EP0196363A1 - Single or multistage axial compressor - Google Patents

Abstract

1. A single or multi-stage axial compressor with clearance spaces inside the compressor housing, characterised in that the clearance spaces present within the axial compressor are provided as resonator chambers and that the axial compressor is equipped with at least one wide-band absorption resonator (7) as a pulsation absorber, and that for coupling the absorption resonator (7) to the gas stream circumferentially extending slots (8), which form the throat of the absorption resonator, are arranged in front of or behind a rotatable rotor (3) and that the walls of the absorption resonator (7) are lined with a damping material (D).

Description

The invention relates to a single and multi-stage axial compressor.

Not only flow-dynamic processes, but also acoustic laws are responsible for the occurrence of flow instabilities and pressure pulsations in axial compressors.

When considering the complex flow conditions and the start of detachment of a three-dimensional boundary layer, acoustic influences were also taken into account by Emmons, Pearson and Grant. C.R. Sparks has dealt intensively with the acoustic classification of a radial compressor and the connecting pipelines (Journal of Engineering for Power, Oct. 1983, Vol. 105).

According to CH-PS 646 757 a single-stage radial compressor is known, which is characterized in that a single passage or at least one passage distributed over the circumference is arranged in the unbladed diffuser channel, the diffuser channel having at least one annular pressure compensation chamber arranged behind the diffuser wall connect. Such a design is intended to eliminate pressure pulsations which occur when the delivery capacity is reduced.

The object of the invention is to reduce the amplitude of an existing pulsation spectrum, in particular in the case of multi-stage axial compressors, in order to enlarge the usable working range in the characteristic map of the compressor.

This object is achieved by the measures specified in the patent claims.

According to the invention, an axial compressor is equipped with one or more absorption resonators, so-called Helmholtz resonators.

In multi-stage axial compressors, the absorption resonators are arranged between several stages in a stage group.

In the axial compressor, and here in the case of speed-controllable machines, the peculiarity applies that the pumping point of interest is reached at a constant final pressure, which corresponds to the design pressure, at a speed at which, in the pumping point of the entire compressor, all stages simultaneously reach their pump limit. At lower speeds, the first stages pump first. At higher speeds, however, the last stages pump first.

In order to use the absorption resonators particularly effectively here, it makes sense to arrange them in the middle of the step group. This gives the shortest distance from this point to all pumping axial stages.

The coupling of the absorption resonators is of course not limited to the area of the middle compressor bank. You can also e.g. be coupled to the compressor discharge chamber.

In the case of axial compressors with low-pressure and high-pressure parts, the absorption resonators can be used in both compressor parts.

According to the invention, the dead volumes known in axial compressors within the compressor housing are suitable as resonator chambers. These are made using an all-round slot that is made before or after a run rad is arranged, coupled to the gas stream. Such a design creates a Helmholtz resonator, the circumferential slot forming the mouth of the resonator.

If the axial compressor does not have sufficient dead volumes in the housing, additional dead volumes, which serve as resonator chambers, can be coupled from the outside according to the invention.

In order to flatten the relatively steep resonance curve of the Helmholtz resonator thus formed, the walls of the resonator chambers can be at least partially equipped with a damping material of a certain sound resistance. This can e.g. be an insulating material based on mineral fiber. Damping the neck of the Helmholtz resonator, represented by the circumferential slot, is not possible because of the narrow shape.

The frequency of the pulsation spectrum to be damped depends on the type, number of stages and some dynamic factors of the respective axial compressor and is therefore determined experimentally once for each type.

It is also important whether the intake flow is already pulsating, since such pulsations can be amplified when they pass through the compressor.

The design according to the invention is also suitable for damping pump pulses in the event of a complete stall (deep surge). Although the frequency of this pump is lower, the absorption resonator has a dampening effect.

The invention does not take into account the relatively high frequencies resulting from speed and number of blades, nor the relatively low frequency when the compressor is completely stalled, "pumping".

Rather, the existing broadband pulsation spectrum superimposed on the gas flow in the range from 200 to 800 Hz is considered under "steady-state conditions". As is known, the amplitude of these pulsations increases when the delivery capacity is reduced before the circulating stall flow (rotating stall) and ultimately the complete stall occurs.

The invention is explained in more detail below with the aid of the schematic drawing, which represents an exemplary embodiment.

• Fig. 1 einen Querschnitt durch den oberen Teil des Axialkompressors und
• Fig. 2 einen vergrößerten Querschnitt eines Absoprtions-Resonators.

Show it:

• Fig. 1 shows a cross section through the upper part of the axial compressor and
• Fig. 2 is an enlarged cross section of an absorption resonator.

1 shows the upper part of an axial compressor with the upper housing part 1, in which the rotor 2 with the rotor blades 3 and the guide blades 4 is located. The inflow part of the compressor is denoted by 5 and the outflow part by 6.

The housing space (dead volume) which can be seen between the inflow part 5 and the outflow part 6 is used as the resonator chamber 7. The compressor has a rotating one between a moving blade 3 and a guide blade 4 Slit 8, which serves as a coupling slot for the _A b sorption resonator (resonator chamber) 7 and can also be referred to as the neck of a Helmholtz resonator.

In order to flatten the resonance curve and thus the absorption becomes effective for a wider frequency range, the walls of the resonator chamber 7, as indicated in FIG. 2, are coated with an acoustic insulation layer D, for example mineral wool.

The absorption resonator, as shown in the schematic diagram (Fig. 2), represents a mass-spring resonance system. The volume V gives the spring. The resonator neck (slot 8) with its surface S and the length L gives the mass.

bestimmt.The resonance frequency is according to the formula

certainly.

The expression ((1 + 2Δ 1) denotes the mouth correction for the resonator neck length necessary for this application. In addition, an experimentally determined correction for the resonance frequency at higher frequencies is used, since the oscillating gas mass at the slot outlet is carried away by the high gas flow.

Claims (6)

1. Single and multi-stage axial compressor,
characterized,
that it is equipped with at least one broadband absorption resonator (7, 8). 2. Single and multi-stage axial compressor according to claim 1,
characterized,
that existing dead volumes are provided as resonator chambers (7) in the axial compressor and slots (8) which form all-round slots (8) and form the mouth of the Helmholtz resonator are arranged before or after a rotating impeller (3) for coupling the resonator chambers (7) to the gas flow. 3. Single and multi-stage axial compressor according to claim 2,
characterized,
that the slots (8) are interrupted by webs. 4. Single and multi-stage axial compressor according to the type
sayings 1 - 3,
characterized,
that additional dead volumes are coupled from the outside as resonator chambers (7). 5. Single and multi-stage axial compressor according to the type
sayings 1 - 4,
characterized,
that the walls of the resonator chambers (7) are lined with a damping material (D). 6. Single and multi-stage axial compressor according to the type
sayings 1 - 5,
characterized, that the resonance frequency of the absorption resonators (7, 8) is tuned to the pulsation frequency with the maximum amplitude or to the harmonic frequency.

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