Hot Streak Temperature Research Articles

Aerodynamics and Heat Transfer for a Cooled One and One-Half Stage High-Pressure Turbine—Part I: Vane Inlet Temperature Profile Generation and Migration

As controlled laboratory experiments using full-stage turbines are expanded to replicate more of the complicated flow features associated with real engines, it is important to understand the influence of the vane inlet temperature profile on the high-pressure vane and blade heat transfer as well as its interaction with film cooling. The temperature distribution of the incoming fluid governs not only the input conditions to the boundary layer but also the overall fluid migration. Both of these mechanisms have a strong influence on surface heat flux and therefore component life predictions. To better understand the role of the inlet temperature profile, an electrically heated combustor emulator capable of generating uniform, radial, or hot streak temperature profiles at the high-pressure turbine vane inlet has been designed, constructed, and operated over a wide range of conditions. The device is shown to introduce a negligible pressure distortion while generating the inlet temperature conditions for a stage-and-a-half turbine operating at design-corrected conditions. For the measurements described here, the vane is fully cooled and the rotor purge flow is active, but the blades are uncooled. Detailed temperature measurements are obtained at rake locations upstream and downstream of the turbine stage as well as at the leading edge and platform of the blade in order to characterize the inlet temperature profile and its migration. The use of miniature butt-welded thermocouples at the leading edge and on the platform (protruding into the flow) on a rotating blade is a novel method of mapping a temperature profile. These measurements show that the reduction in fluid temperature due to cooling is similar in magnitude for both uniform and radial vane inlet temperature profiles.

Tip Clearance Effects on Inlet Hot Streak Migration Characteristics in High Pressure Stage of a Vaneless Counter-Rotating Turbine

In this paper, three-dimensional multiblade row unsteady Navier–Stokes simulations at a hot streak temperature ratio of 2.0 have been performed to reveal the effects of rotor tip clearance on the inlet hot streak migration characteristics in high pressure stage of a vaneless counter-rotating turbine. The numerical results indicate that the migration characteristics of the hot streak in the high pressure turbine rotor are dominated by the combined effects of secondary flow, buoyancy, and leakage flow in the rotor tip clearance. The leakage flow trends to drive the hotter fluid toward the blade tip on the pressure surface and to the hub on the suction surface. Under the effect of the leakage flow, even partial hotter fluid near the pressure surface is also driven to the rotor suction surface through the tip clearance. Compared with the case without rotor tip clearance, the heat load of the high pressure turbine rotor is intensified due to the effects of the leakage flow. And the results indicate that the leakage flow effects trend to increase the low pressure turbine rotor inlet temperature at the tip region. The air flow with higher temperature at the tip region of the low pressure turbine rotor inlet will affect the flow and heat transfer characteristics in the downstream low pressure turbine.

Superposition Predictions of the Reduction of Hot Streaks by Coolant From a Film-Cooled Guide Vane

The turbine section of a gas turbine engine is subjected to hot gases flowing from the combustor that typically have high temperature regions known as “hot streaks.” These hot streaks pass through the nozzle guide vanes, either impacting the vanes or passing through the passages between vanes. Generally the vanes are highly film cooled, and the coolant from the vanes interacts with the hot streak resulting in a reduction of the hot streak temperature. In this study, predictions of the reduction of hot streaks were made using superposition of measured temperature distributions due to coolant injection and measured temperature distributions of hot streaks. These predictions were compared to the measured hot streak reduction to determine the accuracy of the superposition technique. Results showed that the superposition predictions generally underpredicted the reduction of the peak hot streak temperature, but were within at least 20% of the peak temperature value. The superposition technique was also found to be useful for determining the hot streak reduction for different hot streak locations, and different coolant and hot streak operating conditions.

Influence of Hot Streak Temperature Ratio on Low Pressure Stage of a Vaneless Counter-Rotating Turbine

In order to explore the influence of hot streak temperature ratio on the low pressure stage of a vaneless counter-rotating turbine, three-dimensional multiblade row unsteady Navier–Stokes simulations have been performed. The predicted results show that hot streaks are not mixed out by the time they reach the exit of the high pressure turbine rotor. The separation of colder and hotter fluids is observed at the inlet of the low pressure turbine rotor. After making interactions with the inner-extending and outer-extending shock waves in the high pressure turbine rotor, the hotter fluid migrates toward the pressure surface of the low pressure turbine rotor, and most of the colder fluid migrates to the suction surface of the low pressure turbine rotor. The migrating characteristics of the hot streaks are dominated by the secondary flow in the low pressure turbine rotor. The results also indicate that the secondary flow intensifies in the low pressure turbine rotor when the hot streak temperature ratio is increased. The effects of the hot streak temperature ratio on the relative flow angle at the inlet of the low pressure turbine rotor are very remarkable. The isentropic efficiency of the vaneless counter-rotating turbine decreases as the hot streak temperature ratio is increased.

Numerical Investigation on the Influence of Hot Streak Temperature Ratio in a High-Pressure Stage of Vaneless Counter-Rotating Turbine

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.

Analysis of Hot Streak Effects on Turbine Rotor Heat Load

The influence of inlet hot streak temperature distortion on turbine blade heat load was explored on a transonic axial flow turbine stage test article using a three-dimensional, multiblade row unsteady Euler code. The turbine geometry was the same as that used for a recently reported testing of hot streak influence. Emphasis was placed on elucidating the physical mechanisms by which hot streaks affect turbine durability. It was found that temperature distortion significantly increases both blade surface heat load nonuniformity and total blade heat load by as much as 10–30 percent (mainly on the pressure surface), and that the severity of this influence is a strong function of turbine geometry and flow conditions. Three physical mechanisms were identified that drive the heat load nonuniformity: buoyancy, wake convection (the Kerrebrock–Mikolajczak effect), and Rotor–Stator interactions. The latter can generate significant nonuniformity of the time-averaged relative frame rotor inlet temperature distribution. Dependence of these effects on turbine design variables was investigated to shed light on the design space, which minimizes the adverse effects of hot streaks.

Investigation of Hot Streak Temperature Ratio Scaling Effects

Investigation of Hot Streak Temperature Ratio Scaling Effects

Demonstration of Ceramic Design Methodology for a Ceramic Combustor Liner

Successful application of ceramics in the gas turbine environment involves brittle material design and analysis, unique material properties, and laboratory demonstration of components. Alternative ceramic structures for application in a hybrid ceramic-metal combustion system were considered. Thermal stresses and probabilities of failure were calculated for tube, ring, and stave designs. The stress levels are relatively low for axial and radial temperature gradients in all 6 in. (152 mm) diameter combustors. Scaling to larger sizes is also considered. A hot streak temperature distribution resulted in stresses in the stave and tube which were three times the stresses in the ring design. Bend specimens were cut from one end of a 6 in. (152 mm) diameter, 10 in. (254 mm) long REFEL silicon carbide tube to assure a representative flaw distribution. Strength, strength scatter, and strength degradation were evaluated at 2200°F (1200°C) and were incorporated in the stress analysis. A low probability of failure was predicted. The REFEL tube was tested in the hybrid ceramic-metal combustion system at gas temperatures in excess of 2660°F (1460°C), 16 atm pressure, and 6.9 lb/s (3.1 kg/s) mass flow while burning No. 2 fuel oil. Successful ceramic performance was demonstrated at 2000°F (1090°C) steady state and at 2000°F (1110°C) per minute shutdown cooling rate.