The effect of airfoil thickness on the efficiency of low-pressure (LP) turbines has been investigated experimentally in a multistage turbine high-speed rig. The rig consists of three stages of a state of the art LP turbine. The stages are characterized by a very high hade angle, reverse cut-off design, very high lift, and very high aspect ratio airfoils. Two different sets of stators have been designed and tested. The first set of stators is made of airfoils with a thickness to chord ratio around 10% along the span with the exception of a small areas close to the end walls. In those areas, the thickness has been increased above the previous value to reduce the secondary flows. These types of airfoils have been referred to in the literature as “spoon” airfoils. The second set of stators has been designed to have the same spanwise distribution of pressure coefficient (Cp) on the suction surface than the first set. However, the thickness to chord ratio was increased along the span up to values around 20% to raise the velocity of the flow and to remove any separation bubble on the pressure side. The resulting shape of the profiles is representative of “hollow” airfoils. The velocity triangles, chord distribution, leading and trailing edge locations, and flowpath have been maintained between both sets. They have been tested with the same blades and at the same operating conditions with the intention of determining the impact of the profile thickness on the overall efficiency. The turbine characteristics: sensitivity to speed, specific work, Reynolds number, and purge flows have been obtained for both sets. The comparison of the results suggests that the efficiency of both types of airfoils exhibit the same behavior; no significant differences in the results can be distinguished.

One of the most important new engine concepts is the Geared turbofan. In these engines a gear box allows the decoupling between fan and turbine rotational speeds. As a consequence, the separate aerodynamic optimization of both components becomes possible leading to an increase in engine bypass ratios, higher propulsive efficiency and lower specific fuel consumption. The multi-stage intermediate pressure turbine (IPT) is one of the key parts of the thermodynamic cycle in geared turbofan architectures. During the characterization of a LPT NGV row, it is important to have detailed pressure losses measurements as accurate as possible. Because of the aerodynamic differences with conventional low pressure turbines (LPT), this becomes mandatory when the NGV is designed for an IPT. The main error sources are related to circumferential anisotropy, to repeatability of US and DS measurements, to effects of instrumentation in 2D losses and to static pressure measurement in the probe environment.

The effect of airfoil thickness on the efficiency of Low Pressure (LP) Turbines has been investigated experimentally in a multistage turbine high-speed rig. The rig consists of three stages of a state of the art LP turbine. The stages are characterized by a very high hade angle, reverse cut-off design, very high lift and very high aspect ratio airfoils. Two different sets of stators have been designed and tested. The first set of stators is made of airfoils with a thickness to chord ratio around 10% along the span with exception of a small areas close to the endwalls. In those areas, the thickness has been increased above the previous value to reduce the secondary flows. These types of airfoils have been referred in the literature as “spoon” airfoils. The second set of stators has been designed to have the same spanwise distribution of pressure coefficient (Cp) on the suction surface than the first set. However, the thickness to chord ratio was increased along the span up to values around 20% to rise the velocity of the flow and to remove any separation bubble on the pressure side. The resulting shape of the profiles is representative of “hollow” airfoils. The velocity triangles, chord distribution, leading and trailing edge locations and flowpath have been maintained between both sets. They have been tested with the same blades and at the same operating conditions with the intention of determining the impact of the profile thickness on the overall efficiency. The turbine characteristics: sensitivity to speed, specific work, Reynolds number and purge flows have been obtained for both sets. The comparison of the results suggests that the efficiency of both types of airfoils exhibit the same behaviour, no significant differences in the results can be distinguished.

The effect of turning angle on the loss generation of Low Pressure (LP) Turbines has been investigated experimentally in a couple of turbine high-speed rigs. Both rigs consisted of a rotor-stator configuration. All the airfoils are high lift and high aspect ratio blades that are characteristic of state of the art LP Turbines. Both rigs are identical with exception of the stator. Therefore, two sets of stators have been manufactured and tested. The aerodynamic shape of both stators has been designed in order to achieve the same spanwise distribution of Cp (Pressure coefficient) over the airfoil surface, each one to its corresponding turning angles. Exit angle in both stators is the same. Therefore the change in turning is obtained by a different inlet angle. The aim of this experiment is to obtain the sensitivity of profile and endwall losses to turning angle by means of a back-to-back comparison between both sets of airfoils. Because the two sets of stators maintain the same pressure coefficient distribution, Reynolds number and Mach number, each one to its corresponding velocity triangles, one can state that the results are only affected by the turning angle. Experimental results are presented and compared in terms of area average, radial pitchwise average distributions and exit plane contours of total pressure losses. CFD simulations for the two sets of stators are also presented and compared with the experimental results.

The multi-stage intermediate pressure turbine (IPT) is a key enabler of the thermodynamic cycle in geared turbofan engine architectures, where fan and turbine rotational speeds become decoupled by employing a power gearbox between them. This allows for the separate aerodynamic optimization of both components, an increase in engine bypass ratios, higher propulsive efficiency, and lower specific fuel consumption. Due to significant aerodynamic differences with conventional low pressure turbines (LPTs), multi-stage IPT designs present new aerodynamic, mechanical and acoustic trade-offs. This work describes the aerodynamic design and experimental validation of a fully featured three-stage IP turbine, including a final row of outlet guide vanes. Experiments have been conducted in a highly engine-representative transonic rotating wind tunnel at the CTA (Centro de Tecnologías Aeronáuticas, Spain), in which Mach and Reynolds numbers were matched to engine conditions. The design intent is shown to be fully validated. Efficiency levels are discussed in the context of a previous state-of-the-art LPT, tested in the same facility. It is argued that the efficiency gains of IPTs are due to higher pitch-to-chord ratios, which lead to a reduction in overall profile losses, and higher velocity ratios and lower turning angles, which reduce airfoil secondary flows and three-dimensional losses.