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ABSTRACT: The present paper reports on an experimental investigation on the aerodynamic stability of cylinders with different cross-sectional shapes that are inclined at different angles to the free stream. The shapes of the cylinders investigated are square, trapezoidal and triangular. Test were conducted in a wind tunnel at a Reynolds number of 3 X 10". The magnitude of the normal force coefficient (CN) and its variation with the angle of attack (a) were found to show a strong dependence on the after body shape. By analyzing the CN versus a curves and in particular the sign and magnitude of aCN laa at "a = 0ยท, it can be concluded that at a = 0ยท, the square, trapezoidal and triangular cylinders are unstable, stable and neutrally stable to galloping oscillation respectively. From the measured phase angle, () at different reduced velocity (U,) the above suggested stability for the three cylinders is also being supported. It was found that, the magnitude of the Strouhal number (S) and its variation with a are cross-sectional shape dependent. At a = 00, S was found to be about 0.13 for the square and 0.14 for the trapezoidal and triangular cylinders. S initially increases with a up to a maximum value of 0.16, 0.19 and 0.23 for the square, trapezoidal and, triangular cylinders respectively at their respective angle of attachment. In the range a > a S decreases with a. Griffin's (1981) Strouhal Number (S.,) was calculate for the three shapes. Sc for the Square and Trapezoidal cylinders agree quite well with the value of 0.176 suggested by Griffin. However, for the Triangular cylinder although the data "are found to be fairly constant, they are at a different value of 0.12. All the present data for square cylinder agrees well with those reported in the literature.
ABSTRACT: The now development past a rotating circular cylinder in a viscous nuid is investigated. A new diffusion-vortex method is employed and extended to calculate the now problem. The variations with time of the pressure and vorticity distribution, the lift and drag forces exerted by the nuid on the cylinder surface, are determined for the selected values of the Reynolds number and rotation rate, and compared with the published experimental results. The results show a variety of unusual and complex now patterns around the rotating cylinder. INTRODUCTION The flow around a rotating circular cylinder in uniform flow is a rather complex flow. It includes the unsteady boundary layer separation flows which interact with the thin shear layers and wake flow, and generate complex unsteady lift and drag forces. The unsteady features of the near-wake flow are still not fully understood. These problems have attracted experimental and theoretical interests for a long time because of their relevance to aerodynamics and offshore engineering applications. The experimental investigation of the complex flow field, especially the pressure distribution around the cylinder is difficult because of the cylinder's rotation. In the present work, the essential objective of study is to obtain numerical solutions of the Navier-Stokes equations by using diffusion-vortex method in order to examine the effect of increased rotation on the flow structure at high Reynolds number, which simulates the combined effects of ocean current and rotation of the drill in offshore oil exploration. It is hoped that the present calculation will throw some light on the complex interaction of a flow near a moving wall and wake, the formation of vortex streets behind a rotat, ing cylinder at high Reynolds number, and the forces acting on it at various speed of rotation in a uniform flow.
ABSTRACT: In flow past a finite length circular cylinder, experimental data show that the presence of the free end appears to have significant effects on the surface pressure only in the range e > 50". The wake pressure is more negative near the free end but is normally still less negative than the two-dimensional flow value. The drag coefficient is spanwise position dependent and is larger near the free end. Both the spanwise and overall drag coefficients are lower than the two-dimensional flow drag coefficient. Regular vortex shedding can be detected only at the mounting board half of the hid = 8 cylinder and the corresponding Strouhal number is slightly smaller than the two-dimensional flow value. INTRODUCTION Circular cylinder-is one of the most frequently encountered shapes in engineering applications including offshore and polar engineering applications. A good understanding of flow past circular cylinder (in the present paper from now on tlie word "circular" will be omitted for brevity and unless otherwise stated the word "cylinder" should be interpreted as meaning "circular cylinder") is therefore important. The above is despite the fact that due to the more complicated nature of the flow, more data will have to be collected and their interpretation will become a lot more difficult. Experiments conducted on flow past a single finite length cylinder include the work by Farivar (1981), Ayoub and Karamcheti (1982), Kawamura et al (1984), Uematsu (1986), Sin and So (1987), Saban et al (1989) and Saban and So (1991a and b) etc. The objective of the present paper is to supplement or make comparison with the information already available in the literature which include the papers mentioned above by carrying out further experimental measurements on the flow past a finite length cylinder, with special interest in the effects caused by the free end.