stall and surge of axial compressor

7/23/2019 Stall and Surge of Axial Compressor

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Turbo Machinery Theory Muhammad Ammar

Assignment # 04 04-6-1-013-2014 (ME-13)

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Compressor Surge and Stall

A compressor stall is a local disruption of the airflow whereas complete disruption of the flow

through the compressor is called compressor surge.

There are two types of compressor stall

Rotating stall

Axi-symmetric stall or compressor surge

Rotating stall

It is the local disruption of airflow within the compressor. Although it continues to provide

compressed air but with reduced efficiency. Rotating stall, also called propagating stall, occurs

when large stall zones, or patches, cover several blade passages and propagate in the direction of

rotation. The stalled airfoils create pockets of relatively stagnant air which rotate around the

circumference of the compressor rather than moving in the flow direction. The Rotating stall can

lead to increase vibratory stresses and cause blade resonance.

Figure 1: Model illustrating mechanism of stall cell propagation

Considering a portion of a blade row, as illustrated in Figure 1 to be affected by a stall patch. This

patch must cause a partial obstruction to the flow which is deflected on both sides of it. Thus, the

incidence of the flow onto the blades on the right of the stall cell is reduced, but the incidence to

the left is increased. As these blades are already close to stalling, the net effect is for the stall patch

to move to the left, the motion is then self-sustaining.


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Assignment # 04 04-6-1-013-2014 (ME-13)

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Compressor Surge

Compressor surge has been the root cause of several compressor blade failures. If prolonged surge

occurs, the blades can be severely damaged because of the excitation caused by flow reversals.

Further and rapid speed changes can occur as the unit is loaded and unloaded. When a compressor

goes into surge the effects are usually quite dramatic. Generally, an increase in noise level is

experienced, indicative of a pulsation of the air flow and of mechanical vibration.A typical axial

compressor map is shown below which determines the operation of axial compressor.

Figure 2: Axial Compressor Surge Map

A compressor will only pump air in a stable manner up to a certain pressure ratio. Beyond this

value the flow will break down and become unstable. This occurs at what is known as the surge


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Assignment # 04 04-6-1-013-2014 (ME-13)

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line on acompressor map.The term stall margin is often used to describe the relative position of

the operating line and the surge line.

Surge can be caused by:

Movement of operating line to the left (towards the surge line). Typical causes are over

temperature, turbine nozzle blockage, and excessive back pressure.

Movement of surge line itself to the left, narrowing the gap between surge and operating

line. This could be caused by excessive compressor fouling, dirt, plugged air filters or

erosion. The erosion of blades can affect boundary layer development and increase the

tendency of flow separation on the blade surfaces.

Movement of both surge and operating line reducing the stall margin.
https://en.wikipedia.org/wiki/Compressor_maphttps://en.wikipedia.org/wiki/Compressor_map

stall and surge of axial compressor

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