Aerothermal Study of the Unsteady Flow Field in a Transonic Gas Turbine With Inlet Temperature Distortions

Abstract

Computational fluid dynamics (CFD) prediction of the unsteady aerothermal interaction in the HP turbine stage, with inlet temperature nonuniformity, requires appropriate unsteady modeling and a low diffusive numerical scheme coupled with suitable turbulence models. This maybe referred to as high fidelity CFD. A numerical study has been conducted by the University of Florence in collaboration with ONERA to compare capabilities and limitations of their CFD codes for such flows. The test vehicle used for the investigation is a turbine stage of three-dimensional design from the QinetiQ turbine facility known as MT1. This stage is a high pressure transonic stage that has an unshrouded rotor, configured, and uncooled with 32 stators and 60 rotor blades. Two different CFD solvers are compared that use different unsteady treatments of the interaction. A reduced count ratio technique has been used by the University of Florence with its code HYBFLOW, while a phase lag model has been used by ONERA in their code, ELSA. Four different inlet conditions have been simulated and compared with focus on the experimental values provided by QinetiQ in the frame of TATEF and TATEF2 EU Sixth Framework Projects. The differences in terms of performance parameters and hot fluid redistribution, as well as the time- and pitch-averaged radial distributions on a plane downstream of the rotor blade, have been underlined. Special attention was given to the predictions of rotor blade unsteady pressure and heat transfer rates.

Multiple-Frequency Phase-Lagged Unsteady Simulations of Experimental Axial Compressor

“…The first limit is that the spinning-mode hypothesis [Eqs. (3)(4)] assumes that the sources of unsteadiness are linked to the wheel rotation and that the unsteady phenomena can be modeled by spinning modes (supposing that information travels in the azimuthal direction). The method assumes that the flowfield is governed by deterministic frequencies linked to the periodicity of the adjacent rows; therefore, it is not valid for flow configurations including a priori unknown deterministic frequencies such as a rotating stall or vortex shedding.…”

“…T HE relative motion between adjacent rotor and stator blade rows encountered in turbomachinery configurations gives rise to a wide range of unsteady flow mechanisms such as wake interactions [1], potential effects [2], hot streak migrations [3], shock wave propagations [4], or unsteady transitional flows [5]. All these phenomena, which can have a crucial impact on the performance of gas turbines, cannot be captured accurately with a steady mixingplane approach [6] since the averaging treatment at the rotor/stator interface filters all unsteady effects.…”

Uncertainty Quantification of Non-Dimensional Parameters for a Film Cooling Configuration in Supersonic Conditions

“…The non-dimensional coolant total pressure is 1.01 with respect to main-flow inlet total pressure and the non-dimensional coolant total temperature is 0.557 with respect to main-flow inlet total temperature. For each investigated case, the numerical value has been calculated using Equation (1) in accordance with the experimental definition:…”

“…A widely used strategy to increase efficiency and specific power output of gas turbines consists of increasing the Turbine Entry Temperature (TET). Therefore, metal temperatures approach the melting point of the alloys used in high-pressure nozzles, which are greatly loaded as shown in [1]. Advanced cooling systems such as film cooling are necessary to protect nozzles from high temperatures.…”

Film-cooling performance in supersonic flows: effect of shock impingement

“…In high pressure stages the oblique shocks shed from the trailing edge, impinge the suction side of adjacent vane. Furthermore, non-uniformity in the turbine entry temperature distribution is responsible for an increased vane heat load and positive jet effects, as described by Salvadori et al [1][2] [3]. Efficiency of film cooling must be evaluated taking into account the presence of oblique shocks and their interaction with the flow on the suction side.…”