Study of Fluid Flow and Heat Transfer Around a Hemispherical Body

Abstract

ABSTRACT: The airflow and forced convective heat transfer characteristics over the smooth wall surface of a heated and tilted aluminium hemisphere immersed in a fully developed flow in a sub-sonic wind tunnel have been investigated experimentally and numerically. The hemispherical model is studied at three different tilt angles, namely; a = 0°, 30° and 52°, and inclined vertically to the y-axis. The investigation is performed at air velocities ranging from 5 to 25 m/s, in increments of 5 m/s. An experimental method involved maintaining a constant surface heat flux to the hemisphere by means of power supply and filament heater. K-type thermocouples are used to analyze the flow structure for different regions of flow domain around the front and back surfaces of the model. Obtained results are presented in the form of dimensionless temperatures distribution over front (stream-wise and span-wise) directions, and on the back surface. The total drag and lift forces over the hemisphere are experimentally measured in the tunnel with electronic balance sensors at the test flow velocity. The results of total drag and lift coefficients have shown dependency on the inclination of the hemisphere. The pressures in the wake region downstream of the hemisphere are also measured in the tunnel with electronic manometer bank. The results of wake pressure variations become significant at high Reynolds number, Re ≥ 2.0×105. A smoke flow visualization technique is also carried out in order to obtain qualitative information concerning the flow field structure adjacent to the model surfaces. A two dimensional (2D) numerical computational fluid dynamics (CFD) model was adopted to simulate the fluid flow field and heat transfer, and to visualize the flow reversal, separation, horseshoe vortices, and recirculation zone downstream and back surface of the hemisphere and to validate the experimental results. It is shown that the flow characteristics vary on the stream-wise and back surfaces as the flow becomes transitional and unsteady. It is found that as Reynolds number increases, the local Nusselt number over front and back surfaces increases. The local and average Nusselt number shows a strong dependence on the oncoming flow velocity. It is found that the total heat transfer rate over hemisphere surfaces (front and back) is enhanced as the tilt angle, a increases, wherein the increase was found to be about (6% ~ 8.3%) and (5%~9%) in comparison to that in a = 0° and 30°, respectively. A comparison between obtained experimental and numerical total average Nusselt number over entire surfaces of the hemisphere is carried out, and the results are closely match namely at higher range of Reynolds number, between 2.0×105 ≤ Re≤ 2.5×105. The results obtained in numerical simulations are also validated by comparing with the published correlations.