A compressor stall is a local disruption of the airflow in the
compressor
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
of a
gas turbine
A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directi ...
or
turbocharger
In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...
. A stall that results in the complete disruption of the airflow through the compressor is referred to as a compressor surge. The severity of the phenomenon ranges from a momentary power drop barely registered by the engine instruments to a complete loss of compression in case of a surge, requiring adjustments in the fuel flow to recover normal operation.
Compressor stall was a common problem on early jet engines with simple aerodynamics and manual or mechanical
fuel control unit
A fuel control unit is a control system for gas turbine engines.
Fundamentals of turbine engine control
Gas turbine engines are primarily controlled by the amount of fuel supplied to the combustion chambers. With this in mind we can say that, ...
s, but has been virtually eliminated by better design and the use of hydromechanical and electronic control systems such as
Full Authority Digital Engine Control
A full authority digital engine (or electronics) control (FADEC) is a system consisting of a digital computer, called an "electronic engine controller" (EEC) or "engine control unit" (ECU), and its related accessories that control all aspects of ai ...
. Modern compressors are carefully designed and controlled to avoid or limit stall within an engine's operating range.
Types
![Axial compressor](https://upload.wikimedia.org/wikipedia/commons/c/ca/Axial_compressor.gif)
There are two types of compressor stall:
Rotating stall
Rotating stall is a local disruption of
airflow within the compressor which continues to provide compressed air, but with reduced effectiveness. Rotating stall arises when a small proportion of
airfoil
An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or turbine.
...
s experience
airfoil stall, disrupting the local airflow without destabilising the compressor. The stalled airfoils create pockets of relatively stagnant air (referred to as ''stall cells'') which, rather than moving in the flow direction, rotate around the circumference of the compressor. The stall cells rotate with the rotor blades, but at 50 to 70% of their speed, affecting subsequent airfoils around the rotor as each encounters the stall cell. Propagation of the instability around the flow path annulus is driven by stall cell blockage causing an incidence spike on the adjacent blade. The adjacent blade stalls as a result of the incidence spike, thus causing stall cell "rotation" around the rotor. Stable local stalls can also occur which are axi-symmetric, covering the complete circumference of the compressor disc, but only a portion of its radial plane, with the remainder of the face of the compressor continuing to pass normal flow.
A rotational stall may be momentary, resulting from an external disturbance, or may be steady as the compressor finds a working equilibrium between stalled and unstalled areas. Local stalls substantially reduce the efficiency of the compressor and increase the structural loads on the airfoils encountering stall cells in the region affected. In many cases however, the compressor airfoils are critically loaded without capacity to absorb the disturbance to normal airflow such that the original stall cells affect neighbouring regions and the stalled region rapidly grows to become a complete compressor stall.
Axi-symmetric stall or compressor surge
Axi-symmetric stall, more commonly known as
compressor surge A compressor stall is a local disruption of the airflow in the compressor of a gas turbine or turbocharger. A stall that results in the complete disruption of the airflow through the compressor is referred to as a compressor surge. The severity of t ...
; or pressure surge, is a complete breakdown in compression resulting in a reversal of flow and the violent expulsion of previously compressed air out through the engine intake, due to the compressor's inability to continue working against the already-compressed air behind it. The compressor either experiences conditions which exceed the limit of its pressure rise capabilities or is highly loaded such that it does not have the capacity to absorb a momentary disturbance, creating a rotational stall which can propagate in less than a second to include the entire compressor.
The compressor will recover to normal flow once the
engine pressure ratio The engine pressure ratio (EPR) is the total pressure ratio across a jet engine, measured as the ratio of the total pressure at the exit of the propelling nozzle divided by the total pressure at the entry to the compressor.
Jet engines use either ...
reduces to a level at which the compressor is capable of sustaining stable airflow. If, however, the conditions that induced the stall remain, the return of stable airflow will reproduce the conditions at the time of surge and the process will repeat.
[Kerrebrock 1992, p.261.] Such a "locked-in" or self-reproducing stall is particularly dangerous, with very high levels of vibration causing accelerated engine wear and possible damage, even the total destruction of the engine through the breaking of compressor and stator vanes and their subsequent ingestion, destroying engine components downstream.
Causes
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 line on a
compressor map A compressor map is a chart which shows the performance of a turbomachinery compressor. This type of compressor is used in gas turbine engines, for supercharging reciprocating engines and for industrial processes, where it is known as a dynamic co ...
. The complete engine is designed to keep the compressor operating a small distance below the surge pressure ratio on what is known as the operating line on a compressor map. The distance between the two lines is known as the surge margin on a compressor map. Various things can occur during the operation of the engine to lower the surge pressure ratio or raise the operating pressure ratio. When the two coincide there is no longer any surge margin and a compressor stage can stall or the complete compressor can surge as explained in preceding sections.
