Flow visualization study using dye mixtures on a hydrokinetic turbine in a water tunnel

A simple gravity-feed dye injection system is developed in this study and used as a flow visualization technique for dye mixtures consisting of dye with water (DW) and dye with water and milk (DWM) with combination ratios of 1:9, 3:7 and 5:5 for DW; and 1:5:4, 3:3:4 and 5:1:4 for DWM. All dye mixtures are investigated under dynamic flow regimes at 0.085, 0.119 and 0.80 m/s water flow speed, respectively. The practicality of the mixtures is analysed in terms of dye clarity, rate of dispersion, and dye flow path to determine the best dye mixture for each flow regime. A hydrokinetic turbine model is placed in the test section of the water tunnel to study the flow structures across the model. At 0.085 m/s, the DW with 1:9 ratio is the best dye mixture provided the turbine is placed not more than 6 cm from the injector. At 0.119 m/s, DWM with a 3:3:4 ratio is the best solution, because milk prolongs the dye diffusion thus retaining the dye traces in the water, whereas at 0.80 m/s, the effect of milk in reducing the dye dispersion is more significant. A clear dye flow pattern can be observed when the dye concentration is increased; thus, DWM with the ratio of 5:1:4 is found to be the best dye mixture for that flow speed. A reliable flow visualization study can be achieved if a suitable dye mixture is used for a specific flow regime.