Large Eddy Simulations of a Highly Loaded Transonic Blade With Separated Flow

Abstract

Efficient design of highly loaded pressure blades often leads to the generation of a separation bubble on the pressure side of highly curved blades. For this specific region, fundamental, numerical and experimental studies have indicated the importance of the turbulence present in the main stream in determining the size of the bubble before its reattachment to the blade. Despite this important finding, many complex phenomena remain and are still present and can influence the overall flow response. In this paper, explorations of high-fidelity unsteady Large Eddy Simulations of a separated flow are studied for the high pressure T120 blade from the European project AITEB II (Aerothermal Investigation on Turbine Endwalls and Blades). For this investigation, simulations are carried out at the nominal operating point with and without synthetic turbulence injection at the inlet condition to comply with the specification from the experiment. Based on these predictions, the near wall flow structure and turbulent fields are specifically investigated in an attempt to identify the key mechanisms introduced by the turbulent main stream flow. Results show that the turbulence specification at the inlet enables the recovery of the correct pressure distribution on the blade surface contrary to the laminar inlet condition if compared to the experiment. Investigations of the boundary layer profiles show a strong impact of the freestream turbulence on the shape factor from the leading edge. As a consequence, the recirculation bubble located downstream on the pressure side is impacted and reduced when turbulence is injected. Due to this change in mean flow topology, the mass flow distribution in the passage appears strongly affected. Investigations of loss fields furthermore show that the freestream turbulence dramatically increases the loss production within the computational domain.

A mesh adaptation strategy for complex wall-modeled turbomachinery LES

“…In that case, a meshing effort is made inside the blade passage, the wake, as well as between the inlet and the leading edge, to convect properly the injected turbulence. Results are available in Harnieh et al [34,35] , showing very good agreement with experimental measures. They are therefore a relevant reference to gauge the effect of wall modeling for such flows.…”

“…On the suction side, a transition to turbulence is also present induced by a sonic shock in the inner blade channel. The accurate prediction of this flow is particularly challenging and inlet turbulence is seen to significantly affect the generation of the re-circulation bubble on the pressure side impacting the average pressure distribution within the inner vane passage (Harnieh et al [35] ). In this current Section 3 , successive mesh-adaptations are engaged for a wall-modeled LES to evaluate the proposed strategy to address this challenging flow in a wall-modeled context.…”