1,720,965 research outputs found
EXPERIMENTAL INVESTIGATION OF THE FLOW WITH A FREE-SURFACE IN AN IMPULSIVELY ROTATING CYLINDER
No full textAn experimental investigation was made of the impulsive spin-up from rest of a liquid in a partially filled cylindrical container. The main impetus was placed on delineating the effects of the presence of a free surface on the transient development of flow. Of particular interest were the situations in which the free surface intersected either or both of the endwall disks during the course of spin-up. Extensive flow visualizations were carried out by using suspended metal particles. An image processing technique was utilized to determine accurately the propagating velocity shear front as well as the time-dependent free surface contour. Precise measurements of the fluids velocities were obtained by using a laser Doppler velocimeter. The transient velocity profiles were mapped out, and they were found to be in satisfactory agreement with the predictions based on the simplified analysis. The radial location, Rs(t), of the propagating shear front was measured by applying the image processing technique to the visualized azimuthal flow field. The experimental data were found to be consistent with the numerical predictions
Microwave Absorption Response of FSS Impinged Bi-layered Composite Absorber for Antiradar Applications
No full text
DISCRETE VORTEX SIMULATION OF PULSATING FLOW BEHIND A NORMAL PLATE
No full textA numerical study is made of the separated flow behind a flat plate. The plate is placed normal to the direction of the approach flow. The oncoming freestream velocity contains a pulsating part, U infinity = U-0(1+A(0)cosf(p)t). The temporal behavior of vortex shedding patterns is scrutinized over broad ranges of the two externally specified parameters, i.e., the pulsation amplitude (A(0) less than or equal to 0.6), and the dimensionless pulsation frequency, (f(b) less than or equal to 0.32). A version of the discrete vortex method is utilized. The variable-position nascent vortex technique is applied, and it proves to be adequate for pulsating approach flows. The numerical results clearly capture the existence of lock-on when f(p) exceeds a threshold value. The modulation of vorticity shedding is also detected when f(p) is reasonably low. The influence of A(0) on the flow characteristics is examined in detail. As A(0) increases to a moderate value (e.g., A(0) less than or equal to 0.6), an appreciable broadening is seen of the range of f(p) for which lock-an occurs. Based on the numerical results, three characteristic flow modes in the wakes are identified. These findings are qualitatively consistent with the existing flow visualization studies for a cylinder
Pulsating flow and heat transfer in an annulus partially filled with porous media
No full textA numerical study is made of heat transfer characteristics from pulsating flow in a concentric annulus partially filled with porous media. The unsteady Navier-Stokes equations with the Brinkman-Forchheimer-extended Darcy model in the porous region are solved by using finite volume techniques. Changes in convective heat transfer and in effective axial heat conduction due to pulsation are investigated over broad ranges of the relevant parameters, i.e., the thickness of the porous layer and the frequency and amplitude of pulsation. The results obtained indicate that the effective axial thermal conductivity is substantially increased by pulsation, and this augmentation is more pronounced by partial fillings of porous material
EXPERIMENTAL-STUDY OF UNIFORM-SHEAR FLOW PAST A ROTATING CYLINDER
No full textAn experimental study is made of two-dimensional uniform-shear flow (U=U-c + Gy) past a rotating cylinder of diameter D. A water-tunnel, equipped with a shear generator was constructed. Laser-Doppler velocity measurements were undertaken to describe the wake characteristics. Data are compiled over the ranges of 600 less than or equal to Re less than or equal to 1,200, the shear parameter K[=GD/U-c] up to 0.15, and the value of the cylinder rotation parameter alpha[=omega D/2U(c)], -2.0 less than or equal to alpha less than or equal to 2.0. The power spectra of velocity measurements at downstream locations were analyzed to examine the vortex shedding patterns. In general, the dominant shedding frequency is shifted to a higher value as \alpha\ and K increase. When \alpha\ increases beyond a certain threshold value, the dominant frequency becomes less distinct. If \alpha\ takes a value larger than around 1.5, the velocity field becomes randomized and diffuse, and the organized Karman vortex street activity weakens. The variations of the Strouhal number with K and alpha are described The evolution of mean velocity profiles in the wakefield is depicted. Characterizations of the velocity profiles, as K and alpha vary, are made based on the measurement data
- …
