DIFFERENCES IN INVISCID ISENTROPIC MODELS USED FOR FINITE DIFFERENCE CALCULATION OF TRANSONIC FLOW WITH SHOCKS ABOUT AIRFOILS;THE PREDICTION OF WAVE DRAG

摘要

Properties of inviscid isentropic flow models underlying finite dif-ference methods for the calculation of two-dimensional transonic flows with embedded shocks about airfoils are discussed and compared. Attention-is drawn to the fact that the isentropic time—dependent model described-by Magnus and Yoshihara and the isentropic model used in relaxation—type methods (e.g. Steger/Loraax/, Garabedian/Korn, Jameson) are fundamentally different. It is pointed out that the two models each imply a different wave drag mechanism.nProm a comparison of the shock-jump relations of the different isen¬tropic model with the Rankine-Hupcniot jump relations and a semi-quanti¬tative analysis of wave drag, it is concluded that the model described by Magnus and Yoshihara provides the best approximation to non-isentropic Hankine-Huponiot flow. In calculations of steady flow, however, the use of this model has no real advantage over using non-isentropic Rankine— Huponipt flow as a model.