Abstract
The results of recent studies have shown that combustor exit temperature distortion can cause excessive heat load of high-pressure turbine (HPT) rotor blades. The heating of HPT rotor blades can lead to thermal fatigue and degrade turbine performance. In order to explore the influence of hot streak temperature ratio on the temperature distributions of HPT airfoil surface, three-dimensional multiblade row unsteady Navier-Stokes simulations have been performed in a vaneless counter-rotating turbine (VCRT). The hot streak temperature ratios from 1.0 (without hot streak) to 2.4 were used in these numerical simulations, including 1.0, 1.2, 1.6, 2.0, and 2.4 temperature ratios. The hot streak is circular in shape with a diameter equal to 25%of the span. The center of the hot streak is located at 50%of span and 0%of pitch (the leading edge of the HPT stator vane). The predicted results show that the hot streak is relatively unaffected as it migrates through the HPT stator. The hot streak mixes with the vane wake and convects towards the pressure surface (PS) of the HPT rotor when it moves over the vane surface of the HPT stator. The heat load of the HPT rotor increases with the increase of the hot streak temperature ratio. The existence of the inlet temperature distortion induces a thin layer of cooler air in the HPT rotor, which separates the PS of the HPT rotor from the hotter fluid. The numerical results also indicating the migration characteristics of the hot streak in the HPT rotor are predominated by the combined effects of secondary flow and buoyancy. The combined effects that induce the high-temperature fluid migrate towards the hub on the HPT rotor. The effect of the secondary flow on the hotter fluid increases as the hot streak temperature ratio is increased. The influence of buoyancy is directly proportional to the hot streak temperature ratio. The predicted results show that the increase of the hot streak temperature ratio trends to increase the relative Mach number at the HPT rotor outlet, and decrease the relative flow angle from 25%to 75%span at the HPT rotor outlet. In the other region of the HPT outlet, the relative flow angle increases when the hot streak temperature ratio is increased. The predicted results also indicate that the isentropic efficiency of the VCRT decreases with the increase of the hot streak temperature ratio.
Highlights
Vanless counter-rotating turbine (VCRT), which is composed of a highly loaded single-stage high-pressure turbine (HPT) coupled with a vanless counter-rotating LPT, is used to increase significantly thrust-to-weight ratio of propulsion system while improving reliability and reducing costs (Keith et al [1]; Haldeman et al [2]; Weaver et al [3])
The hot streak is relatively unaffected as it migrates through the HPT stator
This paper is to study the effects of the hot streak temperature ratio on the HPT temperature distributions in the VCRT
Summary
Vanless counter-rotating turbine (VCRT), which is composed of a highly loaded single-stage HPT coupled with a vanless counter-rotating LPT, is used to increase significantly thrust-to-weight ratio of propulsion system while improving reliability and reducing costs (Keith et al [1]; Haldeman et al [2]; Weaver et al [3]). Butler et al (see [12]) carried out an experimental investigation on hot streak migration using the large scale rotating rig (LSRR), which was often used in hot streaks investigations They found that the temperature gradients could not alter the flow within the turbine stator but to have significant impact on the flow field of rotor blade rows when the total pressure in the distortion was uniform. Shang et al (see [29]) performed hot streak experiments in the BTTR in order to investigate the effects of hot streak migration on blade surface temperature at high speed. Hot streak temperature ratios of between 1.0 and 2.4, including 1.0, 1.2, 1.6, 2.0, and 2.4 temperature ratios, are used in the numerical simulations of flow through the VCRT
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