What is the benefit of the spiraled shape? More efficient? If so how come…also why not have an impeller inside a straight tube?
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The shape you are referring to is called a centrifugal compressor / turbine. The spiral shape helps extract energy from the airflow the entire time as it turns towards the center (and the opposite for the compressor). This design is effective for the pressure ratios required by a vehicle, and are very space efficient.
The “impellers in a straight tube” is kind of the idea behind an axial compressor / turbine commonly found in gas turbine engines (like those on aircraft). Axial compressors require a set of rotating blades, followed by a set of stationary blades. The rotor blades extract energy to the flow and send it rotating, and the stator blades turn the flow back to flowing axially. Axial compressors / turbines usually require a few stages of rotors and stators in a row to efficiently function. Therefore, they tend to be a lot longer, and therefore require more space. This space is available in an aircraft engine nacelle, where a long tube is also aerodynamically efficient, but less possible when squeezed in amongst an internal combustion engine. Axial compressors tend to operate more efficiently when higher pressure ratios are required. Cars don’t require the high compression ratios that aircraft do
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