Professor Aksit, is explaining the basics of gas turbine engines in it’s simplest form.
As explained before the Turboshaft and turboprop engines convert jet propulsion to torque generation. (Hence HP ratings.)
A gas turbine engine pulls air from outside and pushes (compresses) it in to combustion chamber by compressor blades. These blades can be designed to allow axial flow of air (along the length of the engine) or radial flow of air (in a circular motion in side the engine). In a turbo shaft or turboprop engine, since you do not need jet propulsion by exhausting hot gasses, to use the radial flow system is more convenient and in some cases more efficient method of design. Plus you may not need multiple compressor sections to provide enough air flow.
A radial compressor like below will rotate air inside the engine centrifugally.
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An axial compressor like below will push air into the engine along the axis of the engine - along the length of the engine.
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All turbofan and turbojet engines, if thrust is needed must have axial flow of air. Even if some sections are radial to improve air intake, the resultant air flow has to be axial. You need as much hot axial thrust as possible, to achieve healthy jet propulsion.
TS1400 and CTS800 have radial compressors. To make TS1400 in to a turbofan, you have to change the compressor section and with it, most of the innards of the engine. Then add a fan to push more air in to the path of the axial compressors. And redesign the engine so that air bypass canals are introduced.
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So TS1400 doesn’t really become TJ1400. But may be TJ4000 or TJ4500. It will not be as powerful as a turbofan. But will have jet propulsion.