Session: 37-12 LES, DES and Scale Resolving Methods

Paper Number: 83081

83081 - Large Eddy Simulation of Turbulent Flow Through a Compressor Cascade 

Typical blade Reynolds numbers in axial compressors are high enough (million) that the flow is turbulent nearly everywhere, but transition in suction surface boundary layers can occupy a significant extent.  Since accurate transition prediction with mean flow (RANS) codes can be difficult, Large Eddy Simulation (LES) can be a useful alternative.  We report LES of flows through a compressor cascade at Reynolds numbers of 380000 and 640000 based on blade chord and axial velocity, at conditions of an experiment and provide assessments based on comparisons of surface pressure, mean velocity and fluctuation profiles.

The LES uses an explicit filtering approach for sub-grid-scale modelling.  Spatial derivatives were calculated using an 8th order explicit scheme, and 2nd order, Runge-Kutta integration in time. An overset grid arrangement was used which an O-grid was wrapped around the blade and embedded in a background Cartesian grid.  Data was exchanged using 4th-order Hermite interpolation.  Isotropic turbulence was added to the mean uniform stream at the inflow plane.  At both Re, blade surface pressure distributions agree well with those from experiments.  Velocity profiles at several stations along the suction surface agree at Re = 380000.  However, at higher Re of 640000, in the LES there is an attached turbulent boundary layer on the suction
surface, while the velocity profiles from the experiment had a significant reverse flow.  In a previous paper, RANS simulations (k-w-SST, and Reynolds stress model) had also shown a similar inconsistency. With a view to examining any contamination from sidewalls, additional LES with sidewalls were performed.  While the
present LES is internally consistent, and had been successful at the lower Re of 380000 and 210000 (reported before) the discrepancy with experiment remains.  In both cases (Re = 380000, 640000) the LES reveals free stream turbulence induced streaks inside the boundary layers.  On the pressure side they do not form the turbulent spot, and a fast transition occurs near the leading edge.  On the suction side, at 380000, reattachment from a laminar separation around the mid-chord is the last stage of transition.  At the higher Re of 640000 there is no separation but the slower transition occurs via the formation of spots which merge downstream and turbulent flow fills the span.

Presenting Author: Joseph Mathew Indian Institute of Science

Presenting Author Biography: Dr. Joseph Mathew is Professor and Chair of the Department of Aerospace Engineering, Indian Institute of Science, Bangalore. He obtained his B. Tech from the Indian Institute of Technology Madras (1984), MS from the University of Missouri-Rolla (1986) and PhD from the Massachusetts Institute of Technology (1990), all three from<br/>Mechanical Engineering Departments. After post-doctoral positions at ICOMP, NASA Glenn Research Center, Cleveland, and National Aerospace Laboratories, Bangalore, he joined IISc as an Assistant Professor in 1995. His research interests comprise Turbulence, transition, stability and wave propagation, DNS/LES and applications to<br/>turbomachinery, aeroacoustics and combustion. He has had research collaborations on LES with TU-Munich (2000-2011) and AFRL, Dayton (2004-5). He is a Fellow of the Indian National Academy of Engineering and an Associate Fellow of AIAA. He has been closely associated with ASME Gas Turbine conferences in India, serving as<br/>Review Chair in 2013 and 2015, and was Chair of the Executive Committee for ASME Gas Turbine India 2017-2019.

Authors:

Syed Anjum Haider Rizvi Indian Institute of Science
Joseph Mathew Indian Institute of Science