Characterization of the Unsteady Aerodynamics of Optimized Turbine Blade Tips through Modal Decomposition Analysis

Bogdan C Cernat,Sergio Lavagnoli

doi:10.3390/ijtpp4020012

Abstract

The present research focused on the analysis of the leakage flows developing from advanced blade tip geometries. The aerodynamic field of a contoured blade tip and of a high-performance rimmed blade were investigated against a baseline squealer rotor. Time-resolved numerical predictions were combined with high-frequency pressure measurements to characterize the tip leakage flow of each tip design. High spatial and temporal resolution measurements provided a detailed representation of the unsteady flow in the near-tip region and at the stage outlet. Numerical computations, based on the nonlinear harmonic method, were employed to assess the unsteady blade row interactions and identify the loss generation mechanisms depending on the tip design. The space- and time-resolved flow field was analysed by modal decomposition to identify the main periodicities of the near-tip and outlet flow and classify the most relevant sources of aerodynamic unsteadiness and entropy generation across the stage.

Highlights

In the pursuit of increased engine performance and durability, novel design solutions have been conceived in recent years to shape the high pressure turbine (HPT) rotor tips and gain control over the tip leakage streams
A modal analysis was performed in space and time to identify the most relevant sources of aerodynamic and entropic unsteadiness within the stage blade rows
This paper presents a combined experimental and numerical analysis of the time-resolved flow field of an HP turbine stage mounting three different rotor tip designs

Summary

Introduction

In the pursuit of increased engine performance and durability, novel design solutions have been conceived in recent years to shape the high pressure turbine (HPT) rotor tips and gain control over the tip leakage streams. From an engine manufacturer standpoint, an optimal rotor sealing design must minimize the amount of working fluid spilled through the gap [1], while limiting the harmful thermal loads. On the other hand, employ a contoured surface to control the acceleration of the leakage stream in the gap and force it to choking conditions [8]. This allows effectively decoupling the blade tip load from the spillage mass flow, breaking the mutual dependency between the work extraction process and the blade aerodynamic performance [9]

Methods

Results

Conclusion