Experimental investigation on unsteady pressure fluctuation of rotor tip region in high pressure stage of a vaneless counter-rotating turbine

Abstract

An experimental investigation has been performed to study the unsteady pressure fluctuation of rotor tip region in high pressure stage of a vaneless counter-rotating turbine. The experiment is carried out on a blow-down short duration turbine facility. The investigation indicates that the blow-down short duration turbine facility is capable of substituting continuous turbine facilities in most turbine testing. Through this experimental investigation, a distinct blade-to-blade variation is observed. The results indicate that the combined effects of vane wake, tip leakage flow, complicated wave systems and rotor wake induce the remarkable blade-to-blade variations. The results also show that the unsteady effect is intensified along the flow direction.counter-rotating turbine, pressure fluctuation, unsteady effect, short duration experimentIn the recent few years, more and more attentions have been paid to counter-rotating turbine (CRT) because it can offer some significant benefits compared with conventional two-stage turbine, such as the elevated thrust-to-weight ratio of aero-engine, the improved performance of aircraft, and so on. At present, 1-1 stage counter-rotating turbine has been used in some advanced active duty aero-engines, and vaneless counter-rotating turbine (VCRT, 1-1/2 stage counter-rotating turbine), which is composed of a highly loaded single stage high pressure turbine (HPT) and a vaneless counter-rotating single stage low pressure turbine (LPT), has been also applied in some up-to-date test engines in Euro-American developed countries. It is obvious that the VCRT will be widely adopted in real aero-engines in the future. From the 1950s, counter-rotating turbines have been carefully investigated [1][2][3][4][5][6][7][8] . Researchers focus on aerodynamic design of CRT, flow field analysis in CRT, and so on. These conclusions drawn by predecessors drive the development of the CRT technology.Some of approaches to increase efficiency or decrease loss need to be applied to enhancing specific work and reducing fuel consumption of gas turbine engines. In modern high load turbines, the loss induced by tip clearance leakage flow is remarkable. A number of investigations on tip clearance leakage flow have been performed by many researchers [9][10][11][12][13][14][15][16][17][18][19][20][21][22] to decrease the flow loss. Farokhi [9] analyzed the tip clearance loss in an axial flow turbine and proposed a model that accounts for tip pressure loading, relative wall motion and stage characteristics. A simple two-dimensional model for the calculation of the leakage flow over the blade tips of axial turbine was described in ref.[10]. In the model, the importance of pressure gradients along the blade chord was emphasized as a major factor influencing the tip leakage flow. Liu and Bozzola [11] investigated the tip clearance flow structures, leakage vortex, flow underturning, and the effect of the tip clearance on blade loading and losses by means of a three-dimensional code. The predicted