Impact of 2D engine nacelle flow on buffet

Abstract

Numerical studies on the interaction of nacelle and airfoil shock dynamics are performed. To keep the computational cost at an acceptable level, first 2D investigations on the interaction of nacelle and airfoil are performed that cover basic dynamic phenomena of this configuration. The transonic flow around the OAT15A airfoil is computed at buffet conditions, i.e., freestream Mach number Ma∞=0.73\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Ma{_\\infty } = 0.73$$\\end{document}, chord-based freestream Reynolds number Rec=2·106\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Re_c = 2\\cdot 10^6$$\\end{document}, and angle of attack α=3.5∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha = 3.5^\\circ $$\\end{document} using wall-modeled LES. Two configurations are considered, one which includes a generic 2D ultra-high bypass ratio (UHBR) engine nacelle geometry and one without an engine, which is denoted the baseline case. In addition to the airfoil shock, the flow field of the nacelle configuration is characterized by a shock wave on the upper part of the nacelle. Furthermore, the introduction of the UHBR-engine nacelle leads to a reduced effective angle of attack and Mach number in the flow to the airfoil. The changes in the topology of the flow to the airfoil caused by the nacelle lead to a reduced strength of the airfoil shock and a less developed buffet, which resembles the behavior close to the stability limit. The reduced shock dynamics yields lower pressure fluctuations at the airfoil trailing edge. A frequency analysis of time series data from the airfoil shock location shows a reduction of the buffet frequency for the nacelle configuration. Further investigations of the flow field dynamics using sparsity-promoting dynamic mode decomposition reveal a mutual mode between the airfoil shock and the nacelle shock. The existence of this mode has consequences for future investigations of nacelle airfoil interaction in transonic flow.