This means that if the exit velocity is maintained at a higher value than free stream velocity, and simultaneously, the engine flow rate (m dot) is kept as high as possible, the high engine flow will produce a high thrust in a turboprop engine. Even though a large amount of air is ingested, the change in velocity is very minimal between the intake and the exit so that the exit velocity is at a low value (Low exit velocity). Due to the large value of m dot, a high thrust is developed.
If we denote the free stream conditions by “0”, the propeller exit conditions by “1”, core exit conditions by “e” and core entrance conditions by “c”, then from the basic thrust equation we get:
In Turboprop engine, the mass flow rate through the propeller is much greater than that of core engine(High mass flow ). The mass flow rate entering the core is almost equal to the mass flow rate exiting the core. The exit velocity from the core is almost the same as inlet velocity into the core(Low exit velocity). Hence the thrust equation can be rounded off to get:
Components and Purpose: The intake also called the inlet serves three purposes, namely (1) recovering as much of the total pressure of the free air stream required for combustion, from free-stream conditions to the conditions and deliver this pressure to the entrance of fan or compressor, (2) delivering air to the compressor under all flight conditions with minimum turbulence and (3) to have minimum drag. The inlet is generally not defined by any particular part, but is formed by structural support parts which are located in front of compressor. The design of subsonic inlet differs from that of supersonic inlet. In subsonic inlets of engines fitted in nacelles air enters in different streamline patterns at different speeds of operation as shown in Fig-1 (Mattingly,p759).
Supersonic inlets are