عنوان مقاله [English]
This article focuses mainly on a numerical study of the overall performance and flow structure in an axial turbine .In addition, the effect of a film cooling on the performance characteristics is examined. To this aim, a two-stage axial turbine is simulated using the ANSYS-CFX commercial software. Initially, to ensure the accuracy of the results, good agreement has been observed from axial turbine performance curve comparison with the experimental one. Different analyses present that the rate of blowing ratio (B.R) equal to 0.82 and the velocity ratio (V.R) equal to 0.4 with a 30 degree jet angle are appropriate for cooling holes. Because of the high importance of leading edge and coolant inject to the stagnation region, as well as increasing the temperature at the pressure side relative to the suction side, there is a higher flow rate for cooling in these areas. The study of the turbine performance curve shows a slight reduction in the pressure ratio and efficiency due to the application of cooling that can be compensated by the possibility of increasing the inlet temperature. The streamlines around the blade has provided a layer of flow with low temperature, which is an obstacle between the hot flow and the blade surface. The application of cooling reduces the temperature of the pressure and suction surface of the blade at about 300° C and the temperature of the front surface of the blade is about 200°. Investigating the radial and axial variation of the thermodynamic parameters indicates that by applying the cooling, the mach number and total temperature of the flow at inlet and outlet are reduced and the pressure drop increased. These results require the use of suitable conditions for discharge, cooling velocity and temperature of the fluid.