An experimental investigation was conducted to study compressibility effects on dynamic stall for an airfoil pitching at a constant rate. Instantaneous, whole field velocity data was acquired using an on-line, video-based particle image velocimetry (PIV) system, which incorporated a passive, optical, displacement bias technique to eliminate the sign ambiguity inherent in PIV measurements of reversed flows. Vorticity data were subsequently computed from the corresponding velocity field. Free stream Mach numbers were 0.23 and 0.45, and corresponding Reynolds numbers were 280,000 and 620,000, respectively. Non-dimensional pitch rates were 0.010, 0.030, and 0.060. Although the flow was near sonic in the high speed case, no shocks were observed. The sequence of events at high speed was remarkably similar to that at both low speed and to that observed in water tank experiments. The dynamic stall process is initiated with formation and convection aft of a single, discrete, vortex. Formation and initial release of the structure is probably initiated by a van Dommelen-Shen unsteady separation. A region of closed vorticity forms over the forward portion of the airfoil, caused by periodic reattachment and shedding of discrete vortical structures of positive sign from the leading edge. These structures and the adverse pressure gradient then induce production of negative vorticity near the airfoil surface, which is convected forward and accumulates near the quarter chord. Subsequently, coherent negative vorticity is ejected into the outer flow, isolating the initial structures from the leading edge. Subsequent interaction induces separation from the surface of the dynamic stall vortex, which is composed of several small, interacting structures rather than a single, large structure. / The data complement Schlieren and surface pressure investigations, which are useful but provide no information about local flow direction. The data also demonstrate the utility of PIV for investigating highly unsteady, reversed flows with dynamic boundary conditions at compressible or transonic speeds. / Source: Dissertation Abstracts International, Volume: 54-12, Section: B, page: 6318. / Major Professor: Anjaneyulu Krothapalli. / Thesis (Ph.D.)--The Florida State University, 1993.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_77068 |
| Contributors | Crisler, William Paul., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 164 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
Page generated in 0.0022 seconds