Comparative Assessment of Local Accuracy of High-Order Spatial Schemes for Rotorcraft Aeroacoustics

Abstract

High-order spatial schemes, which effectively treat the dissipative characteristics of computational fluid dynamics solvers, are known to assure the precise prediction of rotorcraft aeroacoustics. However, such schemes may differ in numerical performance, even if they have the same theoretical accuracy. This is because the nonlinear part in a high-order spatial scheme locally reduces the order of accuracy depending on the grid number and flow characteristics. Therefore, it is necessary to compare each scheme in terms of local accuracy and to identify which numerical characteristics are required to retain high-order accuracy. In this study, a local-order-of-accuracy index (LAI) is newly proposed to quantitatively measure the accuracy of a spatial scheme. The LAI represents the local accuracy of each scheme, including the effect of the grid number and local flowfield characteristics. A comparative assessment of five high-order spatial schemes is conducted using the LAI analysis. The resulting LAI analysis indicates two requisites for an aeroacoustic prediction of rotorcraft performance: 1) an advanced shock-sensing mechanism in each scheme, and 2) hybrid central-upwind characteristics. Details of the LAI analysis results are presented, including practical rotorcraft applications.