On the Influence of an Acoustically Optimized Turbine Exit Casing Onto the Unsteady Flow Field Downstream of a Low Pressure Turbine Rotor

Abstract

Modern low pressure turbines (LPT) are designed in order to fulfil a various number of requirements such as high endurance, low noise, high efficiency, low weight, and low fuel consumption. Regarding the reduction of the emitted noise, different designs of LPT exit guide vanes (aerodynamically and/or acoustically optimized) of the turbine exit casing (TEC) were tested, and their noise reduction capabilities and aerodynamic performance were evaluated. In particular, measurements of TEC-losses were performed, and differences in the losses were reported. Measurements were carried out in a one and a half stage subsonic turbine test facility at the engine relevant operating point approach. This work focuses on the study of the unsteady flow field downstream of an unshrouded LPT rotor. The influence on the upstream flow field of a TEC design including acoustically optimized vanes (inverse cut-off TEC) is investigated and compared with a second TEC configuration without vanes (Vaneless TEC), by means of fast response aerodynamic pressure probe (FRAPP) measurements. The second configuration served as a reference concerning the influence of turbine exit guide vanes (TEGVs) onto the upstream located LPT rotor. The interactions between the stator and rotor wakes, secondary flows, and the TEGVs potential effect are identified via modal decomposition according to the theory of Tyler and Sofrin. The main structures constituting the unsteady flow field are detected, and the role of the major interaction effects in the loss generation mechanism and in the acoustic emission is analyzed. This study based on the modal analysis of the unsteady flow field offers new insight into the main interaction mechanisms and their importance in the assessment of the aerodynamic and aeroelastic performance of modern LPT exit casings.

Experimental and Numerical Flow Analysis of an Engine Realistic State-Of-The-Art Turbine Rear Structure

“…The ITTM department at TU-Graz has performed several experimental and numerical studies of TRS aerodynamics. For example, Selic et al [15] studied the effect of tip-leakage on the TRS, Simonassi et al [16] studied acoustically optimized vanes and Zenz et al [17] studied TRS-vanes with riblets.…”

Experimental and Numerical Study of Laminar-Turbulent Transition on a Low-Pressure Turbine Outlet Guide Vane

“…The effect from surface roughness was studied experimentally in this facility by Jonsson et al [6] and numerically by Deshpande et al [7]. Acoustics in a TRS was investigated by Simonassi et al [8]. Steady-state heat transfer measurement on the outlet guide vane (OGV) was performed by Jonsson et al [9].…”