Analysis of a high-pressure multistage axial compressor at off-design conditions with coarse Large Eddy Simulations

Abstract

This paper aims at evaluating Large Eddy Simulations (LES) for the prediction of the performance line and flow at off-design conditions in a multistage high-pressure compressor. A coarse and an intermediate grid are specifically investigated, since their associated computational cost appears affordable in an industrial context. Several operating conditions of the 3.5 stages high-pressure compressor CREATE are simulated, then results are compared to experimental data and to an existing URANS simulation. Both grids yield iso-speed performance lines close to experimental measurements, but only the intermediate one is able to correctly predict the experimental point at lowest mass flow rate. The unstable regime is specifically investigated in the last stage of the intermediate grid, showing the presence of rotating instabilities. Their amount and spinning velocity are similar to experimental observations and previous URANS results. Hence coarse LES appears as an interesting tradeoff for off-design predictions of flow in a multistage compressor.

The Current State of High-Fidelity Simulations for Main Gas Path Turbomachinery Components and Their Industrial Impact

“…This analysis was extended to the four incidence angles investigated, and revealed how the loss split differs between RANS and LES, although the overall loss level may be similar. More recently Laborderie et al [57] completed a wall modeled LES of a three-stage axial compressor with IGV with the specific intent to investigate off-design performance and compare with measurements. They concluded, not unexpectedly, that sufficient grid resolution was critical in order for the LES to improve the match with measurements over URANS.…”

Comparison of Various CFD Codes for LES Simulations of Turbomachinery: From Inviscid Vortex Convection to Multi-Stage Compressor

“…The numerical parameters of the simulations are detailed in [13], [14]. The CPU cost, directly related to the mesh size and the time step, increases from one order of magnitude from M1 to M2 and M2 to M3, as shown in Table 6.…”

“…Going beyond HPC evaluation, some comparisons with available experimental data have been performed [13], [14], and the main outcomes are recalled here. The turbulent structures simulated by LES are shown in Figure 26 Measured iso-speed characteristic curves of CREATE2bis compressor at 11 543 rpm are shown in Figure 28 and Figure 29 in terms of total pressure ratio and isentropic efficiency respectively.…”

“…Moreover this refinement level allows to closely approach the last stable experimental operating point identified as off-design conditions. This suggests that wall-modeled LES with intermediate refinement could be a viable approach for performance prediction at off-design conditions [14] for which low order techniques often fail to provide correct results. For M3, statistics have been recorded during the last revolution and corresponding points are shown as green triangles.…”

“…Note that close to the tip, the turbulence intensity is underestimated by all simulations, most refined ones being the closest but a clear deficit is still observed. For more analysis of these results, please refer to [13] and [14].…”