Pressure Bifurcation Phenomenon on Supersonic Blowing Trailing Edges

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.

Coanda Flow Characterization on Base Bleed Configurations Using Global Stability Analysis

“…6-right). This flow system has been carefully studied in the past [11,14], so it is briefly described here. As the boundary layers of upper and lower sides approach the trailing edge, they separate forming two symmetric shear layers that confine a subsonic recirculation area, the base region.…”

“…However, as it was found by Saracoglu et al [11], the injection of flow in the base region can lead to the apparition of non-symmetrical configurations related to a bifurcation phenomena associated to the intensity of the injected flow ( Fig.2). Based on those results, Martinez-Cava et al [14] performed a detailed study of a simplified turbine trailing edge combining RANS simulations and global stability analysis. Results showed that for jet intensities above certain value, a difference in pressure between the upper and lower sides of the trailing edge will appear, forcing the flow to change its direction through an induced Coanda effect.…”

Domain reduction strategy for the stability analysis of complex aerodynamic flows

“…As a final test case, we consider the EVP arising in the study of the flow in refrigerated turbine stages whenever supersonic jets blowing from the blade trailing edge are used as cooling strategy. The detailed study of this configuration and a description of its complex flow topology can be found in References , and . Their investigation aims to understand the flow behavior in turbine blades operating in the transonic‐supersonic regime: a complex shock wave system is established at the trailing edge.…”

“…Under certain circumstances, the purged flow generates nonsymmetrical configurations due to the pressure imbalance provoked by the injected flow. Martinez‐Cava et al and Wang et al combined RANS simulations and global stability analysis to investigate the physical reasons behind this flow bifurcation. An antisymmetric global mode was ultimately identified as the responsible of triggering the main mechanism forcing the changes in the flow topology.…”

“…As a side benefit, the DR technique allows to increase resolution into the region of interest, balancing the overall computational effort. Several works have employed DR techniques to address the study of, initially unfeasible, stability analysis …”