.

In order to increase operational reliability, it is advisable to increase the gap between the impeller and the stator to values guaranteeing trouble-free operation of the turbine.

It is known that the greatest influence on the efficiency of a centripetal turbine is exerted by energy losses at the output speed. They reach a minimum value with the axial direction of flow (in the absence of swirl). The increase in gaps for reliability reasons leads to such a significant increase in losses with leaks of the working fluid that in the total amount of losses they become decisive.

The technical result of the invention is to reduce the leakage of the working fluid through the gap between the blades of the impeller and the casing and, therefore, to increase the efficiency of the turbine.

To ensure a technical result, a centripetal turbine is proposed, comprising a housing, a radial-axial impeller of the turbine equipped with a blade apparatus. An annular protrusion is made on the housing at the outlet of the working fluid from the scapular apparatus of the radial-axial impeller, overlapping the gap between the housing and the blades of the impeller. The distance between the outlet edge of the impeller vanes and the protrusion on the centripetal turbine housing does not exceed the gap between the periphery of the blade apparatus and the centripetal turbine housing. An annular protrusion from the outlet side of the working fluid can be made with a flat surface normal to the incoming flow of the working fluid.

The turbine constructively consists of two main elements: a rotor and a stator (housing), between which during operation there should be no contact.

Since gaps between the rotor and the stator (housing) necessarily occur in the flow path, leaks in these gaps occur in the process of expansion of the working fluid, bypassing the main flow, which performs useful work.

In order to increase the efficiency of the turbine, it is advisable to minimize these gaps, however, this is not always possible, because due to the requirements for operational reliability (to prevent the rotor from hitting the casing), in all operating modes it is necessary to increase the gap between the rotor blades of the rotor and the casing. The increased clearance, in turn, leads to additional losses and reduced turbine efficiency.

The structure of the flow of the working fluid in the interscapular space of the impeller of a centripetal turbine has the following peculiarity: the part of the flow with the highest speed is concentrated at the periphery of the scapular apparatus, i.e. in the area of the gap between the blades and the casing.

At the exit of the rotor impeller, the flow changes direction from centripetal to axial and a sharp deflection of the flow occurs in the direction opposite to the rotation of the wheel due to the shape of the blades. In this case, the part of the flow with the highest kinetic energy rushes into the gap between the housing and the outlet edges of the rotor impeller. Obviously, reducing the leakage of the working fluid through the gap will increase the efficiency of the turbine.

The leakage reduction effect in the present invention is achieved due to the fact that the annular protrusion on the housing at the outlet of the working fluid creates hydraulic resistance to the flow of the working fluid in the region of the gap at the outlet edges of the blade apparatus and causes it to deviate into the interscapular space, where the flow performs useful work.

The annular protrusion is separated at some distance from the outlet edges of the blades and has such dimensions as to cover the gap between the turbine casing and the working blades. From the side of the flow of the working fluid, the protrusion may have a flat surface normal to the incident flow of the working fluid.

The invention is illustrated in the drawing.

Drawing - a meridional section of a centripetal turbine is shown. The drawing shows: 1 - housing, 2 - radial - axial impeller, 3 - rotor, 4 - annular protrusion, 5 - output edge of the scapular apparatus of the radial-axial impeller, 6 - nozzle apparatus.

Centripetal turbine operates as follows.

The working fluid (gas) is fed into the cavity (not shown in the drawing) in front of the nozzle apparatus 6, which is a collection of channels formed by nozzle blades. The working fluid flows onto the nozzle blades 6 in a radial direction from the periphery to the center.

In the interscapular channels of the nozzle apparatus 6, the flow of the working fluid expands, accelerates and deviates tangentially in the direction of rotation of the radial-axial impeller 2. After that, the gas flow enters the interscapular space of the radial-axial impeller 2 and into the gap δ between the casing and the blade apparatus impeller.

An annular protrusion made on the housing 1 at the outlet of the working fluid from the scapular apparatus creates hydraulic resistance to the flow of the working fluid that has fallen into the gap and contributes to its deflection into the interscapular space, where it, together with the main flow of the working fluid, does useful work.

=0,05-0,07, позволяет уменьшить суммарные потери (по выходной скорости и утечкам через зазор) и повысить КПД турбины примерно на 2%.Calculations (numerical experiments) using the ANSYS software package showed that the presence of an annular protrusion that overlaps the gap at the exit of the radial-axial impeller, if the relative gap is

= 0.05-0.07, it allows to reduce the total losses (in terms of output speed and leakages through the gap) and increase the turbine efficiency by about 2%.

Information sources

1. USSR author's certificate No. 1574967 of 06.30.90

2. US Patent No. 5,975,845 dated November 2, 1999.

Claims (2)

1. Centripetal turbine comprising a housing, a radial-axial impeller of the turbine equipped with a blade apparatus, characterized in that an annular protrusion is made on the housing at the outlet of the working fluid from the blade apparatus of the radial-axial impeller, covering the gap between the housing and the blades of the impeller, and the distance between the outlet edge of the impeller blades and the protrusion on the centripetal turbine housing does not exceed the gap between the periphery of the blade apparatus and the centripetal housing th turbine. 2. The centripetal turbine according to claim 1, characterized in that the annular protrusion on the outlet side of the working fluid is made with a flat surface normal to the oncoming flow of the working fluid.

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