- #1
ank_gl
- 741
- 0
Hi
I have been trying to figure out the force experienced by individual components of a gas turbine engine.
Generally, the thrust of the engine is defined / calculated as the change in the momentum of the fluid. Usual formula is mass flow X (C_jet - C_intake) + the pressure difference in case the nozzle is under/over expanded.
What I am interested to know is, how is this thrust transferred to the engine mounts? The only way the fluid can interact with the hardware is through pressure (& shear, but let’s forget it here). I reckon if pressure is integrated all over the surface of the engine, we should get the thrust value.
Now let’s go through various parts of the engine(let’s assume a single spool turbojet):
1. Intake
More or less, the intake is cylindrical, so the pressure integral will not have any large component in the axial direction. If compressor is supported on 2 bearings, front bearing housing (covered by nose cone) will be pushed backwards, ie it is a dragging component.
2. Compressor
Compressor rotor blades can be thought of as being airfoils. Lift & drag produced by the airfoil can be thought as being equivalent to forward force & torque (strictly force about the shaft) requirement respectively. This forward force is transferred to the shaft, to the bearings, to the casing & to the engine mounts.
Similarly, compressor stator blades due to their orientation will also experience a forward force & counter torque.
3. Combustion Chamber
Due to the geometry of the combustion chamber, it also is a dragging component.
4. Turbine
Similar to the compressor rotor & stator blades, turbine blades will experience backward force; turbine is also a dragging component.
Exhaust cone though experiences force in forward direction.
5. Jet pipe & nozzle
Owing to their shape & continuously decreasing pressure, jet pipe does not contribute to any force and pressure distribution on the nozzle pushes it backwards.
From these considerations, only major component which pushes the engine forward is the compressor. Rest all are dragging components. Turns out that gas ‘turbine’ engine is more of a misnomer, compression propulsion system would be a better choice it seems. Turbine is merely driving the compressor. So the question is, what exactly is the nozzle doing?
From the control volume point of view, formula relating change in momentum to the net force makes perfect sense, but how is that force transferred to the engine mounts?
Regards,
Ankit
I have been trying to figure out the force experienced by individual components of a gas turbine engine.
Generally, the thrust of the engine is defined / calculated as the change in the momentum of the fluid. Usual formula is mass flow X (C_jet - C_intake) + the pressure difference in case the nozzle is under/over expanded.
What I am interested to know is, how is this thrust transferred to the engine mounts? The only way the fluid can interact with the hardware is through pressure (& shear, but let’s forget it here). I reckon if pressure is integrated all over the surface of the engine, we should get the thrust value.
Now let’s go through various parts of the engine(let’s assume a single spool turbojet):
1. Intake
More or less, the intake is cylindrical, so the pressure integral will not have any large component in the axial direction. If compressor is supported on 2 bearings, front bearing housing (covered by nose cone) will be pushed backwards, ie it is a dragging component.
2. Compressor
Compressor rotor blades can be thought of as being airfoils. Lift & drag produced by the airfoil can be thought as being equivalent to forward force & torque (strictly force about the shaft) requirement respectively. This forward force is transferred to the shaft, to the bearings, to the casing & to the engine mounts.
Similarly, compressor stator blades due to their orientation will also experience a forward force & counter torque.
3. Combustion Chamber
Due to the geometry of the combustion chamber, it also is a dragging component.
4. Turbine
Similar to the compressor rotor & stator blades, turbine blades will experience backward force; turbine is also a dragging component.
Exhaust cone though experiences force in forward direction.
5. Jet pipe & nozzle
Owing to their shape & continuously decreasing pressure, jet pipe does not contribute to any force and pressure distribution on the nozzle pushes it backwards.
From these considerations, only major component which pushes the engine forward is the compressor. Rest all are dragging components. Turns out that gas ‘turbine’ engine is more of a misnomer, compression propulsion system would be a better choice it seems. Turbine is merely driving the compressor. So the question is, what exactly is the nozzle doing?
From the control volume point of view, formula relating change in momentum to the net force makes perfect sense, but how is that force transferred to the engine mounts?
Regards,
Ankit