In the last decade, three-dimensional numerical simulation of gas turbine components has been studied intensely. One of the most important issues in design and analysis of gas turbine components is flow field insight, losses and instabilities prediction. These losses and instabilities include return flows, rotational stall, local shocks, surge and local and global instabilities reducing life and performance of system components, severely. On the other hand, predicting the performance characteristics of turbine and compressor without costly experimental tests is a significant advantage for gas turbine design. Hence, In the last decade with upgrade of computers, numerical study of effective parameters on the performance of turbine and compressor such as axial distance between stages, end wall contouring methods of turbine passage effects, of roughness and airfoils on losses and effects of clearance between the rotor blades and casing have been considered to be studied. Therefore, in the present study, three-dimensional numerical analysis of rotating components of a turbo-shaft engine involving 3-stage axial compressor, one-stage centrifugal compressor and one-stage high-pressure axial turbine is done for its recognition. Also, feasibility study of its promotion to a turbojet engine is done by adding a nozzle at the end of high pressure turbine. 3D Numerical analysis of flow inside the compressor and turbine is done separately by CFX software. Compressible flow equations are solved by using pressure based method with second order accuracy and SST turbulence model. Performance characteristic curves of compressor and turbine are obtained separately by changing inlet and outlet boundary conditions of the compressor and turbine. Also, internal flow field and local losses in various components are studied in design and off design conditions. Finally, by design of nozzle at the end of the motor and its numerical simulations with high-pressure turbine, possibility of changing this engine into a turbojet engine is assessed. The results of simulations show that in the first stage of axial compressor, a secondary flow is created from hub to tip because of high axial chord of rotor blade. Also, flow in this rotor is transonic. Flow in the turbine nozzle is chocked earlier than in rotor showing upstream flow of the turbine is not affected by downstream flow. Moreover, change of rotor speed does not affect in nozzle flow pattern. Also, flow chocking occurs in the nozzle hub earlier. The feasibility study for promotion of this engine to a turbo jet engine shows that change of the current engine to a turbofan engine is more suitable because of its low mass flow rate. Keywords: Numerical Simulation, Axial Compressor, Centrifugal Compressor, Axial Turbine, Performance Curve
