Turbopump
Encyclopedia
A turbopump is a gas turbine
that comprises basically two main components: a rotodynamic pump
and a driving turbine
, usually both mounted on the same shaft, or sometimes geared together. The purpose of a turbopump is to produce a high pressure fluid for feeding a combustion chamber
or other use.
A turbopump can comprise one of two types of pump
s: centrifugal pump
, where the pumping is done by throwing fluid outward at high speed; or axial flow pump
, where alternating rotating and static blades progressively raise the pressure of a fluid.
Axial flow pumps have small diameters, but give relatively modest pressure increases, and multiple compression stages are needed, but work well with low density fluids. Centrifugal pump
s are far more powerful for high density fluids, but require physically large diameters for low density fluids.
Turbopumps operate in much the same way as turbo units for vehicles. Higher fuel pressures allow fuel to be supplied to higher-pressure combustion chambers for higher performance engines.
. In mid-1935 Wernher von Braun
initiated a fuel pump project at the southwest German firm Klein, Schanzlin & Becker that was experienced in building large fire-fighting pumps. The V-2 rocket
design used hydrogen peroxide decomposed through a Walther steam generator
to power the uncontrolled turbopump produced at the Heinkel plant at Jenbach
, so V-2 turbopumps and combustion chamber were tested and matched to prevent the pump from overpressurizing the chamber. The first engine fired successfully in September, and on August 16, 1942, a trial rocket stopped in mid-air and crashed
due to a failure in the turbopump. The first successful V-2 launch was on October 3, 1942.
was George Bosco. During the second half of 1947, Bosco and his group learned about the pump work of others and made preliminary design studies. Aerojet representatives visited Ohio State University
where Florant was working on hydrogen pumps, and consulted Dietrich Singelmann, a German pump expert at Wright Field. Bosco subsequently used Singelmann's data in designing Aerojet's first hydrogen pump.
By mid-1948, Aerojet had selected centrifugal pumps for both liquid hydrogen
and liquid oxygen
. They obtained some German radial-vane pumps from the Navy and tested them during the second half of the year.
By the end of 1948, Aerojet had designed, built, and tested a liquid hydrogen pump (15 cm diameter). Initially, it used ball bearing
s that were run clean and dry, because the low temperature made conventional lubrication impractical. The pump was first operated at low speeds to allow its parts to cool down to operating temperature
. When temperature gauges showed that liquid hydrogen had reached the pump, an attempt was made to accelerate from 5000 to 35 000 revolutions per minute. The pump failed and examination of the pieces pointed to a failure of the bearing, as well as the impeller
. After some testing, super-precision bearings, lubricated by oil that was atomized and directed by a stream of gaseous nitrogen, were used. On the next run, the bearings worked satisfactorily but the stresses were too great for the brazed impeller and it flew apart. A new one was made by milling from a solid block of aluminum. Time was running out, as the contract had less than six months to go. The next two runs with the new pump were a great disappointment; the instruments showed no significant flow or pressure rise. The problem was traced to the exit diffuser
of the pump, which was too small and insufficiently cooled during the cool-down cycle so that it limited the flow. This was corrected by adding vent holes in the pump housing; the vents were opened during cool down and closed when the pump was cold. With this fix, two additional runs were made in March 1949 and both were successful. Flow rate and pressure were found to be in approximate agreement with theoretical predictions. The maximum pressure was 26 atmospheres and the flow was 0.25 kilogram per second.
Today the Space Shuttle
Main Engine's turbopumps spin at over 30,000 rpm, delivering 150 lb (38 kg) of liquid oxygen and 896 lb (406 kg) of liquid hydrogen to the engine per second.
Most turbopumps are centrifugal - the fluid enters the pump near the axis and the rotor accelerates the fluid to high speed. The fluid then passes through a diffuser which is a progressively enlarging pipe, which permits recovery of the dynamic pressure. The diffuser turns the high kinetic energy into high pressures (hundreds of bar
is not uncommon), and if the outlet backpressure is not too high, high flow rates can be achieved.
