چكيده به لاتين
In recent years, due to the design and construction of low-pressure turbine stage with lower number of blades and higher aerodynamic load distribution, this part of the gas turbine engine has been highly regarded by researchers. Hence in this thesis the effect of free stream turbulence intensity (FSTI) parameter in contrast to the two parameters Reynolds number and incidence angle on the suction surface low-pressure turbine blade were experimentally and numerically investigated. Experimental tests were made in linear cascade facility of CT2 airfoil at Reynolds number between 100000 and 250000, free turbulence intensity between 0.6% and 2.3% and incidence angle between -8 and +8 degree. The blade surface static pressure measurements using high-frequency pressure sensors to detect boundary layer transition and separation was carried out. It also uses a numerical simulation of flow around a low-pressure turbine blade beside the experimental tests, in order to investigate other dimensions of the phenomenon of separation and transition.
The results of the experimental tests has been provided in the forms of incidence angle, free stream turbulence intensity and Reynolds number effect and the numerical simulation in terms of free stream turbulence intensity and Reynolds number. Separation of boundary layer observed at all level of Reynold’s number and free stream turbulence intensity made by the wind tunnel. The high level of Reynold’s number cause transition of a boundary layer in upstream but because of the low level of FSTI, turbulent boundary layer separate at the end of the blade’s surface. In addition, free stream turbulence intensity doesn’t have positive effect on reducing the blades losses and separation of flow at two lower level of Reynold’s number but this parameter act more efficient at higher level Reynold’s number. In the other word, increasing the turbulent kinetic energy of boundary layer without increasing the enough momentum, doesn’t change the flow condition. Free turbulence intensity first reattach the separated boundary layer and then by the transition upstream of the flow, made enough energy for flow to remain attach.Generally, Pressure coefficient doesn’t change that much at all level of free stream turbulence intensity and Reynold’s number. Furthermore, increasing the incidence angle delay the transition of boundary layer. On the other side, decreasing the incidence angle reduce the risk of separation.
According to the results of numerical simulation, increasing the free turbulence intensity and Reynold’s number act in the way of reducing the separation bubble near the leading edge and fluctuation of wakes behind the blade. In addition, increasing the turbulence intensity at all levels of Reynold’s number reduce the thickness of the boundary layer.
