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The wings on aircraft can experience unsteady loads due to atmospheric disturbances (e.g., wind), the wakes of other aircraft, structural vibrations, or some combination of these sources. In some cases flow unsteadiness can be beneficial by augmenting the lift and reducing the drag; under different circumstances temporal variations in the flow can induce stall or cause structural failure. In this study, the response of isolated and tandem airfoils to time-periodic variations in the flow angle and velocity magnitude have been investigated. The predicted results indicate that both sources of unsteadiness can cause the airfoil(s) to produce thrust (instead of drag) during a significant portion of an unsteady oscillation cycle.

Analysis of tandem wing aircraft configurations has been of interest to the aerospace community since the early 1970's. The theoretical performance gains from the use of two similarly-sized wings make this unusual configuration an enticing option for future aircraft designs. In this investigation, a two-dimensional Navier-Stokes analysis previously developed for internal flow geometries has been extended to external flow geometries. The modified flow analysis was validated against two sets of experimental data. A series numerical simulations were then performed for a tandem-airfoil configuration in which the stagger (chord-wise distance between the mid-chord of each airfoil) was varied. At each stagger position, the aerodynamic flow field was investigated at several negative and positive incidence angles. The predicted results indicate that (for moderate-to-large stagger distances) the aft airfoil performs similar to the fore airfoil at lower angles of attack.

The flow through most turbomachinery blade rows is characterized by unsteady, viscous, transitional flow. The accurate prediction of the onset of transition from laminar to turbulent flow is essential for calculating heat transfer and performance quantities. The purpose of this investigation is to evaluate the accuracy of four different algebraic transition models which have been combined with an algebraic turbulence model. Numerical experiments have been performed for flow through a turbine rotor cascade with heat transfer, and a cascade of compressor blades. In addition, a study was performed to determine the effects of the computational grid density on the transition location.