Axial turbopumps also exist - in this case the axle essentially has propellers attached to the shaft and the fluid is forced by these parallel with the main axis of the pump. Generally, axial pumps tend to give much lower pressures than centrifugal pumps, and a few bar is not uncommon. They are however still useful - axial pumps are commonly used as 'inducers' for centrifugal pumps, which raise the inlet pressure of the centrifugal pump enough to prevent excessive cavitation
from occurring therein.
ry this is a severe problem. Turbopumps in rockets are important and problematic enough that launch vehicles using one have been caustically described as a 'turbopump with a rocket attached'- up to 55% of the total cost has been ascribed to this area.
Common problems include:
In addition, the precise shape of the rotor itself is critical.
-powered turbopumps do exist and are employed when there is a source of steam, e.g. the boiler
s of steam ships. Gas turbine
s are usually used when electricity or steam is not available and place or weight restrictions permit the use of more-efficient sources of mechanical energy.
One of such cases are rocket engines
which need to pump fuel
and oxidizer into their combustion chamber
. This is necessary for large liquid rocket
s, since forcing the fluids or gases to flow by simple pressurizing of the tanks is often not feasible; the high pressure needed for the required flow rates would need strong and heavy tanks.
Ramjet
motors are also usually fitted with turbopumps, the turbine being driven either directly by external freestream ram air or internally by airflow diverted from combustor entry. In both cases the turbine exhaust stream is dumped overboard.
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....
that comprises basically two main components: a rotodynamic pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
and a driving turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
, usually both mounted on the same shaft, or sometimes geared together. The purpose of a turbopump is to produce a high pressure fluid for feeding a combustion chamber
Combustion chamber
A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...
or other use.
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
s: centrifugal pump
Centrifugal pump
A centrifugal pump is a rotodynamic pump that uses a rotating impeller to create flow by the addition of energy to a fluid. Centrifugal pumps are commonly used to move liquids through piping...
, where the pumping is done by throwing fluid outward at high speed; or axial flow pump
Axial flow pump
An axial flow pump, or AFP, is a common type of pump that essentially consists of a propeller in a pipe. The propeller can be driven directly by a sealed motor in the pipe or mounted to the pipe from the outside or by a right-angle drive shaft that pierces the pipe.The main advantage of an AFP is...
, where alternating rotating and static blades progressively raise the pressure of a fluid.
Axial flow pumps have small diameters, but give relatively modest pressure increases, and multiple compression stages are needed, but work well with low density fluids. Centrifugal pump
Centrifugal pump
A centrifugal pump is a rotodynamic pump that uses a rotating impeller to create flow by the addition of energy to a fluid. Centrifugal pumps are commonly used to move liquids through piping...
s are far more powerful for high density fluids, but require physically large diameters for low density fluids.
Turbopumps operate in much the same way as turbo units for vehicles. Higher fuel pressures allow fuel to be supplied to higher-pressure combustion chambers for higher performance engines.
History
Early development
High-pressure pumps for larger missiles had been discussed by rocket pioneers such as Hermann OberthHermann Oberth
Hermann Julius Oberth was an Austro-Hungarian-born German physicist and engineer. He is considered one of the founding fathers of rocketry and astronautics.- Early life :...
. In mid-1935 Wernher von Braun
Wernher von Braun
Wernher Magnus Maximilian, Freiherr von Braun was a German rocket scientist, aerospace engineer, space architect, and one of the leading figures in the development of rocket technology in Nazi Germany during World War II and in the United States after that.A former member of the Nazi party,...
initiated a fuel pump project at the southwest German firm Klein, Schanzlin & Becker that was experienced in building large fire-fighting pumps. The V-2 rocket
V-2 rocket
The V-2 rocket , technical name Aggregat-4 , was a ballistic missile that was developed at the beginning of the Second World War in Germany, specifically targeted at London and later Antwerp. The liquid-propellant rocket was the world's first long-range combat-ballistic missile and first known...
