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What do you think of this?. I was a brainwave when I sat on the toilet 
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A typical jet engine compresses the air when it comes into the compressor, burns it with fuel, and expands it in the turbine. Approximating there is no difference of static pressure between the entrance and the nozzle, and neglecting the mass flow of fuel, the integral momentum equation yields:
F=\frac{dm_a}{dt}(U_2-U_1)
is the force applied to the engine structure.
2=flow conditions behind of the engine
1=flow conditions in front of the engine.
Watching the Turbomachinery equations, one can guess that a compressor accelerates the absolute flow: the blades acts on compressing the relative flow, increasing the static and total pressure, decreasing relative velocity to the blade, and increasing the absolute velocity respect to the stator. We can say that behind the compressor the velocity is the largest (but it will have a lot of swirl). By contrast, the turbine deccelerates the flow, but it provides the energy of rotation to the compressor. So that, we are paying a lost of velocity to gain efficiency on the consumption of energy.
The question is: remove only the turbine and put around the compressor fairing a larger fan coaxially (I mean, like the turbofan engines). In flight conditions, the external fan will provide energy to the compressor. Additionally, the combustion chamber will provide with more enthalpy to the flow. So that we have a maximum U_2, without losts of velocity in the turbine.
What do you think?.
.A typical jet engine compresses the air when it comes into the compressor, burns it with fuel, and expands it in the turbine. Approximating there is no difference of static pressure between the entrance and the nozzle, and neglecting the mass flow of fuel, the integral momentum equation yields:
F=\frac{dm_a}{dt}(U_2-U_1)
is the force applied to the engine structure.
2=flow conditions behind of the engine
1=flow conditions in front of the engine.
Watching the Turbomachinery equations, one can guess that a compressor accelerates the absolute flow: the blades acts on compressing the relative flow, increasing the static and total pressure, decreasing relative velocity to the blade, and increasing the absolute velocity respect to the stator. We can say that behind the compressor the velocity is the largest (but it will have a lot of swirl). By contrast, the turbine deccelerates the flow, but it provides the energy of rotation to the compressor. So that, we are paying a lost of velocity to gain efficiency on the consumption of energy.
The question is: remove only the turbine and put around the compressor fairing a larger fan coaxially (I mean, like the turbofan engines). In flight conditions, the external fan will provide energy to the compressor. Additionally, the combustion chamber will provide with more enthalpy to the flow. So that we have a maximum U_2, without losts of velocity in the turbine.
What do you think?.
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