CHAPTER 2. ENGINE COMPRESSOR

2.1. PURPOSE AND DESIGN.

The compressor is used to compress the air and supply it to the combustion chamber.

It is an axial-flow, 12-stage compressor with variable geometry vanes of the inlet guide vane assembly and of the guide vane assembly (stage I-IV), with two air bypass valves. At the max rating compression ratio equals 9,55. Air consumption equals 8,6 kg per second.

The compressor (fig. 2.1, 2.4) comprises an inlet guide vane assembly 3, casings 7, rotor 13, rotor support bearings 5, 11. The compressor stator consists of a casing (4 ring-shaped components), guide vane assembly (12 in number) and a straightening assembly. After the VII stage of the casing there are some radial openings covered with an annular air duct. Two air discharge valves are installed on thisduct. (they are open until n_TC = 84-87%).

There are some flanges on the casing:

The flanges located on the right side are used for visual inspection of the vanes of the VII and VIII stages of the rotor. They are also used for air bleeding from the VII stage, for cooling the free turbine and pressurizing support III and for air supply for other helicopter needs as well.

The flanges located on the left side are used for air bleed from the V stage for pressurizing supports I, IV and V.

The guide vane assemblies are used to slow down the air stream and to increase its pressure and temperature. The vanes of stage I-IV are variable.

The straightening assembly 9 is a load-carrying element. It is essentially a casing where the vanes of the guide vane assembly of the XII stage and vanes of the straightening assembly are installed between 2 rings. The body of the II support is connected to the inner ring of the straightening assembly.

The rotor 13 of disk-drum shape is used to transmit mechanical energy from the turbine to the air stream and to convert it into a pressure, thermal and kinetic energy. The rotor comprises the following parts:

- a disk of the I support;

- a drum welded of separated disk;

- a rear joint;

- operating vanes;

- an inner case.

The front joint is manufactured together with the disc of the II^nd stage and the rear one is attached to the disc of the IX stage by means of the bolts. The vanes are installed in the slots of “dove tail” kind. The labyrinth sailings are fixed in front of and behind the rotor. Inside the joint there are splines for their connection to the drive.

The inlet guide vane assembly 3 is used for smooth entering of air into the compressor. It is essentially a row of hollow variable vanes (30 in number), which are installed in the casing of the I support before the rotor and are cooled with the air supplied by the de-icing system.

The vanes are turned automatically depending on the engine rating and flight conditions.

The rotor supports are used to take up the loads and to transmit them from the rotor to the engine body. I support (see suppl. fig. 4.6) consists of a body, a roller bearing, a graphite seal and a damper. The support is supercharged with air bled from the V stage of the compressor. Oil is supplied to the support through an oil filter and a drive box. Oil is scavenged by gravity and by means of 2 stages of the oil pump directly to the oil tank. The body of the support is used for the following:

1. For attachment of the engine elements: a accessory drive, a fuel filter 8Д2, an actuating mechanism (ИМ-3А), which is designed to shut down the engine if free turbine RPM = 118 ± 2%, oil pump (МА-78), a pipe union of the de-icing system, an oil pressure gauge (ИД-8), a pipe union of air supply from the V stage, engine mounts to the helicopter, a vibration detector (МВ-03).

2. For formation of the inlet duct (between the cowlings and 4 struts),

3. For arrangement of the central drive (on MA-78 oil pump and drive box).

Опора II (см. прилож. рис. 4.6) состоит из корпуса опоры, шарикоподшипника и узла графитового уплотнения. Опора наддувается из-за ХII ступени компрессора.

Сброс воздуха из опоры – по двум трубкам (для снижения осевого усилия на подшипник). Подвод масла к опоре – от маслоагрегата отдельной трубкой. Откачка масла – отдельным маслоотводом через маслоагрегат и маслорадиатор.

Рис. 2.1. Компрессор двигателя:

1 – профилированный обтекатель; 2 – корпус І опоры; 3 – ВНА; 4 – рабочая лопатка І ступени;

5 – роликовый подшипник І опоры; 6, 12 – уплотнение; 7 – корпус; 8 – лабиринт; 9 – выходной спрямляющий аппарат; 10 – корпус ІІ опоры; 11 – шариковый подшипник ІІ опоры; 13 – ротор.

2.2. РАБОТА КОМПРЕССОРА

Принцип работы компрессора основан на повышении давления воздуха при его движении по системе расширяющихся каналов образованных лопатками РК и НА. В каналах лопаток рабочего колеса происходит повышение P, t, С вследствие подвода механической энергии от турбины. В каналах лопаток НА происходит повышение P и t вследствие уменьшения скорости воздушного потока С.

Рис. 2.2. Работа ступени компрессора:

а – схема ступени компрессора;

б – сечение лопаток рабочего колеса и направляющего аппарата.

Support II (see suppl. 4.6) consists of a body, a ball bearing and a graphite seal. The support is supercharged with the air supplied from the XII stage of the compressor.

The air is discharged from the support through 2 pipes (in order to decrease axial force on the bearing). The oil delivered to the support from the oil pump through a separate pipe. The oil is scavenged by means of a separate oil pipeline.

Fig. 2.1. Engine compressor:

1 – front cover; 2 – I support casing; 3 – inlet guide assembly vanes; 4 – I stage operating vane;

5 – I support roller bearing; 6, 12 – seal; 7 – body; 8 – labyrinth; 9 – straightening assembly; 10 – II support casing; 11 – II support ball bearing; 13 – rotor.

2.2. COMPRESSOR OPERATION

The compressor operation is based on the idea of air pressure increase, while it moves through the system of divergent channels between the compressor rotor vanes and inlet guide vanes. In the channels of compressor rotor P, t, С are increased due to the turbine mechanic power supply. In the channels between inlet guide vanes P and t are increase due to the decrease of airflow speed С.

Fig. 2.2. Compressor stage operation diagram:

a – compressor stage and air parameters change diagram;

cross section of operating ring vanes and guide vane assembly, airflow speed triangules.

Рис. 2.3. Схема обтекания рабочих лопаток воздушным потоком:

а – расчетный режим работы;

б – при уменьшенном G_в;

в – при увеличенном G_в.

2.3. ВОЗМОЖНЫЕ НЕИСПРАВНОСТИ

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