Prediction of the unsteady turbulent flow in an axial compressor stage. Part 2: Analysis of unsteady RANS and LES data

Abstract

This paper presents the analysis of URANS and LES database in a stage of an axial subsonic compressor. Details about numerical methods and comparison with experiments can be found in a companion paper. The analysis here focuses on the transition processes that take place in the rotor and stator rows. In the rotor, LES and URANS show that transition develops at mid-chord and is induced by the adverse pressure gradient. In the stator, the flow behavior is more complex since the transition is influenced by the rotor passing wakes, a laminar separation bubble on the suction side and the accumulation of rotor wakes on the pressure side. The analysis also investigates the unsteady flow patterns at the rotor/stator interface, from mid-span to the casing. In the tip region, LES shows the development of frequencies that are not correlated to the blade passing frequency, while URANS only predicts multiples of the blade passing frequency.

Study of KJ-66 micro gas turbine compressor: Steady and unsteady Reynolds-averaged Navier–Stokes approach

“…Besides the extensive study regarding conventional gas turbines, [1][2][3][4][5] ongoing endeavors are made to understand the MGT performance. [6][7][8][9][10][11] MGT differs itself from conventional gas turbine due to its low operating Reynolds number and hence a relatively higher skin friction and heat transfer rate.…”

Reynolds, Mach, and Freestream Turbulence Effects on the Flow in a Low-Pressure Turbine

“…Along the blade, the different terms sharply increase close to the LE before to recover marginal values along the blade. Gourdain [58] observed a similar sharp increase of the TKE energy at the transition location on a compressor blade row before to recover relatively low values of TKE behind the transition location. The TKE production sharply increases close to the LE and more moderately along the remaining of the blade before to increase sharply in the wake (see Fig.…”

“…The different parameters of this simulation have been thoroughly checked, and according to the authors, this flow behavior may indicate a Re effect, i.e., the characteristic Re is around 50,000 at midspan, and depending on the FST characteristics, the boundary layer may still be laminar or transitional. Gourdain [58] observed a laminar-to-turbulent transition on the rotor blade of a compressor at around 40% chord and relatively higher Re = 700,000 with 2% inlet turbulence intensity. The relatively higher turbulence intensity in this configuration (Tu = 6%) may promote the early transition close to the LE for the two highest Re considered.…”

Loss assessment of a counter rotating open rotor using URANS/LES with phase-lagged assumption (draft)

“…For the URANS simulation, an upwind Roe scheme with third-order limiter [35] is used for the convective terms. The Wilcox k-ω two-equations model with Zheng's limiter [47] is used according to the practice provided by Gourdain et al [16,17] in a turbomachinery context. For the LES, a second order centred scheme with a low Jameson artificial viscosity [23] ( κ 4 jam .…”