design used hydrogen peroxide decomposed through a Walther steam generator
Hellmuth Walter
Hellmuth Walter was a German engineer who pioneered research into rocket engines and gas turbines...
to power the uncontrolled turbopump produced at the Heinkel plant at Jenbach
Jenbach
Jenbach is a municipality with 6897 inhabitants in the district of Schwaz in Tyrol, Austria. Many inhabitants of Jenbach believe that the name "Jenbach" is derived from "Jenseits des Baches", which means "Beyond the brook", however earlier versions of the name, for instance "Umbach" give hint that...
, so V-2 turbopumps and combustion chamber were tested and matched to prevent the pump from overpressurizing the chamber. The first engine fired successfully in September, and on August 16, 1942, a trial rocket stopped in mid-air and crashed
Test Stand VII
Test Stand VII was the principal V-2 rocket testing facility at Peenemünde Airfield and was capable of static firing of rocket motors up to 200 tons thrust...
due to a failure in the turbopump. The first successful V-2 launch was on October 3, 1942.
Development from 1947 to 1949
The principal engineer for turbopump development at AerojetAerojet
Aerojet is an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California with divisions in Redmond, Washington, Orange, Gainesville and Camden, Arkansas. Aerojet is owned by GenCorp. They are the only US propulsion company that provides both solid rocket...
was George Bosco. During the second half of 1947, Bosco and his group learned about the pump work of others and made preliminary design studies. Aerojet representatives visited Ohio State University
Ohio State University
The Ohio State University, commonly referred to as Ohio State, is a public research university located in Columbus, Ohio. It was originally founded in 1870 as a land-grant university and is currently the third largest university campus in the United States...
where Florant was working on hydrogen pumps, and consulted Dietrich Singelmann, a German pump expert at Wright Field. Bosco subsequently used Singelmann's data in designing Aerojet's first hydrogen pump.
By mid-1948, Aerojet had selected centrifugal pumps for both liquid hydrogen
Liquid hydrogen
Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...
and liquid oxygen
Liquid oxygen
Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...
. They obtained some German radial-vane pumps from the Navy and tested them during the second half of the year.
By the end of 1948, Aerojet had designed, built, and tested a liquid hydrogen pump (15 cm diameter). Initially, it used ball bearing
Ball bearing
A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races.The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit...
s that were run clean and dry, because the low temperature made conventional lubrication impractical. The pump was first operated at low speeds to allow its parts to cool down to operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
. When temperature gauges showed that liquid hydrogen had reached the pump, an attempt was made to accelerate from 5000 to 35 000 revolutions per minute. The pump failed and examination of the pieces pointed to a failure of the bearing, as well as the impeller
Impeller
An impeller is a rotor inside a tube or conduit used to increase the pressure and flow of a fluid.- Impellers in pumps :...
. After some testing, super-precision bearings, lubricated by oil that was atomized and directed by a stream of gaseous nitrogen, were used. On the next run, the bearings worked satisfactorily but the stresses were too great for the brazed impeller and it flew apart. A new one was made by milling from a solid block of aluminum. Time was running out, as the contract had less than six months to go. The next two runs with the new pump were a great disappointment; the instruments showed no significant flow or pressure rise. The problem was traced to the exit diffuser
Diffuser
Diffuser can refer to any device that diffuses in some manner such as:* In aerodynamics** Diffuser , a shaped section of a car's underbody which improves the car's aerodynamic properties** divergent part of the flute...
of the pump, which was too small and insufficiently cooled during the cool-down cycle so that it limited the flow. This was corrected by adding vent holes in the pump housing; the vents were opened during cool down and closed when the pump was cold. With this fix, two additional runs were made in March 1949 and both were successful. Flow rate and pressure were found to be in approximate agreement with theoretical predictions. The maximum pressure was 26 atmospheres and the flow was 0.25 kilogram per second.
