Hiroshi MAEKAWA (前川 博)

本研究は,境界近傍におけるフィルタの取り扱いが空力音の数値計算に与える影響を渦と壁面との干渉によって発生する空力音を用いて明らかにした.Visbal and Gaitonde(AIAA Paper,(1998))の低次精度コンパクトフィルタおよびGaitonde and Visbal(AIAA Journal,(2000))の6次精度以上の境界コンパクトフィルタを境界近傍のフィルタに適用した場合の空力音計算での問題点を示し,適切と考えられる境界近傍のフィルタリング手法を示した.Compact schemes combined with compact filters are widely used for computational aeroacoustics. As compact filters require special treatment near the boundaries, near boundary filters were proposed by Visbal and Gaitonde (AIAA Paper, (1998)) and Gaitonde and Visbal (AIAA Journal, (2000)). However, these proposed near-boundary filter formulas have several drawbacks, the influence on computations of aerodynamic sound has not been uncovered. In this paper, we focus on the effects of these filters at the near-boundary points on the accurate calculation of aerodynamic sound generated by vortical flows near a wall. The results reveal that the appropriate filtering at the near-boundary nodes with no adverse impact on stability is essential to compute aerodynamic sound. The application of high-order boundary formulas such as 6^ order boundary compact filtering is not appropriate because of an incorrect vortex motion and resultant spurious sound fields. A higher order boundary compact filter is not necessarily suitable for computations of aerodynamic sound due to its spectral function. In the case of using lower order centered filtering formulas approach, the value of a free parameter of the filter and the grid resolution have a serious influence on the computation of aerodynamic sound. Two appropriate filters at the near-boundary are presented.