Dynamic stall often occurs under conditions of simultaneous unsteady pitching and surging (e.g., rotorcraft and wind turbines), but many models employ a dimensionless time base that implicitly assumes that surging is superimposed, in a quasi-steady manner, on dynamic pitching. An unsteady wind tunnel was used to examine this assumption, where a technique was developed to quantify the unsteady effects of surging on a pitching NACA 0018 airfoil. The technique involved performing multiple harmonic pitching experiments under nominally steady freestream conditions that bracketed a corresponding 50% surging amplitude ( 1.25 10 5 R e 3.75 10 5 ). By interpolating these data, unsteady-pitching/quasi-steady-surging data sets were constructed and compared with de facto synchronous pitch and surging experiments, thereby isolating the unsteady effects of surging on a pitching airfoil. Both large and small poststall maximum angles of attack ( α s + 5 ° and α s + 15 ° ) were considered at multiple pitch-surge phase differences. During deep dynamic stall ( α s + 15 ° ), with large-scale separation, surging was seen to have a secondary effect on the unsteady aerodynamics. However, at small poststall maximum angles of attack ( α s + 5 ° ), either light or deep dynamic stall behavior was observed depending upon the pitch-surge phase difference. This was attributed to Reynolds number history effects, exemplified by boundary-layer transition, and thus it can be referred to as “transitional” dynamic stall.


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    Title :

    Dynamic Stall Under Combined Pitching and Surging


    Contributors:

    Published in:

    AIAA Journal ; 58 , 12 ; 5134-5145


    Publication date :

    2020-07-21


    Size :

    12 pages




    Type of media :

    Article (Journal)


    Type of material :

    Electronic Resource


    Language :

    English




    Characteristics of Pitching and Plunging Airfoils Under Dynamic-Stall Conditions

    Rival, D. / Tropea, C. / American Institute of Aeronautics and Astronautics | British Library Conference Proceedings | 2009