Yoshifumi Yokoi

Numerical experiment of flow characteristics of tandem arrangement two symmetrical airfoils

In this study, numerical experiment of flow around the close two airfoils which arranged in parallel with attack angle was performed. The aspect of flow and the instantaneous fluid force act on symmetrical airfoil (NACA0012) with attack angle were investigated using a vortex method at the Reynolds number Re=4.05×105, in ranges of the distance ratio L/c= 0.0, 0.25, 0.50 and 1.0 (here, L/c = 0.0 means single airfoil case) and the attack angle α = 0, 5, 10 and 15 degrees, (here, α =15 degree case is performed on single airfoil case only). As a result of calculations, in the case of two airfoils, the large lift was able to be obtained as compared with the single airfoil, but it was found in it that they are about 1.5 times in the case of single airfoil. And it was shown that the fluid force characteristic of each airfoil of two airfoils differs from the case of single airfoil.

Flow feature around an in-line forced oscillating circular cylinder with splitter plate in low reynolds number

In order to understand the flow feature around an in-line forced oscillating circular cylinder with splitter plate (splitter plate ratio SL/d = 2.0), numerical and visual experiments were performed. As a result, even if it was the case of circular cylinder with splitter plate, the lock-in phenomenon arises. The characteristics of fluid force and typical flow patterns were obtained. It was found that an existence of re-circulation flow supplied to the separating shear layer is important in formation of the vortex shedding flow.

Numerical Experiment of Flow Characteristics of a Circular Cylinder with Splitter Plate

In this study, some investigation about the flow and the fluid force around a circular cylinder with splitter plate in comparatively low Reynolds number (Re = 500) were simulated by the numerical calculation. In order to check the effect of the splitter plate, the numerical calculation to which the length of the splitter plate was varied was performed, and change of the characteristic of fluid force based on the splitter plate length was obtained. Based on the obtained result, some numerical simulations in the state where oscillation was given in the direction of the flow supposing unsteady flow were carried out. As a result, even if it was the case of a circular cylinder with splitter plate, it was shown that the lock-in phenomenon arises. The characteristics of fluid force and typical flow patterns were obtained. It was found that an existence of re-circulation flow supplied to the separating shear layer is important in formation of the vortex shedding flow.

Flow Visualized Observation of a Symmetrical Airfoil with Attack Angle in Fluctuating Relative Flow Velocity

In this study, a visualization experiment was performed in order to confirm the flow pattern around airfoil with relative velocity fluctuation by in-line forced oscillating in the direction of flow. An airfoil NACA0012 with attack angle of 5 degrees produce the separation in the steady state was observed by the experiments using dye streak method at Reynolds number Re=3.6x103. The investigation of the attack angle which does not separate in such low Reynolds number was performed, and it was confirmed that the separation occurs to 3 degrees. And the airfoil with attack angle of 2 degrees which does not cause separation in steady state, was forced to oscillate with two kinds of relative velocity ratio (umax/U=0.4 and 0.8, here, umax and U denote maximum moving speed of airfoil and main flow velocity, respectively.). The flow separation on the surface of airfoil with attack angle which does not produce the separation in the steady state is occurred even if the maximum moving speed of airfoil umax is in the range which does not exceed main flow velocity U.

Numerical Experiment of Flow Around a Two-Dimensional Self-Oscillating Circular Cylinder with Whirling Limitation by a Vortex Method with Boundary Layer Calculation(Fluids Engineering)

In this study, a numerical experiment of flow around a self-oscillating circular cylinder with whirling limitation was performed using the boundary element method combined with the vortex method. The flow feature of vortex shedding and the characteristics of vibration due to the fluid force were simulated about various initial setting position of circular cylinder at the Reynolds number Re=1×105, the mass ratio M=5.15, the damping factor C=0.0 and the reduced velocities Vr=1.8 and Vr=2.4. As a result of calculation, in the case of coaxial setting, the flow feature and the characteristics of cylinder vibration due to the fluid force were as same as a result of self-oscillating case, however, in the case of not coaxial setting, the frequency of cylinders motion was changed and the flow features were changed from the twin type vortex shedding pattern to the Karman type vortex shedding pattern. It was shown that the characteristic of cylinder vibration frequency depended on both of the distance and the direction between the circular cylinder and the wall of pit.