RESPONSE OF A THIN AIRFOIL ENCOUNTERING A STRONG DENSITY DISCONTINUITY

Airfoil theory for unsteady motion has been developed extensively assu ming the undisturbed medium to be of uniform density, a restriction ac curate for motion in the atmosphere, Glauert (1929), Burgers (1935), T heodorsen (1935), Kussner (1936), Karman and Sears (1938), Kinney and Sears (1975). In some instances, notably for airfoils comprising fan, compressor and turbine blade rows, the undisturbed medium may carry de nsity variations or ''spots,'' resulting from non-uniformaties in temp erature or composition, of a size comparable to the blade chord. This condition exists for turbine blades, Marble (1975), Giles and Krouthen (1988), immediately downstream of the main burner of a gas turbine en gine where the density fluctuations of the order of 50 percent may occ ur. Disturbances of a somewhat smaller magnitude arise from the ingest ion of hot boundary layers into fans, Wortman (1975), and exhaust into hovercraft. Because these regions of non-uniform density convect with the moving medium, the airfoil experiences a time varying load and mo ment which we propose to calculate.