Hisanori Ueno

Numerical study on wake patterns and aerodynamic forces of an oscillating cylinder with a circular and rectangular cross-section

We numerically simulate the flows around oscillating cylinders with a circular cross-section and a rectangular cross-section with a side ratio of 1 to 3 at Reynolds number of 103, using the ALE method, and predict features of flow patterns and aerodynamic forces of oscillating cylinders. The results show to be in excellent agreement with the experiments which have been carried out on an oscillating square cylinder. The lock-in phenomenon and the aeroelastic instabilities of the cylinders such as a vortex excitation and a galloping oscillation are investigated. Computed and measured results indicate that aerodynamic characteristics strongly depend on the shape of the cylinders, the forcing frequency and the oscillatory direction and reveal the onset of aeroelastic instability in a certain range of forcing frequencies, which is similar to a free oscillation tests.

Effects of Inner Nozzle Jet on Vortex Frequencies of Double Coaxial Pipe Jets.

This paper describes the results of an experimental study concerning the frequency components of flow fluctuation in double coaxial pipe jets. We examined the effects of velocity ratio, outer pipe length and lip thickness of the inner nozzle on the flow structure and velocity frequencies. It was found that, for velocity ratios u^-i/u^-o l 0.5, the velocity fluctuation is mainly composed of the frequency of the vortex street whose excitation depends on the outer pipe length, and the values of the Strouhal number StLbased on the outer pipe length are constant at 0.64N (N=1, 2, 3...). u^-i/u^-o g 0.5, however, the velocity fluctuation frequency is due to the alternate shedding of lip wake vortices in the inner mixing regions, and behaves in such a way that the Strouhal numbers Stbi, based on the lip thickness of the inner nozzle are constant at about 0.2 for any outer pipe length of the jets.

Visualization of Flow Around Rectangular Cylinders with Phase-Averaging Technique

Flow around two-dimensional rectangular cylinders at high Reynolds number over 104 was visualized by a phase-averaging technique using a tandem type of hot-wire probe. Flow visualization with the aid of a computer was carried out for the cylinders with rectangular section of two different width-to-height ratios. One is a cylinder whose width-to-height ratio is 2. 5, with a mixture of two flow patterns; i. e. a fully separated and a reattached flows around the cylinder, and the other has the ratio of 3. 0 with a periodically (alternately) reattached flow. For the former cylinder, two different flows can be easily separated with a phase-averaging technique. Finally, experimental results distinguish the flows into three modes, and show conspicuous differences among their flow configurations.