Accession Number : ADA190490
Title : Oscillating Airfoils - Achievements and Conjectures.
Descriptive Note : Final rept. Oct 86-Sep 87,
Corporate Author : DOUGLAS AIRCRAFT CO LONG BEACH CA
Personal Author(s) : Cebeci, Tuncer
PDF Url : ADA190490
Report Date : Sep 1987
Pagination or Media Count : 31
Abstract : Recent developments and applications of an interactive boundary layer procedure for unsteady flows are reviewed. The emphasis is on a model problem corresponding to an oscillating thin airfoil in laminar flows and results are reported for different amplitudes and frequencies of oscillation. The use of the characteristic box scheme, with its stability criterion, are shown to allow the accurate calculation of reverse flows and the interaction procedure removes the singularity to allow calculation through regions of separated flow. Although the current focus of the interactive boundary layer procedure has been on the leading edge region, it has general applicability and, together with models for transition and turbulent flows, it can provide the basis for a method to deal with oscillation airfoils and wings and the rapid movement of fixed wing arrangements at angels of attack up to and beyond those of dynamic stall. Calculations at high angles of attack indicate that the behavior of the unsteady separated leading edge flow has similarities to steady flows down-stream of surface corrugations. The use of linear stability theory in the latter case shows that the locations of the onset of transition moves upstream with severity of corrugation and can move inside the separation bubble. In practice this means that the bubbles will be shortened and analogy with unsteady flows suggests that transition may play an important role and preclude the existence of the long separation bubbles determined by the laminar-flow calculations.
Descriptors : *AIRFOILS, *FLOW SEPARATION, *OSCILLATION, *STALLING, *UNSTEADY FLOW, ANALOGIES, BOUNDARY LAYER, BUBBLES, COMPUTATIONS, FIXED WING AIRCRAFT, FLOW, FREQUENCY, HIGH ANGLES, INTERACTIONS, LAMINAR FLOW, LEADING EDGES, LINEARITY, REDUCTION, REVERSIBLE, STABILITY, THEORY, THINNESS, WINGS, AERODYNAMIC CHARACTERISTICS, ANGLE OF ATTACK, NAVIER STOKES EQUATIONS
Subject Categories : Fluid Mechanics
Distribution Statement : APPROVED FOR PUBLIC RELEASE