UNSTEADY AERODYNAMICS OF FLAPPING WING: GROUND EFFECT AND ROTATIONAL LIFT

Abstract

THIS THESIS PRESENTS RESULTS OF COMBINED EXPERIMENTAL AND NUMERICAL STUDIES ON UNSTEADY AERODYNAMICS OF FLAPPING WING. IT CONSISTS OF TWO RELATED TOPICS. THE FIRST TOPIC AIMS TO INVESTIGATE THE GROUND EFFECT ON A TWO-DIMENSIONAL (2-D) OSCILLATING AIRFOIL AND THREE-DIMENSIONAL (3-D) FLAPPING WINGS IN HOVER MODE. THE PRESENT RESULTS SHOW THAT THE CYCLE-AVERAGED LIFT AND DRAG COULD BE BROADLY CATEGORIZED INTO THREE DISTINCT REGIMES WITH RESPECT TO THE GROUND CLEARANCE, NAMELY FORCE ENHANCEMENT, FORCE REDUCTION AND FORCE RECOVERY. THE FLOW DYNAMICS BEHIND THE GROUND EFFECT VARIED BETWEEN 2-D AND 3-D CASES. THE SECOND TOPIC IS RELATED TO THE ROTATIONAL LIFT OF FLAPPING WINGS, AND IT IS A NUMERICAL SIMULATION OF FLOW PAST A ROTATING 2-D CYLINDER OF DIFFERENT THICKNESS RATIOS; THE OBJECTIVE IS TO STUDY HOW INCREMENTAL CHANGES IN THE CROSS SECTION, FROM A CIRCLE TO A THIN ELLIPSE, INFLUENCE THE TRANSITION OF LIFT-GENERATING MECHANISM FROM MAGNUS-LIKE EFFECT TO CIRCULATORY LIFT.