Analysis on the Effect of a Nonuniform Inlet Profile on Heat Transfer and Fluid Flow in Turbine Stages

Abstract

This paper presents an investigation of the aerothermal performance of a modern unshrouded high-pressure (HP) aero-engine turbine subject to nonuniform inlet temperature profile. The turbine used for this study was the MT1 turbine installed in the QinetiQ turbine test facility based in Farnborough (UK). The MT1 turbine is a full scale transonic HP turbine, and is operated in the test facility at the correct nondimensional conditions for aerodynamics and heat transfer. Datum experiments of aerothermal performance were conducted with uniform inlet conditions. Experiments with nonuniform inlet temperature were conducted with a temperature profile that had a nonuniformity in the radial direction defined by (Tmax−Tmin)/T¯=0.355, and a nonuniformity in the circumferential direction defined by (Tmax−Tmin)/T¯=0.14. This corresponds to an extreme point in the engine cycle, in an engine where the nonuniformity is dominated by the radial distribution. Accurate experimental area surveys of the turbine inlet and exit flows were conducted, and detailed heat transfer measurements were obtained on the blade surfaces and end-walls. These results are analyzed with the unsteady numerical data obtained using the in-house HybFlow code developed at the University of Firenze. Two particular aspects are highlighted in the discussion: prediction confidence for state of the art computational fluid dynamics (CFD) and impact of real conditions on stator-rotor thermal loading. The efficiency value obtained with the numerical analysis is compared with the experimental data and a 0.8% difference is found and discussed. A study of the flow field influence on the blade thermal load has also been detailed. It is shown that the hot streak migration mainly affects the rotor pressure side from 20% to 70% of the span, where the Nusselt number increases by a factor of 60% with respect to the uniform case. Furthermore, in this work, it has been found that a nonuniform temperature distribution is beneficial for the rotor tip, contrary to the results found in open literature. Although the hot streak is affected by the pressure gradient across the tip gap, the radial profile (which dominates the temperature profile being considered) is not fully mixed out in passing through the HP stage, and contributes significantly to cooling the turbine casing. A design approach not taking into account these effects will underestimate the rotor life near the tip and the thermal load at midspan. The temperature profile that has been used in both experiments and CFD is the first simulation of an extreme cycle point (more than twice the magnitude of distortion of all previous experimental studies): It represents an engine-take-off condition combined with the full combustor cooling. This research was part of the EU funded Turbine AeroThermal External Flows 2 program.

Optimal control of diffuser shapes for non-uniform flow

“…Expanding channels, known as diffusers, have the function of converting high-speed low-pressure flow to low-speed high-pressure flow. Diffusers have numerous applications, from turbines in aerospace to hydropower [1–3] to automotive design [4]. There is a large body of literature on diffusers in the case where the inflow is uniform (see [5]), but only a limited literature available for non-uniform inlet flows [6].…”

Development of an Engine Representative Combustor Simulator Dedicated to Hot Streak Generation

“…f ¼ frequency (Hz) k ¼ turbulent kinetic energy (m 2 /s2 ) M ¼ Mach number _ m ¼ mass flow rate (kg/s) MFR ¼ mass flow ratio P ¼ static pressure (Pa) R ¼ radius (m) Re ¼ Reynolds number S N ¼ Swirl number St ¼ Strouhal number T ¼ total temperature (K) T ¼ mean total temperature (K) TU ¼ turbulence intensity u ¼ velocity (m/s) Y þ ¼ nondimensional wall distance b ¼ azimuthal position (deg) c ¼ ratio of specific heat l ¼ dynamic viscosity (PaÁs) q ¼ density (kg=m 3 ) Subscripts amb ¼ ambient cool ¼ effusion cooling r ¼ radial direction ref ¼ swirler inlet conditions rms ¼ root mean square sw ¼ mainstream (swirler) x ¼ axial direction 40 ¼ plane 40 h ¼ circumferential direction…”

Unsteady Analysis on the Effects of Tip Clearance Height on Hot Streak Migration Across Rotor Blade Tip Clearance

“…8 and Fig. 10(a), it can be deduced that the nonuniform inlet temperature distribution decreases the heat load on the blade tip [21], especially near the leading edge. Generally speak ing, the heat load in the region where hot fluid arrives is higher than in other regions.…”

“…Jonathan and Robert [16] simulated the unsteady migration of hot streak in an HP turbine stage and proposed a new configura tion to improve the cooling of the hub region. An experimental and numerical study was accomplished by Simone et al [21] in the QinetiQ turbine test facility. An experimental and numerical study was accomplished by Simone et al [21] in the QinetiQ turbine test facility.…”