Today the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
Main Engine's turbopumps spin at over 30,000 rpm, delivering 150 lb (38 kg) of liquid oxygen and 896 lb (406 kg) of liquid hydrogen to the engine per second.
Centrifugal turbopumps
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
is not uncommon), and if the outlet backpressure is not too high, high flow rates can be achieved.
Axial turbopumps
Cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...
from occurring therein.
Complexities of centrifugal turbopumps
Turbopumps have a reputation for being extremely hard to design to get optimum performance. Whereas a well-engineered and debugged pump can manage 70-90% efficiency, figures less than half that are not uncommon. Low efficiency may be acceptable in some applications, but in rocketRocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
ry this is a severe problem. Turbopumps in rockets are important and problematic enough that launch vehicles using one have been caustically described as a 'turbopump with a rocket attached'- up to 55% of the total cost has been ascribed to this area.
Common problems include:
- excessive flow from the high pressure rim back to the low pressure inlet along the gap between the casing of the pump and the rotor
- excessive recirculation of the fluid at inlet
- excessive vortexVortexA vortex is a spinning, often turbulent,flow of fluid. Any spiral motion with closed streamlines is vortex flow. The motion of the fluid swirling rapidly around a center is called a vortex...
ing of the fluid as it leaves the casing of the pump - damaging cavitationCavitationCavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...
to impeller blade surfaces in low (fluid) pressure zones
In addition, the precise shape of the rotor itself is critical.
Driving Turbopumps
Steam turbineSteam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
-powered turbopumps do exist and are employed when there is a source of steam, e.g. the boiler
Boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
s of steam ships. Gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....
s are usually used when electricity or steam is not available and place or weight restrictions permit the use of more-efficient sources of mechanical energy.
One of such cases are rocket engines
Spacecraft propulsion
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...
which need to pump fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
and oxidizer into their combustion chamber
Combustion chamber
A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...
. This is necessary for large liquid rocket
Liquid rocket
A liquid-propellant rocket or a liquid rocket is a rocket engine that uses propellants in liquid form. Liquids are desirable because their reasonably high density allows the volume of the propellant tanks to be relatively low, and it is possible to use lightweight pumps to pump the propellant from...
s, since forcing the fluids or gases to flow by simple pressurizing of the tanks is often not feasible; the high pressure needed for the required flow rates would need strong and heavy tanks.
Ramjet
Ramjet
A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill...
motors are also usually fitted with turbopumps, the turbine being driven either directly by external freestream ram air or internally by airflow diverted from combustor entry. In both cases the turbine exhaust stream is dumped overboard.
See also
- TurboexpanderTurboexpanderA turboexpander, also referred to as a turbo-expander or an expansion turbine, is a centrifugal or axial flow turbine through which a high pressure gas is expanded to produce work that is often used to drive a compressor....
- Gas-generator cycleGas-generator cycle (rocket)The gas generator cycle is a power cycle of a bipropellant rocket engine. Some of the propellant is burned in a gas-generator and the resulting hot gas is used to power the engine's pumps. The gas is then exhausted...
- Staged combustion cycleStaged combustion cycle (rocket)The staged combustion cycle, also called topping cycle or pre-burner cycle, is a thermodynamic cycle of bipropellant rocket engines. Some of the propellant is burned in a pre-burner and the resulting hot gas is used to power the engine's turbines and pumps...
- Expander cycleExpander cycle (rocket)The expander cycle is a power cycle of a bipropellant rocket engine meant to improve the efficiency of fuel delivery.In an expander cycle, the fuel is heated before it is combusted, usually with waste heat from the main combustion chamber. As the liquid fuel passes through coolant passages in the...
External links
- Book of Rocket Propulsion
- Turbopumps for Liquid Rocket Engines – From RocketdyneRocketdyneRocketdyne was a Rocket engine design and production company headquartered in Canoga Park, California, United States. The company was related to North American Aviation for most of its history. NAA merged with Rockwell International, which was then bought by Boeing in December, 1996...
's Engineering Journal of Power Technology