Optimisation of the Experimental Conditions for the Smoke Wire Technique in a Boundary Layer Wind Tunnel

Optimal experimental conditions, namely the nozzle size, wire diameter, power value, and wind speed, for a smoke wire technique (SWT) with a control dripping valve (CDV) and tensioner system were proposed to ensure dense, straight, and continuous streaklines for flow visualisation experiments. The investigation was conducted using a single heated nichrome wire in a small-scale boundary layer wind tunnel (BLWT) constructed at Universiti Malaysia Pahang As-Sultan Abdullah, Malaysia. Through the CDV, the water-based solution is automatically replenished to the heated single nichrome while maintaining a consistent wire strain with the aid of a specifically designed tensioner system. A simple shape, a surface-mounted finite circular cylinder, was utilised as the rigid body to observe the flow pattern during the experiment, which was verified with findings from previous literature. A high-speed digital camera, the MEMRECAM HX-7s system, was used to record instantaneous images of the streaklines. Clear images of dense, straight, and continuous smoke lines were captured at a free-stream velocity of 1.5 m/s using a 0.5 mm nichrome wire diameter, a 0.6 mm nozzle diameter, and 35 W power conditions.