Design and Development of Smoke Flow Visualization Apparatus for Wind Tunnel

Abstract

For the flow visualization around the airfoil, bluff body or an airplane model, there is a need for the technique by which one can visualize the air flow, understands the flow physics around it or can even design new parameters based on it. Flow visualization techniques such as tufts, powder, China clay etc. were used by different investigators in the wind tunnel. One of the methods for flow visualization is smoke flow technique. Smoke flow visualization can be implemented by various techniques such as oil smoke, dry ice smoke, titanium tetrachloride smoke etc. In the present study, the design of smoke generator was done for the existing low-speed wind tunnel available in the laboratory. The wind tunnel fan is fitted with the Variable Frequency Drive (VFD) to produce the wind speed in the range of 3 to 32 m/s with fan speed of 150 to 1500 rpm. The design of smoke generator was done according to Preston Sweeting Mist Generator principle corresponding to the free stream velocity of 3 m/s to make the streamline visible. The working fluid for the smoke generation was selected as kerosene because of its low cost and low toxicity as compared to other fuels. The kerosene was boiled and the vapors generated were condensed in the presence of cold air supplied by the blower to produce dense white smoke. A controlled smoke generator consisting of kerosene reservoir, controlled heater, blower, liquid column height adjustment mechanism, valves etc. have been designed and fabricated. The smoke generator has produced the smoke at the rate of 154 cm³/s which was close to the design flow rate of 149 cm³/s. To supply the required quantity of smoke in the wind tunnel, the smoke rake of NACA 0010 profile was developed and installed in the rapid contraction section of the wind tunnel to achieve the streamlined flow. The parametric studies were done on the smoke generator at different power inputs and its effects were studied on smoke temperature, smoke discharge and boiling time of the kerosene. It was found that, when power input was varied from 32 W to 626 W; the smoke temperature, smoke discharge and boiling time were changed in the range of 37 to 76ºC, 61 to 154 cm³/s and 45 to 3 minutes respectively at an air velocity of 4.8 m/s in the mixing chamber. The flow visualization was carried out on NACA 0015 airfoil and the images were captured to examine the flow physics around it under different operating conditions.