Factors which erode compressor surge margin
The following, if severe enough, can cause stalling or surging.
*Ingestion of
foreign objects which results in damage, as well as sand and dirt erosion, can lower the surge line.
*Dirt build-up in the compressor and wear that increases compressor tip clearances or seal leakages all tend to raise the operating line.
*Complete loss of surge margin with violent surging can occur with a
bird strike
A bird strike—sometimes called birdstrike, bird ingestion (for an engine), bird hit, or bird aircraft strike hazard (BASH)—is a collision between an airborne animal (usually a bird or bat) and a moving vehicle, usually an aircraft. The term ...
. Taxiing on the ground, taking off, low level flying (military) and approaching to land all take place where bird strikes are a hazard. When a bird is ingested by a compressor the resultant blockage and airfoil damage causes compressor surging. Examples of debris on a runway or aircraft carrier flight deck that can cause damage are pieces of tire rubber, litter and nuts and bolts. A specific example is
a metal piece dropped from another plane. Runways and aircraft carrier flight decks are cleaned frequently in an attempt to preclude ingestion of foreign objects.
* Aircraft operation outside its design envelope; ''e.g.'', extreme flight manoeuvres resulting in airflow separations within the engine intake, flight in icing conditions where ice can build up in the intake or compressor, flight at excessive altitudes.
* Engine operation outside its flight manual procedures; ''e.g.'', on early jet engines abrupt throttle movements (''slam acceleration'') when pilot's notes specified slow throttle movements. The excessive over-fuelling raised the operating line until it met the surge line. (Fuel control capability extended to automatically limit the over-fuelling to prevent surging).
* Turbulent or hot airflow into the engine intake, ''e.g.'', use of
reverse thrust
Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine's thrust for it to act against the forward travel of the aircraft, providing deceleration. Thrust reverser systems are featured on many jet aircraft to ...
at low forward speed, resulting in re-ingestion of hot turbulent air or, for military aircraft, ingestion of hot exhaust gases from missile firing.
* Hot gases from gun firing which may produce inlet distortion; ''e.g.'',
Mikoyan MiG-27
The Mikoyan MiG-27 (russian: Микоян МиГ-27; NATO reporting name: Flogger-D/J) is a variable-sweep ground-attack aircraft, originally built by the Mikoyan-Gurevich design bureau in the Soviet Union and later licence-produced in Ind ...
.
Effects
![PAK FA T 50 compressor stall on MAKS 2011](https://upload.wikimedia.org/wikipedia/commons/5/58/PAK_FA_T_50_compressor_stall_on_MAKS_2011.jpg)
Compressor axially-symmetric stalls, or compressor surges, are immediately identifiable, because they produce one or more extremely loud bangs from the engine. Reports of jets of flame emanating from the engine are common during this type of compressor stall. These stalls may be accompanied by an increased exhaust gas temperature, an increase in rotor speed due to the large reduction in work done by the stalled compressor and — in the case of multi-engine aircraft —
yawing in the direction of the affected engine due to the loss of thrust.
Response and recovery
The appropriate response to compressor stalls varies according to the engine type and situation, but usually consists of immediately and steadily decreasing thrust on the affected engine. While modern engines with advanced control units can avoid many causes of stall, jet aircraft pilots must continue to take this into account when dropping airspeed or increasing throttle.
Notable stall occurrences
Aircraft development
Rolls-Royce Avon engine
The
Rolls-Royce Avon
The Rolls-Royce Avon was the first axial flow jet engine designed and produced by Rolls-Royce. Introduced in 1950, the engine went on to become one of their most successful post-World War II engine designs. It was used in a wide variety of ai ...
turbojet engine
The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and ...
was affected by repeated compressor surges early in its 1940s development which proved difficult to eliminate from the design. Such was the perceived importance and urgency of the engine that
Rolls-Royce
Rolls-Royce (always hyphenated) may refer to:
* Rolls-Royce Limited, a British manufacturer of cars and later aero engines, founded in 1906, now defunct
Automobiles
* Rolls-Royce Motor Cars, the current car manufacturing company incorporated in ...
licensed the compressor design of the
Sapphire
Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphir ...
engine from
Armstrong Siddeley
Armstrong Siddeley was a British engineering group that operated during the first half of the 20th century. It was formed in 1919 and is best known for the production of luxury vehicles and aircraft engines.
The company was created following ...
to speed development.
