Large Eddy Simulation of Turbulent Flow Through a Compressor Cascade

A study of large eddy simulations (LES) for compressor blade flows has been undertaken and assessed by comparisons with the measurements of Hobson et al. (AIAA J. Prop. Power, 17, 154 (2001)) on a linear cascade of controlled-diffusion airfoils at Reynolds numbers based on blade chord and inflow velocity of 210 000, 380 000 and 640 000. LES of the latter two conditions are reported here. LES is by an explicit filtering method. Compressible flow equations in curvilinear coordinates were solved with 8th-order, central, finite differences and 2nd order Runge-Kutta integration. At 380 000 there is close quantitative agreement of the blade surface pressures and blade normal profiles of velocity magnitudes and fluctuations. Features of the initial development of the suction surface boundary layer is typical of transition induced by freestream turbulence, but end-stage turbulent spots are missing because of premature completion of transition over a mid-chord separation bubble. At 640 000 this separation is absent and turbulent spots appear before transition is completed. Blade surface pressure distribution from the LES agrees closely with that from experiment and is consistent with absence of separation, as are velocity profiles. Velocity profiles from experiment however had shown substantial open separation from the suction surface. This discrepancy had been noted before and was supposed to be an endwall effect, but our LES, including one with endwalls, does not support that view.