Force and Flow Field Measurement System for Tandem Flapping Wings

Abstract

A test rig is developed to investigate the force and flow field characteristics of tandem flapping wings. The setup comprises a low Reynolds number recirculating water tunnel, two sets of plunge and pitch motion rigs, and a force and flow field acquisition system. A program for the motion and data acquisition is developed based on the NI LabVIEW platform. The water tunnel mainly consists of a water tank, a contraction section, a test section, and a centrifugal pump system. Many kinematic parameters of the tandem flapping motion can be adjusted in our developed test rig. These parameters are the phase angle between flapping motions of the forewing and hindwing, as well as the spacing distance, flapping frequency, and amplitude of the forewing and hindwing. The prominent feature of the motion rigs is that the phase angle can be adjusted continuously from 0 to 360°. The thrust and lift on the flapping wing are measured by a three-dimensional force sensor. A square wave produced by the program is used to identify the start of the flapping motion. The flow field around the flapping wing can be captured by a digital particle image velocimetry (DPIV) at the desired phases of the motion because the DPIV can be triggered by a square wave at any time within a cycle. The boundary of a vortex is determined according to the λ2-criterion with DPIV measurement data, and then its circulation can be computed.