Design and Fabrication of Smoke Flow Visualization Setup for Existing Wind Tunnel at Pulchowk Campus

Abstract

Flow visualization methods have been used to understand and demonstrate invisible flow structures in aerodynamics and other fields. Visualization in wind tunnel is a major technique used to study the flow pattern around different objects. There are mainly two methods of visualization, intrusive and non-intrusive. Non-intrusive methods using laws of optics require the variation of density in the flow which is not suitable for low-speed subsonic wind tunnels. Smoke flow visualization using smoke rake is one of the frequently used intrusive techniques for wind tunnel flow visualization. A laminar smoke filament is injected through some mechanism to the flow field in this method. The requirement for this smoke filament is to be laminar and sufficiently long to see flow around test object. In this research work, a simple smoke introducing mechanism setup was made. The smoke rake with airfoil profile of NACA 0012 with extruding pipe for smoke injection is designed and flow around it analyzed using 2d numerical simulation to see its disturbance in flow field. Its disturbance is found to be dissipated and flow to be laminar before entering test section region. For the smoke generation, fog machine of 1500 W is used and the smoke is pushed through the smoke reservoir into the smoke rake using AC fan. The test is conducted around cylinder, airfoil and ramp structure. In cylinder, turbulent wake region was clearly visible and Karman Vortex Street was also visualized. Flow separation region in cambered airfoil was also visualized. For constant, steady injection of the smoke into the wind tunnel variable speed fan is recommended in the smoke reservoir.