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This study focuses on drag prediction in the near-wake of a circular cylinder by use of mean velocity profiles and discusses the closest location where a wake survey would yield an accurate result. Although the investigation considers both the mean and fluctuating velocities, the main focus is on the mean momentum deficit which should be handled properly beyond a critical distance. Digital Particle Image Velocimetry (DPIV) experiments are performed in a Reynolds number range of 100 to 1250. Wake characteristics such as vortex formation length (L) and wake width (t) are determined and their relations to drag prediction are presented. Drag coefficients determined by momentum deficit formula are found to be in good agreement with experimental and numerical literature data in present Reynolds number regime.

Investigations on the design and applications for Micro Air Vehicles (MAV) attract increasing attention to the fields of study on low Reynolds number flows. Generation of thrust and locomotion mechanism of swimming and flying animals may improve the design and development of engineered systems that take advantage of similar unsteady aerodynamic mechanisms. Biological inspiration offers a means to enhance the performance of the next generation of small-scale air vehicles over existing fixed and rotary wing systems. A 2D oscillating wing with SD7003 airfoil profile undergoing pitching and plunging motions was investigated in a previous study and the vortical structures were categorized for various flapping parameters. In this study, three-dimensional models (AR=4) with four different airfoil profiles (SD7003, NACA0012, t/c=0.05 rounded edge and t/c=0.05 sharp edge flat plates) are used for the cases where thrust or drag production was qualitatively defined based on flow structures. The study is performed in a water channel at the Reynolds number range of 2,000 < Re < 15,000 using the DPIV (Digital Particle Image Velocimetry) technique and a Force/Torque sensor. Quantitative flow visualization results are obtained for three different planes along the span of the test models. The results reveal the time dependent relation between the vortical structures and the forces acting on the test models. The effect of using various airfoil profiles on the vortical structures and thrust/drag production is also investigated.