The engine, as redesigned, went on to power aircraft such as the
English Electric Canberra
The English Electric Canberra is a British first-generation, jet-powered medium bomber. It was developed by English Electric during the mid- to late 1940s in response to a 1944 Air Ministry requirement for a successor to the wartime de Havil ...
bomber, and the
de Havilland Comet
The de Havilland DH.106 Comet was the world's first commercial jet airliner. Developed and manufactured by de Havilland in the United Kingdom, the Comet 1 prototype first flew in 1949. It featured an aerodynamically clean design with four d ...
and
Sud Aviation Caravelle
The Sud Aviation SE 210 Caravelle is a French jet airliner produced by Sud Aviation.
It was developed by SNCASE in the early 1950s and made its maiden flight on 27 May 1955.
It included some de Havilland designs and components developed for t ...
airliners.
Olympus 593
During the 1960s development of the
Concorde
The Aérospatiale/BAC Concorde () is a retired Franco-British supersonic airliner jointly developed and manufactured by Sud Aviation (later Aérospatiale) and the British Aircraft Corporation (BAC).
Studies started in 1954, and France an ...
Supersonic Transport
A supersonic transport (SST) or a supersonic airliner is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound. To date, the only SSTs to see regular service have been Concorde and the Tupol ...
(SST) a major incident occurred when a compressor surge caused a structural failure in the intake. The hammershock which propagated forward from the compressor was of sufficient strength to cause an inlet ramp to become detached and expelled from the front of the intake. The ramp mechanism was strengthened and control laws changed to prevent a re-occurrence.
Aircraft crashes
U.S. Navy F-14 crash
A compressor stall contributed to the 1994 death of Lt.
Kara Hultgreen
Kara S. Hultgreen (October 5, 1965 – October 25, 1994) was an American naval aviator who served as a lieutenant in the United States Navy and was the first female carrier-based fighter pilot in the U.S. Navy. She was also the first female figh ...
, the first female
carrier-based United States Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
fighter pilot
A fighter pilot is a military aviator trained to engage in air-to-air combat, air-to-ground combat and sometimes electronic warfare while in the cockpit of a fighter aircraft. Fighter pilots undergo specialized training in aerial warfare and ...
. Her aircraft, a
Grumman F-14 Tomcat
The Grumman F-14 Tomcat is an American carrier-capable supersonic, twin-engine, two-seat, twin-tail, variable-sweep wing fighter aircraft. The Tomcat was developed for the United States Navy's Naval Fighter Experimental (VFX) program after the ...
, experienced a compressor stall and failure of its left engine, a
Pratt & Whitney TF30
The Pratt & Whitney TF30 (company designation JTF10A) is a military low-bypass turbofan engine originally designed by Pratt & Whitney for the subsonic F6D Missileer fleet defense fighter, but this project was cancelled. It was later adapted with ...
turbofan
The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft engine, aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the ''turbo'' portion refers to a gas turbine engine which ac ...
, due to disturbed airflow caused by Hultgreen's attempt to recover from an incorrect
final approach
In aeronautics, the final approach (also called the final leg and final approach leg) is the last leg in an aircraft's approach to landing, when the aircraft is lined up with the runway and descending for landing.Crane, Dale: ''Dictionary of ...
position by executing a
sideslip
A slip is an aerodynamic state where an aircraft is moving ''somewhat'' sideways as well as forward relative to the oncoming airflow or relative wind. In other words, for a conventional aircraft, the nose will be pointing in the opposite directio ...
; compressor stalls from excessive
yaw angle were a known deficiency of this type of engine.
Southern Airways Flight 242
The 1977 loss of
Southern Airways Flight 242
Southern Airways Flight 242 was a flight from Muscle Shoals, Alabama, to Atlanta, Georgia, with a stop in Huntsville, Alabama. On April 4, 1977, it executed a forced landing on Georgia State Route 381 in New Hope, Paulding County, Georgia, Unit ...
, a
McDonnell Douglas DC-9-9-31, while penetrating a
thunderstorm
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are someti ...
cell over
Georgia
Georgia most commonly refers to:
* Georgia (country), a country in the Caucasus region of Eurasia
* Georgia (U.S. state), a state in the Southeast United States
Georgia may also refer to:
Places
Historical states and entities
* Related to the ...
was attributed to compressor stalls brought on by ingestion of large quantities of water and
hail
Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...
