Session: 10-03-02: Fundamental Issues and Perspectives in Fluid Mechanics - II

Paper Number: 71171

Start Time: Monday, 04:20 PM

71171 - Transitional Flow and Heat Transfer on the Pressure Surface of a C-D Compressor Blade 

The demand for higher efficiency and lift leads to the development of controlled-diffusion (C-D) blades in gas turbine engines. This can enhance the amount of laminar flow in relation to turbulent flow, attributing to delay of flow separation on the suction surface. The aerodynamic loading becomes higher for a C-D blade as compared to the conventional one. There are studies illustrating the separation-induced transition on the suction surface of the blade. However, flow features on the pressure surface are different illustrating the appearance of elongated streaks and a transition to turbulence region. Thus, the objective of the present study is to focus on the transition mechanism and associated heat transfer on the pressure surface.

A high-resolution Large-eddy Simulation (LES) with the dynamic subgrid-scale model is used here to study the flow and heat transfer on 67B C-D compressor blade at Re of 2.1×10⁵ (based on the chord and the inlet velocity) and inlet free-stream turbulence intensity of 1%. An in-house flow solver, where the governing equations are in covariant form, is used on a staggered mesh. The solver has been extensively validated for a variety of transitional and turbulent flows. Flow features on the pressure surface appear laminar at the beginning followed by a sinuous undulation of velocity fluctuations, attributing to the development of streamwise streaks from 27% of the chord. These elongated streamwise streaks undergo a breakdown at the mid-chord region due to the secondary instability. The velocity fluctuations depict that flow ceases to be laminar up to 20% of the chord, where the perturbation levels increase downstream and attend a maximum level with a wide band of spectra near the mid-chord region, indicating a turbulent flow. Flow structures resolved also elucidate the formation of abundant small-scale eddies via the appearance of hairpins and their breakdown with an increase of turbulent heat flux. Further, the saturation of turbulence is evident after 70% of the chord reestablishing the longitudinal streaks that might be due to the local flow acceleration. The universal intermittency curve can be used to describe the transition of the boundary layer, illustrating the significance of the viscous effect. In brief, the present LES resolves the appearance of longitudinal streaks in the first half of the blade attributing to the laminar flow, which is excited evolving three-dimensional motions and lambda structures being the signature of the turbulent flow. The formation of elongated streaks appears again towards the end with a significant decay of turbulence level. However, the relaminarization of flow has not been confirmed.

Keywords: Large-eddy Simulation, Streaks, Transition Mechanism, Heat Transfer, Pressure Surface, Compressor Blade.

Presenting Author: Subrata Sarkar Indian Institute of Technology Kanpur

Authors:

S. Sarkar Indian Institute of Technology Kanpur
S. Katiyar Indian Institute of Technology Kanpur