Accurate Prediction of Loss Using High Fidelity Methods

Abstract

Further improvements in aero-engine efficiencies require accurate prediction of flow physics and incurred loss. Currently, the computational requirements for capturing these are not known leading to inconsistent loss predictions even for scale-resolving simulations depending on the chosen convergence criteria. This work investigates two aspects of loss generation using high-fidelity simulation. In the first case study we look at the effect of resolution on capturing entropy generation rate by simulating a Taylor-Green vortex canonical flow. The second case study focuses on the effect of resolution on flow physics and loss generation and uses a compressor cascade subjected to freestream turbulence. The results show that both resolving local entropy generation rate and capturing the inception and growth of instabilities are critical to accuracy of loss prediction. In particular, the interaction of free-stream turbulence at the leading-edge and development of instabilities in the laminar region of the boundary layer are critical to capturing loss.

Importance of Nonequilibrium Modeling for Compressors

“…For a case with inlet turbulence intensity of 4 percent, the loss generated in the suction surface boundary layer was found to change by less than 1 percent as the mesh size changed from 14M to 102M. The meshes of all three high fidelity simulations meet the requirements set out by Przytarski and Wheeler [10] for acccurate resolution of turbomachinery cascade loss mechanisms, and put the simulations in the wall resolved implicit LES regime. The freestream turbulence spectrum at inlet is compared to the -5/3 law for Cascade C in Fig.…”

“…The high fidelity (LES) simulations were carried out using 3DNS [9][10][11], a compressible finite difference Navier-Stokes solver first presented by Wheeler et. al [9].…”

“…Time [12] and inflow turbulence is prescribed using the method of Philips and Fyfe [13]. The decay of freestream turbulence using this method was investigated by Przytarski and Wheeler [10], and shown to be comparable with previous high fidelity simulations [14,15]. The LES meshes were created using a combination of Turbogrid software and a suite of Matlab scripts, following the method of Wheeler et al [9].…”

“…Therefore, from C to B to A, the cascades become more engine-representative. The NACA65 profile used in Cascade C has been extensively studied using DNS and LES (see [10,14,18,19]). The spanwise extent of the meshes was 10 percent axial chord for all cascades.…”

“…Przytarski and Wheeler [10] investigated the mesh requirements to appropriately resolve turbomachinery loss mechanisms using high fidelity simulations. Their study was also carried out using 3DNS, using the well-studied NACA65 compressor cascade.…”