Pressure Bifurcation Phenomenon on Supersonic Blowing Trailing Edges

TL;DR

This paper investigates the pressure bifurcation phenomenon at supersonic turbine blade trailing edges, revealing how flow instabilities and shock wave interactions are influenced by purge flow and geometry, using RANS simulations and stability analysis.

Contribution

It introduces a combined RANS and global stability analysis approach to explain flow bifurcation mechanisms at supersonic blade trailing edges, highlighting the role of geometrical expansion and flow parameters.

Findings

Identification of an anti-symmetrical global mode causing flow bifurcation.

Flow bifurcation linked to geometrical expansion of the trailing edge slot.

Flow behavior influenced by purge flow and shock wave interactions.

Abstract

Turbine blades operating in transonic-supersonic regime develop a complex shock wave system at the trailing edge, a phenomenon that leads to unfavorable pressure perturbations downstream and can interact with other turbine stages. Understanding the fluid behavior of the area adjacent to the trailing edge is essential in order to determine the parameters that have influence on these pressure fluctuations. Colder flow, bled from the high-pressure compressor, is often purged at the trailing edge to cool the thin blade edges, affecting the flow behavior and modulating the intensity and angle of the shock waves system. However, this purge flow can sometimes generate non-symmetrical configurations due to a pressure difference that is provoked by the injected flow. In this work, a combination of RANS simulations and global stability analysis is employed to explain the physical reasons of this flow bifurcation. Analyzing the features that naturally appear in the flow and become dominant for some value of the parameters involved in the problem, an anti-symmetrical global mode, related to the sudden geometrical expansion of the trailing edge slot, is identified as the main mechanism that forces the changes in the flow topology.