Postgrads present modelling work at international conferences
MIA postgraduates Awie Vijoen (Doctoral candidate) and Nigel Dhlamini (Masters student), supervised by Prof. Wei Hua Ho, recently presented their modelling studies at international conferences.
Dhlamini presented his paper, “A numerical study of smoke bifurcation flow in large tunnel fires” at the 16th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics and Editorial Board of Applied Thermal Engineering (HEFAT-ATE 2022).
While smoke bifurcation flow has been receiving more attention, large tunnel fires (those in which the fire plume impacts the tunnel ceiling) have rarely been addressed because of the expense and difficulty in conducting large fire tests. The paper sought to extend the understanding of smoke bifurcation flow for these fires.
A chemically reacting flow CFD model (Figure 1) was used to simulate combustion in a long tunnel. Smoke bifurcation flow was observed as the ventilation velocity increased. The flame angle was found to be insensitive to heat release rate for large fires, as postulated in previous work.
The research will assist in the placement of temperature and gas sensors in tunnels for early fire detection, particularly in underground mines. Currently, these sensors are placed on the centreline of the ceiling, but these findings show that the heat and smoke bifurcates and moves along the sidewalls. The model also predicts the location of the maximum temperature on the ceiling, aiding tunnel designers in creating structures that can withstand damage.
Figure 1: Temperature contour for a 30MW fire under 6m/s longitudinal ventilation velocity (a) longitudinal symmetry plane (b) top view (N Dhlamini)
Viljoen presented his work “Analysis of a flapping blade in two-phase flow” at the International Conference on Computational Fluid Dynamics (ICCFD-11) in Hawaii.
When insects fly close to water, they sometimes fall in. They then use a mechanism, known as hydro-foiling, to generate forward motion. Hydro-foiling involves a flapping of their wings (with only the ventral side in full contact with the water), generating ripples on the surface that propel them forward. The study details the numerical modelling of hydro-foiling by combining moving boundaries to simulate the kinematics and also to evaluate the force-generating mechanisms (Figure 1). Kinematic data taken from Roh and Gharib’s (2019) initial work was digitized, curve-fitted and then used as input to the CFD model. Measured acceleration data from Roh and Gharib (2019) was used for validation. Generally, the model results compared well with the literature, as shown in Figure 2.
Figure 2: Comparison of simulation and literature (A Viljoen)