چكيده به لاتين
Increasing the efficiency of gas turbine engines has always been one of the important issues for designers and users of these engines, which is directly related to the reduction of aerodynamic losses generated inside the engines. In the present study, in order to control the tip leakage flow as one of the effective factors in reducing the efficiency, the passive control of the optimization of the tip geometry has been used by replacing the plane tip of the blade with winglet and winglet-Squealer. For this purpose, the variation of Winglet width and Reynolds numbers are studied experimentally and numerically. Experimental tests were made in linear cascade of CT2 airfoils in aerodynamic and compressible turbo machines lab, in the Reynolds numbers 100k, 120k and 140k for a w/p= 2.64%,5.28%,7.92%. The measurement of the static pressure on the surface of the blade in 50%, 75% and 90% sections of span was carried out to investigate the changes in the blade load and on the end wall at the tip of the blade to investigate the local effects of the leakage flow on the tip. Also in numerical solution, using computational fluid dynamics software, the effects of the chosen optimization method on the tip leakage flow, when combined with the main flow in the downstream have been examined.
The results are presented in the experimental section by examining the static pressure coefficients in the middle of the span and at 90% of the span, the pressure contours in the pressure and suction side of the blade and the end wall by examining the effects of increasing the width of the Winglet in different Reynolds numbers. Winglet increases the loading considerably at the suction side by delaying the separation of the tip leakage flow and at the pressure side by decreasing the tip leakage flow rate. Delaying the separation also significantly reduces the destructive effects of oscillatory loading performed by the tip leakage vortex. Also, this type of geometry in the optimal width to pitch ratio reduces the tip leakage flow considerably and creates a uniform flow on the tip.
In the end, the effects of the winglet-squealer are studied in the same way. The main effect of the squealer is in the tip region of the blade. This kind of geometry, by creating a gap on the tip, traps the tip flow and causes a sharp decrease the tip flow velocity. Combining this kind of geometry with the Winglet will increase the efficiency of the turbo-machine performance.
Numerical simulations have also confirmed the empirical results, and, in addition, the Winglet and winglet- squealer operation are not specific to the tip leakage flow and have significant effects on reducing the effects of passive vortices.
