On pitching motion of two opposite double flappers in water tunnel at Re = 25,000 as basis of human crawl-stroke swimming

A pair of two flat plates undergoing pure pitching flapping but in opposite directions was studied. This double-flapper set was used to simulate the human’s leg undergoing crawl-stroke swimming motion (stretched straight legs without bending at the knees). Likewise, this work can be extended to the understanding of the dragonfly’s flight, when the forewings and hindwings beat at opposite direction in certain flight. The two flat plates rotate about the same axis in similar manner to the human legs (rotating about the hip). By varying the pitching amplitude (angles) and pitching frequencies corresponding to its travelling speed and pure thrust produced, the optimum sets of flapping motion, either for maximum thrust or maximum propulsive efficiency for range and endurance can be sought. Hence, this is to give light for understanding best swimming condition for crawl-stroke motion and/or dragonfly’s beating flight.