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Geissler, W.

Publications and source records attributed to Geissler, W..

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Dynamic Stall Measurements and Computations for a VR-12 Airfoil with a Variable Droop Leading Edge

High density-altitude operations of helicopters with advanced performance and maneuver capabilities have lead to fundamental research on active high-lift system concepts for rotor blades. The requirement for this type of system was to improve the sectional lift-to-drag ratio by alleviating dynamic stall on the retreating blade while simultaneously reducing the transonic drag rise of the advancing blade. Both measured and computational results showed that a Variable Droop Leading Edge (VDLE) airfoil is a viable concept for application to a rotor high-lift system. Results are presented for a series of 2D compressible dynamic stall wind tunnel tests with supporting CFD results for selected test cases. These measurements and computations show a dramatic decrease in the drag and pitching moment associated with severe dynamic stall when the VDLE concept is applied to the Boeing VR-12 airfoil. Test results also show an elimination of the negative pitch damping observed in the baseline moment hysteresis curves.

Martin, P. B.↗
NASA NTRS1993

Viscous/Inviscid Interaction On An Oscillating Airfoil

Viscous/inviscid-interaction procedure developed for computation of two-dimensional flow of air about airfoil, angle of attack of which oscillates at high amplitude. Purpose of procedure to study flow effects in dynamic stall. Bulk of flow treated as inviscid, while effects of viscosity treated only on surface of airfoil and in boundary layer. Inviscid part of flow simulated via time-marching, unsteady-subsonic-flow panel method incorporating appropriate distributions of unsteady surface and wake singularities.

Carr, L. W.↗
NASA NTRS1988

Viscous/inviscid interaction procedure for high-amplitude oscillating airfoils

A coupling procedure between an inviscid potential theoretical panel method and an unsteady interactive boundary layer calculation procedure has been developed for calculating unsteady airloads on oscillating airfoils in the high-incidence regime. A coordinate transformation into a time-dependent surface coordinate has been incorporated into the boundary layer code to avoid a quasi-steady treatment of the viscous flow equations in the leading edge region. The upper and lower sides of the airfoil are calculated with the complete set of unsteady equations. The interactive region of the boundary layer calculation can be straightforwardly extended over the complete upper surface of the airfoil while accounting for interaction areas in the region of strong adverse pressure gradients with incipient separation. Comparisons of sample calculations with experimental data show reasonably good agreement even for unsteady drag coefficients.

Geissler, W.↗
NASA NTRS1983

Unsteady laminar boundary-layer calculations on oscillating configurations including backflow. Part 2: Airfoil in high-amplitude pitching motion. Dynamic stall

A previously developed finite-difference procedure for calculating unsteady, incompressible, laminar boundary layers on an oscillating flat plate is applied to a wing section undergoing high-amplitude pitching oscillations about various mean incidences. To start the entire boundary-layer calculation, appropriate initial conditions and outer boundary conditions are specified, using a stagnation-point fixed frame of reference. The breakdown of the numerical calculation procedure in the x,t-domain is interpreted to coincide with unsteady separation. Details of the boundary-layer behavior in the vicinity of separation are investigated, and a close analogy between the present results and those for a three-dimensional steady separation is found.

Geissler, W.↗
NASA NTRS1983

Unsteady laminar boundary-layer calculations on oscillating configurations including backflow. Part 1: Flat plate, oscillating in its own plane

A finite difference method has been developed to calculate the unsteady boundary layer over an oscillating flat plate. Low- and high frequency approximations were used for comparison with numerical results. Special emphasis was placed on the behavior of the flow and on the numerical calculation procedure as soon as reversed flow has occurred over part of the oscillation cycle. The numerical method displayed neither problems nor singular behavior at the beginning of or within the reversed flow region. Calculations, however, came to a limit where the back-flow region reached the plate's leading edge in the case of high oscillation amplitudes. It is assumed that this limit is caused by the special behavior of the flow at the plate's leading edge where the boundary layer equations are not valid.

Geissler, W.↗