. The stalls caused blades to clash with stationary vanes in both of its
Pratt & Whitney JT8D-9
The Pratt & Whitney JT8D is a low-bypass (0.96 to 1) turbofan engine introduced by Pratt & Whitney in February 1963 with the inaugural flight of the Boeing 727. It was a modification of the Pratt & Whitney J52 turbojet engine which powered th ...
turbofan engines. The stalls were so severe as to cause the destruction of the engines, leaving the flight crew with no choice but to make an
emergency landing
An emergency landing is a premature landing made by an aircraft in response to an emergency involving an imminent or ongoing threat to the safety and operation of the aircraft, or involving a sudden need for a passenger or crew on board to term ...
on a public road, killing 62 passengers and another eight people on the ground.
1997 Irkutsk Antonov An-124 crash
An
Antonov 124
The Antonov An-124 Ruslan (; russian: Антонов Ан-124 Руслан, , Ruslan; NATO reporting name: Condor) is a large, strategic airlift, four-engined aircraft that was designed in the 1980s by the Antonov design bureau in the Ukraini ...
transport plane was destroyed when it
crashed
"Crashed" is the third U.S. rock Single (music), single, (the fifth overall), from the band Daughtry (band), Daughtry's debut album. It was released only to U.S. rock stations on September 5, 2007. Upon its release the song got adds at those stat ...
immediately after takeoff from
Irkutsk-2 Airport in Russia. Three seconds after lifting off from Runway 14, at a height of about , the number 3 engine surged. Climbing away with a high
angle of attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
, engines 1 and 2 also surged, causing the aircraft to crash some past the end of the runway. It struck several houses in a residential area, killing all 23 on board, and 45 people on the ground.
Trans World Airlines Flight 159
On November 6, 1967,
TWA Flight 159, a
Boeing 707
The Boeing 707 is an American, long-range, narrow-body airliner, the first jetliner developed and produced by Boeing Commercial Airplanes.
Developed from the Boeing 367-80 prototype first flown in 1954, the initial first flew on December 20, ...
on its
takeoff roll from the then-named
Greater Cincinnati Airport
Cincinnati/Northern Kentucky International Airport is a public international airport located in Hebron, Kentucky, United States. It serves the Cincinnati tri-state area. The airport's code, CVG, is derived from the nearest city at the time of ...
, passed
Delta Air Lines
Delta Air Lines, Inc., typically referred to as Delta, is one of the major airlines of the United States and a legacy carrier. One of the List of airlines by foundation date, world's oldest airlines in operation, Delta is headquartered in Atla ...
Flight 379, a
McDonnell Douglas DC-9
The McDonnell Douglas DC-9 is an American five-abreast single-aisle aircraft designed by the Douglas Aircraft Company. It was initially produced by the developer company as the Douglas DC-9 until August 1967 and then by McDonnell Douglas.
After ...
stuck in the dirt a few feet off the
runway
According to the International Civil Aviation Organization (ICAO), a runway is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". Runways may be a man-made surface (often asphalt concrete, as ...
's edge. The first officer on the TWA aircraft heard a loud bang, now known to have been a compressor stall induced by ingestion of exhaust from Delta 379 as it was passed. Believing a collision had occurred, the copilot aborted the takeoff. Because of its speed, the aircraft overran the runway, injuring 11 of the 29 passengers, one of whom died four days later as a result of the injuries.
Scandinavian Airlines Flight 751
In December 1991
Scandinavian Airlines Flight 751
Scandinavian Airlines System Flight 751 was a regularly scheduled Scandinavian Airlines passenger flight from Stockholm, Sweden, to Warsaw, Poland, via Copenhagen, Denmark. On 27 December 1991, a McDonnell Douglas MD-81 operating the flight, r ...
, a
McDonnell Douglas MD-81
The McDonnell Douglas MD-80 is a series of five-abreast single-aisle airliners developed by McDonnell Douglas. It was produced by the developer company until August 1997 and then by Boeing Commercial Airplanes. The MD-80 was the second gene ...
on a flight from Stockholm to Copenhagen, crashed after losing both engines due to ice ingestion leading to compressor stall shortly after takeoff. Due to a newly installed auto-throttle system designed to prevent pilots reducing power during the takeoff climb, the pilot's commands to reduce power on recognising the surge were countermanded by the system, leading to engine damage and total engine failure. The airliner successfully made a forced landing in a forest clearing without loss of life.
See also
*
Axial fan design
An axial fan is a type of fan that causes gas to flow through it in an axial direction, parallel to the shaft about which the blades rotate. The flow is axial at entry and exit. The fan is designed to produce a pressure difference, and hence forc ...
*
Surge in compressors
References
The Jet Engine — Rolls-Royce plc, 1995. .
Notes
Bibliography
*Kerrebrock, Jack L. "Aircraft Engines and Gas Turbines", 2nd edition. Cambridge, Massachusetts: The MIT Press, 1992. .
External links
{{Aircraft gas turbine engine components
Aviation risks