Investigation of Effects Contributing to Dynamic Stall Using a Momentum-Integral Method.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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Dynamic stall effects are analyzed in this investigation for cases of an inertially static airfoil in a flow field rotating at constant rate gust response, and an airfoil pitching at constant rate in a steady flow field. The method used is a boundary layer solution of the momentum-integral equation by a modified von Karman-Pohlhausen technique. Previous work using this method to match Kramers experimental results for gust response is reviewed, corrected, and continued. The validity of the closure equation and the assumptions key to its derivation are examined, concluding that the closure equation is justified. A better match of Kramers airfoil sections results in dynamic stall predictions very close to experimental data. The effect of varying airfoil thickness and camber is investigated. By consideration of the non-Newtonian motion of the boundary layer on the surface of a pitching airfoil, the momentum-integral method is extended to the second case. Using the Moore-Rott-Sears model for flow separation criteria, analytical results were computed and compared with experimental data. Reduction in adversity of the pressure gradient accounts for only a fraction of the total dynamic effect, and it is proposed that mass introduction into the boundary layer from the free stream may be a strongly contributing factor. This phenomena is demonstrated to have a large effect, and an argument is presented for the proper amount of mass introduction.
- Numerical Mathematics
- Fluid Mechanics