Dynamic Stall on Advanced Airfoil Sections

Abstract

Abstractwall interference, and experimental uncertainties. These are serious problems even The dynamic stall characteristics of for static stall, as indicated by the eight airfoils have been investigated in results plotted in Fig. 1 for two very sinusoidal pitch oscillations over a wide different airfoils. The shaded band shows, range of two-dimensional unsteady flow for the classical NACA 0012, the spread of conditions. The results provide a unique measured values of the maximum lift coefcomparison of the effects of section geomficient from our experiment and from those etry in a simulated rotor environment, reported previously.

Compressibility effects on dynamic stall

“…However, no clear conclusion can 19e made concerning the impact of this supersonic flow. For instance, although McCroskey et al (7) showed that supersonic flow existed on seven of the eight airfoils tested in their experiment, no shocks were visible in any shadowgraph measurements made during that test. On the other hand, Coulomb (39'4°) presented Schlieren images of the VR-7 airfoil which clearly showed the presence of a shock for an airfoil which did not show a shock in the McCroskey et al (7) test at nominally the same test conditions.…”

“…For instance, although McCroskey et al (7) showed that supersonic flow existed on seven of the eight airfoils tested in their experiment, no shocks were visible in any shadowgraph measurements made during that test. On the other hand, Coulomb (39'4°) presented Schlieren images of the VR-7 airfoil which clearly showed the presence of a shock for an airfoil which did not show a shock in the McCroskey et al (7) test at nominally the same test conditions. Chandrasekhara et al (38) present images that clearly shows the presence of multiple shocks in interferograms taken at conditions typical of model helicopter flight.…”

“…These are conditions which can be experienced by helicopters without severe penalty. The light-dynamic-stall condition, defined by McCroskey et al (7) as a condition where the static-stall angle is exceeded, but the dynamic pitching moment does not exceed the maximum value occurring at static stall, serves as a good example. There already have been instances where light-dynamic-stall conditions have been chosen as acceptable flight boundaries (e.g.…”

Computational Investigation of Airfoil Stall Flutter

“…= VJx cosa + y sina) + J^h rds-J^0 ds 2k j In (16) Equation (16) (17) Once the boundary conditions are defined the system of (n) equations can be solved for (n+1) unknowns. …”

Some Important Problems in Unsteady Boundary Layers Including Separation. II. Unsteady Boundary Layers Close to the Stagnation Region of Slender Bodies.

“…The experimental investigations have been carried out mainly to improve understanding of flow around helicopter rotor blades and include the low-speed measurements of McCroskey et al (1982), Carr et al (1977), Carr and McAlister (1983), Young (1982), Geissler (1983) and Cousteix et al (1981) and transonic flow measurements of Tijdeman (1977), Davis and Malcolm (1979). The range of measurements of McCroskey et al and Carr et al, in particular, is extensive and includes more than fifty combinations of Mach number and parameters of the unsteady motion for each of eight airfoil sections.…”